Composite beam behaviour in braced frames

Journal of Constructional Steel Research 49 (1999) 271–289

Composite beam behaviour in braced frames

U.I. Dissanayakea,*, J.B. Davisonb, I.W. Burgessb

aDepartment of Civil Engineering, University of Peradeniya, Peradeniya, Sri LankabDepartment of Civil and Structural Engineering, University of Sheffield, Sheffield S1 3JD, UK

Received 26 March 1997; received in revised form 20 March 1998; accepted 17 April 1998

Abstract

A numerical study has been conducted to investigate the influence of composite beam-to-steel column joints on the behaviour of composite beams, for a number of subframes rep-resenting the spans and loading arrangements of current commercial buildings in the UK. Atwo-stage analysis has been performed on each of these subframes, varying the steelworkconnection, the percentage of reinforcement over the support and the degree of shear connec-tion between the steel beam and the concrete slab. The studies use a computer model whichhas been developed to simulate the behaviour of steel-framed buildings with composite floordecks. The program is capable of simulating the behaviour of two-dimensional subframes, andconsiders their two-stage behaviour, both during unpropped construction and as fully com-posite beams. It is also capable of taking into account the partial interaction between the steelbeam and the composite slab, the orientation of the profiled metal deck, the effect of additionalreinforcement over supports and the semi-rigid nature of the joint between the composite beamand steel column. In contrast to the usual observations made in isolated joint tests, the studyindicates very low values of strains in reinforcing bars at the composite beam-to-steel columnjoint at the ultimate limit state. The results also indicate that the common types of compositejoints available are capable of providing the rotation capacity required to sustain the ultimateload with about 1% of reinforcement over the support, without the use of expensive columnweb stiffeners. 1999 Elsevier Science Ltd. All rights reserved.

Keywords:Composite frames; Partial interaction; Semi-rigid joints; Finite element analysis; Steelconstruction

* Corresponding author.

0143-974X/99/$ - see front matter 1999 Elsevier Science Ltd. All rights reserved.PII: S0143 -974X(98)00205-3

272 U.I. Dissanayake et al. / Journal of Constructional Steel Research 49 (1999) 271–289

1. Introduction

The introduction of composite framing systems using profiled steel decking as apermanent formwork, which eliminates the need for the propping of slabs duringconstruction, has played a very large part in the renaissance of structural steel formulti-storey commercial buildings in recent years. In their simplest form, compositeframes of the type here considered comprise a bare-steel frame of H-section columnssupporting I-section beams laid out in the typical primary and secondary manner,supporting an overlaid composite floor deck. The composite floor deck system con-sists of cold-formed profiled steel sheets which act not only as the permanentformwork for an in-situ cast concrete slab but also as the tensile reinforcement [1].The overall structural behaviour of a steel–concrete composite framed building ofthis type may be divided into three phases, namely the construction-stage behaviour,composite-slab behaviour and composite-beam behaviour.

During the construction stage the profiled steel sheeting alone carries the weightof wet concrete, workmen and tools, which will in turn be transferred to the support-ing beams. As the composite action between the concrete slab and the steel beamhas not yet been developed, the bare steel frame will have to support this load byitself unless it is propped. Props and temporary formwork are, however, rarely usedin practice as they hinder the speed and convenience of construction, which is oneof the main reasons for the recent popularity of this form of composite construction.Therefore the bare steel frame will sustain the load with consequent deflection ofbeams and resulting rotations of beam-to-column joints. It should be noted here thatit is the bare steel beam-to-column joint which is subjected to rotation at this stage.During the second stage of the structural behaviour the hardened concrete slab, actingcompositely with the profiled steel deck, spans between the supporting beams andcarries the imposed live loads. The steel deck acts as the tensile reinforcement tothe slab, and the development of composite action depends entirely upon adequatetransfer of horizontal shear forces at the interface between steel deck and concrete.The third and final stage of behaviour may be identified when the concrete slabinteracts with the supporting beam and develops composite action. Although fullinteraction between the steel beam and the composite slab is almost impossible toachieve as the shear studs between the slab and beam are rarely stiff enough toprevent all slip at the interface, if sufficient studs are used high levels of interactionare possible enabling the beam to be designed with "full interaction".

To simulate the real physical behaviour of a steel-framed building a computerprogram has been developed which is capable of analysing frames with compositefloor decks, taking into account both geometrical and material nonlinearities. Theanalysis tool has been developed with the capability to predict the behaviour oftwo-dimensional subframes during both the construction phase (when the frame iseffectively bare steel) and the later composite-beam stage. Partial interaction betweenthe steel beam and the concrete slab, the orientation of the profiled metal deck, theeffect of additional reinforcement over the supports and the semi-rigid nature of thejoint between the composite beam and the steel column are all included in the analy-sis. Although full details of the formulation and validation of the program are avail-

273U.I. Dissanayake et al. / Journal of Constructional Steel Research 49 (1999) 271–289

able elsewhere [2–4], the following section briefly outlines the main features of theprogram before explaining the findings of the studies undertaken.

2. Features of the computer program

2.1. Construction stage behaviour

Behaviour during construction is modelled by a program module capable of ana-lysing semi-rigidly connected plane frames of I-sections [2,3]. The program utilisestwo types of elements; a beam–column element of I-section to represent steel mem-bers and a spring element to represent semi-rigid joints. The accuracy of the programwas tested by comparison with experimental data from a full-scale, flexibly connec-ted, non-sway frame [5]. All steel-to-steel connections were modelled using datafrom isolated-joint tests. Comparison of the load–deflection response and jointrotations for both test and analysis showed close agreement [4]. Construction loadis applied to the bare steel frame within a specified number of load increments(usually five). Once this load is reached, the program automatically terminates andstores the necessary information for the next stage of the analysis into an ASCII file.Information stored into the ASCII file includes the strains at the top and the bottomof the steel beam at each Gauss point for all elements and the relative rotations atall steel-to-steel connections.

2.2. Composite-beam behaviour

The module of the computer program to simulate the composite-beam behaviouressentially consists of three distinct finite elements, namely the steel-only columnelement, the partial-interaction composite beam element and the composite beam-to-steel column connection element [2,3]. The strains and rotations developed duringthe construction stage in the steel beam at a given cross-section are added to strainsdeveloped in the steel beam at the same cross-section during the composite-beamstage. This procedure is conducted at every cross-section, at each iteration and loadstep until failure. The rotations mobilised in the bare steel-to-steel joint during theconstruction stage are accounted for by curtailing the steel-to-steel moment rotationcurve for a given connection by the amount of rotation that the particular connectionhas undergone during the construction stage, and using this modified moment–rotation data as input for the second stage of the analysis. To verify the validity ofthis approach a simply supported composite beam was analysed as an unproppedand a propped beam, using the above procedure for the former case. The resultsshowed the two beams to fail at approximately the same load, as expected since themethod of construction does not affect the ultimate strength. However, the unproppedcase showed earlier nonlinearity caused by the greater strains developed in the baresteel beam as a result of the application of the construction loads.


2.3. Partial interaction

Partial interaction between the steel beam and the concrete slab is simulated bytreating the composite beam as two parallel beam elements, one for the steel beamand the other for the concrete slab, connected through a continuous shear mediumrepresenting stud shear connectors. The slip at the interface between the steel beamand the concrete slab is calculated by superposing the effect of the curvature of thecross-sections due to bending into the difference between the horizontal displace-ments of the centroids of the steel sections [3]. The shear–slip modulus and theinternal force per unit length required can be calculated from the load slip behaviourof a single stud, by averaging the elastic or ultimate shear force per stud, or pair ofstuds, over the inter-stud spacing. A tri-linear characteristic typical of those used inthe present analysis is shown in Fig. 1 and compared with curves due to Johnsonand Molenstra [6] and Aribert [7]. To test the validity of the treatment of partialinteraction in the formulation, the analysis was compared with test results from asimply supported composite beam tested by Chapman and Balakrishnan [8] and ana-lytical results for the same test by Yam and Chapman [9]. The comparisons showgood agreement in terms of initial stiffness, failure load and the onset of nonlin-earity [2,4].

2.4. Semi-rigid connection

Composite beams are typically designed as simply supported with the beam-to-column connection being selected to carry only the design shear load, enabling the

Fig. 1. The stud shear–slip characteristic used in the modelling.


simplest and most economic types of steelwork connections to be used. In compositeconstruction, however, there is an additional but inherent strength and stiffness asso-ciated with the composite beam-to-steel column joint, due to the continuity of theconcrete slab with anti-crack mesh around the column support. Recent studies [10]indicate that the design efficiency of composite structures may be improved if theinherent strength and stiffness are recognised in the design. As the anti-crack meshtends to behave in a very brittle manner, it appears to be unwise to rely on thecontinuity provided by only mesh reinforcement. This problem may be overcomevery cheaply by introducing reinforcing bars into the concrete around the columnsupport.

The inherently semi-rigid nature of the composite beam-to-column column con-nection is modelled by taking into account the following components of defor-mation [11]:

O Steelwork connection flexibility, due to the application of balanced moments oneach side of the column axis.

O Column web shear deformation flexibility. This is the shear deformation of thecolumn web panel, which may be characterised by the relative rotation betweenthe column web panel and the column axis, assuming that the angle between thecolumn and the beam remains unchanged.

O Flexibility due to deformation and bending of the reinforced concrete slab zone.O Flexibility of shear connectors between the steel beam and the concrete slab,

producing slip at the interface between them.

A macro-element model to represent the behaviour of the composite joint has beendeveloped [2,3] by adding together the effect of each component independently,neglecting the interaction of the various effects. In order to validate this approach,direct comparisons were made against five sets of experimental results from threedifferent research centres: Warwick [12], Nottingham [13] and Rennes [14]. All fivetest series employed a cruciform arrangement, and featured a variety of steel connec-tion types (with known moment–rotation characteristics) and reinforcement levels.Comparison of test results against analysis showed good agreement, although thecomposite joints with cleated steel connections were not as accurately predicted asthose with end-plates, probably because of the greater variability inherent in cle-ated connections.

The ability of the program to predict the behaviour of a semi-rigidly connected(propped) composite beam was examined by comparison (Fig. 2) with test resultsfrom experiments conducted by Jarrett and Lennon [15] on a single-bay frame, aswell as with results from Grantham and Jarrett [16] on a two-bay subframe for whichthe comparison is reported elsewhere [4].

3. Parametric study

One of the main objectives of the parametric investigation was to investigate theinfluence of the composite beam-to-steel column joint on composite beam response.


Fig. 2. Comparison of model predictions with test results of Lennon and Jarrett[16] test results on thesingle-bay frame NR2.

A parametric study was conducted considering the behaviour of five distinctsubframes selected from three generic buildings, representing the spans and loadingconditions common in modern commercial buildings in the UK [17]. The followingthree parameters have been identified as the main factors that influence the behaviourof the composite beam-to-steel column connection [2].

O The type of steelwork connection. Two hypothetical moment–rotation character-istics have been selected to represent the type of steelwork connections to be usedin the parametric study. The F-type (flexible) is a typical seating cleat whereasthe S-type (semi-rigid) is a typical flush end-plate.

O The amount of reinforcement over the support. A steel area of 0.2% of the continu-ous concrete slab above the metal deck has been selected to represent the meshreinforcement only and a steel area of 1% has been selected to represent the meshplus reinforcing bars over the support.

O The type and concentration of shear connectors. Three distinct values have beenselected for the degree of interaction to represent "full interaction", the "lowestacceptable interaction" and an "intermediate interaction" according to BS5950:Part 3: Section 3.1 [18].

Subframes selected for the parametric study may be summarised as shown in Table1, which indicates the spans and loading types used.

3.1. Finite element model

The subframes selected for the each case study are illustrated in Figs. 3–5. Inmost cases, by considering half the axial stiffness of the column at the centre lineand restraining both lateral displacements and moments along it, only one half ofthe actual subframe needs to be modelled. Composite beams have been modelledby using eight elements, in order to obtain a fair representation of steel strainsdeveloped during the construction stage. An effective flange width of the composite


Table 1Summary of subframes used for the parametric study

Case study Span/s (m) Type of loading

1 7.5 (3 bays) Point load at mid span2 7.5 (4 bays) Uniformly distributed load3 6.0 (4 bays) Point load at mid span4 6.0, 7.5 (2 bays) Uniformly distributed load5 6.0, 9.0, 6.0 (3 bays) Point loads at third-points for 9.0

m span beam and point loads atmid-span for 6.0 m span beams

Fig. 3. Building B[10]—main structural details.

slab is taken as span/4 throughout. For the steel columns, only the length betweenthe points of contraflexure, above and below the floor deck, is modelled by usingfour elements as shown in Figs. 6–10. The column ends are allowed to rotate butare restrained against displacement. The length of each column stub is selected as1.80 m, which is half the storey height of all the composite frames [17]. All com-


Fig. 4. Building A[10]—main structural details.

posite beam-to-steel column connections are modelled using the proposed "macroelement" model.

3.2. Subframe configurations

For each case study there are 12 different subframe configurations available usingpermutations of three variables—the degree of shear connection, the steel percentageover the support and the type of steelwork connection.

The three degrees of shear connection selected for case study 2 are 49%, 86%and 118%, according to BS5950. In these cases 49% corresponds to the actual design,118% represents the lowest shear connection above 100%, for which a uniform 19mm stud spacing corresponding with the decking trough spacing (300 mm) can befound, and 86% is approximately midway between these values but again uses astud spacing which fits with the decking troughs. In addition to the 12 cases men-tioned, one span of the subframe has been analysed assuming simple support to thebeams, giving rise to three additional cases corresponding to each degree of shearconnection. Table 2 summarises all 15 cases, indicating case numbers.

A two-stage analysis has been carried out for all these 15 cases, using the approachdiscussed previously. The initial load is set in such a way as to reach the wet concreteload in five steps.


Fig. 5. Main structural details of Cardington test frame, at 5th floor level.

4. Results

Table 3 shows the results of the analyses of 25 cases—five for each subframe—at the 49% shear interaction assumed in the design calculations. The table thus sum-marises the effects of including the inherent stiffness of the composite joints in sometypical building frames, in terms of load carrying capacity and service deformations.In addition to loads and deflections the rotations experienced by the composite jointsand the strain in the reinforcement are also presented.

4.1. Load–deflection response at service loads

Consider first the effect of semi-continuous construction on deflections. Althoughthe absolute values of deflection are not large in any case, mainly as a result of themodest spans investigated, the improvement in performance of the beams can beseen from the comparisons with the computed values for a simple beam. In orderto visualise the increase in both strength and stiffness, the load–deflection responseof the composite frame in subframe 2 is compared directly with that of an equivalentsimply supported beam in Fig. 11. The increase in stiffness from construction-stageto composite-stage behaviour is in the range 67 to 81% for the case with 49% shear


Fig. 6. Finite element model for case study 1.




Table 2Different configurations for case study 2

Configuration Case no. Steelwork Steel percentage Degree of shearconnection over support connection (%)

Subframe CS-13 49CS-14 Flexible/ 0.2% 86CS-15 pinned 118CS-16 49CS-17 (F-type) 1.0% 86CS-18 118CS-19 49CS-20 Semi-rigid/ 0.2% 86CS-21 partial-strength 118CS-22 49CS-23 (S-type) 1.0% 86CS-24 118

Simply BS-4 49supported BS-5 NA NA 86

beams BS-6 118

283U.I. Dissanayake et al. / Journal of Constructional Steel Research 49 (1999) 271–289T

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Fig. 11. Comparison of load–deflection response at 49% shear connection.

connection, which is the design case, the exact improvement depending on the con-nection and reinforcement details.

In all the case studies, the relatively close performance of the beams with 0.2 and1.0% levels of reinforcement occurs because the construction load was applied tothe bare steel section with either a flexible or semi-rigid connection, and so thedeflection associated with this component of loading was unaffected by the reinforce-ment. The differences in deflections shown between the various cases are due onlyto the imposed load component, which is applied after the beam has become com-posite. The deflection due to imposed load only is shown in column 6 of Table 3,and may be compared with the imposed load deflection calculated in accordance withthe design approach of BS5950, which assumes the beam to be simply supported.

It is clear that the real levels of deflection that occur in a composite frame willnormally be less than those calculated from design calculations, because of the inbuiltand desirable conservatism in the design method. This will be enhanced as a directresult of the inherent, but neglected, stiffness at the connections which arise from


both the bare steel beam-to-column connection and the composite joint. Althoughmany designers may prefer not to utilise this reserve in performance explicitly, butinstead to retain it as an implicit safety level, the improved behaviour is there to beused if required, at little or no extra cost in construction.

4.2. Load capacity at the ultimate limit state

Table 3 summarises the capacity of the subframe beams accounting for the semi-rigid action of the bare steel and composite connections. In all cases the degree ofshear interaction used was the same as that adopted for the design calculations. Thetable gives the "failure load" for each case considered. This is the load at which thecomputer simulation terminated because of runaway deflection. Also shown is theratio of the computed failure load with semi-rigid joint action included to the com-puted failure load of a simple beam. This gives a measure of the improvement incapacity attributable to the presence of the semi-continuous joints. For completeness,the table also gives the ratio of computed failure load to the BS5950 design resist-ance, calculated assuming pinned connections.

It is evident from the table that even connections with modest stiffness and strength(classified here as flexible) have a significant effect on load-carrying capacity. Suchimprovements are typically 15–20% when the connections are combined with meshreinforcement and 20–30% when used with reinforcing bars. For steel connectionswith greater strength and stiffness (the flush end-plate for example) the correspondingimprovements are even more pronounced, of the order 20–30% with mesh reinforce-ment and more than 30% with reinforcing bars. It is important to note that the fabri-cation and construction details of these connections do not differ from current prac-tice except in the provision of additional reinforcing bars around the column. Theimprovements in load-carrying capacity arise from taking into account in analysiseffects such as continuity across column lines, which are known to occur but areignored in current design practice.

4.3. Joint rotations and reinforcement strains

Concerns have been expressed about the reliability of mesh reinforcement in com-posite connections after a number of tests [12] showed fracture of the wires at rela-tively low rotations. Furthermore, design codes [18,19] exclude mesh reinforcementwhen calculating moment capacity. However, the authors are unaware of any build-ings reported to have serious cracking at connections in service. For this reason thestudy considered the strains attained in the reinforcement in each case, and the jointrotations at failure. Table 3 reports the average strain in the reinforcement eitherside of the column for all the subframes, at three levels of loading-loads equivalentto the service condition, design ultimate load (assuming the beam to be pinned) andthe load actually required to fail the beam under consideration.

The rotations of the composite joints and the strains in reinforcement over thesupports have been recorded for all 12 configurations of subframe 2. Table 4 showsthe rotations and strains at three different levels of loading, namely the service load,


Table 4Joint rotations and strains in reinforcement at different load levels for subframe 2 at three levels of interac-tion

Test Average joint rotation (mrad) at Average strain in mesh/bars (%) at

Service Ultimate Service UltimateFailure load Failure load

load load load load

CS-13 7.0 14.2 38.4 0.24 3.02 11.32(49-F-0.2)CS-16 6.8 13.1 32.0 0.08 0.12 0.16(49-F-1.0)CS-19 7.7 14.5 40.1 0.29 2.84 11.2(49-S-0.2)CS-22 7.2 13.4 34.1 0.08 0.12 0.16(49-S-1.0)CS-14 5.2 9.6 24.5 1.51 4.62 12.96(86-F-0.2)CS-17 3.8 7.5 21.2 0.10 0.16 2.72(86-F-1.0)CS-20 6.0 10.6 22.6 1.82 4.65 11.83(86-S-0.2)CS-23 4.5 8.1 20.8 0.11 0.16 2.33(86-S-1.0)CS-15 4.5 8.7 20.7 2.18 5.47 13.95(118-F-0.2)CS-18 2.5 4.5 17.1 0.11 0.19 7.01(118-F-1.0)CS-21 5.2 9.1 19.6 2.64 5.49 13.25(118-S-0.2)CS-24 3.0 5.1 16.8 0.12 0.19 6.71(118-S-1.0)

the ultimate load and the failure load indicated by the program. Only the averagevalues of rotations and strains experienced by the composite beam-to-steel columnjoint in bay 3 are given, in order to make the table less complicated. It should alsobe mentioned that the F and S types of steelwork connections at bay 3 experienced8.50 and 4.25 mrads of rotation, respectively, during the construction stage, inaddition to the values mentioned in Table 4. At service load, joint rotations are ofthe order of 7 mrad for the design case but reduce to 2.5–5.2 mrad when the degreeof interaction between beam and slab is increased to 118%. At a load level corre-sponding with the design ultimate load, joint rotations are of the order of 14 mradfor the design case but reduce significantly to 4.5–9.1 mrad when high levels ofinteraction are present.

With 1% reinforcement over the support, steel reinforcing bar strains, in the range0.12–0.19%, remained well below the yield strain even at the ultimate load level,and the reinforcing bar elongation at failure was very low, in the range 0.16–7.01%.Thus, even when the total rotation required for construction and service conditions


Table 5Composite connection test results [13]

Reinforcement ratio Ultimate rotationSpecimen Joint type Web stiffening

(%) (mrad)

SCJ1 Seating cleat 0.2 None 14.3SCJ11 Seating cleat 0.7 None 26.3SCJ3 Flush end plate 0.2 None 7.2SCJ Flush 1.0 None 23.4

is considered the values remain relatively low. As an indication of the levels ofrotation capacity available in composite joints, tests performed by Xiao et al. [13]have been compared with the analysis. Table 5 provides extracts from Xiao’s seriesof joint tests. Of the tests shown only the flush end-plate with mesh reinforcement(SCJ3) gives cause for concern. Although these tests did not include a "constructionphase", so that loads were not applied to the bare steel connection, it can be seen thatthe ultimate rotation recorded in SCJ3 was 7.2 mrads, which would be insufficient tomobilise the full capacity in all the comparable analytical studies (14.5 mrad in CS-19, 10.6 mrad in CS-20 and 9.1 mrad in CS-21). Tests SCJ11 and SCJ4, in whichadditional reinforcement was provided, had rotation capacities greater than required.

4.4. Summary of joint rotations and reinforcing bar strains for other case studies

Table 6 presents the composite beam-to-steel column joint rotations and the rein-forcing bar strains for all five case studies mentioned in Table 1. Results show verylow values of reinforcing bar strains and joint rotations. It can be seen that thereinforcing bar strains at ultimate limit state are well below 17%, at which the frac-ture of reinforcing bars has been observed [12]. The reason for the indication ofvery low values for the composite beam-to-steel column rotation may be attributedto the use of unpropped construction and full shear connection in the isolated jointtests, resulting in less slip at the steel–concrete interface, with consequently larger

Table 6Summary of composite joint-rotations from all five case studies

Joint rotations (at service) Joint rotations (at ultimate) Rft. strains atCase no.

ultimate (%)Design case Other cases Design case Other cases

1 5.0 3.3–5.2 8.5 5.5–7.6 0.08–0.182 7.0 2.5–5.2 14.0 4.5–9.1 0.12–0.193 3.0 2.0-3.2 5.5 3.7-5.9 0.11-0.164 5.3 2.1–4.1 10.5 3.8–7.6 0.10–0.175 2.5 1.7–2.0 5.0 3.3–4.1 0.08–0.12


reinforcing bar strains. In practice, the degree of interaction is likely to be lower,permitting more slip and a consequent reduction in reinforcement strains.

5. Conclusions

A parametric study has been conducted to investigate the effect of joint continuityin composite braced frames. The results have shown significant improvements inbeam performance at both the serviceability limit state of deflection and the ultimatelimit state of bending resistance. These improvements are attributable to the stiffnessand strength inherent in relatively simple beam-to-column connections, augmentedin some cases by the addition of modest levels of additional reinforcement.

Careful consideration of the ductility available from semi-continuous compositejoints reinforced with mesh alone suggests that these are inadequate for use in prac-tice, particularly at high levels of shear interaction, due to the limitation on elongationbefore fracture of the mesh fabric reinforcement occurs. For the typical framearrangements studied, there would appear to be adequate ductility in simple com-posite joints, provided that they are reinforced with reinforcing bars rather than mesh.

The inclusion of the semi-continuous action in composite beam design withinbraced frames would therefore appear to be beneficial at both serviceability andultimate limit states. Some caution must however be exercised when using the resultsof modelling in this way, because not all of the phenomena which can occur inpractice are easily modelled. An example of relevance here is the localisation ofrotation and reinforcement straining, which may happen in the hogging region at thebeam–column joint when cracking of the concrete slab occurs, which may causefailure of reinforcing bars at a relatively small rotation if only a very short gaugelength of bar is being strained. A possible design solution to this "ductility" problemmay be by deliberately detailing for a de-bonded length of reinforcing bar acrossthe connection zone.

References

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[4] Dissanayake, U.I., Davison, J.B., Burgess, I.W., Modelling of composite frame behaviour inunpropped construction. (In press).

[5] Davison, J.B., Strength of beam-columns in flexibly connected steel frames. PhD thesis, Universityof Sheffield, 1987.


[6] Johnson RP, Molenstra IN. Partial shear connection in composite beams for buildings. Proceedingsof the Institution of Civil Engineers 1991;91(20):679–704.

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[18] BS 5950, Structural use of steelwork in building. Section 3.1: Code of practice for design of simpleand continuous composite beams. British Standards Institution, 1990.

[19] Eurocode 4, Design of composite steel and concrete structures. Part 1.1. General rules for buildings,DD ENV 1994-1-1. European Committee for Standardisation, 1994.

Composite beam behaviour in braced frames

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