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METHODST9

MEASUREMENT OF THE DEFLECTION AND RADIUS OF CURVATURE OF A ROAD PAVEMENT

1 SCOPE This method covers the measurement of the deflection and radius of the longi-tudinal curvature of a road pavement under the dual wheels of a loaded truck with a standardized axle load, fyre size, tyre spacing and lyre pressure. The de-flection is measured by means of a deflection beam and the radius of curvature by either the deflection beam or the curvature meter,

2 APPARATUS 2.1 A deflection beam (See Figure ST9!1). 22 Two dial gauges with 0,01 mm graduations and a range of 25 mm, or electronic

measuring devices accurate to 0,01 mm (see 5.1). 2.3 A device for calibrating a deflection beam (see Figure ST9d'). 2.4 A curvature meter (see Figure ST9!!11) . 2.5 A heavy truck with a single rear axle having dual wheels loaded on a level sur-

face to effect a rear axle load of 80 kN (40 kN on each dual wheel). The rear axle should be fltted with 1 100 x 20 tyres or 1 000 x 20 tyres with a road con-tact length of 200 mm. The spacing between the walls of the two lyres on each dual wheel should be between 75 and 90 mm.

2.6

(Spacer rings will probably have to be inserted between Ihe wheel flanges to at tain this spacing.) Two load meters, complete with ramps. and two wedge-shaped wooden blocks of the same height for supporting the front wheels of the truck (only if checking and reloading are to be done on the road).

2.7 An accurate tyre pressure gauge and pump. (The pump can be a compressor driven by the truck's engine .)

2.8 An indicator rod for the truck driver. attached to the truck with a G-clamp Of by other means.

2.9 (Optional) Pointers that can be attached to the truck's body 1,2 m in front of the centre of the rear axle and in line with the spacing between the dual tyres of each rear wheel. (Similar pointers can also be attached behind the rear wheels as gUides to facilitate aiming and the positioning of the deflection beam and curvature meter.)

2.10 A fold-up template, marked in suitable divisions.

2.11 A thermometer (mercury in glass or rotary dial type) 0 to 100C, accurate to 1 ae.

2.12 Miscellaneous items such as: a measuring tape, chalk. paint and brush, safety hard hats. a hammer. steel pegs, etc.

Special methods Orat! TMH6. Pretona. South Africa, 1984 37

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3 3.1 3.1. 1

METHOD Preparatton prior to taking measurements Selection of test point(a) Test points are normally selected in the wheel paths of the lane to be tested. These spots may be selected in a random fashion or marked at regular inter-vals. If a fairly long section of road is to be surveyed, all the test spots may be selected and marked with road paint before the measurments are taken.

3.1.2 Checking of loada on rear wheels

3.1.3

The truck described in 2.5 is pre-loaded and the load on the rear wheels checked. This load should under normal conditions not require re-checking . It IS realised that the crossfal! and/or grade of roads change, and that . due to over-hang. the loads on the rear wheels may change considerably from one point to another. However, the 80 kN axle as obtained by loading on a leve! surface can be considered to be the standard axle. If. however. a load of precisely 40 kN is required for a specific purpose, the following procedure should be used for each test point in lire with and about 4 m away from the test point < Set up the two load meters with a ramp in front of each rear outSIde whee l, and t;,e wedge-shaped wooden blocks in front at the front wheels. Drive the truck onto the load meters and ' blocks so that the rear outside wheels stop squarely over the weighplates of the !oad meters. With the driver seated, adjust the load to effect a loadmg of 40 kN or. each of the two rear outside wheels . (If only one load meter is being used, the outside wheel on the other side of the truck must be supported with a block of the same height as that of the load meter.)

Marking of testing layout 3,1.3.1 At points where it is Important that the toe of the deflection beam and the

curvature meter should be placed precisely on a selected test point Secure the indicator rod firmly to the body of the truck ensuring that it is con-veniently placed and clearly visible to the driver from his cab. Guide the driver until the appropriate dual wheels are directly over the test spot. Place the fold up template on the road alongside and parallel to the truck with its zero mark di-rectly under the point of the indicator rod and then mark oft with chalk or paint the final stop position 3 m ahead of the truck from the zero mark on the tem-plate (see Figure ST9/IV). As soon as the marking has been done, reverse the truck to the" -1.2 m" position indicated on the template. Do not leave the truck standing on the test point for longer than is necessary. An alternative and more convenient procedure is possible if pointers as described in 2.9 are available. The truck is positioned so that the pOinter 1 ,2 m in front of the centre of the rear axle is directly over the test point. The template is then placed on the road alongside and parallel to the truck with its .. -1 ,2m" mark directly under the point of the driver's indicator rod. The final stop position is then marked off 3 m ahead of the zero mark on the template (see Figure ST9/IV).

3.1.3.2 For a deflection and curvature survey over fairly long sections of road where accurate positioning on the preselected test points Is not neces-sary

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Where a great number of points are to be dealt with, deflections and curvatures are normally measured at the same time using the deflection beam and the cur-vature meter simultaneously. It is then only necessary to provide marks for the driver. Two marks must be made for each test point - one for the initial position of the truck and one 4,2 m ahead of the initial point for the final stop position.

Specia! methods Draft fMH6, Pretoria. South Africa, 1984

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3.1.4

3.2 3.2.1

These marks are normally made on the lane lines and the driver's indicator is lengthened so that he can use the lane lines as a guide while the wheels of the truck are still in the wheel paths (see 5.8). Pointers similar to those described in 2.9 are then used to facilitate the corrsct piacing of the deflection beam and curvature meter.

Installation of'thermometer (on asphalt surfaces only) Using a steel peg, punch a hole about 25 mm deep into the road surface near the test area. Insert the thermometer and ensure good thermal contact by filling the space around the thermometer with fine sand.

Measurement ot deflection with the deflection beam Calibration Of deflection beam (see 5.1) Position the deflection beam 50 that the toe of the movable beam rests on the calibration device when the beam is undamped. Adjust the dial gauge attached to the calibration device so that the spindle shaft 01 the gauge rests on top of the beam. Switch on the vibrator to reduce any effects of friction in the instru-ment and zero the deflection beam and calibration device gauges Apply the following series of adjustments to the calibration deVIce by means of the adjust-ment screw and record the corresponding readings indicated on the deflection beam's dial gauge or indicator. Since the lengths of the movable beam on either side of the pivot are in a 2: 1 ratio, the readings obtained on the deflection beam gauge must be multiplied by 2: 0-100-0, then 0,5. 10, 50, 100.50. 10.5. hundredths of a mm (see 5.1) If the differences between the two sets of values do not exceed 0,02 mm, the deflection beam IS functioning satisfactonly (see 5.2). However, if backlash is indicated. i.e. the difference exceeds 0.02 mm. the equipment is not working satisfactorily. Oust may be fouling the splndie shafts of the dial gauges and/or the bearing in the pivot-action support of the mcvable beam. Remedy any er-ror in the readings due to friction by cleaning the spindie shafts and bearing thoroughly with benzine. All such moving parts must also be kept dry and should never be oiled or greased. Moisture or dampness cause friction on the dial gauge spindle shaft and this part must be cleaned often in humid or rainy weather. After cleaning, the catibration procedure should be repeated. If the two sets of values still do not agree satisfactorily, the equipment must be checked for fauity components.

3.2.2 Checking of tyre pressures Check the tyre pressure of the rear dual wheels with a lyre pressure gauge and. if necessary. adjust the pressure to 520 kPa.

3.2.3 Installation of beam between dual wheels With the truck standing at the .. -1.2 m" position and the engme idling. position the beam between the appropriate rear duat wheels so that the toe of the mov-able beam is directly above the test spot Ensure that there is sufficient clear-ance on either side of the movable beam for the dual wheels to bypass the

1 beam without touching it. To do this take a sighting between the dual wheels from behind, noting and correcting the placement of the instrument between them so that the pair of wh~els will eventually move forward on either side of

SpecIal methods Draft TMH6. Pretona. South Afnca, 1984 39

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the beam and paralle! to it. The positioning of the beam will be made easier If a set of pointers as described in 2.9 is available. Unclamp the movable beam and bring it to the centre of its play with the fear sliding adjustment. Switch on the vibrator to reduce any effects of friction in the instrument and adjust the dial gauge to zero (see 5.1 and 5.2)

3.2.4 Measurement of deflections Drive the truck forwtrd slowly and smoothly to the " + 3 m" final stop pOSItion. Record the initial zero dial gauge readjng. the maximum reading as the dual wheels move over and past the lest point and the final reading when the truck is stationary at the;final stop position. Reverse the truck to the" -1.2 m" position (see 5.4) . Repeat the procedure un-til three sets of well-correlated deflection readings have been obtained (see 5.8) . Record the road temperature (on asphalt surtaces only - see 5.9).

3.3 DeterminatIon of radius of curvature 3.3.1 USing the deflection beam

3.3.2

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Follow the safT'e procedure as described in 31 to 31 .3.1 and 3.2.1 to 3.2.3 in-clusive. Drive the truck forward slowly and smoothly to about the "+ 0,6 m" position, stopping briefly at the "-0.15 m" and "+0,15 m~ positions on the template. Re-cord the dia! gauge readings at the latter two pOints. as well as the maximum reading as the dual wheels move over and pass the test point. Reverse the truck to the "_1 ,2 m" position. Repeat the procedure until three sets of well-corre lated deflection readings have been obtained . Record the road temperature (on asphalt surfaces only - see 5.9) .

Using the curvature meter Follow the same procedure as described in 3.1 and 3.2.2. With the truck standing at the "-1 .2 m" position and the engine idling , place the curvature meter on the test point with the gauge centred over this mark. the dial facing to the rear of the truck. Ensure that there is sufficient clearance on either side of the instrument for the dual wheels to bypass it witllout touching it. To do this take a sighting between the dual wheels from behind, noting and cor-recting the placement of the instrument so that the pair of wheels will eventually move forward on either side of the instrument parallel to it. With the instrument correctly positioned, adjust the dial indicator needle to its top zero poSition by turning the adjusting nut which is sitUated at the opposite end of the bar to the dial gauge. It is essential to ensure that not more than one-eighth of the total travel range of the spindle is traversed in making this ad-justment to zero, since sufficient range must be left on the spindle to ailow for unexpectedly high readings. Drive the truck forward slowly and smoothly to the "+3 m" final stop position. Record the initial zero dial gauge reading. the maximum reading as the dua! wheels move over and past the test point and the final reading when the truck is stationary at the final stop position. Reverse the truck to the .. -1,2 m" posi-tion.

SpeCial methods Draft TMH6 Pretona. South Africa. 1984

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Repeat the procedure until three sets of well-corre!ated readmgs have beer! ob tained (see 5.6 to 5.8).

3.4 Recording of readings Record the road temperature as well as the deflection and curvature readings on data sheets such as Forms ST91, ST9,2 and ST9i 3 (see aiso 5, 1 and 5,9).

4 CALCULATIONS 4,1 Oeflections 4,1 .1 Calculate the corrected maximum deflection 10 the nearest 0.1 mm for each of

the three sets of readings using the following formula (see also Form ST9 1 and 5,1 ):

. ~ (D! + Dn] Dc.::; 2 Om - ._--2

where Dc = corrected maximum deflectior in tenths of a mm Om := maximum reading observed in hundredths of a rnm Oi ;;::. initial zero reading Of =- final reading at the" + 3 m" final stop position In h~Jndredths of a mm,

4,1 2 Calculate the average of the three corrected maximum defleehon values ob-tained in 4,1,1 above 10 the nearest 0.1 mm, This average is the deflection va -lue for the test point (see 5,8).

4.2 4,2,1 4.2.1,1

Radius of curvature From deflection beam Calculate the radius of curvature to the nearest ~ m for each at the three sets of readings from the following formula (see also Form ST9,2),

1 125 R::::-------

2[Dm - (01 t 02) where 2

R = radius of curvature in m Om = maxImum observed deflection reading in hundredths of a mm 01 and 02 == deflection readings at the "-0.15 m" and" + 0.15 m" pOSItions In

hundredths of a mm, 4,2.1.2 Calculate the average of the three radius of curvature values obtaned in 4.2.1 .1

above to the nearest 1 m, This average is the radius ot curvature for the test point (see 5,8).

4,2.2 From curvature meter 4.2,2.1 Calculate the radius of curvature to the nearest 1 m for each of the three sets of

readings from the following formula (see also Form ST9i3): 1400

R=-----0- (01 + D2)

2 Soeclal methods Draft TMH6. PretOria, SOllth Atnca, 198': 41

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where A -= radius of curvature in m D = maximum observed reading in hundredths ot a mm D1 = initial zero reading D2 = final reading at the" + 3 m" final stop position in hundredths of a mm ,

4.2.2,2 Cal~late the average of the three radius of curvature values obtained In 4,2.2.1 above to the nearest 1 m. This allerage is the radius of curvature for the test point (see 5,8).

4.3 Recording of resutls Record the following results on Forms ST9;1. ST9i2 or Sr913. as applicable, lor each test point: (a) Radius of curvature to the nearest 1 m (b) Deflection to the nearest 0.1 mm (c) Road temperature to the nearest 1 cc (d) Serial number or mark of the deflection beam and or curvature meter

used.

5 NOTES 5,1 Some deflection beams are fitted with electronic measuring devices giving a

digital readout of deflection or are fitted to record these readings. Moreover, some work on a different principle to the Benkelmann Beam and the 2: 1 ratio may not be applicable . The calibration procedure for these machines may also be slightly different and reference should be made to the operating manuals,

5.2 It is essential to maintain a functional degree of aecur aey in the deflection beam. Besides the calibration carried out before the first lest each day. It is ad-visable to carry out at least one more calibration later in the day. The necessity for further calibrations wi!! depend on the agreement between the results ob-tained at a particular test point and is left to the discretion of the operator.

5.3 Strong winds on the beam can cause the dial gauge needle to oscillate exces-sively. This may be largely overcome by placing over the rear portion of the beam a wooden box that acts as a wind-screen and/or by placing a suitable weight on the front portion of the movable beam.

5.4 The instrument should preferably not be removed from the test point until the whole test is complete. and it is therefore necessary to take extreme care not to disturb or damage it when reversing the truck. However. should it be necessary to move the instrument, it should be replaced in the same position as before.

5.5 If it is required to measure deflections and curvatures with the deflection beam at the same time, it will be necessary for the truck to move over the full dis-tance. Le. from the" -1,2 m" mark to the" + 3 m" final stop position, The rel-evant calculations remain the same,

5.6 If there is evidence of friction in the dial gauge (for example, erratic movement of the indicator needle) during a test run, the spindle shaft must be cleaned with benzine and the run repeated. If it still does not function satisfactorily, the gauge must be repaired or replaced.

5.7

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The deflection beam and curvature meter may be used simultaneously under the same pair of dual wheels. When this is done, the curvature meter is placed

SpeCial methods Draft TMH6. Pretoria, South Afnca. 1984

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in longitudinal alignment with the deflection beam so that the adjusting-nut end of the curvature meter is right in front of the beam point and thus virtually on the test spot. with the dial gauge iacing to the rear of the truck. Readings are then taken by observing the meter through the dual wheels from the rear as the wheel passes the test paint The operator must take care to stay clear of the wheels when obtaining the maximum reading as the truck moves forward. When a large number of measurements are to be taken in both wheei paths , testing time can be greatly reduced by using a deflection beam and curvature meter simUltaneously ur.der each paIr of dual wheels.

5.8 If deflection and'or radius of curvature measurements are required over a fairly long section of road. the measurements need not be dene fn triplicate . Instead single measuremeri!s may be taken, provided a greater number of points are tested . The single measurements will obviate the difficult and time-consuming proce-dure of reversing the trUCK at eac~ point. arId at the same time give a r.lcre 'po-resentative picture of the deflection and or radIUS nf curvature of the road. The deflections are hen statisticAlly cmalysec and the ~epresenlative dellectlon is calculated (usuaHv ~he 95tr. oercer:tiie mu!tiplled by correstion factors fOt c: i rnate a:1(1 tempemt1re: see also 59)

59 ThE deliectlon (8StnS are usuaHy corrected to r !empe:atl;re , cill;1ate . subgrade mOIsture cor :ient, etc before be:ng used III design w(1~k T~e5 [aslo; 5 '!,fi2 not given here II the deflection beam is only used to compare deHect!ons during constructlcn. Ie. when no asphaa iayers are involved, no temperature measurernents or cor-rection factors are necessary.

REFERENCES 1. NATIONAL INSTITUTE FOR TRANSPORT AND ROAD RESEARCH. The

use of the Benke/mann Beam for the measurement of deflections and cur-vatures of a road surface between dual wheels, Special Report R2. Pre-toria. CSIR, 1961,

2. JOOSTE, J P (Compiler). The measurement of deflection and curvature of road surfaces NITRR Manual K16, Pretoria, CSIR, 1971.

Special methods Draft TMH6, Pretofla, South Afnca, 1984 43

FIGURE ST9/1: A DEFLECTION BEAM

FIGURE ST9111: DEVICE FOR CALIBRATING A DEFLECTION BEAM

44 Special methods

Draft TMH6, Pretona, South AfTica. 1984

FIGURE ST9IIII: A CURVATURE METER

Special methods Draft TMHS, Pretoria. South Afn

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T -FINAL STOP POSITION I t I_CHAlK LINE IOPTIONAL I I I I I

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""""'--TEMPLATE

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ROAO PAD C/JRFN.lI3EWAY RYBMN S\.RF'ACE OPPERVLAKTE OATE DATUM

Deflection meter reo:!i'lg Corrected AverOQe Test point Oefleksiemeter-lesin9 deflection defle

ROAD PAD ClARRWJEWAY RYBAAN

OPPERVl..AKTE DATE OATUM

Deflecrioo meter ~ Radius of AveroQe Tesf point Deflek~-leq clS\lOtl.l'e RofC. Cond i hon of rood Temp.

Initial Max. Fino I Kromming- Gemidc:lelde To.staod V

ROAD PAD

ClATE OATUM

Test point

Toe tspu"lt

FOAMST9I3

Speciai methods

Deflection meter" reading Radius of Aver~ ctXWtt.n! R.ot . CondI'tOn of rood Oefleksiemeter -lesing Temp.

ot/bot Max. ot/by Krommil'l9- GemiQ:Jelde Toestand \Ql per:! 0.15 m MOkl.~ stroot Ks.

HnMdr 'tG'V'-'Iit$ m m c

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RADIUS OF CURVATURE (BENKElMANN BEAM MEASURE-MENTS)

0nIft TMH6, Pretoria, South Africa, 1984 49

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TMH 6-1TMH 6-2TMH 6-3