0

––––––

1

LITERATURE:

A penetration test to evaluate wood to the Loggia monument decay and its application

E. Giuriani e A. Gubana pag. 4

Materials and Structures, 1993, 26, 8-14

- Introduction

- Experimental Method and Equipment

- Correlation between penetration test results a standard wood fkexural test

- Conclusions

- References

Conventional compressive strength parallel to the grain and mechanical resistance of wood

against pin penetration and microdrilling established by in-situ semidestructive devices

Michal Kloiber, MilosˇDrda´cky, Jan Tippner, Jaroslav Hrivna ´k pag. 8

Materials and Structures DOI 10.1617/s11527-014-0392-6

- Introduction

- Materials and Methods

- New devices construction

- Experiments

- Results and Analysis

- Conclusions

- References

In situ assessment of structural timber using semi-destructive techniques

Thomas Tannert, Ronald W. Anthony, Bohumil Kasal, Michal Kloiber, Maurizio Piazza, Mariapaola

Riggio, Frank Rinn, Robert Widmann, Nobuyoshi Yamaguchi pag.17

Materials and Structures (2014) 47:767–785 DOI 10.1617/s11527-013-0094-5

- Resistancedrilling

- Drilling Speed

- Number of drillings

- Results and interpretation

- Factor influencing drilling profiles

- Conclusions

- Radial cores to determine compressive strenght

- Equipment

- Application

- Results and interpretation

- Conclusions

- References

2

Mechanical properties of wood examined by semi-destructive devices

Michal Kloiber, Jan Tippner, Jaroslav Hrivna´k pag. 24

Materials and Structures (2014) 47:199–212 DOI 10.1617/s11527-013-0055-z

- Introduction

- Materials and methodology

- Experiment

- Results and analysis

- Conclusions

- References

Resistographic inspection of ancient timber structures for the evaluation of mechanical

characteristics

C. Ceraldi, V Mormone and E. Russo Ermolli pag.31

Materials and Structures/Mat6riaux et Constructions, Vol. 34, January-February2 001, pp 59-64

- Introduction

- Test Equipment

- Resistograph as a density meter

- Non destructive density evaluation of beech structural elements

- Evaluation of axial compressive strenght by mean density

- Conclusions

- References

Using drill resistance to quantify the density in coarse woody debris of Norway spruce

Tiemo Kahl, Christian Wirth, Martina Mund, Gerhard Boehnisch, Ernst-Detlef Schulze Pag. 40

Eur J Forest Res (2009) 128:467–473 DOI 10.1007/s10342-009-0294-2

- Introduction

- Materials and Methods

- Drill resistance measurements

- Results

- References

3

All the following articles are taken from “On site Assessment of Concrete, Masonry and Timber Structures SACoMaTiS 2008”

NDT methods for the assessment of structural timber: report on researches carried out at the

university od Trento (Italy)

Maurizio Piazza and Mariapaola Raggio pag.48

- The test material

- Testing equipment and testing procedures

- Analysis of the results

- Concluding remarks

Geometric assessment and non-destructive evaluation of two timber king-post trusses

Jorge M. Branco, M. Piazza and Paulo J. Cruz pag.50

- Hardness test

- Pilodyn 6J method

- Resistograph

- Discussion

- Conclusions

Post fire investigation of St. Bernard’s church, New Jersey, USA

Ronald W. Anthony, Edmund P. Meade and Annabelle R. Trenner pag 52

- Quantification of deterioration

- Extent of deterioration

- Construction layup at the base of the trusses

Non destructive evaluation at mission San Miguel achievements and limitations

Douglas W. Porter and Ronald W. Anthonyn pag.53

- Quantification of deterioration using non destructive evaluation techniques

- References

- Summary

TECHNICAL DEVICES pag.55

4

Materials and Structures, 1993, 26, 8-14

A penetration test to evaluate wood to the Loggia monument

decay and its application

E. GIURIANI, A. GUBANA

INTRODUCTION

In yard practice, a very simple test frequently adopted is based on the penetration of a nail hit by a

hammer without damaging the wood. In reality this test gives only qualitative information about the

wood condition, which consists of the penetration of a steel pin into wood with repeated blows

transmitted by a rebound hammer. In this way deep wood layers can be reached to obtain information

about the interior of beams. The proposed method can be regarded as an extension of the dynamic

penetration test used for soil investigation. An operative technique is proposed which makes penetration

resistance measurement possible for layer after layer. This approach gives more information than that

given by the penetration of a semispherically ended rod or steel balls, as specified by the codes, because

these tests only give indications about the superficial layer conditions. Also, the pylodin technique gives

information about the average strength of superficial layers of about 4 cm depth, but not detailed results.

As in the soil penetration test, particular attention is devoted to the problem of wood-to-steel-rod friction.

In fact the friction of the steel pin may affect the correlation between wood mechanical characteristics

and penetration, especially when the rod reaches the deep layers of the wood.

EXPERIMENTAL METHOD AND EQUIPMENT

The proposed method is based on the penetration of a 3 mm diameter graduated rod, which advances

by means of repeated blows of a 2.2 J impact energy rebound hammer commonly used for concrete.

This particular rebound hammer proved to be well calibrated and very suitable for this purpose, because it

is able to advance the rod about 1 mm per blow in hard wood so that it is possible to investigate deeper

layers up to 10cm with a reasonable number of blows.

Four different types of tip shape (Fig. 3) were investigated with a view to avoiding lateral friction due to

the natural reclosure of wood fibres after the rod penetration. To evaluate the friction effect several tests

were done, first with a constant-diameter rod shank (Fig. 3a and b) and successively with a 25% reduced

rod shank diameter (Fig. 3c and d). The flat tip types (Fig. 3a and c) were tested in order to verify whether

the punching of wood fibres could deter partial reclosure of the hole around the rod.

5

With regard to instability, the 3 mm diameter shank was made of high mechanical characteristic steel to

avoid inelastic bending during penetration. It was observed that the flat-tip rods (Fig. 3a and c) were more

unstable than the others. Shanks of different lengths were used; the shortest of 7 cm length made 6-7 cm

penetration possible, without instability phenomena during the initial blows. A particular connection

between the rod shank and the rebound-hammer plunger (Fig. 4) was studied to avoid bending of the

shank under the blow load when it was not coincident with the axis of the rod. The graduated shanks

were progressively substituted by longer ones to continue the penetration from 7 to 14 cm.

CORRELATION BETWEEN PENETRATION TEST RESULTS AND A STANDARD WOOD FLEXURAL TEST

The penetration test was carried out in a transverse direction with respect to the wood fibres and in a

radial direction with respect to the annual rings. Owing to the very small transverse size of the samples (20

ram) the rod tip (12 mm) was previously hammered into wood and the blows were counted to penetrate

10 ram. The wood humidity was controlled and was about 12% in every sample.

6

7

CONCLUSIONS

1. The technique of measuring rod penetration caused by repeated blows of a rebound hammer for

concrete seems to be effective and reliable for investigating the extent and depth of decay of

wood. It is possible in each layer of wood to distinguish different degrees of decay as a function of

the number of blows necessary for 1 cm penetration.

2. There is a good indication of the possibility of correlating the flexural resistance of wood with the

penetration test results; the correlation curve for spruce wood seems to give a reliable result.

3. The proposed technique was used for a broadbased investigation of the roof vault of the Palazzo

della Loggia and gave useful indications about the condition of the supporting wood structure.

REFERENCES

1. ISO-UNI 3130, 3132, 3133, 3350, 3351, 3787. 2. Terzaghi, K. and Peck, R., 'Soil Mechanics in Engineering Practice' (Wiley, New

York, 1967).

3. Giordano, G., 'Tecnologia del Legno', (UTET, Torino, 1988). 4. Wenzel, F., 'Preservation of Historically Important Buildings', IABSE

Colloquium on Monitoring of Large Structures and Assessment of their Safety, Bergamo, 1987. IABSE Report 56, pp 3-16 (IABSE-

AIPC-IUBH: ETH-Honggerberg, Zurich, Switzerland, 1987). 5. Chudnoff, M., Eslyn, W. E. and McKeever, D. B., 'Decay in mine

timbers. Part III. Species-independent stress grading', Forest Prod. J. 34(3) (1984) 43-50. 6. Franchi, A., Giuriani, E., Gubana, A.,

8

Mezzanotte, G. and Ronca, P., 'Decay and monitoring of Palazzo della Loggia in Brescia', Technical Report (Centro di Studio e di

Ricerca per la Conservazione ed il Recupero dei Beni Architettonici ed Ambientali, Brescia, 1990) (in Italian).

Conventional compressive strength parallel to the grain and

mechanical resistance of wood against pin penetration and

microdrilling established by in-situ semidestructive devices

Michal Kloiber • Milos ˇ Drda ´cky ´ • Jan Tippner • Jaroslav Hrivnàk

Received: 13 February 2014/Accepted: 1 August 2014 RILEM 2014

INTRODUCTION

The most frequently used NDT devices are currently semidestructive devices which identify the range and

location of degradation by means of material resistance to various tools (bit, pin, screw), thus specifying

which timber needs to be replaced.

The new device was constructed with the aim of establishing mechanical properties in situ. It can

measure the conventional strength and a newly created parameter, the modulus of deformability, in a

drilled hole using a small size loading jack whose jaws are pushed apart. No other method has allowed

this so far.

MATERIALS AND METHOD

Used devices

Only the method of a loading jack pushed apart in a hole is based on the determination of mechanical

properties parallel to the grain; the other methods load the timber perpendicular to the grain. The

simplest resistance method used in their tests was measurement of the depth of pin penetration in this

method the pin is shot into a material with a constant energy. The damage of the tested material is very

small and nearly negligible. The device they used, Pilodyn 6 J Forest is a simple mechanical device which

enables the researcher to measure the depth of penetration of the pin with 2.5 mm diameter, shot into

wood at a constant work of 6 J.

However, the maximum depth of pin penetration is limited due to the construction of the device and thus

only surface properties are measured. Similar to pin penetration, the screw withdrawal test also allows

them to measure surface properties. The screw withdrawal test uses a simple manual device (Fig. 1) to

withdraw a standard screw of 4 mm in diameter that has been driven into a depth of 18 mm.

Another method they used was microdrilling, which differs from the dynamic pin penetration and the

screw-withdrawal test mainly by drill penetration of the material, which provides the examiner with an

idea of its internal structure. Microdrilling was carried out using Resistograph 2450p, which records the

9

resistance to the penetration of a small drill 1.5–3.0 mm in diameter. The drill feed speed is constant and

the revolutions are unchangeable. The output is the profile of energy consumption, i.e. a relative

resistance, including eliminated bit energy consumption induced by friction in deeper layers. Peaks in the

graph correspond to high resistance or wood density, while lower points are related to lower relative

resistance of wood.

NEW DEVICES CONSTRUCTION

The advantage of the device is the possible gradual recording of the force and the shift of jaws at different

depths corresponding to the required dimensions of commonly investigated constructions.

EXPERIMENT

The positions of measuring are marked by two vertical lines and a number (Fig. 6). In total, five

measurements were performed for each drilled hole across the entire profile.

In total, the new device measured 140 positions, out of which damage was incurred during the

measurement of 5 positions and these data were therefore excluded. The actual measuring was

conducted in the following way: the measuring part was inserted in the radial hole and the device was

laid on the tested element using the cylindrical shell. The jaws were pushed apart along the grain while

the drawbar was drawn out with the push-apart wedge on which the jaws moved. The prints of the jaws

in the timber are obvious in Fig. 7, which also shows the distances between the individual layers of

measurement across the element. Further, measurement by pin pushing (2.5 mm in diameter, 120 mm in

length) into the timber was conducted at the places adjacent to the drilled holes.

10

For the resistance microdrill Resistograph 2450p assessment, the amount of energy needed to keep

constant drilling speed was recorded by the device. The output is the profile of energy consumption, or

relative resistance, including the elimination of energy consumption of friction in deeper layers. To

compare thiswithphysicalandmechanicalpropertiesoftimber, it is necessary to assess a graphical output

explicitly, therefore, a script was designed in MATLAB to calculate a parameter marked as Resistance

Measure RM [Bits], i.e. this is a resistance feature corresponding to the area under the curve divided by the

width of the measured section. To verify the functionality of the semidestructive devices, we compared

the quantities measured by the devices with the values gained by the testing of standard samples by

destructive tests using the Zwick Z050 universal testing device and the stipulated procedure of the test.

The results were evaluated by the TestXpert v 11.01 application. The basic parameters included in the

analysis for verification of the device were: wood density Density, wood strength in compression parallel

to the grain SC (L) and also hardness according to Janka in the longitudinal H(L) direction. The tests were

performed in compliance with standard European regulations using samples taken from individual

positions adjacent to the locations measured by particular semidestructive devices. The specimens were

closely adjacent so that we could analyze the distribution of properties along the stem radius. At each loci

where measurements were obtained by the small size loading jack, we took two samples sized 20 9 20 9

30 mm (for the test of compression parallel to the grain) and two samples sized 50 9 50 9 50 mm (for the

hardness test).

11

RESULTS AND ANALYSIS

The distribution of the values measured along the element. For four sections of the tie beams is presented

in Figs. 8, 9, 10, 11, 12, 13, 14 and 15. The results of the analyses show statistically significant differences

among the sections. Especially a section of beam 5 manifested considerably higher values of wood

properties than the other three assessed sections. Figure 8 shows that the values of density varied to a

minimum extent only along the length of all four sections.

Microdrilling and pin pushing assess only a local part of the object in the vicinity of the hole, which

explains the minor variability obvious in Figs. 12, 13 caused by the heterogeneous wood structure. The

smallest variance of the values measured was observed in the case of Sect. 3. By contrast, Sects. 2 and 5

manifested a remarkable variance caused by the high proportion of latewood in the element edges

compared to the central layers, where the latewood proportion within a tree ring decreased.

12

13

Both the remaining devices (screw withdrawal and pin penetration) are limited due to the possible

measuring of the material surface only, which distorts the results when compared with the density and

mechanical properties established based on the entire cross-section.

Compressive strength parallel to the grain can be very precisely established using the newly constructed

device with jaws pushing apart in a drilled hole (the small size loading jack).

The pin penetration method only measures the surface of the material; therefore, the determination of the

density and mechanical properties reaches lower correlation coefficients than the other methods used.

The relation between the conventional compressive strength parallel to the grain CSC (L) and the selected

wood properties Density, SC (L) is described by the linear regression, Figs. 20 and 21. Determination

coefficients R2 prove a very close dependence, especially in the case of the determination of the

compressive strength parallel to the grain. The derivation of density and strength by resistance measure of

microdrilling and the average force of pin pushing yield similar results (Figs. 22, 23, 24, 25).

As regards the prediction of hardness, the determination coefficients show slight relationships, more

considerable for microdrilling, pin pushing and screw withdrawal. Pin penetration was least correlated

with hardness.

14

CONCLUSIONS

The other examined semidestructive

methods were pin pushing, screw

withdrawal, microdrilling and pin

penetration. They tried to identify the

variability of properties caused by the

distribution of properties along the

radius and the length of a beam

(section). The material used for the

experiment was sections of tie beams

made of silver fir (Abies alba Mill.)

extracted during the renovation of the

historical truss of the church in Vranov

nad Dyjı ´. The accuracy of the

mechanical properties predicted by

means of semidestructive devices was

verified using correlations with

mechanical properties as determined by

standard tests. Theywere able to verify

the new device, which proved to be

sufficiently sensitive to natural differences

among various elements of historic

timber, natural changes in properties

(distribution along the width and length

of sections, occurrence of defects).

Strong correlations were found mainly

between CSC (L) conventional strength

parallel to the grain andSC (L) strengthof

thestandard samples (correlation

coefficient 0.93). The relations were best

described by simple linear regression

models. The conventional compressive

strength parallel to the grain correlates

with the other examined wood

parameters, e.g. density (correlation

coefficient 0.92) and H(L) hardness

parallel to the grain (0.81).

15

The distribution of properties along the length was not statistically proven due to the short span of the

sections used for the experiment, but the differences between the sections were statistically significant.

However, for a common usage of the device in the field they recommend measuring in at least two holes

in an element on different edges. To guarantee a flat drilled hole and eliminate sideways motion of the

bit, the drill has to be fixed in a special stand during drilling to ensure fixation to the element assessed. It is

recommendable to control the drilling speed, especially the feed speed, to guarantee quality of drilling.

The drilling should be done in undamaged places of the element without natural defects and obvious

damage. Like other in situ methods used for the diagnostics of integrated timber, the presented method

of strength and modulus of deformability measurement manifests a significant dependence on the

content of water in the material examined.

In the case of constructional/technical surveys, it is recommended to combine the method with

endoscopy to visually assess the element’s internal structure. Another suitable combination can be

Resistograph to determine the hidden damage extent.

The correlations were more often weaker in the cases of screw withdrawal and dynamic pin penetration.

These results also prove that surface properties measured locally by pin penetration to a small depth

cannot be extrapolated to the entire element.

16

REFERENCES

1. Borsky ´ P (2009) Kostel Nanebevzetı ´ Panny Marie ve Vranove ˇ nad Dyjı ´– Stavebne ˇhistoricky ´ pru ˚zkum (Churchof the

Assumption of the Virgin Mary in Vranov – Architectural and Historical Survey) 2. Cai Z, Hunt MO, Ross RJ, Soltis LA (2002) Screw

withdrawal: a means to evaluate densities of in-situ wood members. In: 13th International symposium on nondestructive testing

of wood, Richmond, USA, pp. 277–281 3. Cruz H, Yeomans D, Tsakanika E,Macchioni N,Jorissen A, Touza M, Mannucci M,

Lourenc¸o PB (2013) Guidelines for the on-site assessment of historic timber structures. Int J Archit Herit.

doi:10.1080/15583058.2013.774070 4. Divos F, Kiss FS, Takats P (2011) Evaluation of historical wooden structures using. In:

SHATIS ´ International Conference on Structural Health Assessment of Timber Structures, Lisbon, Portugal, 6 pp 5. Drda ´cky ´ M,

Jirovsky ´ I, Slı ´z ˇkova ´ Z (2005) On the Structural Health and Technological Survey of Historic Timber Structures. Proceedings

of the International Conference: The Conservation of Historic Wooden Structures, Florence, Vol. I, pp. 278–284 6. Drda ´cky ´ M,

Kloiber M (2013) In-situ compression stressdeformation measurements along the timber depth profile. In: Advanced Materials

Research 778: Trans Tech Publications, Switzerland. pp 209–216 7. Drda ´cky ´ M, Kloiber M, Kotlı ´nova ´ M (2006) Low invasive

diagnostics of historic timber. In: In-situ evaluation & nondestructive testing of historic wood and masonry structures, RILEM

Workshop, Prague, Czech Republic, pp. 24–40 8. Go ¨rlacher R (1987) Non-destructive testing of wood: an in situ method for

determination of density. Holz as Rohund Werkstoff 45:273–278 9. Kasal B, Drda ´cky ´ M, Jirovsky I (2003) Semi-destructive

methods for evaluation of timber structures. Structural Studies, Repairs and Maintenance of Heritage Architecture VIII. In: Brebia

CA (ed) Advances in Architecture. WIT Press, Southampton, pp 835–842 10. Kloiber M, Kotlı ´nova ´ M, Tippner J (2009)

Estimation of wood properties using pin pushing in method with various shapes of the penetration pin. In: Acta Universitatis

Agriculture et Silviculturae Mendelianae Brunensis, no. 2, Brno, Czech Republic, pp. 53–60 11. Kloiber M, Tippner J, Hrivna ´k J

(2014) Mechanical properties of wood examined by semi-destructive devices. Mater Struct 47(1):199–212 12. Kloiber M, Tippner

J, Hrivna ´k J, Praus L (2012) Experimental verification of a new tool for wood mechanical resistance measurement. Wood Res

57(3):383–398 13. Pellerin RF, Ross RJ (2002) Nondestructive Evaluation of Wood, Forest Service, Forest Products Laboratory,

Madison, WI, 210 pp 14. Riggio M, Piazza M (2011) Hardness test. In: Kasal B; Tannert T (eds) In situ assessment of structural

timber: discussion of classical and modern non-destructive and semi-destructive methods for the evaluation of woodstructures;

Series: RILEM State of the art reports, Springer, Dordrecht, 85–95 15. Rinn F (1994) Catalogue of relative density profiles of trees,

poles and timber derived from

Resistograph

microdrillings. 9th International Symposium on Non-destructive Testing. Madison, USA, pp. 61–67 16. Rinn F, Schweingruber F,

Scha ¨r E (1996)

Resistograph

and x-ray density charts of wood comparative evaluation of drill resistance profiles and x-ray density charts of different wood

species. Holzforschung 50(4):303–311 17. Yamaguchi N (2011) Screw Resistance. In: Kasal B, Tannert T (eds) In situ assessment of

structural timber: discussion of classical and modern non-destructive and semi-destructive methods for the evaluation of wood

structures; Series: RILEM State of the Art Reports, Springer, Dordrecht, 81–86.

17

In situ assessment of structural timber using semi-destructive

techniques

Thomas Tannert • Ronald W. Anthony • Bohumil Kasal • Michal Kloiber • Maurizio Piazza • Mariapaola

Riggio • Frank Rinn • Robert Widmann • Nobuyoshi Yamaguchi

RESISTANCE DRILLING

Any area that shows external signs of potential internal decay, such as insect damage, should be drilled.

Ideally, the needle should penetrate the tree rings perpendicularly. In this direction, the drilling path

deflects less, and itis easier to interpret the profiles and to reliably distinguish between incipient decay and

soft but intact wood. If drilling has to be done in tangential or unknown directions, the number of drillings

required for proper evaluation is higher because more reference profiles are needed.

DRILLING SPEED

If the resistance drill has different advancement rates for the needle, the drilling should always be done as

fast as possible in order to achieve maximum sensitivity which makes the distinction between intact wood

and decay easier. An accelerated feed rate may cause needle breakage, however, especially inconifers if

the needle hits a knot. Lowering the feed rate in order to limit needle breakage leads to a correspondingly

lower sensitivity of the profiles, which can prevent reliable identification of deterioration. Consequently, it

is recommended to adapt the feed rate speed to the wood species.

18

NUMBER OF DRILLINGS

In some applications, the resistance drilling inspection is expected to provide data on both the

identification of decay and quantification of the decay parameters in order to provide accurate

information for damage repair.

RESULTS AND INTERPRETATION

Provided the drill is properly aligned for accurate needle penetration without deflection, local wood

density at the position of the needle’s tip determines the mechanical penetration resistance. Consequently,

density variations between early- and latewood treering structure and the penetration angle determine

the shape of the resistance profiles.

FACTOR INFLUENCING DRILLING PROFILES

Latewood is mostly much denser than earlywood. Broad tree rings are mostly dominated by earlywood

inconifers and latewood in ring-porous wood.

In narrow conifer rings, the relative amount of latewood is higher and consequently the density is higher.

Earlywood width in ring-porous trees does not show strong variations.

Latewood dominates in wider oak rings leading to higher density.

Beside the needle tip geometry and the technical resolution of the machine, the drilling angle determines

the visibility of intra-annual tree-ring density structures.

REFERENCING AND COMPARING PROFILES

If a single profile cannot be interpreted, additional drillings at other locations are required. If possible, it is

preferred to drill at another point into the same fibres at the same angle. Because of the significant

influence of feed rate, rotational speed, and needle geometry, profiles of different resistance drills of the

same element can vary significantly—as long as the device is not calibrated to density. Thus, evaluating the

differences between profiles of different machines requires an understanding of each device.

CONCLUSIONS

(1) Conventional, visual inspection generally identified less than 30 % of total damage that was present in

the structures (because it was hidden internally or in beams that were not accessible for visual inspection).

(2) In most buildings, internal decay in timber is more prevalent than external damage.

19

(3) Many beams and structures evaluated as needing ‘to be replaced’ based on visual inspection alone

have been preserved because resistance drilling provided quantifiable data on here maining cross

section. Visual inspection generally overestimates the amount of strength loss due to decay.

(4) A large percentage of inaccessible timber covered in ceilings and walls was identified as intact

although expected to be decayed—saving work and money to uncover the beams and eliminating

unnecessary repairs.

(5) Repairs based on resistance drilling surveys were carried out on schedule and within the estimated

cost plan.

(6) High planning safety, knowledge of timber condition and corresponding repair work always led to

significant cost reductions (about 50 % as compared to conventional restorations without technical

inspection).

RADIAL CORES TO DETERMINE COMPRESSIVE STRENGHT

BASICS

Testing of radial cores is a semi-destructive method based on small cylindrical samples that are used for

testing compression strength and the modulus of elasticity (MOE) parallel to the grain by means of a

special loading device. Cores provide information on the local data of the tested property; however, this

can be used to make inferences on the element’s overall strength.

EQUIPMENT

The samples are taken using a special core drilling device developed at ITAM (Academy of Sciences,

Czech Republic) and North Carolina State University. The device, consists of a modified commercial drill,

hollow bits for core taking, a screw feed which ensures constant progress, and a drill attachment to

prevent any movement. The samples should be placed in sealed containers if a direct measurement of the

moisture contents (MCs) is required.

APPLICATION

The core samples should be extracted from healthy and undamaged material in radial direction—

perpendicular to annual rings (Fig. 3, right). To prevent shear failure of the cores during extraction

process, the special device described above is used to ensure linear and stable drilling. The drill bits must

be sharp and clean as blunt and dirty drill bits cause damage to samples. Soap or wax can be applied to

reduce friction between the tool and the material. Radial cores are 4.8 mm in diameter and need to be at

least 20 mm long to eliminate the variability due to the alternation of early- and latewood in the annual

ring; it is recommended to extract cores 30–50 mm long. The holes that remain after the cores have been

removed are smaller than most knots found in structural wood and do not considerably reduce the

strength of the element. The holes that occur after sampling can be plugged. The test setup must ensure

20

that the load is applied perfectly perpendicular to the core axis. Two LVDTs are used for monitoring the

distance between the jaws, which is an indicator for the deformation.

Any misalignment of the core creates an angle between the fibers and the direction of loading, which

increase variability of results.

RESULTS AND INTERPRETATION

The compressive core strength is calculated using Eq.

fc= Fmax/ ldc

where fc is the compression strengthof the core, Fmax the maximal applied force as determined from the

load deformation diagram, l is radial core length, and dc is the radial core diameter. To establish Young’s

MOE, it is necessary to measure the elastic response of the core. This can be achieved by partially

unloading the sample.

CONCLUSIONS

The method of radial cores is suitable for strength determination of clear, defect-free wood. The method

will, however, always underestimate the true material properties due to the misalignment effect.

Noncompact and damaged cores shouldnot betested.Cores need to be cut perpendicular to annual

rings so that mechanicalpropertiesparalleltothegraincanbetested. To prevent shear failure of the cores

during drilling, the core drill needs to progress in a linear direction and at a constant speed. To be able to

take high quality samples, it is necessary to provide enough space for a perpendicular placement of the

auxiliary device, which controls the speed and stability of the drill.

21

NEEDLE PENETRATION

BASICS

Needle penetration is the penetration of a pin shaped striker into a wood specimen as a result of a

defined impact loading on that striker. With this method it is possible to determine the condition of a

wood member at or near the surface. Similar to the results of screw withdrawal tests, the results of

penetration tests are primarily related to wood density. The penetration method can be easily executed

using a pin shaped device (often also referred to as needle, nail, pin or striker) which is being driven into

the wood with defined and/or measured impact (e.g., from an instrumented impact hammer). A simple

device with the brand name ‘‘Pilodyn’’ is being used almost exclusively for the purpose of needle

penetration tests, leading to the word ‘‘Pilodyn’’ becoming a synonym for such tests. The needle

penetration method is mainly being used to (i) determine wood density and/ or diseases of standing

trees, (ii) detect fungal attackin wood members that show signs of deterioration and/or in ground- or

water-contact, and (iii) to determine the relative density of structural timber elements.

EQUIPMENT

The Pilodyn is a hand held device consisting of aspring loaded striker and housing, shown in Fig. 9. Three

parameters influence the indentation depth of the striker: the available impact energy, the geometry of the

striker, and the use of spacers. The most popular version of the Pilodyn provides an impact energy of 6J.

According to product literature, versions with 12J and 18J are also available. The basic physical principles

for all versions are similar but the recommendations given in this chapter are related to the 6J version. In

general, woods with higher densities require the use of lower diameter strikers; however, strikers with small

diameters buckle easily and represent a limitation of the technique.

22

APPLICATION

The indentation depth of the striker can be read directly on a scale attached to the Pilodyn. The depth of

the indentation is an indication of the wood’s resistance to the penetration of the striker: the shallower the

indentation, the higher the resistance. Several factors will influence the penetration depth of a given

striker applied with the same impact energy, which include the wood species, wood density, striker-to-

year-ring orientation (radial, tangential, intermediate), presence of reaction wood, knots and other

structural irregularities, and MC.

Penetration devices like the Pilodyn contain energy loaded strikers that are capable of causing severe or

even fatal injuries when handled improperly.

RESULTS AND INTERPRETATION

Studies on Pilodyn measurements were often done on living trees or on logs and wood poles.

For the assessment of structural timber elements, Pilodyn was examined as a tool for grading procedures

and delivered reliable results on round wood, primarily because the measurement is carried out in the

radial direction.

Another important consideration for the interpretation of the results is that a penetration resistance

measurement represents only a local measurement. This is true for the position along the surface where

the measurement takes place as well as in the direction of the measurement, where the indentation

depth represents the limit of the investigation zone. With the measurements only the outer 30–40 mm of

a wood member can be assessed.

CONCLUSIONS

Penetration resistance measurements with a Pilodyn represent a simple and rapid test method to

determine wood conditions at the surface and to a limited depth. It is based on the indentation depth of a

striker into the wood under a defined impact load. The significance of the results strongly depends on the

presence of a suitable reference sample for calibration of the indentation values. The method is well suited

for the detection of soft rot and/or wood density and related properties at or close to the surface of round

wood and other cross sections, if the measurements are strictly taken in a radial direction. For penetration

directions other than radial, the indentation values can have large variations and thus limit the use of

indentation measurements unless a higher number of measurements per specimen are undertaken.

23

REFERENCES

1. Riggio M, Anthony RW, Augelli F, Kasal B, Lechner T, Muller W, Tannert T (2013) In situ assessment of structural timber using

non-destructive techniques. Mater Struct. doi: 10.1617/s11527-013-0093-6 2. Dackermann U, Crews K, Kasal B, Li J, Riggio M, Rinn

F, TannertT(2013)Insituassessmentofstructuraltimberusing stress-wave measurements. Mater Struct. doi:10.1617/ s11527-013-

0095-4 3. Kasal B, Anthony R (2004) Advances in in situ evaluation of timber structures. Prog Struct Eng Mater 6:94–103 4. Rinn F

(1988) A new method for measuring tree-ring density parameters. Diploma Thesis, University Heidelberg 5. Rinn F, Becker B,

Kromer B (1990) Density profiles of conifers and deciduous trees. In: Proceedings of the symposium on tree rings and

environment. Lund University, Sweden 6. Rinn F, Schweingruber FH, Scha ¨r E (1996) Resistograph and X-ray density charts of

wood. Comparative evaluation of drill resistance profiles and X-ray density charts of different wood species. Holzforschung

50:303–311 7. Bra ¨ker OU (1981) Der Alterstrend bei Jahrringdichten und Jahrringbreiten von Nadelho ¨lzern und sein

Ausgleich. Mitteilungen der forstlichen Bundesversuchsanstalt Wien 142:75–102 8. Kasal B (2003) Semi-destructive method for in-

situ evaluation of compressive strength of wood structural members. For Prod J 53:55–58 9. ASTM D 143-94 (2000) Standard test

methods for small clear specimens of timber. ASTM International, West Conshohocken 10. Kasal B, Kloiber M, Drdacky M (2006)

Field investigation of the 14th century Castle Pernstejn before and after fire damage. In: Proceedings of the Architectural

Engineering Institute conference, Omaha, USA 11. Lear GC (2005) Improving the assessment of in situ timber members with the

use of nondestructive and semi-destructive testing techniques. MSc Thesis, North Carolina State University 12. EN 392 (1995)

Glued laminated timber. Shear test of glue lines. European Committee for Standardization (CEN), Brussels 13. EN 386 (2001)

Glued laminated timber—performance requirements and minimum production requirements. European Committee for

Standardization (CEN), Brussels 14. Yang Y, Gong M, Chui YH (2008) A new image analysis algorithm for calculating percentage

wood failure. Holzforschung 62:248–251 15. Scott CT, Hernandez R, Frihart C, Gleisner R,Tice T (2005) Method for quantifying

percentage wood failure in blockshear specimens by a laser scanning profilometer. J ASTM Int 2:1–10 16. Winandy JE, Lebow PK,

Nelson W (1998) Predicting bending strength of fire-retardant-treated plywood from screw-withdrawal tests, FPL-RP-568. Forest

Products Laboratory, Madison 17. Divos F, Sismandy F, Takats P (2011) Evaluation of historical wooden structures using

nondestructive methods. In: Proceedings of the international conference on structural health assessment of timber structures

(SHATIS), Lisbon 18. Yamaguchi N (2011) Withdrawal resistances by screwbased probesfor in situassessment ofwood. In:

Proceedings of the international conference on structural health assessment of timber structures (SHATIS), Lisbon 19. Hansen CP

(2000) Application of the Pilodyn in forest tree improvement. DFSC Series of Technical Notes TN55. Danida Forest Seed Centre,

Humlebaek 20. Meierhofer U, Richter K (1990) Grading and quality of structural timber. Schweizer Ingenieur Architekt 39:1100–

1106 21. Goerlacher R (1987) Nondestructive testing of wood ‘‘Insitu’’-method for determining wood density. Holz Als RohUnd

Werkstoff 45:273–278 22. Feio AO (2005) Inspection and diagnosis of historical timber structures: NDT correlations and structural

behaviour. PhD Thesis, Universidade do Minho 23. Kloiber M, Tippner J, Drdacky M (2011) Semi-destructive tool for ‘‘In-situ’’

measurement of mechanical resistance of wood. In: Proceedings of the international conference on structural health assessment

of timber structures (SHATIS), Lisbon 24. Piazza M, Turrini G (1983) Il recupero dei solai in legno. Esperienze e realizzazioni.

Recuperare 7 25. Piazza M, Riggio M (2008) Visual strength grading and NDT of timber in traditional structure. J Build Apprais

3:267–296

24

Mechanical properties of wood examined by semi-destructive

devices

Michal Kloiber • Jan Tippner • Jaroslav Hrivnàk

Received: 9 November 2012/Accepted: 15 March 2013/Published online: 22 March 2013 RILEM 2013

INTRODUCTION

The establishment of the relations between particular semi-destructive methods (screw withdrawal,

microdrilling, pin penetration and pin pushing, fig.1) and the comparison with destructive standard

compression tests were performed in order to yield a methodology to determine mechanical properties of

a material and bearing capacity of timber elements (from semidestructive devices directly). As we wanted

to explore the relationships between the methods for mechanical properties assessment, we carried out

the experiments using selected wood species, which were represented by an entire tree trunk each

spruce, fir and pine.

25

MATERIALS AND METHODOLOGY

Devices used

The simplest resistance method used in our tests was the measuring of a depth of pin penetration—in this

method the pin is shot into a material with a constant energy.

Another method we used was microdrilling, which differs from the dynamic pin penetration and

screwwithdrawal test mainly by gradual penetration of the material which provides the examiner with its

internal structure. Microdrilling was carried out using Resistograph 2450p, which records the resistance to

the penetration of a small drill 1.5–3.0 mm in diameter. The drill shift is constant and the revolutions are

unchangeable. The output is a profile of energy consumption, i.e. a relative resistance, including

eliminated bit energy consumption induced by friction indeeperlayers.Peaks inthegraph correspond to

high resistance or wood density, while lower points are related to lower relative resistance of wood.

EXPERIMENT

The verification of the mechanical properties prediction accuracy of the semi-destructive devices was

conducted using three basic softwood species;

The species were selected in correspondence with the most commonly used material composition of

historical trusses in the Czech Republic.

The trees grew at a site with typical ecological conditions, without negative anemoorographic effects or

negative impacts due to social positionin the stand. Wood processing was fully under authors’ control;

the selected trees were extracted individually, the trunks were cut to 3 m logs and those were cut into

quarters so that each quarter corresponded to a cardinal direction of the trunk growth. The quarters were

then cut so that a radial plank, 60 mm thick, was obtained from the centre. The 24 planks from each

trunk, i.e. each wood species, were then used for the measuring.

After gradual drying of the planks and conditioning to 12 % moisture, all four mentioned semi-destructive

tests were conducted, one by one. All measuring was conducted in clearly radial direction; pin

penetration by Pilodyn and screw withdrawal by the new device were only superficial, pin pushing by

the new device went to a depth of 110 mm and microdrilling by Resistograph was done through the

whole plank profile, each one meter of the length of plank, from 1 to 18 m of the trunk height and for

each cardinal direction separately. In total, we had 72 positions for each species.

When using the resistance microdrill—Resistograph 2450p (Fig. 5), the Resistance Measure RM the

resistance characteristic corresponding to the area below the curve divided by the width of the measured

section, was calculated using the MATLAB program.

The basic parameters used in the analysis for device verification were the height of the position in the

trunk (Tree Height), wood density (Density), wood strength in compression parallel to the grain [SC(L)],

26

proportional limit in the radial direction [SC(R)], modulus of

elasticityincompressionparalleltothegrain[MOE(L)] and perpendicular to the grain [MOE(R)] and also

hardness according to Janka in longitudinal [H(L)], radial [H(R)] and tangential [H(T)] directions. The tests

were performed in compliance with standard European regulations using 20 9 20 9 30 mm (or 50 9 50 9

50 mm in the case of hardness tests) samples taken at individual positions adjacent to places of measuring

by particular semi-destructive devices.

RESULTS AND ANALYSIS

The average force, the resistance measure, the depth, the maximum force, the hardness in radial

direction, the density and the strength in compression parallel to the grain of the three wood species are

presented in Fig. 7. The results of this analysis prove significant differences among different species, the

sensitivity of the device and the necessity to take account of the species when using the device. Figure 7

also shows that the value of pin pushing average force and resistance characteristic of microdrilling for

pine are substantially lower. This is caused by the presence of sapwood as nearly a half of the pin pushing

or screw withdrawal depth goes through this pliable part of timber. The values of the average density,

SC(L) and MOE(L) are comparable with fir. The relatively higher resistance of fir wood corresponds to the

data presented in literature, worse machinability of fir wood (mainly when compared with pine

machinability) and the ability to keep connecting elements. The last property also corresponds to the

found higher proportion of friction when pushing and withdrawing the pin and especially the screw

withdrawal test where the resistance of fir was about 15 % higher than resistance of pine.

The distribution along the trunk height cannot be neglected. As the wood originated from a closed

canopy stand, the influence of orientation is less probable and can be rejected. That has practical reasons

because the original orientation of the tree in cardinal directions can hardly be established in

incorporated timber.

Using both the devices (pin pushing and microdrilling) it is possible to evaluate the distribution of

properties along an incorporated element, which can overlap with a biotic damage within an in situ

survey. The first 8 m of height represent a decrease in the measured values of up to 1/3, which is often a

difference interpreted as timber defect within a field survey.

The differences in values for particular cardinal directions are not statistical significant (Duncan’s test) and

they correspond to the distribution of density and mechanical properties. The distribution of the measured

values of FAVG and Depth along the trunk height of fir and spruce is also insignificant, only for pine a

significant difference was found. The pine reached a difference of up to 200 kg m-3 of density along the

trunk height; this was revealed even by the superficial measuring using screw withdrawal and pin

penetration. Both of these devices are limited by their ability to measure only the surface of the material,

which causes some distortion when compared with the density and mechanical properties established

from the whole profile.

27

It is recommendable to respect the effect of the longitudinal distribution and to create alternatives which

respect and neglect this effect. Table 1 shows the correlations between the monitored parameters and

the average force of pin pushing. Especially the relation with density and hardness can be considered

strong for all species. The character of pin pushing is closest to the character of damage caused during

hardness tests, which is proved by the closest dependence.

Table 2 shows the correlations between the monitored parameters and the resistance measure for

microdrilling. The relationships are similar to pin pushing, the only difference being the correlation

coefficients, which are 10–20 % lower.

28

Screw withdrawal and pin penetration are methods that only measure the superficial layers of the

material; therefore, the density and mechanical properties manifest lower correlation coefficients than pin

pushing and microdrilling. The smallest variance of measured values for both pin pushing and

microdrilling has been found for pine, where the largest variance of density has been found at the same

time.

29

CONCLUSIONS

A comparative evaluation of semi-destructive and destructive timber testing has been conducted. Semi-

destructive methods were represented by screw withdrawal test, microdrilling, dynamic pin penetration

and a new construction of a diagnostic device for in situ timber evaluation based on the principle of

measuring resistance to gradual pin pushing into timber.

The correlation coefficient for strength parallel to the grain reaches 0.7 for spruce, 0.68 for fir and 0.84 for

pine. The values of the coefficient for density are 0.55 for spruce, 0.59 for fir and 0.84 for pine. The

average force correlates with the other monitored parameters more or less. E.g. the correlation

coefficients for Janka hardness measured in the longitudinal direction reach values from 0.6 to 0.74. The

results of microdrilling are only slightly worse than the new pushing method. The values of the correlation

coefficient for density are 0.65–0.75; for strength in compression parallel to the grain they are 0.52–0.64.

Except for pine, the remaining methods reached worse results. Correlation coefficient values range from

0.54 to 0.59 and even 0.84 for pine in the case of density; the values are considerably lower in the case of

strength parallel to the grain (below 0.4, again except for pine—0.83). It is obvious that closer

dependencies have been found for pine, which in spite of presence of sapwood and heartwood

manifests the lowest variability of properties.

Lower values of coefficients were found for microdrilling (0.3–0.59),

30

REFERENCES

1. Cai Z, Hunt MO, Ross RJ, Soltis LA (2002) Screw withdrawal—a means to evaluate densities of in-situ wood members. In: 13th

International symposium on nondestructive testing of wood, Richmond, pp 277–281 2. Divos F, Kiss FS, Takats P (2011)

Evaluation of historical wooden structures using. In: SHATIS’ international conference on structural health assessment of timber

structures, Lisbon 3. Drda ´cky ´ M, Jirovsky ´ I, Slı ´z ˇkova ´ Z (2005) On the structural health and technological survey of

historic timber structures. In: Proceedings of the international conference: the conservation of historic wooden structures, vol I,

Florence, pp 278–284 4. Drda ´cky ´ M, Kloiber M, Kotlı ´nova ´ M (2006) Low invasive diagnostics of historic timber. In: In-situ

evaluation & nondestructive testing of historic wood and masonry structures, RILEM workshop, Prague, pp 24–40 5. Emerson R,

Pollock D, Kainz J, Fridley K, McLean D, Ross R (1998) Non-destructive evaluation techniques for timber bridges. In: Proceedings of

the 5th World conference on timber engineering, vol I, Montreux, pp 670–677 6. Go ¨rlacher R (1987) Non-destructive testing of

wood: an in situ method for determination of density. Holz as Rohund Werkstoff 45:273–278 7. Gryc V, Holan J (2004) Influence

of position within the tree stem according to growth-ring of spruce (Picea abies/L./ Karst.) with compression wood. Acta Univ

Agric Silvic Mendel Brun 4:59–72 8. Kasal B, Drda ´cky ´ M, Jirovsky I (2003) Semi-destructive methods for evaluation of timber

structures. Structural studies, repairs and maintenance of heritage architecture VIII. In: Brebia CA (ed) Advances in architecture.

WIT Press, Southampton, pp 835–842

9. Kasal B, Tannert T (2011) In situ assessment of structural timber. Stateof the Art reports. Springer,ISBN 978-94-0070559-3 10.

Kloiber M, Kotlı ´nova ´ M, Tippner J (2009) Estimation of wood properties using pin pushing in method with various shapes of

the penetration pin. Acta Univ Agric Silvic Mendel Brun 2:53–60 11. Kloiber M, Tippner J, Drda ´cky ´ M (2011) Semi-destructive

tool for ‘‘In-situ’’ measurement of mechanical resistance of wood. In: SHATIS’ international conference on structural health

assessment of timber structures, Lisbon 12. Kloiber M, Tippner J, Hrivna ´k J, Praus L (2012) Experimental verification of a new tool

for wood mechanical resistance measurement. Wood Res 57(3):383–398 13. Machado JS, Cruz H (1997) Evaluation of the

conservation of wooden structures. Determination of the density profile for non-destructive methods. Portugal J Struct Eng 42:

15–18 14. Marc ˇok M, Reinprecht L (1997) Detection of wood decay with ultrasonic method. Wood Res 42(1):11–22 15. Pellerin

RF, Ross RJ (2002) Nondestructive evaluation of wood. Forest Service, Forest Products Laboratory, Madison 16. Rinn F,

Schweingruber F, Scha ¨r E (1996) Resistograph and X-ray density charts of wood

comparative evaluation of drill resistance profiles and X-ray density charts of different wood species. Holzforschung 50(4):303–

311 17. Rinn F (1994) Catalogue of relative density profiles of trees, poles and timber derived from

Resistograph microdrillings. In: 9th International symposium on non-destructive testing,

Madison, pp 61–67 18. Tippner J, Kloiber M, Hrivna ´k J (2011) Derivation of mechanical properties by pushing of a pin into

wood. In: 17th International nondestructive testing and evaluation of wood symposium, Sopron, pp 575–582

31

Resistographic inspection of ancient timber structures for the

evaluation of mechanical characteristics

C. Ceraldi, V Mormone and E. Russo Ermolli

INTRODUCTION

In the field of the restoration of ancient timber structures, non-destructive testing methods are gaining

great interest and development. These methods can be grouped in two classes: global methods and local

methods. The first ones, specially ultrasonic and vibrational techniques, measure longitudinal elasticity

modulus and can be employed for the classification of timber logs. Local methods, as electronic

penetrometers and superficial hardness methods, are generally used in situ to help and power visual

inspection of timber structures; that remains the first approach to study standing structures to be restored.

Among the non-destructive testing techniques, the method employing Resistograph, showed great

efficiency, because resistographic inspection goes in depth across the examined timber section, and

consequently, it gives more reliable information than the methods whose action is limited to the

superficial layers. In structural inspections, the Resistographic method has widespread applications: - in

measuring real dimensions of transversal sections of structural elements, when they are not directly

accessible; in evaluating the residual resistant section, taking away rotten portions and in detccting not

visible defects. Nowadays, this method is not employed for a quantitative analysis of mechanical properties

of timber structures, even if many research works have been carried out in this field. Examining the

possible employment of Resistographic method to study the variability of the mechanical characteristics of

transversal sections on ancient timber structures is the main scope of the present work. After verifying that

the Resistograph is sensible to density variations, a method to detect local axial compressive strength,

relative to the examined section, once density has been measured, is exposed. Consequently, a sample of

wood worm damaged beech (Fagns sylvatica L.) timber has been experimentally studied, as wood worm

attack determines, in this wood species, a relevant density variation along the whole timber section.

TEST EQUIPMENT

Non-destructive tests have been performed with Resistograph E300PX, a drilling system with a resolution

of 0.1 mm, six advance speed stages (from 70 mm/min to 750 mm/min), three sensitivity level (high,

medium and low) and a maximum penetration depth of 280 mm. This instrument (Fig. 1) shows several

advantages as the easy employment in narrow conditions and the possibility to select the most efficient

advance speed sensitivity combination for the wood species under study, even if it requires frequently

maintenance and calibration work during time. The speed stage employed in the present study has been

Stage 2 (approximately 150 mm/min) with a medium sensitivity level. Of course, diagrams obtained with

the employed instrument are not directly comparable with those obtained with other Resistographic

instruments. The instrument is connected with an electronic storage unit in which the printer for the

32

registration in real time of resistographic charts is incorporated. Those diagrams are printed in 1:1 scale.

Post processing of diagrams is possible due to a dedicated software. The moisture content has been

measured with an electrical hygrometer, the Protimeter mini of Meter House, the range of which is 6-28%.

RESISTOGRAPH AS DENSITY METER

The Resistograph is an electronic drill which drives a small and long needle, with a shaft diameter of 1 -

1.5 ram, into the wood element with constant advance and rotational speeds. The special geometry of

the tip was designed to guarantee that drill resistance mainly affects the tip. Power consumption of the

drilling device is measured electronically as a relative measure of drilling resistance, if constant advance is

guaranteed. These values are recorded relative to penetration depth, on resistographic charts traced in

real time. In the case of dry wood, the drill resistance mainly depends on density. So wood density is

deducible from mean drill resistance reported in resistographic charts, as described in. The resistographic

charts also give the depth of annual rings in the inspected sections and so allow the determination of

annual ring growth. This is correlated to wood density and for some wood species has also been

correlated to ultimate axial compressive strength. To evaluate Resistograph sensibility as density meter,

some tests on coniferous and broadleaf wood have been done. With this aim two sandwiches of

different species, built gluing 25-mm thick layers of each kind, have been tested: one of conifers (pine, fir

and douglas), one of broadleaf (maple, beech, poplar and chestnut) (Fig. 2).

Five resistographic tests for each sandwich have been made. For every species a resistographic measure

has been obtained from resistographic charts corresponding to the main height of the portion of the

diagram relative to the specific wood. In other words, the resistographic measure chosen is the quotient

33

of the diagram integral to thickness of the single layer. Then, n.16 prismatic specimens 25 x 25 x 50 mm

have been taken from each layer and tested to measure density and axial compression strength (UNI ISO

3787/85) for each species. In this way, for each resistographic chart, the resistographic measure taken

from the diagram can be compared with density and strength values corresponding to the mean values

of specimens disposed on the two sides of every drilling (Fig. 3). Density and axial compressive strength

values of the whole sample, consisting of hardwoods and softwoods, are reported as functions of the

resistographic measure in the diagrams of Fig. 4, where linear interpolation curves of resistographic

measure/density and resistographic measure/strength diagrams are shown. While the linear correlation

of density with resisto- graphic measure is good enough (R 2 = 0.6662), between resistographic measure

and axial compressive strength, there is no correlation, as the whole sample consists of different kinds of

wood.

34

35

NON-DESTRUCTIVE DENSITY EVALUATION OF BEECH STRUCTURAL ELEMENTS

As it has been verified that the Resistograph primarily detects density variations, experimental research has

been done to investigate the Resistograph sensibility to register even small density variations along a

structural timber section. With this aim a wood worm damaged beech (Fagus sylvatica L.) timber has

been chosen, as this wood species is subjected to wood worm attack not only in the superficial part and,

consequently, this kind of damage generates density variations for the whole section depth. The sample

submitted to non-destructive and destructive experimental investigations consists of a beech beam,

diameter 210 mm, taken from a demolished floor of the Cathedral in Cava dei Tirreni (Salerno - South of

Italy). This Cathedral (Fig. 5), with a three-aisle basilical plan, was built from 1517 to 1587. The apse and

the transept were rebuilt after the earthquake of 1732; in this period an Archconfraternity was added on

the right side, consisting of a group of vaulted mortuary chapels on the ground floor and a rectangular

chapel on the first floor. The Cathedral was seriously damaged by the earthquake of 1980. The beech

beams come from the Arch- confraternity timber floor that, during restoration, had been demolished, as

not recoverable. The use of beech wood as structural timber is quite unusual; in fact the Cathedral

covering timber structures were all in chestnut, but it could be explained by the large presence of beech

trees in the area.

Sample moisture content, measured by an electrical hygrometer (UNI 9091/87), varied during

experimentation which took almost a year, from 11% and 12%. Four resistographic tests, with different ori-

entations, have been done on seven sections traced at a distance orS0 mm (Fig. 6). Once resistographic

inspection has taken "~ place, the log has been cut across previously -~ described sections, giving eight

slices, 50 mm ~, thick. So resistographic charts corresponding to each section represent wood

characteristics referred to the slices disposed on the right and left sides of the section itself. Superimposing

resistographic charts on slices faces reveals that the reduction in the ordinate of the resistographic chart

occurs in correspondence of wormeaten regions (Fig. 7). Prismatic 25 x 25 x 50 mm specimens have

been taken from each slice for density measure- ments. Specimen dimension has been chosen to allow

performance of axial compression tests as prescribed in existing rules, referring to small clear speci- mens

and not dimensional lumbers. As for sandwiches described in the previous paragraph, resistographic

measures can be correlated to density values for specimens disposed along the resistographic traces. The

resistographic value is compared to the mean value of densities corresponding to specimens taken from

right and left slices on each side of the resistographic drilling (Fig. 8). The resistographic measure/density

diagram in Fig. 9 is based on those mean values.

Starting from a resistographic chart, it is then possible to calculate the mean resistographic measure

relating to the whole thickness of the inspected timber log and to deduce corresponding mean density

from the diagram of Fig. 9. This mean value is relative to a single resistographic chart. At the same time,

the mean value of the resisto- graphic measures of more charts referring to the same timber section,

allows the definition of a reliable value for the mean density of that section.

36

37

EVALUATION OF AXIAL COMPRESSIVE STRENGTH BY MEAN DENSITY

Density and axial compressive strength have been measured on a sample consisting of 235 specimens,

taking those utilized to trace the diagram of Fig. 9 and those cut off the remaining portions of log slices.

Density values and compressive strength values distributions are reported in the histograms of Figs. 10

and 11, respectively. In Fig. 10 class dimension is 35 kg/m3 in a range of S00 to 920 kg/m3; in Fig. 11

class dimension is 5 MPa in a range of 15 - 70 MPa. In the distribution of density values a condensation in

the range of 605 - 815 can be seen, which corresponds to 89% of the specimens. On the contrary,

strength values are distributed on the whole range, as a consequence of too many factors influencing

compressive strength (grain deviation, etc.). Corresponding mean values x m, standard deviation S.D.,

coefficient of variation C.O.V. and characteristic values x~, calculated as in the appendix to Eurocode 5,

are summarized in Table 1. Characteristic value x K is given by the product of mean value x m times

coefficient K. What is deduced from histograms of Figs. 10 and 11 is confirmed by Table 1; in fact, the

coefficient of variation relative to density, when compared with strength, denotes less dispersion and

consequently, there is less penalization in the calculus of the characteristic value. The whole sample is

reported in the diagram of Fig. 12 in which regression curves and confidential limits are deduced as

explained in the previous paragraph. Consequently, by this diagram, it is possible to associate, with the

same confidence, an interval of axial compressive strengths to the mean density value of each structural

section. The inferior limit of that interval gives the local strength value for the inspected section on which

relay for the structural calculations. It is obvious that this value does not provide the compressive strength

of the dimension lumbers and that other kind of inspections are needed to give a classification parameter,

that is outside the scope of the present research. On the other hand, those strength values can play a

fundamental role in planning restoration of ancient timber structures

38

CONCLUSIONS

The proposed methodology is a first approach to the hypothesis of Resistograph use as a characteristic

strength measurer for timber. When visual inspection and other non-destructive and less time consuming

tests allow to propose recoverability of a structural element, resistographic inspection can be employed to

estimate the characteristic axial compressive strengths of transversal sections, that, even if they are only

local parameters, give important data for the structural calculations. The experimentation on beech wood

proved significant as density and corresponding resistographic measure variations due to wood-worm

attack are quite evident. But the proposed methodology can be extended to other wood species which

are used for structural timber, measuring the density and the related local strength variations in the

damaged elements, disregarding the cause of damage. Of course for each species a preliminary experi-

mental study is needed to construct the resistographic measure/density and density/strength diagrams. In

the present research, this preliminary study has been done on beech, that is a few documented wood

species; so results reported in Table 1 give an interesting contribution to the knowledge of this timber. The

evaluation of beech axial compressive strength has been carried out with small clear wood specimens, as

determination of dimensional lumber strength was not pursued in this research.

39

REFERENCES

[l] Talnpone, G., 'Timber structure rehabilitation', (only available m Italian) 1st ed. (Hoepli, Milano,1996). [2] Baldassini, N., Piazza, M.

and Zanon, P., 'In situ evaluation of mechanical properties of timber structural elements', in Proceedings of the 10th International

Symposium on NDT of Wood, Lausanne, Aug. 1996 (Presses Polytechniques et Universitaires Roman&s, 1996) 369-378. [3] Kuklik,

P. and Doipjs, J., 'Nondestructive evaluation of structural timber', in Proceedings of 5th World Conference on Timber Engineering,

Montreux, Aug. 1998 (Presses Polytechniques et Universitaires Romandes, 1998) Vol.I 692-699. [4] Gori, tL. and Paggiarin, C., 'Non

destructive vibration tests on timber truss elements', in Proceedings of 1st RILEM Symposium on Timber Engineering, Stockhohn,

Sept. 1999 (RILEM Publications, Cachan, 1999) 285-294. [5] Renn, R. J. and Kim, J. B., 'Nondestructive evaluation of the stiffness

and strength of in situ timber structural members', in Proceedings of 1st RILEM Symposium on Timber Engineering, Stockholm,

Sept.1999 (RILEM Publications, Cachan, 1999) 275-284. [6] Mattone, M., 'Non destructive inspections for the evaluation of timber

structures conservation', (only available in Italian), Adrastea 9 (1997) 20-27. [7] Uzielli, L., 'Evaluation of timber elements bearing

capacity', (only available in Italian), L'Edilizia 12 (1992) 753-762. [8] Uzielli, L., 'Diagnosis and classification of standing timber struc-

tures' (only available in Italian), in 'Timber: a structural material from the past to the future', Proceedings of the 48th General

Council, RILEM Workshop, Sept. 1994, 88-103. [9] Rinn, F., 'Resistographic inspection of construction timber, poles and trees', in

Proceedings of Pacific Timber Engineering Conference, Gold Coast, Australia, Jul. 1994. [10] Bertolini, C., Brunetti, M., Cavallaro, P.

and Macchioni, N., 'A non destructive diagnostic method on ancient timber structures: some practical application examples', in

Proceedings of 5th World Conference on Timber Engineering, Montreux, Aug. 1998 (Presses Polytechniques et Universitaires

Roman&s, 1998) VoL 1456-465. [11] Rinn, F., 'Inspection and documentation of historic timber con- structions', in Proceedings of

5th World Conference on Timber Engineering, Montreux, Aug. 1998 (Presses Polytechniques et Universitaires tt, omandes, 1998)

Vol. I1368-374. [12] Rinn, F., Becker, B. and Kromer, B., 'Penetration resistance measurements: density profiles of conifers and

deciduous trees', in Proceedings of Lund Symposium on Tree Rings and Environment, Ystad, Aug. 1990. [13] Giordano, G.,

'Timber structures engineering' (only available in Italian) ,5th Edn. (Hoepli, Milano, 1999). [14] UNI ENV 1995 1-1 Appendix A

'Determination of characteris- tic values of 5th percentile from test results and sample accepta- tion criteria'.

40

Using drill resistance to quantify the density in coarse woody

debris of Norway spruce

Tiemo Kahl Christian Wirth Martina Mund and Gerhard Bohnisch Ernst-Detlef Schulze

The relationship between drill resistance and gravimetric wood density relationship is sensitive to the

decay status. Therefore, the best model combines drill resistance and decay class (adj. R2 = 0.732). An

additional experiment showed that drill resistance is also sensitive to the moisture state (fresh vs. oven-dry)

of the sample. The major potential of the method lies in its non-destructive nature which allows repeated

sampling in long-term ecosystem studies or in protected areas where destructive sampling is prohibited.

The limitations of the method are discussed and recommendations for applications are given.

INTRODUCTION

Usually wood discs are taken at different positions along sample logs in various stages of decay. The discs

are dried in the laboratory and the density is calculated as the ratio of dry weight and fresh volume. These

data are then used to establish a relationship between the ‘decay class’ assessed in the field and the

relative density loss.

Drill resistance has been used to measure density and concentrations of carbon and nitrogen in CWD of

red spruce (Picea rubens Sarg.) and Fraser fir [Abies fraseri (Pursh) Poir.] (Creed et al. 2004). Creed et al.

(2004) could show that drill resistance measurements can be employed within a certain range of CWD

density, but nevertheless that they are less precise than displacement or mensuration density

determination. In this paper, they explore drill resistance in combination with fast quantitative field

methods as a method for measuring wood densities across a gradient of decay classes in managed

spruce forests. They use a resistograph that measures the drill resistance in wood. Drill-resistance

measurements are mainly used by arborists or by construction engineers (Rinn 1996; Costello and Quarles

1999; Eckstein and Saß 1994; Niemz et al. 2002) to detect defects either in living trees or in construction

timbers. Furthermore, the method has been used to assess wood density in living trees (Isik and Li 2003)

and to evaluate annual tree ring characteristics (Wang et al. 2003). The method is based on the drill

resistance of a thin drilling needle while it penetrates the wood (Rinn 1996; Rinn et al. 1996).

MATERIALS AND METHODS

A total of 44 deadwood logs of Norway spruce were randomly selected to represent the decay classes 1–

4 (Table 1) and different positions (standing, hanging, downed). For gravimetric density determination in

the laboratory, 10 cm thick discs were cut with a handsaw from the dead wood logs. From logs longer

than 2 m, every meter one sample was taken but at least three samples per tree according to the

41

following scheme: two discs 0.3 m from the base and the top, respectively, and one from the middle. Disc

diameter ranged from 4.7 to 19 cm with a mean of 11.3 cm. To avoid fragmentation of strongly decayed

wood during cutting and transportation, the discs were either taken at temperatures below 0C in a frozen

state or wrapped with 5-cm-wide Velcro fastener. The discs were either processed immediately after

thawing or stored at -20C until further processing. In the laboratory, the thickness, circumference and

weight of the fresh discs were recorded and the drill-resistance measurements obtained. Afterwards the

discs were dried at 70C (not at 103C, to avoid changes in C/N ratios in later measurements) to constant

weight followed by a second drillresistance measurement. The gravimetric density (D [gdw cm-3]) of the

discs was computed as the ratio of dry mass to fresh volume.

DRILL RESISTANCE MEASUREMENTS

They used a RESISTOGRAPH 3450S (RINNTECH, Frank Rinn Engineering and Distribution, Bierhelder Weg

20, 69126 Heidelberg, Germany) to obtain a proxy measurement of dead wood density. The resistograph

uses a microdrillingdeviceequippedwithaneedleof3 mmdiameterand 45 cm length and an automatically

adapted protrusion speed mechanism (Rinn 1996). The resistance to drilling is recorded at a spatial

position resolution of 0.01 mm. The data are stored electronically and printed on paper for visual

inspection in the field (Fig. 1). One measurement usually takes 2–3 min. The number of consecutive

measurements is limited by battery lifetime (30–80 measurements) rather than by data storage capacity

(*400 measurements). Every 80–100 measurements, this equals about 10 m of total drilling length, the

needle was replaced. The drillresistance was measured for each disc along two perpendicular diameters.

The average per disc was used in the statistical analysis. To calculate the average drill resistance per disc,

the dead wood was computationally divided into concentrically, 1/100-mm-wide rings (Fig. 2). The

average was calculated by weighting each measurement (e.g., R1; Fig. 2) by its respective area (A1).

42

RESULTS

Drill resistance R alone explained 65% of the variation in dead wood density (Table 2, model 9). This

model was markedly better than any models containing any or several of the conventional predictors.

These were either models containing the fast quantitative field methods (Table 2, models 1–7), the

subjective classification based on qualitative traits (Table 2, model 8) or combinations of the two predictor

classes (Table 2, models 12–18). Model 9 could be further improved by adding the decay class DC as

categorical variable (Table 2, model 10) indicating that the relationship between drill resistance and

gravimetric wood density is influenced by changes in the wood structure as the log decays. At a given

value of drill resistance, the range of predicted gravimetric wood density spans a range of 0.14 gdw cm-3

and differences between consecutive decay classes are about 0.045 gdw cm-3. Within a given decay

class the relationships are visibly linear down to densities of 0.1 gdw cm-3 and the variances are

homoscedastic (Fig. 3). Allowing the slopes of individual decay classes to vary did not improve the model

performance (Table 2, model 11). A paired test revealed that moisture influences the drill resistance. Oven-

dry CWD has significantly lower drill resistance than fresh material [t[129] = 13.19, P\0.001, mean

43

difference 108.6 (95% CI: 92.3–124.8) drill resistance units]. The difference between the drill resistances in

fresh- and oven-dry state of CWD for the same sample excludes the effect of wood density and should

mainly reveal the effect of moisture content on the drill resistance. However, there was no significant

linear relationship between the moisture content (%) of fresh CWD and the difference between drill

resistance in fresh and oven-dry state (y =-0.006x ? 109, R2 = 0, P = 0.927).

44

45

DISCUSSION

Drill resistance in combination with decay classes provides a useful proxy of the absolute wood density in

decaying wood in situ. The resulting predictive model explained approximately 75% of the variance of

wood density and was therefore superior to models relying on conventional predictors. Next to its

potential as proxy for density, the method has several distinct advantages. First of all, it is a nondestructive

method. Its main application is in long-term ecosystem studies where destructive sampling of logs should

be avoided to minimize the effect of the sampling on the decay process itself and to allow repeated

sampling at multiple positions along an entire log. The method can also be used in areas where

destructive sampling is legally prohibited. This is important because in many industrialised countries the

highest stocks and the highest diversity of coarse woody debris are found in protected nature reserves.

Another advantage of the method lies in the additional information provided by the measurement.

Because in many tree species early and late wood exhibit vastly different wood densities, tree rings are

visible on the 1/100-mm resolution output from which information regarding the age and the ring width

pattern can be extracted. Furthermore, the method would be useful to study the process of

fragmentation and the spatial pattern of decay because the resistograph easily detects small cavities,

boreholes of insects, and cracks in the wood.

A limitation of the method is that drill resistance is influenced by a range of wood features other than

density. The fact that the categorical variable decay class was significant in the best candidate model

illustrated that changes in wood structure and chemical composition that go along with the decay

process influences the relationship between drill resistance and density. Preliminary analyses of studies in

laboratory with wood of various other species revealed significant species specific differences in the

relationship between drill resistance and wood density. The lowest detectable drill resistance values with

the resistograph are between 100 and 200 which were in this study sufficient to detect the lowest wood

densities down to about 0.1 g cm-3 . In the case of lower wood density, the resistograph would not be

able to detect any changes. This could cause problems when adapting this method to highly decayed

wood of other tree species where no more drill resistance can be detected but still woody material is left.

As shown above, also the moisture state of the wood influences the relationship between drill resistance

and density with moist wood (fresh state) exhibiting a higher drill resistance than oven-dry CWD.

However, the offset between moist and oven-dry CWD is itself not a function of the moisture content. This

is evidenced by the lack of a significant linear relationship between moisture content and the difference

between drill resistance in moist (fresh state) and oven-dry state. Therefore, when estimating the wood

density with drill resistance measurements, the moisture content of CWD should not to be taken into

account. For the application, it is therefore important to calibrate the resistograph for each tree species

and decay class separately and to conduct the measurements in samples of comparable moisture status.

With these caveats in mind, the drill resistance measurements represents a powerful method in the field

of dead wood ecology.

46

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Burnham KP, Anderson DA (1998) Model selection and inference—a practical information-theoretic approach. Springer, New

York Christensen M, Hahn K, Mountford EP, Odor P, Standovar T, Rozenbergar D, Diaci J, Wijdeven S, Meyer P, Winter S, Vrska T

(2005) Dead wood in European beech (Fagus sylvatica) forest reserves. For Ecol Manag 210:267–282. doi:10.1016/j.foreco.

2005.02.032 Costello LR, Quarles SL (1999) Detection of wood decay in blue gum and elm: an evaluation of the

Resistograph and the portable drill. J Arboric 25:311–318 Crawley MJ (2002) Statistical

computing—an introduction to data analysis using S-Plus. Wiley, Chichester Creed IF, Webster KL, Morrison DL (2004) A

comparison of techniques for measuring density and concentrations of carbon and nitrogen in coarse woody debris at different

stages of decay. Can J For Res Rev Can Rech For 34:744–753. doi:10.1139/ x03-212 Eckstein D, Saß U (1994)

Bohrwiderstandsmessungen an Laubba ¨umen und ihre holzanatomische Interpretation. Holz Roh Werkst 52:279–286 Graham

RL, Cromack K (1982) Mass, nutrient content, and decayrate of dead boles in rain forests of Olympic-National-Park. Can J For Res

Rev Can Rech For 12:511–521. doi:10.1139/x82-080 Grove SJ (2002) Saproxylic insect ecology and the sustainable management

of forests. Annu Rev Ecol Syst 33:1–23. doi: 10.1146/annurev.ecolsys.33.010802.150507 Harmon ME, Sexton J (1996) Guidelines

for measurements of woody detritus in forest ecosystems. Rep No US LTER Publication No. 20 Harmon ME, Franklin JF, Swanson

FJ, Sollins P, Gregory SV, Lattin JD, Anderson NH, Cline SP, Aumen NG, Sedell JR, Lienkaemper GW, Cromack KJ, Cummins KW

(1986) Ecology of coarse woody debris in temperate ecosystems. Adv Ecol Res 15:133– 302. doi:10.1016/S0065-2504(08)60121-

X Heilmann-Clausen J, Christensen M (2003) Fungal diversity on decaying beech logs—implications for sustainable forestry.

Biodivers Conserv 12:953–973. doi:10.1023/A:1022825809503 Isik F, Li BL (2003) Rapid assessment of wood density of live trees

using the resistograph for selection in tree improvement programs. Can J For Res Rev Can Rech For 33:2426–2435.

doi:10.1139/x03-176 Jonsson BG (2000) Availability of coarse woody debris in a boreal old-growth Picea abies forest. J Veg Sci

11:51–56. doi:10.2307/ 3236775 Jonsson BG, Kruys N, Ranius T (2005) Ecology of species living on dead wood—lessons for dead

wood management. Silva Fenn 39:289–309 Korpel S (1997) Totholz in Naturwa ¨ldern und Konsequenzen fu ¨r Naturschutz

und Forstwirtschaft. Forst Holz 52:619–624 Lonsdale D, Pautasso M, Holdenrieder O (2008) Wood-decaying fungi in the forest:

conservation needs and management options. Eur J For Res 127(1):1–22. doi:10.1007/s10342-007-0182-6

472 Eur J Forest Res (2009) 128:467–473-123

Mund M, Schulze ED (2006) Impacts of forest management on the carbon budget of European beech (Fagus sylvatica) forests.

Allg Forst Jagdztg 177:47–63 Naesset E (1999a) Decomposition rate constants of Picea abies logs in southeastern Norway. Can J

For Res Rev Can Rech For 29:372–381. doi:10.1139/cjfr-29-3-372 Naesset E (1999b) Relationship between relative wood density

of Picea abies logs and simple classification systems decayed coarse woody debris. Scand J For Res 14:454–461. doi:10.1080/

02827589950154159 Neter J, Kutner MH, Nachtsheim CJ, Wassermann W (1996) Applied linear statistical models, 4th edn.

McGraw–Hill, Boston Niemz P, Bues CT, Herrmann S (2002) Die Eignung von Schallgeschwindigkeit und Bohrwiderstand zur

Beurteilung von simulierten Defekten im Fichtenholz. Schweiz Z Forstwesen 153:201–209. doi:10.3188/szf.2002.0201 Norden B,

Paltto H (2001) Wood-decay fungi in hazel wood: species richness correlated to stand age and dead wood features. Biol Conserv

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101:1–8. doi:10.1016/S0006-3207(01)00049-0 Rinn F (1996) Resistographic visualization of tree-ring density variations. In: Dean

JS, Meko DM, Swetnam TW (eds) Tree rings, environment, and humanity, radiocarbon. Department of Geosciences, The

University of Arizona, Tucson, pp 871– 878

Rinn F, Schweingruber F-H, Scha ¨r E (1996) RESISTOGRAPH and X-ray density charts of wood comparative evaluation of drill

resistance profiles and X-ray density charts of different wood species. Holzforschung 50:303–311 Rouvinen S, Kouki J (2002)

Spatiotemporal availability of dead wood in protected old-growth forests: a case study from boreal forests in eastern Finland.

Scand J For Res 17:317–329. doi:10.1080/ 02827580260138071 Speight MCD (1989) Saproxylic invertebrates and their

conservation. Council of Europe, Strasbourg, France Wang SY, Chiu CM, Lin CJ (2003) Application of the drilling resistance

method for annual ring characteristics: evaluation of Taiwania (Taiwania cryptomeribides) trees grown with different thinning

and pruning treatments. J Wood Sci 49:116–124. doi: 10.1007/s100860300018 Weber K, Mattheck C (2001) Taschenbuch der

Holzfa ¨ulen im Baum. Forschungszentrum Karlsruhe GmbH, Karlsruhe Wirth C, Schwalbe G, Tomczyk S, Schulze ED,

Schumacher J, Vetter M, Bo ¨ttcher H, Weber G, Weller G (2004) Dynamik der Kohlenstoffvorra ¨te in den Wa ¨ldern Thu

¨ringens. Landesanstalt fu ¨r Wald und Forstwirtschaft, Gotha Yatskov M, Harmon ME, Krankina ON (2003) A chronosequence of

wood decomposition in the boreal forests of Russia. Can J For Res Rev Can Rech For 33:1211–1226. doi:10.1139/x03-03

48

NDT METHODS FOR THE ASSESSMENT OF STRUCTURAL

TIMBER: REPORT ON THE RESEARCHES CARRIED OUT AT THE

UNIVERSITY OF TRENTO (ITALY)

Maurizio Piazza and Mariapaola Raggio

THE EXPERIMENTAL ACTIVITY

THE TEST MATERIAL

In the researches reported in this paper, different types of specimens have been analysed, with regards to

their dimensions, species, geographic origin, age, condition and moisture content.

On the other hand, tests were also carried out on samples at smaller scale, obtained from portions of old

beams.

A total of 46 elements were investigated, among which the 65% in structural size.

All tests were carried out on old timber, recovered from disassembled structures, whose age globally

spans five centuries.

The species analysed are three softwoods, spruce and larch, and a hardwood, chestnut, that are typically

present in traditional timber structures in Italy.

Test material has been labelled, in order to recognize its species and origin.

TESTING EQUIPMENT AND TESTING PROCEDURES

Among the global ND testing, the following measures have been taken:

- (NDT1) fundamental frequency of longitudinal vibration with the element centrally supported;

- (NDT2) fundamental frequency of longitudinal vibration with the element centrally restrained;

- (NDT3) fundamental frequency of trasversal vibration with the element simply supported at the ends;

- (NDT4) propagation time of stress waves along the entire lenght of the beam;

- ultrasonic waves velocities;

- (NDT5) transducer placed at the ends of the element, parallel to the grain

- (NDT6) transducer equally spaced at a fixed distance, on the same element face for local piecewise

readings;

Among the local non-destructive methods test invented by Piazza and Turrini was used to estimate the

longitudinal modulus of elasticity (NDT7) by measuring the load force R required to embed 5mm a 10mm

diameter steel emispherical bit. The measure were made in five positions, equally spaced along the

element , for each lateral side, each measure is the mean of five different tests.

49

Measure on saturated samples were taken using NDT5 and NDT7.

For the indirect measure of the density of the wood, the following tests where chosen:

- Measure of the penetration of a steel pin (Pylodin), driven into the wood with a constant energy (NDT8);

measurement were taken close to the ends and at the mid-span of each element.

- (NDT9) measure of the drilling resistance during penetration into the wood of a drill bit (Resistograph);

tests were carried out on the three sections equally spaced along the element; for each section two tests

were performed along the apparently tangential direction and one along the apparently radial direction.

The data for density are derived from ratio between mass and volume of the entire element. Because,

most of the elements were characterized by the presence of geometrical irregularities, notches, wane and

splits, measures have been taken at every 100cm along the element axe, for the volume determination.

Density values obtained by direct weighting have been compared with the mean values resulting from

indirect measurements. A visual inspection on each tested element was preliminary performed, searching

for main natural defects and biological degradation.

ANALYSIS OF THE RESULTS

For conditioned wood, the mean differences in percentage between the elastic modulus obtained from

static bending test and the adopted NDT methods are 15% for the dynamic tests (NDT1), 30% for the

ultrasonic tests and 2% for the hardness tests (NDT7). For saturated wood, the mean error is 21% for

NDT5 and -7% for NDT7.

CONCLUDING REMARKS

For the chestnut elements the adopted NDT techniques showed lower correlations than for the tested

softwood species. This is due to the fact that the most of the NDT methods were conceived and tested

especially for species that are more widely used in modern constructions while hardwood species, such as

chestnut, are common in traditional structures, especially in the Mediterranean area.

A correlation between Resistograph data and density can be found only when the element shows similar

Resistographic curves in the different tested sections. This means that the method is not able to predict

density (or related mechanical properties, in cases of elements with local macroscopic heterogeneites.

Finally, different methods have to be combined and the obtained data have to be critically analyzed, in

order to predict reliable values of the investigated parameters.

50

GEOMETRIC ASSESSMENT AND NON-DESTRUCTIVE

EVALUATION OF TWO TIMBER KING-POST TRUSSES

Jorge M. Branco, M. Piazza and Paulo J. Cruz

Non destructive tests can be classified in two distinct groups based in the amount of material used in the

evaluation. Hardness tests Pylodin and Resistograph are based in local evaluation of the material. In situ,

where the assessment of entire structural element can be difficult, techniques based on local evaluation

can be represent some advantages. However, local evaluation if some precautions are not taken into

account, may represent only the evaluation of a small part of the material. NDT methods oblige to have a

considerable number of test results, in order to be indicative of the entire piece. Fortunately, usually, non

destructive test are easy to handle.

NON DESTRUCTIVE TESTS

HARDNESS TEST

Hardness is generally defined resistance to indentation. Actually, wood hardness involves compression,

shear strength and fracture toughness. Wood hardness is positively correlated to density, and as a

consequence to the material strength properties. Moreover hardness is inverse proportion to the moisture

content.

In the performed tests, harness has been estimated by measuring the load force R required to embed

5mm a 10mm diameter steel emispherical bit. The test area must be clear, that is without visible defect.

The value of R was obtained by averaging the tests results made in the four longitudinal faces of the

element, in numbered sections every 80cm wide. Each test consisted in five measures taken in each tested

area.

PILODYN 6J METHOD

The Pilodyn method uses a steel pin the of a fixed diameter driven into the material by a dynamic force.

The depth of penetration is correlated with material density.

RESISTOGRAPH

The use of a small diameter needle like drill was introducted by Rinn. The cutting resistance of a needle is

recorded as a function of depth as the needle penetrates the timber. The resulting profile can be used to

determine the location and extent of voids and variation in material density. This technique is highly

effective for quantifying the extent of deterioration in timbers. Some researchers have tried to use the

results of the Resistograph as prediction of the mechanical properties.

51

The area of a resistance drilling plot can be affected by multiple parameters including drill bit sharpness

and general equipment use such as drill orientation. On a single member, changes in the orientation of

the drill with respect to growth rings will change the calculated RM value with each drilling. Nevertheless,

resistance drilling can be used to estimate mechanical properties of members based on the quantification

of deterioration and basing calculation on the remaining sound material and information on clear

strength that can be estimated with other non and semi destructive testing.

In this work, Resistograph was used mainly with the purpose to detect deterioration and to evaluate the

voids existing inside the timber members. The main objective of using this technique was not to predict

mechanical properties but to complete the information given by the others non-destructive tests realised.

In particular the evaluation of the deterioration level and the voids existing inside the members, and for

that, not visible, were the main purpose of the use of resistograph in the two trusses analysed. In each

element of the two trusses, a small number of sections were selected in which two resistograph charts

were collected.

DISCUSSION

Others researchers have tried to correlate the Resistance Measure obtained with the resistograph test with

density. The same attempt was made but the correlation obtained is very poor (r^2= 0,02). The difficulties

involved in this kind of test were already pointed out. The area of a resistance drilling plot can be affected

by multiple parameters including drill bit sharpness and general equipment use such as drill orientation.

These uncertainties are amplified in the case of old timber elements, with splits and slope of grain caused

by moisture content variation and shrinkage. These is defects have a significant impact in the area of the

resistance drilling plot used to calculate Resistance Measure.

Difference between old and new wood properties results in different velocity due to different wood

density. Görlacher investigated the correlation between modulus of elasticity and strength of old wood

and he found that correlation coefficients are approximately the same for old and new wood.

CONCLUSIONS

Resisting drilling obtained with the Resistograph, the penetration depth achieved with the Pilodyn and the

hardness Turrini-Piazza tests results were correlated with the density values.

52

POST FIRE INVESTIGATION OF ST. BERNARD'S CHURCH NEW

JERSEY USA

Ronald W. Anthony, Edmund P. Meade and Annabelle R. Trenner

QUANTIFICATION OF DETERIORATION

In addition to a preliminary inspection inspection of wood elements using a combination of visual

observation and probing, resistance drilling was conducted to determine loss of material due to wood

decay. Resistance drilling is a quasi non destructive technique that is used for determining the relative

density of wood. Quantification of the extent of deterioration was needed by the structural engineers to

analyze the capacity of the remaining elements to take loads from material self weight, wind, snow and

other loads. In addition, the architects were concerned that concealed wood deterioration had occurred

due to poor building maintenance, especially along the roof eaves and at valleys and other deteriored

flashing locations observed on the exterior.

EXTENT OF DETERIORATION

The primary area of interest for the investigation was the base of trusses where they bear on the timber sill

plates at the top of the masonry walls. The placement of the scaffolding enabled resistance drilling near

the base of the truss chord that performs as principal rafters in supporting the roof. A wooden skirt and

decorative trim restricted the ability to drill at the bottom of the truss chord. Therefore, resistnce drilling

was conducted as low as possible to the bottom of the truss chord just above the wooden skirt.

The wooden skirt had been removed at one truss, exposing the base of the truss member and the timber

sill. This truss chord and the sill had visible deterioration due to decay fungi. This was the only truss

location where direct access to the truss/sill plate was possible.

The architects selected this location because it was in the valley behind the North Tower and vulnerable

to water ingress. Resistance drilling near the base of the other trusses that were accessible by the

scaffolding did not reveal deterioration due to insect or decay activity.

Although deterioration was found at the base of only one truss, the inability to drill at the interface of the

truss chord and the sill plate is worth noting. The findings of this investigation were that deterioration was

not present a short distance above the truss base.

CONSTRUCTION LAYUP AT THE BASE OF THE TRUSSES

Initial resistance drilling through the truss chord near the base produced puzzling profiles of the cross

section. What appeared to be intemal voids in the cross section did not appearance of voids due to decay

or insect attack. Additionally the voids (or lack of solid wood) were so consistent that further examination

53

of the profile of the truss chord was conducted Initially thought to be solid, large eross seetion timbers, the

truss chords were found to consist of a layup of three wood members that were fastened together, This

was verified by the distinct resistance drilling results shown in Figure 3. It is clear that while drilling across

the face of the truss chord three pieces of wood were penetrated. Near the base of the truss chord the

center member was the brace for the arch.

NON DESTRUCTIVE EVALUATION AT MISSION SAN MIGUEL

ACHIEVEMENTS AND LIMITALIONS

Douglas W. Porter and Ronald W. Anthony

QUANTIFICATION OF DETERIORATION USING NONDESTRUCTIVE EVALUATION TECHNIQUES

In addition to visual inspection, resistance drilling and digital radioscopy were employed to drilling

damage patterns and quantify in typical elements, Resistance is a quasi non-destructive technique for

determining the relative density of is best suited for determining internal problems in timbers that do not

show obvious signs of deterioration such as surface decay insect bore holes. Internal voids at the lo drilled

can be detected by observing the relative density of the wood as it is printed on the strip. Resistance

drilling was conducted on four vigas within the nave using the lML RESI M300 Resistance Drilling system

(Figure 3). The vigas were selected for testing based on their appearance to determine if it might be

possible to establish a correlation between the extent of staining on the viga surface and the extent of

internal damage. The drilling locations were selected to give an indication of the typical pattern of internal

damage. It was discovered that, with the larger-dimension elements like vigas, corbels, and deck timbers,

the distribution of water staining is not a reliable indicator of termite damage on the interior of the

elements. Resistance drilling of vigas encountered section losses, occasionally in excess of 50 percent,

though damage levels were typically much lower than this; section losses were encountered in water

stained elements and in elements relatively free of surface damage. In general, damage was found to be

concentrated along adobe walls, structural elements in projecting sections of the retablo were not

similarly available to visual inspection, and it important to determine deterioration levels without removing

casework or darniging early nineteenth century finishes. Resistance drilling provided accurate results

relatively quickly and without any dismantling of the woodwork Examination of structural elements fixing

the wooden pulpit to the adobe wall using resistance drilling confirmed insect damage in the threshold

but discovered relatively little damage in the softwood elements supporting the pulpit. However, plaster

around lookouts was damaged in the last earthquake, indicating some movement in the woodwork and

pulpit and canopy appear to be somewhat out of plumb, This raises obvious question about the

condition of pulpit and canopy anchorages which must be investigated in the next phase of work.

54

SUMMARY

Resistance drilling and digital radioscopy were used to investigate the condition of wood components at

Mission San Miguel. These non-destructive evaluation techniques were successful in achieving the

following

- The extent of deterioration and remaining cross section of the vigas and other structual wood

components could be quantified where they were not embedded more than 10-20 cm in the adobe

walls.

- The pattern of deterioration in the vigas due to insect attack could be determinod through either

resistance drilling or digital radioscopy. -Resistance drilling was able to provide a more rapid assessment of

damage iti the timbers radioscopy because of set-up and data analysis time required.

-The representative pattem of deterioration in the decorative ceiling baards due to insect attack could be

determined through digital radioscopy

REFERENCES

On site Assessment of Concrete, Masonry and Timber Structures SACoMaTiS 2008

Varenna, Italy 1-2 September 2008

Edited by L. Binda, M. Di Prisco and R. Felicetti volume 2

RILEM publications S.A.R.L.

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TECHNICAL DEVICES

COMPARISON: RESISTOGRAPH 4452 (RINNTECH) VS. PENETROGRAFO F400 (BOVIAR)

http://www.rinntech.de/content/view/8/34/lang,english/index.html

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Applications

For street, park and forest trees

Detection of decay, cavities and cracks

Determination of the wood quality

For construction timber, poles and playground equipment

Wood inspection

Determination of wood quality

Detection of cracks, cavities and decay

Properties and advantages

Low weight of 4.0 kg

Speed of up to 40 cm/min

More than 50 drillings in hard wood with a single battery charge, more than 100 drillings with the

extended PowerPack

Computer-controlled feedrate

Drilling depth: 45 cm

Needle returns automatically

Rechargeable long-life battery without memory effect

Synchronous printing on integrated printer

Storage of up to 500 profiles in the internal data memory

Available models (examples):

RESISTOGRAPH® 4453-P with 45 cm drilling depth

Specific design for professional diagnosis of trees and timber.

Package includes:

Resolution 1/10 mm

Speed of up to 40 cm/min

PowerPack 12V power supply (172 Wh)

Integrated thermo printer

Control electronics

Memory for up to 500 measurements

PC interface

USB adapter cable for data transmission to PC

DECOM™ Professional software for data transmission and processing

shoulder bag for PowerPack and system case for complete system

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RESISTOGRAPH® 4453-S with 45 cm drilling depth

Specific design for scientific diagnosis of trees and construction timber.

Package includes:

Resolution 1/100 mm

Speed of up to 40 cm/min

PowerPack 12V power supply (312 Wh)

Integrated thermo printer

Control electronics

Memory for up to 500 measurements

PC interface

USB adapter cable for data transmission to PC

DECOM™ Scientific software for data transmission and processing (including tree ring analysis)

shoulder bag for PowerPack and system case for complete system

RESISTOGRAPH® 4452-S with 45 cm drilling depth

Specific design for scientific diagnosis of tropical trees and timber.

Package includes:

Resolution 1/100 mm

Speed of up to 30 cm/min

PowerPack 12V power supply (312 Wh)

Integrated thermo printer

Control electronics

Memory for up to 500 measurements

PC interface

USB adapter cable for data transmission to PC

DECOM™ Scientific software for data transmission and processing (including tree ring analysis)

shoulder bag for PowerPack and system case for complete system

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