welded jt designto5950

8/7/2019 welded jt designto5950

1/47

DesignofSHSWeldedJoints885950 andENV 1993-1-1-ANNEX K

dO


2/47

CONTENTS

2

3

4

5

6

7

8

INTRODUCTION 2

SCOPE 33556

2.12.22.32.4

Joint GeometryMaterialMultiplanar jointsLoad and moment interaction

GENERAL DESIGN GUIDANCE 77810

3.13.23.3

Structural AnalysisWeldingFabrication

PARAMETERS AFFECTING JOINT CAPACITY 12121214151516

4.14.24 . 34 . 44 . 54 . 6

GeneralJoint Failure ModesJoints with a Single BracingJoints with a Gap between BracingsJoints with Overlapped BracingsJoint Reinforcement

JOINT DESIGN FORMULAE 1919242931

5.15.25.35 . 4

CHS Chord JointsRHS Chord JointsSpecial Joints in RHSI-section Chord Joints

DESIGN EXAMPLES 3434353538

6.16.26.36 . 4

Girder Layout and Member LoadsDesign PhilosophyRHS Girder DesignCHS Girder Design

LIST OF SYMBOLS 424243

7.17.2

General Alphabetic ListPictorial List

REFERENCES 44


3/47

1 INTRODUCTIONIn constr-uction with structural hollow sections the members are generallydirectly welded to each other and member sizing, therefore, has a directeffect on both the joint capacity and the cost of fabrication, As a result, inorder to obtain a technically secure, economic and architecturally pleasingstructure, both the architect and design engineer must, from the verybeginning, be aware of the effects that their design decisions can have onthe joint capacity, the fabrication, the assembly and the erection of thestructure,

Structural hollow sections have a very advantageous strength to weight ratiowhen compared to open section profiles, such as 1-, H-, [- and L- sections,They also require a much smaller weight of protection material, whether thisis a fire protection or corrosion coating, because of their lower external area.

A properly designed steel construction usmq structural hollow sections willnearly always be lighter in terms of material weight than a similar constructionmade with open section profiles and, although structural hollow sections aremore expensive than open section profiles on a per tonne basis, the overallweight saving of steel and protective coatings will very often result in a muchmore cost effective construction,

This publ ication has been produced to show how the joint capacity can becalculated and how it can be affected by both the geometric layout and thesizing of the members,

Considerable international research into the behaviour of structural hollowsection (SHS) welded joints for lattice type constructions has enabledcomprehensive design recommendations to be developed which embracethe large majority of manufactured structural hollow sections,

These design recommendations have been developed by CIDECT (ComiteInternational pour la Developpement et l'Etude de la Construction Tubulaire)and the IIW (International Institute of Welding) and, as a result, have gainedconsiderable international recognition and acceptance. They have been usedin a series of CIDECT Design Guides [1,2] and are now incorporated intoEurocode 3 : Annex K.[3]

The joint capacity formulae, reproduced in section 5, were developed and arepresented in a limit states form and are therefore fully compatible with therequirements of BS 5950 : Part 1 [4] and Eurocode 3,

A software program [5j, called CIOJOINT, has been developed by CIOECT forthe design of most of the joints described in this design publication. TheCIOJOINT design program requires MS-Windows version 3,x (or higher),


4/47

2 SCOPEThis publication has been written mainly for plane frame girder joints under predominantly static axialand/or moment loading conditions, however, some advice on non-planar frame Joints is also given.Note: In calculations this publication uses the convention that tensile forces and stresses are positive(+ ) and compressive ones are negative (-).

2.1 Joint GeometryThe main types of joint configuration covered in this publication are shown in figure 1, however, othertypes of connections to structural hollow section main members, such as fin plates and cross plates,are also discussed.

t X-joints T-and V-joints+o d~------~II~ ~

K-and N-joints with gap K-and N-joints with overlap

+DdFigure 1 : Joint geometries

The angle between the chord and a bracing or between two bracings should be between 30 and 90inclusive. Ifthe angle is less than 30 then:

1. the designer must ensure that a structurally adequate weld can be made in the acute angleand 2. any joint capacity calculation should be made using an angle of 30 instead of the actual angleWhen K- or N-joints with overlapping bracings are being used, the overlap must be made with the firstbracing running through to the chord and the second bracing either sitting on both the chord and thefirst bracing (partial overlap) or sitting fully on the first bracing (fully overlapped) as shown in (figure 2a).The joint should never be made by cutting the toes from each bracing and butting them up together(figure 2b), because this is both more difficult to fit together satisfactorily and, more importantly, canresult injoint capacities up to 20% lower than those calculated by the joint design formulae given insection 5. A modified version of the type of joint shown in (figure 2b) can, however, be used providedthat a plate of sufficient thickness is inserted between the two bracings - see section 4.6.3 on RHSchord overlap joint reinforcement.

---_ ..._-------------------


5/47..

a) Correct method b) Incorrect method

Figure 2 : Method of overlapping bracings

2.1.1 Validity RangesIn section 5 validity ranges are given for various geometric parameters of the joints, These validityranges have been set to ensure that the modes of failure of the joints fall within the experimentallyproven limits of the design formulae. If joints fall outside of these limits other failure modes, not coveredby the formulae, may become critical. As an example, no check is required for chord shear in the gapbetween the bracings of CHS K- and N-joints, but this fai lure mode could become critical outside thevalidity limits given.However, in general, if just one of these validity limits is slightly violated, and all of the joint 's othergeometric parameters are well inside the limits, then we would suggest that the actual joint capacityshould be reduced to about 0.85 times the capacity calculated using the design formulae.

2.1.2 Joint symbolsA list of al l the symbols used in this publication is given in section 7, however the main geometricsymbols for the joint are shown below in figure 3.

_________f _t o

Figure 3 : Joint geometric symbols


6/47

2.2 MaterialThe design formulae, given in section 5, have only been verified experimentally for SHS material with amaximum nominal yield strength of 355N/mm2 (EN 10210-1 grade S355J2H [6]). Care should be takenif materials with higher nominal yield strengths than this are used, since it is possible that, in somecircumstances, deformations could become excessive and critical to the integrity of the structure.British Steel hot finished structural hollow sections are usually manufactured in EN 10210-1 steelgrades S275J2H and S355J2H, with dimensions to EN 10210-2 [7].

2.3 Multiplanar jointsMultiplanar Joints, such as those found in triangular and box girders, can be designed using the samedesign formulae as for planar joints, but with the multiplanar factor, u, given in table 1, applied to thecalculated capacity. The factors shown in table 1 have been determined for angles between the planesof 30 to 900. Additional'y the chord must be checked for the combined shear from the two sets ofbracings.

Joint type CHS chords RHS chords

TT-joint u = 1. 0 u = 0. 9

f.I=0 .9 (1 +0 .3 3( N 2 , A p p / N 1 , A p p ) )

taking account of the sign (+ or -) and withI N 2 ,A pp l ~ I N 1 ,A pp l

xx -joint

KK-joint u = 0, 9 u = 0, 9

Table 1 : Multiplanar factors

To determine ifa joint should be considered to be a multiplanar joint or a planar joint refer to figure 4

Design as a plane frame jointwith bi or di = x and resolvebracing axial capacity into thetwo planes

Design as a planar joint andmultiply by the releventmultiplaner factor from table 1

Figure 4 : Multiplanar joints


7/47

2.4 Load and moment interactionIf primary bending moments as well as axial loads are present in the bracings at a connection then theinteraction effects of one on the other must be taken into account. Annex K of Eurocode No.3 givesthe following interaction formulaeFor CHS chord joints the interaction formula is :-

[M A ] 2 M A+ p,l, pp + op,i, pp :::; 1,0MiP,i Mop,i

For RHS chord joints the interaction formula is :-

Ni.App Mip,i.App Mop,i.APP-- + + :::; 1.0Ni Mip,i Mop,i


8/47

3 GENERAL DESIGN GUIDANCE

3.1 Structural AnalysisLattice structures have traditionally been designed on the basis of pin-jointed frames with theirmembers in tension or compression and the loads noding (meeting at a common point) at the centre ofeach joint. The usual practice is to arrange the joint so that the centre line of the bracing membersintersect on the centre line of the chord member, as shown inf igure 5.

-r-

I

.-- - - ,.,--__J

Figure 5 : Noding joints

The member sizes are determined in the normal way to carry the design loads and the welds at thejoint to transfer the loads in the members. However, a latt ice girder constructed using structural hollowsections is almost always welded, with one element welded directly to the next, e.g. bracing to chord.This means that the sizing of the members has a direct effect on the actual capacity of the joint beingmade. It is therefore imperative, if a structurally efficient and cost effective design is to result, that themember sizes and thicknesses are selected in such a way that they do not compromise the capacityof the joint. This is explained further in section 4.While the assumption of centre line noding and pinned connections enables a good approximation ofthe axial forces in the members to be obtained, clearly in a real girder with continuous chords andwelded connections, bending moments will be introduced into the chord members due to the inherentstiffness of the joints. In addition, in order to achieve the desired gap or overlap conditions between thebracings it may be necessary to depart from the noding conditions.Many of the tests that have been carried out on welded joints, to derive the joint designrecommendations, have incorporated noding eccentricities (see figure 6), some as large as dcl2 orhcl2.


9/47

e>Oa) gap joint with positive eccentricity b) overlap joint with negative eccentricity

Figure 6 : Definition of joint eccentricity

The effects of moments due to the Joint stiffness, for joints within the parameter limits given in section5, and noding eccentricities, within the limits given below, are automatically taken into account in thejoint design formulae given in section 5. It is good practice, however, to keep noding eccentricities to aminimum, particularly if bracings node outside the chord centre line (positive eccentricity, figure 6 a).The joint design formulae in section 5 be should not be used for eccentricit ies outside the limits givenbelow.

-0.55 (do or ho) ~ e ~ +0.25 (do or ho)

The effect of eccentricities outside these limits should be checked with reference to section 2.4 withthe moments due to the eccentrici ty being taken into account. In most instances, the chords will bevery much stiffer than the bracings and any moment, generated by the eccentricit ies, can beconsidered as being equally distributed to each side of the chord.

3,2 WeldingOnly the main points regarding welding of structural hollow section lattice type joints are given here.More detailed information on welding methods, end preparation, weld strengths, weld types, welddesign, etc. is given in reference 8.When a bracing member IS under load, a non-uniform stress distribution is set up in the bracing closeto the joint, see figure 7, and therefore, the welds connecting the bracing to the chord must bedesigned to have sufficient resistance to allow for this non-uniformity of stress.The weld should normally be made around the whole perimeter of the bracing by means of a buttweld, a fil let weld or a combination of the two. However, in partially overlapped bracing joints thehidden part of the connection need not be welded provided that the bracing load componentsperpendicular to the chord axis do not differ by more than 20%. In the case of 100% overlap joints thetoe of the overlapped bracing must be welded to the chord. In order to acheive this, the overlap maybe increased to a maximum of 110% to al low the toe of the overlapped bracing to be weldedsatisfactorily to the chord.


10/47

Figure 7 : Typical localised stress distribution at a joint

For bracing members in a lattice construction, the design resistance of a fil let weld should not normallybe less than the design resistance of the member. This requirement will be satisfied if the throat size (a)is at least equal to or larger than the values shown in table 2, provided that electrodes of an equivalentstrength grade to the steel, in terms of both yield and tensi le strength, are used, see also figure 8.The requirements of table 2 may be waived where a smaller weld size can be justified with regard toboth resistance and deformational/rotational capacity, taking account of the possibility that only partof the weld's length may be effective

Steel gradeE N1 02 1 0-1

Minimum throatsize, a mm

Electrode gradeEN 499

S275J2HS355J2H

0.94 x t*1.09 x t*

E352 x x x xE42 2 x x x x

* see figure 8Table 2 : Prequalified Weld Throat Size

Figure 8 :Weld throat thickness


11/47

The weld at the toe of an inclined bracing is very important, see figure 9. Because of the non-uniformstress distribution around the bracing at the chord face, the toe area tends to be more highly stressedthan the remainder of its periphery. As a result it is recommended that the toe of the bracing should bebevelled and a butt weld should always be used if the bracing angle, 8, is less than 600 If the angle is60 or greater then the weld type used for the remainder of the weld should be used, i.e. either a filletor a butt weld.

Figure 9 : Weld detail at bracing toe

3.3 FabricationIn a lattice type construction the end preparation and welding of the bracings is generally the largestpart of the fabrication costs and the chords the smallest. For example, in a typical 30m span girder,whilst the chords would probably be made from three lengths of material with straight cuts and twoend-to-end butt welds, the bracings would number some twenty to twenty-five and each would requirebevel cutting or profil ing, if using a CHS chord, and welding at each end.As a general rule the number of bracing members should be as small as possible and this can usuallybest be achieved by using K- type bracings rather than N-type bracings. Hollow sections are muchmore efficient in compression than open sections, such as angles or channels, and as a result therequirement to make compression bracings as short as possible does not occur and a K-type bracinglayout becomes much more efficient.The ends of each bracing in a girder with circular hollow section chords have to be profile shaped to fitaround the curvature of the chord member, see figure 10, unless the bracing is very much smaller thanthe chord. Also for joints with CHS bracings and chords and with overlapping bracings the overlappingbracing has to be profi le shaped to fit to both the chord and the other bracing.

Figure 10 : Connections to a circular chord


12/47

For joints with RHS chords and either RHS or CHS bracings, unless the bracings partially overlap, onlya single straight cut is required at the ends of the bracings.As well as the end preparation of the bracings, the ease with which the members of a girder, or otherconstruction, can be put into position and welded will effect the overall costs. Generally it is mucheasier, and therefore cheaper, to assemble and weld a girder with a gap between the bracings than asimilar one with the bracings overlapping. This is because with gap joints you have a much slackertolerance on fi t up and the actual location of the panel points can easily be maintained by slightadjustments as each bracing is fit ted; this is not possible for joints with overlapping bracings, especiallypartial overlapping ones. and unless extra care is taken it can result in accumulated errors in the panelpoint locations.


13/47

4 PARAMETERS AFFECTING JOINT CAPACITY

4.1 GeneralThe effect that the various geometric parameters of the joint have on its load capacity is dependantupon the joint type (single bracing, two bracings with a gap or an overlap) and the type of loading onthe joint (tension, compression, moment), Depending on these various conditions a number of differentfailure modes, see section 4,2, are possible,Design is always a compromise between various conflicting requirements and the following noteshighlight some of the points that need to be considered in arriving at an efficient design,1)The jointa) The joint capacity wil l always be higher If the thinner member at a joint si ts on and is welded to

the thicker member rather than the other way around,b) Joints with overlapping bracings will generally have a higher capacity than joints with a gap

between the bracings, all other things being equal.c) The joint capacity, for all joint and load types (except fully overlapped JOints),will be increased if

small thick chords rather than larger and thinner chords are used,d) Joints with a gap between the bracings have a higher capacity if the bracing to chord width ratio

is as high as possible. This requires large thin bracings and small thick chords.e) Joints with partially overlapping bracings have a higher capacity if both the chord and the

overlapped bracing are as small and thick as possible.f) Joints with fully overlapping bracinqs have a higher capacity ifthe overlapped bracing is as small

and thick as possible. In this case the chord has no effect on the JOintcapacityg) On a size for size basis, joints with CHS chords will have a higher capacity than joints with RHS

chords2) The overall girder requirementsa) The overall girder behaviour, e. g. lateral stability, is increased if the chord members are large and

thin. This also increases the compression chord strut capacity, due to its larger radius of gyration.b) Consideration must also be given to the discussion on fabrication in section 3.3.

4.2 Joint Failure ModesJoints in structural hollow sections can fail in a number of different failure modes depending on the jointtype, the geometric parameters of the joint and the type of loading. These various types of failure aredescribed in figures 11 to 16.Ifthe relevant geometric parameter limits given in section 5 are adhered to then the number of failuremodes is limited to those defined there; however, if this is not the case then other failure modes maybecome critical.


14/47

Chord face deformation, figure 11, is the most common failure mode for ioints with a single bracing,if the bracing to chord width ratio (B)is less than 0.85 and for K- and N-joints with a gap between thebracings.

MODE DESCRIPTION

Chord facedeformation

Figure 11 : Chord face deformation

Chord side wall buckling, figure 12, usually only occurs when the B ratio is greater than about 0.85,especially for joints with a single bracing. The failure mode also includes chord side wall yielding if thebracing carries a tensile load.

MODE DESCRIPTION

Chord sidewallbuckling 8

Figure 12 : Chord side wall buckling

Chord shear, f igure 13, does not often become critical, it is most likely to become so if rectangularchords with the width (bo) greater than the depth (ho) are being used. Ifthe validity ranges given insection 5 are met then chord shear does not occur with CHS chords.

MODE DESCRIPTION

Chord shear

Figure 13 : Chord shear

Chord punching shear, figure 14, is not usually critical but can occur when the chord width tothickness ratio (2y ) is small.

MODE DESCRIPTION

Chordpunching shear

Figure 14 : Chord punching shear


15/47

Bracing effective width failures, figure 15, are generally associated with RHS chord gap joints whichhave large B ratios and thin chords. It is also the predominant failure mode for RHS chord joints withoverlapping RHS bracings.

MODE DESCRIPTION

Bracingeffective width

Figure 15 : Bracing effective width

Localised buckling of the chord or bracings, figure 16, is due to the non-uniform stress distr ibutionat the joint, and will not occur if the validi ty ranges given in section 5 are met.

MODE DESCRIPTION

Chord or bracinglocalised buckling

Figure 16 : Localised buckling of the chord or bracings

4.3 Joints with a Single BracingThe statements given in table 3 will only be true provided that the joint capacity does not exceed thecapacity of the members. In al l cases the capacity is defined as a load along the axis of the bracing.

Joint parameter Parameter value Effect on capacity

Chord width tothickness ratio reduced increased

Bracing to chordwidth ratio increased increased(1 )

Bracing angle e reduced increasedBracing to chordstrength factor reduced increased

Note (1) - provided that RHS chord side wall buckling does not become critical, when B > 0.85Table 3 : Effect of parameter changes on the capacity of T-, Y- and X-joints


16/47

4.4 Joints with a Gap between BracingsThe statements given in table 4 will only be true provided that the joint capacity does not exceed thecapacity of the members. In all cases the capacity is defined as a load along the axis of the bracing.

Joint parameter Parameter value Effect on capacity

Chord width to bo It o or do I tothickness ratioBracing to chord d1 I d o or b1 I bowidth ratioBracing angle 8Bracing to chord fY1t1--strength factor fy O toGap between gbracings

reduced increased

increased increased(1 )reduced increased

reduced increased

reduced increased(2 )

Note (1) - provided that RHS chord side wall buckling does not become critical , when B> 0.85(2) - only true for CHS chord joints

Table 4 : Effect of parameter changes on the capacity of K- or N-joints with gap

4.5 Joints with Overlapped BracingsThe statements given in table 5 will only be true provided that the joint capacity does not exceed thecapacity of the members. In al l cases the capacity is defined as a load along the axis of the bracing.

Joint parameter Parameter value Effect on capacityChord width tothickness ratio bo It o or do I to reduced increased

Overlappedbracing width tothickness ratio

reduced increased(1 )

Bracing to chordwidth ratio increased increased(2)Bracing angle 8 reduced increased(3 )Overlappedbracing tochord strengthfactor

reduced increased

Bracing tobracing strengthfactor

reduced increased

Overlap ofbracings increased increased

Note (1) - only true for RHS joints(2) - provided that RHS chord side wall buckling does not become cri tical, when B > 0.85(3) - only true for CHS chord joints

and suff ix j refers to the overlapped bracingTable 5 : Effect of parameter changes on the capacity of K- or N-joints with overlap


17/47

4.6 Joint ReinforcementIf a joint does not have the design capacity required, and it is not possible to change either the jointgeometry or the member sizes, it may be possible to increase the design capacity with the use ofappropriate reinforcement. Adding reinforcement to a joint should only be carried out after carefulconsideration. It is relatively expensive from a fabrication point of view and can be obtrusive from anaesthetics view point.The type of reinforcement required depends upon the criterion causing the lowest capacity. Methodsfor reinforcing both CHS and RHS chord joints are given below. An alternative to the methods shownis to insert a length of chord material, of the required thickness, at the joint location, the length of whichshould be at least the same as the length, h., given in the following methods.The required thickness of the reinforcement, t., should be calculated by re-arranging the relevantformula given in section 5 to calculate the required chord thickness, to, this is then the thickness of thereinforcement required. In the case of CHS chord saddle and RHS chord face reinforcement only thereinforcement thickness, and not the combined thickness of the chord and reinforcement, should beused to determine the capacity of the reinforced joint, For RHS chord side wall reinforcement thecombined thickness may be used.The plate used for the reinforcement should be the same steel grade as the chord material. For CHSsaddle and RHS chord face reinforcement the plate should have good through thickness propertieswith no laminations. The weld used to connect the reinforcement to the hollow section chord membershould be made around the total periphery of the plate.When plates are welded al l round to the chord face, as is the case for the reinforcement plates shownin sections 4.6.1 and 4.6.2, special care and precautions should be taken if the structure issubsequently to be galvanised.

4.6.1 R ein fo rc em en t o f CHS c ho rd jo in tsThe only external reinforcement method used with a CHS chord is saddle reinforcement, where either acurved plate or part of a thicker CHS is used. The size and type of reinforcement is shown in figure 17.The dimensions of the saddle should be as shown below.

ds = n do /2h, ~ 1.5 [d1 / sin81 + g + d2 / sin82]

for K- or N-gap joirrtsh, ~ 1.5 d1 / sin81

for T-, X- or V-jointst, = required reinforcement thickness

Figure 17 : CHS chord saddle reinforcement


18/47

4.6.2 R e in fo rcem en t o f R H S ch o rd gap jo in tsA gap joint with RHS chords can be reinforced in several ways depending upon the critical designcriterion. Ifthe critical criterion is chord face deformation or chord punching shear or bracing effectivewidth then reinforcing the face of the chord to which the bracings are attached is appropriate (seefigure 18). However. if the critical criterion is either chord side wall buckl'lng or chord shear then plateswelded to the side walls of the chord should be used (see figure 19). The required dimensions of thereinforcing plates are shown below.

Figure 18 : RHS chord face reinforcement

br

Figure 19 : RHS chord side wall reinforcement

h, 2 1.5 [hi / sin8i + g + h2 / sin82lfor K- or N-gap joints

hr;:: hi/ sin8i + ~(br(br-bi))and 2 1.5 hi / sin8i

for T-, X- or V-joints

tr = required reinforcement thickness

h, = 1 .5 [hi / sin8i + g + h2 / sin82lfor K- or N-gap joints

hr = 1.5 hi / sin8ifor T-, X- or V-joints

tr = required reinforcement thickness


19/47

4.6.3 Reinforcement of RHS chord overlap iointsAn overlap joint with RHS chords can be reinforced by using a transverse plate as shown in figure 20.The plate width b, should general ly be wider than the bracings to allow a fi llet weld with a throatthickness equal to the bracing thickness to be used.This should be treated as a 50 to 80% overlap joint with tr being used instead of the overlappedbracing thickness tj in the calculation of beov (see section 5.2). This type of reinforcement can be usedin conjunction with the chord face reinforcement. shown in figure 18, if necessary.

DFigure 20 : RHS chord transverse plate reinforcement


20/47

5 JOINT DESIGN FORMULAE

When more than one failure criteria formula is given the value of the lowest resulting capacity should beused. In all cases any applied factored moment should be taken as that acting at the chord face andnot that at the chord centre l ine.

5.1 CHS Chord Joints5.1.1 CHS chord joint parameter limits

Joint type Bracing typeT-,K- andN-joints CHSX-jointsT-joints Transverse

plateX-jointsT-joints Longitudinal

plateX-jointsT-joints RHS and 1 - or

H- sectionX-joints

do/to d/tj: : ; ; 5 0

: : ; ; 5 0: : ; ; 4 0: : ; ; 5 0: : ; ; 4 0: : ; ; 5 0: : ; ; 4 0: : ; ; 5 0: : ; ; 4 0

Gap/lap Brace anglegap ~ t1+t2lap ~ 25%~ 0.2

h 1 / d o ::;; 4 . 0 *t/do : : ; ; 0.2

b1/do ~ 0.4h 1 / d o ::;; 4 . 0 *

* can be physically> 4, but should not be taken as > 4 for calculation purposes

5.1.2 CHS chord joint functionsThe following functions are used during the calculation of CHS chord joint capacities

Chord end load function, f(np) - see figure 21

f(np) = 1 + 0.3oplfyO - 0.3 (Op/fyo)2 but not greater than 1.0,

Op = the least compressive factored applied stress in the chord.adjacent to the joint and is negative for compression

aplfyOis the chord stress ratio shown in figure 21

Gap/lap function, f(9) - see figure 22

f(g) = Y 0.2 [1 + 0_ ._02_4_Y_1_ .2__]1 + exp(0.5 glto - 1.33)

Gap (g) is positive for a gap joint and negative for an overlap joint


21/47

a. 1.0c.;=-c 0.80: ; : : : ;0C::l 0.6. . . . ."0l.2"0 0.4c(])"0. . . . 0.20..c0

0.0

I- ~c->:_ _ .

I- .>, . . , . -V---1.0 -0.8 -0.6 -0.4 -0.2 0.0

Chord stress ratio - O p If yoFigure 21 : CHS joint - Chord end load function

4.5 r---r-----,,-----,------r-----;-----;----,_ 4 ~d ~d ~~ ~4 ~5 ~~ ~~ ~- -4 -~ -- 4_ -- -- 4_ -- -- ~- -- -~9 ................... ddto=50----- ----- --_ ........~ 3.5~d'd~to-_~40~-------------+--------------~---~_~~,~',,~--+-----_I_-----1n 3~d=d~to~=-351_.. .-..-...-...-..-...+ . -. . .-. . .-..-. . .- . ~ F = ~ - - ~ ~ 4 ~ ' ~ ' ~ ~ , , ~ + _ - - - - ~ - - - - _ 1c ddto=30 > ~ < \.2 --.... .....,'-~ 2.5~d'd~to-_~25rl=====~~~==~-~-~-----_~_~~~.~.....~~~~~'~~---I------1

C D ddto=20 ---------------- -----__ .'-,""""...~~ ~2 ~~~~-----+------~----~~~~~~~~_=~ddto=15 ~.:.:.:.:.~~; ..~-::;_~1.5~----1------+------~----1------+--~~~~--4

I I I I I I I I I I I I I I I I I I

-16 -12 -8 -4 0 4 8 12Gap I chord thickness ratio - g/to

Figure 22 : CHS joint - Gap/lap function

T- and V-joints5.1.3 CHS chords and CHS bracings with axial loads

fy O t02Chord face deformation, N1 '" ----- (2.8 + 14.2 B2) yO.2 f(np)

sin81X-joints

fy O t02Chord face deformation, N1 '" -----

sin81 (1 - 0.81 B)

K- and N-joints

5.2

fy O t02Chord face deformation, N1 '" ----- (1.8 + 10.2 d1/do) f(g) f(np)

sin81sin81

Chord face deformation, N2 '" ----- x N1sin82


22/47

For all these joint types, except those with overlapping bracings, the joint must also be checked forchord punching shear failure when di ::;do - 2to

Chord punching shear, Nj =

5.1.4 CHS cho rd s and CHS brac ings with m om entsT-, Y-, X-joints and K- and N-joints with gap

Chord face deformation criterion - this should be checked for all geometric joint configurations

In-plane moments, Mjp,j = 4.85 -_-

fyo to 2 di 2.7Out-of-plane moments, Mop,j = f(no)

sin 8j 1 - 0.81 B

Punching shear cri terion - this must also be checked for these joint types when dj ::; do - 2 to

In-plane moments, Mjp,j =

Out-of-plane moments, Mop,j =

5.1.5 CHS c ho rd s with transverse gusset plates

T-joints axial load chord face deformation

X-joints axial load chord face deformation

(1 - 0.81 B) - -


23/47

T- and X-joints out-of-plane moment chord face deformation

T- and X-joints in-plane moment chord face deformation

Mip,1 ~ 0

T- and X-joint chord punching shearIn al l cases the fol lowing check must be made to ensure that any factored applied axial loads andmoments do not exceed the chord punching shear capacity.

5,1,6 CHS chords with longitudinal gusset plates

I+-I~---+l.lh1 ~ ~._____I_ I _ _ _ , I 6

T- and X-joints axial load chord face deformation

T- and X-joints out-of-plane moment chord face deformation

Mop,1 ~ 0

T- and X-joints in-plane moment chord face deformation



24/47

5.1.7 CHS ch o rd s an d I - H - or R HS brac in gs

T-joints chord face deformation

X-joints chord face deformation

(1 - 0.81 B )


For RHS sections (Napp / A1+ Mapp / WeI.1) t1 ~ fyOto / ..)3


25/47

5.2 RHS Chord Joints5.2.1 RHS chord joint parameter limits

Joint type Bracing type (boor hol (bj or hj or di) / ti (dj or bi)/ bo Gap/lapto Compression Tension

T- and RHS 2: 0.25X-joints :::;35:::;35 and :::;35

~K- and N- :::;34.5...J(275/fyi) 2: 0.35 and gap ~ t1 + t2gap joints 2: 0.1 + and ~ O.5(bo-(b1+ b2)/2)0.01 bolto b ut s1.5(bo-(b1+b 2)/2)K- and N- s 40 s 30.4...J(275/fyi) 2: 0.25 25%:::; lap slap joints 100%

s 41.5...J(275/fyi)2: 0.4 andAll types CHS As above :::;50 :::;0.8 As above

Transverse :::;30 2: 0.5T- and plateX-joints Longitudinal t1/bo:::; 0.2s 30plate h1/bo:::; 4.0*Note: in gap joints, if the gap is greater than 1.5(bo-bi), then it should be treated as two separateT-

or Y-joints* can be physically> 4, but should not be taken as > 4 for calculation purposes

The angle between the chord and either an RHS or a CHS bracing should be between 30 and 900inclusive. Longitudinal plates should be at about 900

5.2.2 RHS chord joint functionsThe following functions are used during the calculation of RHS chord joint capacities

Chord end load function, f(n), f(m)For alljoints except those with a longitudinal gusset plate - see figure 23

f(n) = 1.3 + --- but not greater than 1.0,

For joints with a longitudinal gusset plate only - see figure 24

f(m) = 1.3(1 + a 0 / fyoJ but not greater than 1.0,00 = the most compressive factored applied stress inthe chord adjacent to the joint and is

negative for compression

00 / fyOis the chord stress ratio shown in figures 23 and 24


26/47

~ 1.0 -bj/bO=1.00~ ~:..:..~~p' 0.8 b,/bo=O.SO ..'V .-.~/j 06 - b,/bo=O.60 ............:, .-/ ..>./a l . V../....//

5 2 -b,/bo=O.50 .. ...... /"0 0.4 .-" ./~ -bj/bo=OAO ~": .. Vo 0.2 .'6 bj/bo=O.35 ..' /

- bj/bo=O.3Y,O.O~~--~~-L--~--~~--~--~--~--~--~~-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0Chord stress ratio - 00 IfyoAll except longitudinalgusset platejoints

Figure 23 : RHS joint - Chord end load function (All except longitudinal gusset plate joints)

E 1.0~c 0.80Uc.2 0.6"0ell52"0 0.4c(])" E0 0.2_c0

0.0

f- -:- /- /V- //-/.

-1.0 -0.8 -0.6 -0.4 -0.2 0.0Chord stress ratio - 00 If yoLongitudinalgusset plateonly

Figure 24 : RHS joint - Chord end load function (Longitudinal gusset plates only)

Bracing effective width functions10 fyO to

Normal effective width, bef f = -- -- bi but s bibalto fyi ti

10Punching shear effective width, bep

10 fyj tjOverlap effective width, beov = -- -- bi but s bi

b/tj fyi ti(Suffix 'j' indicates the overlapped bracing)

Chord design strength for T-, Y- and X-joints, f(fb}For tension in the bracingFor compression in the bracing f(fb) = fc for T- and Y-joints

f(fb) = 0.8 fc sin8i for X-jointsWith fc obtained from BS5950 Table 27 (a) or Eurocode 3 Clause 5.5.1 for a slendernessratio, A,of 3.46 (ho/to - 2) / ~(sin8i) ..


27/47

Chord shear area, AvThe chord shear area, Av ' in uniplanar K- and N-joints with a gap is dependant upon the type ofbracings and the size of the gap

with e x =1 +

0.5

4 g2

and e x = 0 for CHS bracings

for RHS bracings

In multiplanar girders the shear area, Av, given below should be used for the two shear planesrespectively, irrespective of the type of bracing.

Av = 2(ho - to) to or 2(bo - to) to

5.2.3 R HS ch ord s an d R HS brac in gs with axial load sA number of fai lure modes can be critical for RHS chord joints. In this section the design formulae forall possible modes of failure, within the parameter limits, are given. The actual capacity of the jointshould always be taken as the lowest of these capacit ies.

T-, Y- and X-joints

Chord face deformation, N1 =(8 s 0.85 only)

C ho rd S he ar ,(X-joints with a < 90 only)

Chord side wall buckling, N1 =(P=1.0)'

r2h1 j---+ 4..)(1- 8) f(n)

(1 - 8) sin81 bo sin81

N1=----'\)3 sin81

where a= 0 in A vf(fb) to r_2_h1_ + 10 '.sin81 sin81

Chord punching shear, N1 = _fy_o_to_ r_2h_1_ + 2 bepj(0.85 s 8 s (1 - 2to/bo) only) ";3 sin81 sin81

Bracing effective width, N1 = fY1t1 [2h1 - 4t1 + 2beff J(8 ~ 0.85 only)

For 0.85 s 8 s 1 use linear interpolation between the capacity for chord face deformation at 8 = 0.85and the governing value for chord side wall failure (chord side wall buckling or chord shear) at 8 = 1.0


28/47

K- and N-gap joints6.3 fyo to2 -.Jbo lb1 + h, + b2 + h21

Chord face deformation, Nj = -- f(n)sinej - . J to 4bO

Chord shear between bracings, Nj =

Bracing effective width, Nj = fyj tj [ 2 hj - 4 tj + bj + beff 1

Chord punching shear, Nj =(B ::; (1 - 2tO /bo) only)

K- and N-overlap [olntsOnly the overlapping member i need be checked. The efficiency of the overlappedmember j should be taken as equal to that of the overlapping member.i.e. Nj = Nj (Aj fyJ)/(Aj fyj)

25%::; o, < 50%Bracing effective width, Nj = fyj tj [(Ov / 50) (2 hj - 4 tj) + beff + beovl50%::; o; < 80%Bracing effective width, Nj = fyj tj [2 hj - 4 tj + beff + beovlo, ~80%Bracing effect ive width, Nj = fyj tj [2 hj - 4 tj + bj + beovl

5.2.4 RHS chords and CHS bracingswith axial loadsFor all the joints described in section 5.2.3, if the bracings are CHS replace the bracing dimensions,bj and hj, with dj and multiply the resulting capacity by rr/4

5.2.5 RHS chords and RHS bracingswith momentsTreat K- and N-gap joints as individual T- or Y-joints

5.2.5.1 T- and X-joints with in-plane moments

Chord face deformation, Mjp,1 = fyO to2 h1 r ~ + __ 2_ + h1/bo lf(n)( B : : ; 0.85 only) l2 h1/bo - . J ( 1 - B ) 1 - B J

Chord side wal l crushing, Mjp.1 = 0.5 fyk to (h1 + 5 to)2(0.85 ::; B : : ; 1.0 only) with fyk = fyO for T-joints and 0.8 fyO for X-joints

Bracing effective width, Mjp,1 = fY1 [Wpl,1 - (1 - beff/b1) b1 h1 t11(0.85 s B S 1.0 only)


29/47

5.2.5.2 T- and X-joints with out-of-plane moments

l h1(1 + B)Chord face deformation, M op,1 = fyOt02 +(B : 0 ; : 0.85 only) 2 (1 - B) l 2bO b1(1 + B ) 1 0 . 5 1 f(n)(1 - B)Chord side wall crushing, Mop,1 = fyk to (hi + 5 to) (bo - to)(0.85 :::;B ::: ; 1.0 only) with fyk = fyOfor T-joints and 0.8 fyOfor X-joints

Bracing effective width, Mop,1 = fY1[Wpl,1 - 0.5(1 - beff/b1)2 b12 t1](0.85:::; B :::;1.0 only)

Chord distortional failure (Iozenging), Mop,1 = 2fyOto [hi to +(bo hOto (bo + ho))D5](T -joints only)

5.2.6 R H S ch o rd s w ith gusse t p lates o r I - o r H -sec tio n brac in gsTransverse gusset plate

Plate effective width, N1 = fY1t1 beff

Chord side wall crushing, N1 = fyOto (2 t1 + 10 to)(b1 ~ bo - 2 to only)

fyOtoChord punching shear, N1 = -- (2 t1 + 2bep)(b1 :::;bo - 2 to only) - . J 3

Longitudinal gusset plate

1 + - , " - - - - . J . , h1 - - - - . j ~.._____I_I - - - - , I 8Chord face deformation, N1 =

In-plane moment, Mip,1 = 0.5 hi N1


30/47

5.3

1-or H-section bracings

Base axial load capacity, N 1 , upon two transverse plates, similar to it's flanges, as specif ied in 5.2.6above, ie

Plate effective width, N 1 = 2 fY1 t 1 beffChord side wall crushing, N 1 = 2 fyOto (2 t1 + 10 to)(b1 ~ bo - 2 to only)

2 fyOtoChord punching shear, N 1 = - - - (2 t1 + 2 bep)(b1 :


31/47

1.0 ,---_,.----,--.....,....---.----,------, bOIto10

15

o0.91------+---+_---t-----t-----::::7"=+----IOJ~,~ 0.8I----'\-+-.::::::=~~=---+--+----+-----icC])'(3

~ O.7I -- --~ .. ... It-_".",=-+_---t-----t-=_""'T----I-c~ 0.6 L- -~~~r_ ; ;; ; ;; ; ;: : :: : :I== = := : :~= __1==120oOJ

0.5L-i - - f" ' , : : - r ; : ; : : : : : : : : : : : t :==t=====: : j30----~----~--~35

0.4 ................-J.....J......J.--'-J....."--'-L...J.....J......J.--'-'-'- ..........-J.....J......J.--'- ..................-J.....J......J0.0 0.5 1.0 1.5 2.0 2.5 3.0

RHS shape ratio - bO Ih OFigure 26 : Knee joint efficiency for e :


32/47

5.4 I - or H-section Chord Joints

5.4.1 I-or H-section chord joint parameter limitsJoint type bf / tf dw/tw (b, or hj or d.) / tj Gap/lap bi/bCompression Tension J

: : . : ;X-joints 33.2 >/(275/fyo) bi / ti and bi / ti

hi / ti::.:; and hi / tiT- and Y- 30.4 >/(275/fyi) ::.:;35joints s

20.7 >/(275/fyo) sK- and N- 41.5 >/(275/fyO) gap ~ t1 + t2gap joints and s 1.5(brbildi / ti::.:; di / ti

41.5 >/(275/fyi) ::.:;50K- and N- 25%::.:; lap ~ 0.75lap joints ::.:;100%

Note: 1) in gap joints, if the gap is greater than 1.5(bf - bi), then it should be treated as two separateT - or V-joints.2) the web depth dw should not be greater than 400mm

5.4.2 I-or H - section chord joint functionsBracing effective width functions

Normal effective width, beff = tw + 2 r + 7 tf fyO/ fyi but ~ biWeb effective length, bw = hi/ sin(8i) + 5(tf + r) but ~ 2 ti + 1O(tf+ r)

Overlap effective width, beov =

(Suffix 'j' indicates the overlapped bracing)

III


33/47

Chord shear area, AvThe chord shear area, Av, in K- and N-joints with a gap is dependant upon the type of bracings andthe size of the gap

with a =0.5

for RHS bracings

and a = 0 for CHS bracings

5.4.3 I - or H - sectio n c ho rds an d R HS brac in gs w ith axial loadsT-, Y- and X-jointsChord web yielding, N1 = fyOtw bw / sin (e j)Bracing effective width, N1= 2 fY1t1 bet!

K- and N-gap jointsChord web yielding, Nj = fyOtw bw / sin (ej)

Chord shear, Nj=

The bracing effective width failure criterion, below, does not need to be checked provided that:

Bracing effective width, Nj = 2 fyj tj bet!

K- and N-overlap jointsOnly the overlapping member i need be checked. The efficiency of the overlapped member j should betaken as equal to that of the overlapping member.i.e. Nj = Nj (Aj fyj)/(Aj fyj)25% ~ o, < 50%Bracing effective width, Nj = fyj tj [(Ov / 50) (2 hj - 4 tj) + bet!+ beovl50% ~ c; < 80%Bracing effective width, Nj = fyj t j [2 hj - 4 tj + bet! + beovlo, ~80%Bracing effective width, Nj = fyj tj [2 hj - 4 tj + bj + beovl


34/47

5.4.4 I - o r H - section chord s an d R HS bracings with in -plane m om en tsT-, Y- and X-jointsChord web yielding. Mip,1 = 0.5 fyOtw bw h1

Bracing effective width, Mjp ,1 = fY1 t1 bef f (h1 - t1)

K- and N-gap jointsTreat these as two separate T- or V-joints

5.4.5 I - o r H - sectio n chords and CHS brac in gsFor joints with CHS bracings use the above formulae but replace hj and bj with dj and multiply theresulting capacities by J!/4 .


35/47

6 DESIGN EXAMPLESThe example given here is for a simply supported, K-braced girder and is designed firstly for RHS andsecondly for CHS members. For each joint being checked the joint parameters and the joint capacitiesfor all possible failure modes must be calculated. The lowest capacity is then taken as the joint 's actualcapacity.

Note - this process can be undertaken quickly by the use of appropriate computer design software, forexample [5].

6.1 Girder Layout and Member LoadsGirder basic detailsSpanNumber of panelsBracing anglesDepthSpan / depth ratioExternal loadingMaterial

25m10551.785m14100kN factored load per panel point excluding endsEN 10210 grade S275J2H

The structural analysis has been based on the assumption that all member centre lines node, bracingsare pinned and chords are continuous. The girder is symmetrical about its centre, so only half is shownhere. The girder and member load details are shown in figures 29 and 30

~I\;7\t~~ 11 0 12 13 14 @ 115

1, 2 .... etc member numbers: C D , ....etc joint numbers ~Figure 29: Girder layout, member and node numbering

i450100 100

~I100

17441

~All loads in kNFigure 30: Applied member factored loads


36/47

6.2 Design PhilosophyThe following points should be born in mind when determining the member sizes and thicknesses.1. Gap joints are more economic to fabricate than overlap joints.2. For gap joints, smaller thicker chords give higher joint capacities than larger thinner ones.3. For gap joints, larger thinner bracings give higher joint capacities than smaller thicker ones.4. It is usually more economic to restrict the number of bracing sizes to about three, rather than to

match every bracing to the actual load applied to it. This may not be so true if very large numbersof identical girders are to be produced.

5. The material can be obtained in 12.5m lengths, as a result the chords will be made from the samematerial throughout their length ( other lengths are available).

6. The effective length factors for compression members have been taken as 0.9 for chords and 0.75for the bracings between chord centres.

7. It is possible that in order to meet the joint parameter limits, it wi ll be necessary to move away frommember centre line noding. Any moment generated due to joint eccentricities can be considered tobe distributed into the chord only with 50% taken on each side of the joint.

6.3 RHS Girder Design6.3.1 R HS M em ber Selectio n O ption sTop Chord: load -1709kN Bottom Chord : load +1744kNSize Mass Capacity Size Mass Capacity1SOx1S0x10.0 53.0 -1793 1S0x1S0x10.0 53.0 1S57150x150x12.5 53.4 -1767 150x150x12.5 53.4 1S70Bracing 20 : load +548kN Bracing 21 : load -548kNSize Mass Capacity Size Mass Capacity90x90x6.3 16.4 575 SOxSOxS.O 17.S -577SOxSOxS.O 17.S 625 120x120x5.0 18.0 -612120x120x5.0 18.0 629Bracing 22 : load +427kN Bracing 23 : load -427kNSize Mass Capacity Size Mass Capacity70x70x6.3 12.5 436 90x90x5.0 13.3 -43960x60x8.0 12.S 449 80x80x6.3 14.4 -46990x90x5.0 13.3 464 100x1 00x5.0 14.8 -497Bracing 24 : load +304kN Bracing 25 : load -304kNSize Mass Capacity Size Mass Capacity90x90x3.6 9.72 340 90x90x3.6 9.72 -32370x70x5.0 10.1 354 70x70x5.0 10.1 -321Bracing 26 : load +183kN Bracing 27 : load -183kNSize Mass Capacity Size Mass Capacity60x60x3.0 5.34 187 70x70x3.0 6.28 -20140x40x5.0 5.40 189 50x50x5.0 6.97 -190

60x60x4.0 6.97 -212Bracing 28 : load +61kN Bracing 29 : load -61kNSize Mass Capacity Size Mass Capacity40x40x2.5 2.92 102 40x40x2.5 2.92 -67.0


37/47

6.3.2 RHS Member SelectionChord selectionTop and bottom chords will both be 150x150x12.5, since this is smaller and thicker than180x180x1 0.0 and is only 0.75% heavier.

Bracing selectionMinimum brace to chord width ratio is 0.35, so bracings must not be smaller than 52.5mm (0.35x150),from the size range available this means 60x60 minimum.End bracings (20, 21): The lightest section to suit both bracing is 80x80x8, so this is selected.Bracings 22, 23, 24 and 25: 90x90x5 are suitable for 22 and 23, this will also be used for 24 and 25,so that the inner four bracings can be made as l ight as possible.Bracings 26, 27, 28 and 29: The lightest section to suit these is determined by member 27 so 70x70x3is chosen for all.

6.3.3 RHS Joint Capacity Check6.3.3.1 RHS Joint parameter checkThe table below contains all of the parameter checks required for all of the joints in the girderJoint or Parameter Limiting value Actual value RemarksmemberChords bo/to :::;35 150/12.5 = 12 passBracings b/ti :::;35 for tension 130/8 = 10

:::;34.5 for compression 90/5 = 18 all pass70/3 = 23.3

b1/bo ;:::0.35 and 130/150 = 0.53;:::0.1+0.01 bo/to = 0.22 90/150 = 0.60 all pass

70/150 = 0.47Joints1, 9 gap ;:::t1 + t2 = 6 and 19.60 fail - increase to 40mmand 10 ;:::0.5(bo-(b1+b2)/2) = 40 and eccentricity = 14.6

s 1,5(bo-(b1+b2)/2) = 120Joint 2 gap ;:::t1 + t2 = 8 and l .37 fail - increase to 40mm

;:::0.5(bo-(b1 +b2)/2) = 35 and eccentricity = 23.3:::;1,5(bo-(b1+b2)/2) = 105Joints 3, gap ;:::t1 + t2 = 10 and -4.84 (overlap) fail - increase to 40mm7 and 8 ;:::0.5(bo-(b1 +b2 ) /2) = 30 and eccentricity = 32.0

:::;1,5(bo-(b1+b2 ) /2) = 90Joint 4 gap ;:::t1 + t2 = 13 and 1.27 fail - increase to 40mm

;:::0.5(bo-(b1 +b2)/2) = 32.5 and eccentricity = 27.7:::;1,5(bo-(b1+b2)/2) = 97.5

Joint 6 gap ;:::t1+t2=16and l .37 fail - increase to 40mm;:::0.5(bo-(b1+b2)/2) = 35 and eccentricity = 23.3:::;1,5(bo-(b1+b2)/2) = 105..


38/47

In all cases it has been necessary to move away from member centre line noding in order to meet thegap parameter l imits. However, the joints at the centre of the girder (1, 2, 9 and 10) have small shearforces and eccentrrcit ies and the chords, although they are subject to high axial forces, should be ableto accommodate these. At the girder ends, the chords carry relatively small axial loads, and, althoughthe shear forces and eccentricit ies are higher, they should be able to carry the eccentricity moments.

6.3.3.2 RHS Joint capacity check

Generally, it is only necessary to check the capacity of selected joints, e.g. joints with the highest shearloads, joints with the highest chord compression loads or where the bracing or chord sizes change ..Also, it should be noted that a tension chord joint wil l always have as high or a higher capacity than anidentical compression chord joint, because the chord end load function is always 1.0 for tensionchords, but is 1.0 or less for compression chords. Here, however, as an example, each joint has beenchecked for completeness.

The results of the joint capacity checks for the normal K-joints (all except 5 and 11) are given in thetable below.

Joint Factored Calculated joint capacities, kN for failure modes Joint Gap Ecc.number applied unity mm mm

load, kN Chord Chord Chord Bracing factorface shear punching effectivedeformation shear width

Joint 1 N27 ~ -183 270.1 821.8 725.0 221.1 0.83 40 14.6N28 = 61 270.1 821.8 725.0 221.1 0.28

Joint 2 N25 = -304 403.9 821.8 932.2 467.5 0.75 40 23.3N26 = 183 403.9 821.8 725.0 221.1 0.83

Joint 3 N23 = -427 572.2 821.8 932.2 467.5 0.91 40 32.0N24 = 304 572.2 821.8 932.2 467.5 0.65

Joint 4 N21 = -548 626.3 821.8 828.6 633.6 0.88 40 27.7N22 = 427 626.3 821.8 932.2 467.5 0.91

Joint 6 N21 = -548 609.9 821.8 828.6 633.6 0.90 40 23.3N20 = 548 609.9 821.8 828.6 633.6 0.90

Joint 7 N23 = -427 686.1 821.8 932.2 467.5 0.91 40 32.0N22 = 427 686.1 821.8 932.2 467.5 0.91

Joint 8 N25 = -304 686.1 821.8 932.2 467.5 0.65 40 32.0N24 = 304 686.1 821.8 932.2 467.5 0.65

Joint 9 N27 = -183 533.7 821.8 725.0 221.1 0.83 40 14.6N26 = 183 533.7 821.8 725.0 221.1 0.63

Joint 10 N29 = -61 533.7 821.8 725.0 221.1 0.28 40 14.6N28 = 61 533.7 821.8 725.0 221.1 0.28


39/47

The joints 5 and 11 can be regarded as special joints, and, although checked in a similar way to theothers, certain assumptions regarding their behaviour have to be made.Joint 5 is at the end of the girder and the chord will have an end plate of some type to connect it to thecolumn. It has been shown that provided the plate thickness is the higher of either 10mm or the chordthickness (12.5mm in this case) that the joint will behave as a symmetrical K- or N-joint, rather than aweaker Y-joint. This is because the end plate will restrain the chord cross section from distorting.Joint 11 should be treated in one of two different ways depending upon the method by which the twolengths of chord material are connected together at the joint.(a) if the chord/chord connection is a bolted flange site connection, then joint 11 can be treated in asimilar way to joint 5(b) i f the chord/chord connection is a butt weld, then joint '11should be treated as a K-joint with bothbracings loaded in compression.The checks on joints 5 and 11 are given in the table below, in which joint 11a is as for case (a) aboveand joint 11b as for case (b) above.Jointnumber

Factoredappliedload, kN

Calculated joint capacities, kN for failure modes

Chord Chord Chord Bracingpunching effectiveshear width828.6 633.6725.0 221.1

Jointunityfactor

face sheardeformation

Joint 5 N20 = 548 609.9 821.8 0.90Joint 11a N29 = -61 270.1 821.8 0.28Joint 11b N29 = -61

N30 = -61316.3316.3

0.190.19

Thus all the joints are within all the parameter limits, all the factored loads are below the respective jointcapacities and the girder is satisfactory.

6.4 CHS Girder Design6.4.1 CHS Member Selection OptionsTop Chord: load -1709kN Bottom Chord: load +1744kNSize Mass Capacity Size Mass Capacity323.9x6.3 49.3 -1718 219.1 x10.0 51.6 1806219.1 x10.0 51.6 -1801 273.0x8.0 52.3 1832

Bracing 20 : load +548kN Bracing 21 : load -548kNSize Mass Capacity Size Mass Capacity139.7x5.0 16.6 582 139.7x5.0 16.6 567114.3x6.3 16.8 588 114.3x6.3 16.8 562Bracing 22 : load +427kN Bracing 23 : load -427kNSize Mass Capacity Size Mass Capacity114.3x5.0 13.5 472 114.3x5.0 13.5 452Bracing 24 : load +304kN Bracing 25 : load -304kNSize Mass Capacity Size Mass Capacity76.1x5.0 8.77 307 114.3x3.6 9.80 330114.3x3.6 9.80 344 88.9x3.6 10.3 336


40/47

Sracing 26 : load +183kNSize Mass Capacity48.5x5.0 5.34 18760.3x4.0 5.55 195

Bracing 28 : load +61kNSize Mass Capacity26.9x3.2 1.87 6633.7x2.6 1.99 70

Bracing 27 : load -183kNSize Mass Capacity88.9x3.2 6.76 22060.3x5.0 6.82 194

Bracing 29 : load -61kNSize Mass Capacity42.4x3.2 3.09 6348.3x3.2 3.56 86

6.4.2 CHS Member SelectionUsing the same procedure as for the RHS girder the following member sizes were selected.Top and bottom chords: 219.1 x 10.0Bracings 20 and 21 : 139.7 x 5.0Bracings 22 to 25 : 114.3 x 5.0Bracings 26 to 29 : 88.9 x 3.2

6.4.3 CHS Joint Capacity CheckAgain, it has been assumed that gap joints will be used throughout the girder and initially that all centrel ines node, although, in order to meet the joint parameter l imits it wi ll be necessary to move away fromthis.6.4.3.1 CHS Joint parameter checkThe table below contains al l of the parameter checks required for al l of the joints in the girder

Joint or Parameter Limiting value Actual value RemarksmemberChords dc/to ::;50 219.1/10 = 21.9 passBracings d/tj ::;50 for tension 139.7/5 = 27.9

and compression 114.3/5 = 22.9 all pass88.9/3.2 = 27.8

Bracing on d1/do :::0.2 139.7/219.1 = 0.64chord 114.3/219.1 = 0.52 all pass

88.9/219.1 = 0.41Joints1, 9 gap ::: t1 + t2 = 6.4 44.9 all passand 10Joints 2 gap ::: t1 + t2 = 8.2 29.4 passJoints 3,4, gap ::: t1 + t2 = 10.0 [olnt 3 & 7, g = 13.9 pass6,7, and 8 joint 8, g = 44.9 pass

joint 4, g = -1.62 fail, increase gap to12.5, ecc = 10.1

joint 6, g = -17.1 fail, increase gap to12.5, ecc = 21.2


41/47

6.4.3.2 CHS Joint capacity check

The joint capacity check procedure isthe same as for the RHS girder joints, and the general notes forthat girder still apply. The results of the joint capacity checks for the normal K-joints (allexcept 5 and11) are given in the table below.Joint Factored Calculated joint capacities, kN, for failure modes Jointnumber applied unity

load, kN Chord face Chord punching factordeformation shear

Joint 1 N27 = -183 185.2 601.1 0.99N28 = 61 185.2 601.1 0.33

Joint 2 N25 = -304 292.5 772.8 1.04N26 = 183 292.5 601.1 0.63Joint 3 N23 = -427 387.3 772.8 1.10

N24 = 304 387.3 772.8 0.78Joint 4 N21 = -548 542.5 944.6 1.01

N22 = 427 542.5 772.8 0.79Joint 6 N21 = -548 577.7 944.6 0.95

N20 = 548 577.7 944.6 0.95Joint 7 N27 = -427 492.9 772.8 0.87

N28 = 427 492.9 772.8 0.87Joint 8 N25 = -304 360.9 601.1 0.84

N24 = 304 360.9 601.1 0.84Joint 9 N27 = -183 360.9 601.1 0.51

N26 = 183 360.9 601.1 0.51Joint 10 N29 = -61 360.9 601.1 0.17

N28 = 61 360.9 601.1 0.17Joints 2, 3 and 4 all fail due to the chord face deformation cri terion by 4%, 10% and 1% respectively.Either member sizes or joint configurations will have to be changed, or the joints could be reinforced.

6.4.4 CHS Girder ReanalysisThere are various ways of increasing the capacity of the failed joints, for example:1) Change the top chord to one diameter lower and one thickness higher, i .e. 193.7 x 12.5. This wouldincrease the girder weight by 3.84%, it would also mean that the profil ing at each end of a bracingwould be different2) Change the compression bracings 21, 23 and 25 to one diameter up. This would increase theweight by 1.44% and, in this case, increase the number of bracing sizes used in the girder to four. Newsizes would be member 21 - 168.3 x 5.0, members 23 and 25 - 139.7 x 5.0.3) As 2) above, but rational ise the bracing sizes to give three sizes only. The new sizes would bemembers 20 and 21 - 168.3 x 5.0, members 22 to 25139.7 x 5.0 and members 26 to 29 remainingas 88.9 x 3.2. This would increase the girder weight by 2.9%4) Reinforce the six failed joints by adding a saddle plate 12.5mm thick (see section 4.6.1).If only one or two joints are involved, this could be an economic solution.5) Change the joints to overlap joints, This will increase fabrication costs since the ends of the bracingswill require double profiling.The actual choice from the above options will depend upon the circumstances of a particular projectsuch as:- number of identical girders required, material available or in stock, relative costs offabrication and materials, etc. In this particular case option 3) will be used.


42/47

6.4.4.1 Re-selection of CHS sizesThe actual section sizes will now be as followsChords both 219.1 x 10.0, as beforeBracings 20 and 21 - 168.3 x 5.0Bracings 22 to 25 - 139.7 x 5.0Bracings 26 to 29 - 88.9 x 3.2, as beforeThis results in an increase in the girder weight of 2.9%6.4.4.2 Revised CHS girder parameter limits and joint capacity checksThe joint parameter limits are all satisf ied, and the joint capacity check is given in the table below.Due the size changes the bracing gaps result in different eccentricit ies of loading, these are also shownin the table.

Joint Factored Calculated joint capacities, kN, Joint Gap Ecc.number applied for failure modes unity mm mm

load, kN Chord face Chord punching factordeformation shear

Joint 1 N27 = -183 185.2 601.1 0.99 44.9 0.0N28 = 61 185.2 601.1 0.33

Joint 2 N25 = -304 363.8 944.6 0.84 13.9 0.0N26 = 183 363.8 601.1 0.50

Joint 3 N23 = -427 453.9 944.6 0.94 12.5 21.2N24 = 304 453.9 944.6 0.67

Joint 4 N21 = -548 629.5 1138 0.87 12.5 33.6N22 = 427 629.5 944.6 0.68

Joint 6 N21 = -548 670.3 1138 0.82 12.5 46.1N20 = 548 670.3 1138 0.82

Joint 7 N27 = -427 577.7 944.6 0.74 12.5 21.2N28 = 427 577.7 944.6 0.74

Joint 8 N25 = -304 577.7 944.6 0.53 12.5 21.1N24 = 304 577.7 944.6 0.53

Joint 9 N27=-183 360.9 601.1 0.51 44.9 0.0N26 = 183 360.9 601.1 0.51

Joint 10 N29 = -61 360.9 601.1 0.17 44.9 0.0N28 = 61 360.9 601.1 0.17

The joints with the most highly loaded chords, joints 1, 2, 9 and 10, have zero noding eccentric ity andthe chords will not have to carry any moment due to eccentricity. Where there is an eccentricity, thechords have relatively small axial loads (e.g. at joint 3 only 75% of its axial capacity) and will thereforealso be able to carry the moment generated.

Although they have not been checked here, joints 5 and 11 would be checked using the sameprocedure as for the RHS girder.

Thus all the joints are within all the parameter limits, all the factored loads are below the respective jointcapacities and the girder is satisfactory.


43/47

7. LIST OF SYMBOLS

7.1 General alphabetic listAo,AjA vEMjp,jMjp,j,AppMop,jMop,j,AppN jNj,App vWel,jWpl,jabo , bjb ef fbepb eo vbfb rdo, djdsdwef yO ' fy jg

hO ' h jhrqto, tjtft,twaB

00op

area of chord and bracing member i, respectivelyshear area of chordmodulus of elasticity (205 000N/mm2)joint design capacity in terms of in plane moment in bracing member ifactored applied in plane moment in bracing member ijoint design capacity in terms of out of plane moment in bracing member ifactored applied out of plane moment in bracing member ijoint design capacity in terms of axial load in bracing member ifactored applied axial load in bracing member ipercentage overlap, q sinG/ hi x 100%, see figure 31elastic section modulus of member iplastic section modulus of member ifillet weld throat thicknesswidth of RHS chord and bracing member i, respectivelyeffective bracing width, bracing to chordeffective bracing width for chord punching sheareffective bracing width, overlapping to overlapped bracingI-section flange widthwidth of reinforcement plate for RHS chorddiameter of chord and bracing member i, respectivelyarc length of saddle reinforcement plate for CHS chordI-section web depthjoint eccentricitynominal yield (design) strength of chord and bracing member i, respectivelygap / overlap between bracinqs at the chord face, a negative value denotesan overlapheight of RHS chord and bracing member i, respectivelylength of reinforcement plateoverlap between bracings at the chord facethickness of chord and bracing member i, respectivelyI-section flange thicknessthickness of reinforcement plateI-section web thicknessnon-dimensional factor for the effectiveness of the chord face to carry shearmean bracing to chord width ratio, b1/bo or d1/do or b1+b2 or d1+d2-- --2bo 2dochord width to thickness ratio, bol2 to or dol2 tomultiplanar factorangle between bracing member i and the chordefficiency factorfactored applied stress in RHS chord jointfactored applied stress in CHS chord joint

oMember identification suffices, i

2j

the chord memberthe compression bracing for joints with more than one bracing or the bracing whereonly one is presentthe tension bracing for joints with more than one bracingthe overlapped bracing for overlapped bracing joints


44/47

7.2 Pictorial list

sin 8i

Figure 31 : Definition of percentage overlap Figure 32: Definition of SHS chord symbols

d

bf

Figure 33 : Definition of I -section chord symbols

Figure 34 : Definition of bracing symbols


45/47

8. REFERENCES

1. CIDECT - 'Design Guide for Circular Hollow Section (CHS) Joints under Predominantly StaticLoading', Verlag TUV Rheinland, Cologne, Germany, 1991, ISBN 3-88585-975-0.

2. CIDECT - 'Design Guide for Rectangular Hollow Section (RHS) Joints under PredominantlyStatic Loading', Verlag TUV Rheinland, Cologne, Germany, 1992, ISBN 3-8249-0089-0.

3. BS DD ENV 1993-1-1 :1992/A 1 :1994.Eurocode 3 - Design of Steel Structures: Part 1-1 -General Rules and Rules for Buildings: Annex K - Hollow section latt ice girder connections

4. BS 5950 :Part 1 - Structural Use of Steelwork in Building :Part 1 - Code of Practice for Design inSimple and Continuous Construction: Hot Rolled Sections.

5. CIDJOINT software program, a design program requiring MS-Windows version 3.x (or higher)and available in the UK from CSC (UK) Ltd, New Street, Pudsey, Leeds, LS28 8AO.

6. EN 10210-1 - Hot Finished Structural Hollow Sections of Non-alloy and Fine Grain StructuralSteels: Part 1 - Technical Delivery Requirements.

7. EN 10210-2 - Hot Finished Structural Hollow Sections of Non-alloy and Fine Grain StructuralSteels: Part 2 - Tolerances, dimensions and sectional properties.

8. British Steel Tubes and Pipes 'SHS Welding', TD394

Please Note: Care has been taken to ensure that the contents of th is publ icat ion are accurate,but Bri tish Steel pic and its subsidiary companies do not accept responsibil ity for errors or forinformation which is found to be misleading. Suggestions for or descriptions of the end use orapplication of products or methods of working are for information only and British Steel pic and itssubsidiaries accept no liabil ity in respect thereof. Before using products supplied or manufactured byBritish Steel pic the customer should satisfy himself of their suitability. Iffurther assistance is required,Bri tish Steel pic within the operat ional l imits of its research faci li ties may often be able to help.


46/47

Errata to TD393.10E.97*Page 245.2.1 RHS chord joint parameter limits

Replace Gap/lap parameter for K- and N-gap joints In parameter table with;gap ~ t, + t2and ~ 0.5(bo -(b,+bz }/2}

but s1.5(bo -(b,+bz }/2}Page 265.2.3 RHS chords and RHS bracings with axial loadsT-, Y- and X-jolnts

Replace; Chord Shear,(X-joints with 9 S90 only)

With; Chord Shear,(X-joints with 9


47/47

------ ------------ ------- -----------------------

For Free Technical assistanceCALL Freephone 0500 123133

Documents

welded jt designto5950