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Journal of Constructional Steel Research 62 (2006) 771–782www.elsevier.com/locate/jcsr

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Experimental study on semi-rigid composite joints with steel beams andprecast hollowcore slabs

F. Fu, D. Lam∗

School of Civil Engineering, University of Leeds, Leeds, LS2 9JT, UK

Received 8 July 2005; accepted 30 November 2005

Abstract

The concept of semi-rigid composite connection has been widely researched in the past; however, most of the researches arecomposite joints with metal deck flooring and solid concrete slabs. Composite construction incorporating precast concrete hollowcore slab(HCU) is a recently developed composite floor system for buildings. The research on the structural behaviour of the semi-rigid composite jowith HCU is new and without any previous experimental database. In this paper, eight full-scale tests of beam-to-column semi-rigid cojoints with steel beams and precast hollowcore slabs are reported. The variables are stud spacing, degree of the shear connectionslongitudinal reinforcement and slab thickness. The test set-up and instrumentation is described in detail. The experimental behaviourand based on the test data the structural behaviour of these semi-rigid composite joints is discussed. Based on the experimental data,method to predict rotation and moment capacity for this type of composite connection is proposed.c© 2005 Elsevier Ltd. All rights reserved.

Keywords: Semi-rigid; Composite; Joints; Precast; Hollowcore; Steel; Connections; Beam–column

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1. Introduction

In the area of composite construction, extensive reseworks have been focused on semi-rigid connection design sinceit was first proposed by Barnard [1] in the 70s. They showedthese formsof connections when used in design will leadreduction in beam sizes, which in turn will reduce the bedepth, the overall building height and cladding cost, etc. Tmoment rotation characteristic of the semi-rigid composiconnections was first investigated by Johnson and Hope-Gil2]in 1972, they found that neither simple nor rigid beam–coluconnections are ideal. Simple joints are too unpredictable wrigid joints are often too stiff in relation to their strength and aexpensive; therefore, the semi-rigid joint with a large rotaticapacity and a predictable flexural strength that does not reqsite welding or accurate fitting is needed. Numerous researhave been carried out on semi-rigid composite connection3,4], the most common types of floor slab used being solid Rslabs or profiled metal deck floors.

∗ Corresponding author.E-mail address:[email protected](D. Lam).

0143-974X/$ - see front matterc© 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.jcsr.2005.11.013

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Composite beams incorporating precast hollowcore flslabs are a newly developed composite floor system fobuildings. Compared with the other two types of floor systemhas the following advantages: HCU can be manufactured u500 mm in depth, meaning that simply supported floor spanup to 20 m are possible; however, the most common depth150–400 mm. HCU has an excellent structural capacity to sweight ratio, with span/depth ratios in the order of 35 beinpossible for normal office loadings. The volume of the hollcores accounts for up to 50% of the cross section, therefo10 m span floor only weighs 3.5 kN/m2. The standard widthof the units is 1.2 m, enabling fixing rates of around 20002

per week. The floor system does not require a structural scto carry horizontal diaphragm forces thus further reducing tdead weight of the floor. Welding of the shear studs mbe carried out in a factory or at ground level on site wmobile welding equipment usingthe semi-automatic drawn arprocess.

Although the use of precast hollowcore slabs dates bacthe 1940s, research on composite construction incorporasteel beams with precast hollowcore slabs is relatively new.first commercial testing in this area was carried out at SalfUniversity and reported by Hamilton [5]. Tests were carried ou

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772 F. Fu, D. Lam / Journal of Constructional Steel Research 62 (2006) 771–782

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Fig. 1. General arrangementof test set-up.

Fig. 2. End plate connection.

using 150 mm deep slabs and 406× 178× 60 UB with 19mm diameter× 125 mm long headed shear studs. The resshowed more than 70% increase in ultimate moment capawhen compared with its bare steel counterpart. Mode of failwasdue to shearing off of the headed studs.

Research on shear connector strength in precast sconcrete planks was carried out by Moy and Tayler [6] in 1996.Twenty-seven push-off tests were carried out and the resshowed a reduction in strength as the gap of in situ concrdecreased. It is recommended that the width of in situ concshould be a minimum of 100 mm to avoid reductions in shstrength of the shear connectors. It is also recommendedtwo layers of reinforcement must be used in the structutopping to avoid any tensile splitting.

A test on composite beams with precast solid planks wasconducted by Jolly [7] at Southampton University. A 16 m spacomposite beam with 110 mm deep precast concrete plwas tested. The results showed that the dynamic responslong span, shallow composite construction complied withrequirements of BS5950 [8] without the need to increase thminimum number of shear connectors as specified in the co

Shim et al. [9] studied the behaviour of headed shear stuin a precast post-tensioned bridge deck at the Seoul NatiUniversity. Push-out tests were carried out to determine tstructural behaviour of the shear connection in the precast dIt is found that as the thickness of the bedding layer increathe ultimate strength of the shear connection decreases.

Horizontal push-off tests with precast hollowcore slabs wfirst performed by Lam et al. [10] in 1998. They showed thathe shear capacity of the stud for this type of constructwasnot only affected by the tensilecapacity of the stud itself

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Fig. 3. Test specimen before concrete infill.

Fig. 4. Load versus slip curve from push-off test.

Fig. 5. LVDT’s position for measuring beam rotation and interface slip.

but also affected by the gap width, the amount of transvereinforcement,the strength of the in situ concrete infill anthe presence of the longitudinal and transverse joints. Thrfull scale simply supported composite beams with variaparameters were also carried out by Lam et al. [11] to study theflexure behaviour and was compared with the non-compobare steel beams. The results showed two modes of faifailure due to loss of shear studs and failure of the concretedue to yielding of the transverse reinforcement. Neverthethe residual moment capacity of all the beams remaineleast 40% above the moment capacity of the bare steel sectioonly. A beam with a pre-cracked insitu/precast concrete joinwas also tested. Modelling of the headed studs in steel-precomposite beams using the finiteelement analysis softwar

F. Fu, D. Lam / Journal of Constructional Steel Research 62 (2006) 771–782 773

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Fig. 6. Strain gauge on steel reinforcement.

Fig. 7. Strain gauge mountedon steel beam flanges and web.

ABAQUS [12] was carried out by El-Lobody and Lam [13],good agreement was obtained when compared with theresults.

The use of the precast hollowcore slabs in current builddesign is so far limited to simple beam–column connectioAs semi-rigid connection has many advantages oversimple connection, the main objective of this research isinvestigate the structural behaviour of the composite semi-rigconnections with precast hollowcore slabs and to determwhether these kinds of joints can provide sufficient momecapacity and rotation capacity todevelop the mid-span plasthinge for the plastic analysis uses in the composite bdesign.

2. Test arrangement

2.1. Test specimens

All specimens wereof cruciform arrangement as shownFig. 1 to simulate the internal beam–column joints in a semi-rigid composite frame. The specimen was assembled from3300 mm long; 457× 191× 89 kg/m; grade S275 universa

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Fig. 8. Bolt strain gauges.

Fig. 9. Test set-up and loading arrangement.

beams and one 254× 254× 167 kg/m; grade S275 universacolumn to form the cruciform arrangement. The beamsconnected to the column flanges using 10 mm thick flush eplates withtwo rows of M20 Grade 8.8 bolts as shown inFig. 2.The steel connection is a typicalconnection currently used iUK practice for simple joints, this is to ensure that the enhanceperformance of the composite joint is not provided by the bsteel connection. A single row of19 mm diameter headed shestuds is pre-welded to the top flange of the steel beams. Finall


Table 1Strength of concrete from test results

Ref. Compressive strength(N/mm2) Tensile strength(N/mm2) Density7 days Test day 28 days 7 days Test day 28 days (kg/m3)

CJ1 30.9 40.1 45.0 2.25 2.49 2.50 2330CJ2 43.1 49.6 53.5 2.15 2.49 2.90 2384CJ3 40.6 47.9 57.1 2.63 3.55 3.19 2367CJ4 35.7 43.8 41.8 2.15 2.50 3.14 2340CJ5 30.6 41.0 46.8 2.75 3.05 3.45 2336CJ6 33.2 37.3 44.4 2.16 2.48 2.45 2318CJ7 32.8 40.2 44.3 2.43 2.40 2.99 2352CJ8 35.2 42.96 44.7 2.55 2.63 3.17 2346

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two 305× 102× 28 kg/m universal beams were connectedthe column web to make up the full joint arrangement.

Fig. 3 shows the semi-rigid composite joint before castingit can be seen that the ends of the HCUs are chamfered antop of the alternative coresof the units opened for a length o500 mm for the placement of transverse reinforcement. A ga65 mm is formed between the endsof the units. In situ concreteis used to fill the gap between the HCUs and theopened slots. Anominal concrete strength of 40 N/mm2 is used for the in situinfill. The HCUs are tied together transversely by the 16 mdiameter high strength reinforcing bars 1 m long. Longitudireinforcement is provided by the high strength steel reinforcbars across the joint for continuity.

2.2. Material properties

The compressive and tensile strength of the in situ concis shown in Table 1. The in situ infill concrete strength istested at the 7th day, the test day and the 28th day.characteristic concrete strength for the precast hollowcore unitis taken to be 55 N/mm2 as specified by the manufactureThe tensile strengths of the T20 and T16 reinforcing bwere determined in accordance with BS 4449 [14] and theresults are shown inTable 2. Test coupons of the web anflange with thicknessof 10.9 mm and 17.7 mm respectivewere cut from the ends of the steel beams after the twhere stresses had been low. Tensile tests of couponsconducted according to BS EN 10002-1 [15] and the testresults are shown inTable 3. Tensile tests for M20 Grade8.8 bolts were performed and an average ultimate strength678 N/mm2 is obtained. 19 mm diameter× 125 mm heightTRW-Nelson headed shear connectors are used with an avultimate strength of 610.5 N/mm2. Horizontal push-off testswere conducted to determine the load–slip characteristicthe head shear stud and the average load–slip curve is sin Fig. 4, the resultis used to determine the shear capacity adegree of shear connection for the semi-rigid joint tests.

2.3. Instrumentation and loading procedure

Instrumentation comprisedof linear voltage displacementransducers (LVDTs) for measuring slip, beam deflection andbeam rotation is shown inFig. 5. Electrical resistance straigauges (ERSGs) are used to measure strain in reinforcingsteel beams and bolts at the joints. Demac gauges are us

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Table 2The mechanical properties for the reinforcing bar

Ref. Yield strength Ultimate tensile strength Cross section a(N/mm2) (N/mm2) (mm2)

T16 536 621 195.9T20 534 634 305.4

Table 3Tensile test results for steel beam

Ref. Yield strength Ultimate tensile strength Yield stra(N/mm2) (N/mm2) (µε)

Web 382.1 549.4 2379Flange 341.7 503.0 2285

measure the in situ concrete strain at the slab’s surface.strain gauges used to monitor the strain and yielding of the rand steel beam were of the type FLA-5-11 with a gauge lenof 6 mm. The gauges have 120±0.3 � resistances with a gaugfactor of 2.13. Strain gauges areplaced on the longitudinal baand on the transverse reinforcement as shown inFig. 6. Thestrain gauges on the surface of the rebar were coated with eto protect them from damage during concreting. Strain gaugewere also placed on the top flange of the steel beam and oweb to measure the strain on the steel beam to determinposition of the neutral axis throughout the test (Fig. 7). Strainin the bolts was measured using BTM-1C bolt strain gaugesas shown inFig. 8 and their gauge parameters are shownTable 4. The gauges were calibrated before the test and uto measure the bolt forces and elongation of the bolts.

Load is applied by hydraulicjacks simultaneously to eacends of the steel beams as shown inFig. 9. An elastic test iscarried out before test to failure to check the instrumentaand the system. The load was applied at 10 kN intervalscontinued until failure occurred.

2.4. Test parameters

In order to investigate different variables affecting thbehaviour of the composite joint, different emphasesadopted for each test. For the first five tests, the main variaare stud spacing and the degree of the shear connections. Iand CJ7, the main variables are the cross sectional area olongitudinal bar and for the CJ8, the variable is the thicknes


Fig. 10. General arrangement and position of the strain gauges for Test CJ1.





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Table 4Parameters of the BLM bolt strain gauge

Type Gauge (mm) Base (mm) Gauge centre Hole Dia. (mLength Width Length Width a b

BTM-1C 1 0.7 5.6 1.4 1.8 3.8 1.6

farer

Table 5Test arrangement

Reference In situ Longitudinal Hollowcore Studs Position of No. oconcrete cube bars and cross slabs spacing first stud shestrength section area thickness (mm) (mm) stud p(N/mm2) (mm2) (mm) beam

CJ1 39 2 T20(628) 200 300 235 7CJ2 50 2 T20(628) 200 600 235 4CJ3 48 2 T20(628) 200 900, 1200a 990, 540a 2CJ4 44 2 T20(628) 200 400 510, 710a 3CJ5 41 2 T20(628) 200 500 645 3CJ6 37.3 4T16(800) 200 310 465 6CJ7 40.2 2T16(400) 200 1200 900 2CJ8 42.9 4T16(800) 250 450 705 4

19φ × 125 mm long headed shear connectors were used for all the tests.a Stud on theeast side.



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the precast hollowcore slabs. The test arrangement is showTable 5andFigs.10–17. Strain gauges were put on the surfacof the shank of the stud near the weld collar to measurestresses in the studs. In CJ6, CJ7 and CJ8, bolt strain gawere used at the connection to monitor the bolt forces andelongation of the bolt.

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3. Test results

Results of all eight composite joint tests are shownTable 6 and Fig. 18. All tests except Test CJ3 failed inductile manner with beam rotation well in excess of 30 mrand obtained a moment capacity above 0.3 Mp of the be


Fig. 16. General arrangement and position of the strain gauges Test CJ7.

Fig. 17. General arrangement and position of the strain gauges Test CJ8.

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Table 6Test result

Reference CJ1 CJ2 CJ3 CJ4 CJ5 CJ6 CJ7 CJ8

Moment capacity (kN m) 370 363 250 368 363 425 274 439Rotation capacity (mrad) 35.4 33.5 6.1 37.4 31.7 46.8 30 42.Long. reinf. capacity—yield (kN) 326 326 326 326 326 424 212 424Long. reinf. capacity—Ult. (kN) 387 387 387 387 387 486 243 486Shear connector capacity (kN) 896 512 256 384 384 512 256 51Degree ofshear connection (%)a >100 >100 78.5 >100 >100 >100 >100 >100Degree ofshear connection (%)b >100 >100 66 98 98 >100 >100 >100Max. strain in long. reinf.(µε) 26,000 23,000 2031 16,000 13,706 26,000 23,000 23,Maximum end slip (mm) 0.34 0.8 5.8 3.5 3.5 0.84 0.4 1.6Failure mode RF RF CF & SF CF CF RF RF RF

RF – reinforcement fracture; CF – connector fracture; SF – slab shear failure.a Calculated using the yield strength of longitudinal steel bar.b Calculated using the ultimate strength of longitudinal steel bar.

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it can be concluded that these types of joints can provsufficient moment capacity and rotation capacity. Tests CJ1CJ2, CJ6, CJ7, and CJ8failed due to the fracture of longitudinalreinforcement while Tests CJ3, CJ4 and CJ5 failed by fractureof the shear connectors. No yielding or buckling to the coluwas observed. For all the tests conducted, no bond faibetween the in situ and the precast concrete was observed.therefore be concluded that the in situ and the precast conare acting compositely throughout.

The mode of failure can be divided into two main categor(a) fracture of the longitudinal bar as shown inFig. 19, and (b)fracture of shear studs as shown inFig. 20. No othermode offailure was observed in any of the tests.

Fig. 21 shows the strainmeasurement of the longitudinrebars during the test, it can be seen that with the only exceptioof Test CJ3, the longitudinal bars in all tests developed sthardening with the longitudinal rebars in Tests CJ1, CJ2, C

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Fig. 18. Moment versus rotation curves.

CJ7 and CJ8 fractured at the end of the tests. For Tests CJ4CJ5, stud fracture occurred before fracture of the longitudin


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Fig. 19. Mode of failure due to fracture of the longitudinal reinforcing bars.

Fig. 20. Mode of failure due to stud fracture.

bar due to partial shear connection. From these results, itconcluded that full shear connection should be providedenable full mobilisation of the longitudinal reinforcement anpartial shear connection will lead to low moment and rotationcapacity as the longitudinal barscannot be fully mobilised.

A typical strain profile of the longitudinal rebar alonthe beam is shown inFig. 22. It shows that yielding of thelongitudinal reinforcement occurred at the distance betwthe centre line of the columnand the second stud positiothe strain in the other part of the steel bar is very smallremained elastic. This further demonstrates that the positionthe headed studs played an important role in rotation capaof the composite connections.

Fig. 23 shows the end slip for all the tests. As predictelarger slip is obtained for the partial shear connection tests CCJ4 and CJ5 where the amounts of slip are smaller for theshear connection tests. For CJ6 and CJ8, as the ratios oforce in the longitudinal rebar to the longitudinal shear foprovided by the studs are larger than that of CJ1, CJ2 andlarger connector slip resulted.

Strain is measured at the steel top and bottom flangthe steel section for all the tests and the steel beam oeight tests remained elastic throughout. The developmenthe crack pattern around the concrete slab was similar toone shown inFig. 24 for all the composite joint tests. The firscracks were visible at the column flange tips and propag

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Fig. 21. Strain measurement of the longitudinal reinforcement.

Fig. 22. Typical strain profile of longitudinal reinforcing bar along the length

Fig. 23. Moment versus end slip for all the tests.

towards the slabedges before eventually forming the dominatransverse cracks across the complete breadth of the slab. As thwidths of these cracks developed further, a significant losconnection stiffness resulted. This in turn led to a considerwidening of these cracks, causing a high localised strainthe longitudinal reinforcement. Consequently, fracture of tlongitudinal reinforcement occurred.

Fig. 25 shows the strain measurement of the transverse bfor all the joint tests. It showed that the strain in the transvebar is very small. The maximum strains measured in all the t


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Fig. 25. Strain measurement of the transverse reinforcement for all the tests

were less than 900µε and hence the transverse rebars remaelastic. It can be concluded that the transverse bar haseffect on the connection moment capacity.

4. Discussions

4.1. Effect of distance between first stud and column flang

The formation of cracks would appear to be related toposition of the first stud. Fewer cracks are formed in TeCJ1 and CJ2 with a main crack opening near the columfaces and eventually leading to thefracture of the longitudinareinforcement. At failure, little interface slip is recorded ahence little steel connection deformation is observed. Thamounts of slip observed in Tests CJ1 and CJ2 were very sWhen the specimen was dismantled after the test, the studs wfound to be intact.

In Tests CJ4 and CJ5, the first stud position is placed furawayfrom the face of the column. After the formation of thfirst crack, additional cracks were formed between the columnface and the position of the first stud. Cracks betweencolumn face and the first stud distributed evenly rather tconcentrated at a single crack around the column face,led to lesser demand on the percentage of elongation reqby the longitudinal reinforcement. Large interface slip is aobserved.

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4.2. Effect of stud spacing

From the comparison of Tests CJ1 and CJ2, it can be sthat although different stud spacings and numbers of studsused, no distinct difference ofmoment and rotation capacitwas found from the test results. Therefore, it can be concluthat provided the same degree of shear connection and poof first stud is used, the numbers of studs and their spacingnot have much influence on the moment capacity and rotatiocapacity of the connection.

4.3. Effect of the degree of shear connection

In this series of experiments, two methods for calculatthe degree of shear connection are employed. The first methois based on the yield strength of the longitudinal rebaas assumed by many researchers and ignoring the ultistrength of the reinforcing bars. The second method is basethe ultimate strength of the longitudinal rebars to determine thdegree of shear connection, which takes into considerationultimate tensile strength of thelongitudinal bars. In accordancwith method 1, if the shear stud capacity is greater than the ystrength of the longitudinal rebars, then it should be classifiefull shear connection. However, as shown inTable 6, themodeof failure in Tests CJ3, CJ4 and CJ5 is due to stud fractIt is because the shear stud capacities were less than theof longitudinal rebars as calculated using method 2. Thereit suggested that the ultimate strength of the longitudinal rebarshould be taken into consideration when determining the deof shear connection. In test CJ3, the values of interfaceincreased with lower degree of shear connection, which lelow moment and rotation capacity.

Comparison between CJ3 and CJ7 shows that althoughtwo studs wereused in both the tests, Test CJ3 has a vlow degree of shear connection in compared with Test CJ7and hence a small amount of rotation was recorded. It caconcluded that for a joint with partial shear connection, as las the shear stud can allow the longitudinal bar to be mobiluntil the yielding stage, there will be no obvious deductionthe moment and rotation capacity. Otherwise low degrees oshear connection will lead to low moment and rotation capaas yielding and elongation cannot occur in the longitudrebars.

4.4. Effect of amount of longitudinal reinforcement

Comparison among Tests CJ1, CJ2, CJ6 and CJ7 shthat with full shear connection and same slab thicknincreases in the amount of longitudinal reinforcementto higher moment and rotation capacity. Therefore, it cbe concluded that increases in the amount of longitudreinforcement will not only lead to increases in momecapacity but also larger rotation capacity.

The analysis of the test results showed that the incluof a large amount of localised reinforcement is one ofmost effective ways of achieving good rotation capacity. Treinforcement enables cracks to be distributed evenly in the


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concrete, thereby reducing localised strains and allowing higaverage strains to develop in the reinforcement. Approprconnection details can be used to ensure that the averageoccurs over a substantial length, for example by placingfirst shear stud on the beam further away from the columnface. High strains over a substantial length result in ladeformation of the reinforcement. The reinforcement also helpto develop large compressive forces in the lower parts ofsteel section, causing plastification which leads to large strin the steel. Large tensile deformations in the reinforcementcompressive deformations in the steel beam will in turn equto significant connection rotation.

4.5. Effect of concrete cracking on the shear connectcapacity

Shear studs placed within the concrete in the hoggmoment region did not show any deterioration in its strenThe shear stud capacity in the tests agreed well with the ptests carried out in the horizontal push test [16]. Althoughthe concrete was severely cracked, the reinforcing bars wereffective and able to transfer the tensile force. Good interactiobetween the shear studs with the concrete and the conwith the longitudinal rebars were observed, which enablestransmission ofthe longitudinal shear forces.

4.6. Effect of precast slab thickness

With the only difference between Test CJ6 and CJ8 beinthe depth of the precast hollowcore slabs, the result shothat by using deeper slabs, an increase in moment capacity waobtained. The increases in moment capacity are purely duthe increases in the lever arm, but a slight reduction ofrotation capacity with the Test CJ8 was observed with deeslabs.

5. Proposed method to calculate rotation capacity

A simple calculation method [17] based on the componemethod is proposed to predict the rotation capacity,φu forthis form of composite joints as shown in Eq.(1) andFig. 26.The strain profile of the longitudinal reinforcing bar takfrom the test data shows that the steel bar yielded onlthe region between the column centre line and the secshear stud, the strain in the other part of the steel bar ismall and remained elastic. Therefore, the elongation zonthe longitudinal reinforcement,�L can be taken as betweethe centre line of the column and the position of the secstud. Hence, it can assumed that the length for calculatingelongation isp1 + p2 + D/2, wherep1 is the distance betweethe column face and the centre line of the first stud;p2 is thedistance between the centre line of the first stud and the sestud andD is the depth of the column.

φu = �L

Db + Dr+ Slip

Db(1)

�L = εsh

(p1 + p2 + D

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Fig. 26. Force diagram and the components of the composite joint.

Table 7Comparison of test results and the proposed method for rotation capacity

References Test results (mrad) Calculated results (m

CJ1 35.4 28.8CJ2 33.5 37.5CJ3 6.1 8.2CJ4 37.4 39.7CJ5 31.7 36.3CJ6 46.8 40.1CJ7 30 50.4CJ8 42.3 47.8

For full shear connection, reinforcement strain,εsh istaken as the ultimate strain developed in the longitudinalreinforcement. It is because for full shear connection, thelongitudinal reinforcing bars can developed into the strhardening whereas for the partial shear connection,εsh istaken as the maximum strain developed in the longitudinbar. For simplicity, it can be taken as the yield strain othe steel bars if enough shear studs are provided to enyielding of the longitudinal bars. Composite joints wipartial shear connection unable to develop yielding oflongitudinal reinforcing bars will lead to low rotation capacas demonstrated in Test CJ3.Table 7 shows the comparisonbetween the test results and thecalculated results using thproposed method. The results show that the method gaveprediction of the test results on composite connection with sbeams and precast hollowcore slabs.

6. Proposed method to calculate moment capacity

No calculation method for the prediction of momencapacity of composite connection with precast hollowcore slabis currently available. A method to predict the moment capafor this type of semi-rigid connection is proposed [17].

The proposed method assumes thatRf ≥ Rb + Rr ,where,Rf = compressive resistance of the bottom flange of

steel beam,Rr = the lesser of the ultimate tensile strength of t

longitudinal reinforcement or the studs capacity,


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Table 8Comparison of test results and the proposed method for moment capacity

References Test results (kN m) Calculated results (kN

CJ1 370 365.8CJ2 362 365.8CJ3 250 284.5CJ4 368 365.0CJ5 363 366.6CJ6 425 422.3CJ7 274 274.0CJ8 439 446.7

Rb = effective tensile resistance of the bolt group.The moment resistance of the composite connection,Mcc

Mcc = Rr (Db + Dr − 0.5t f ) + Rb(Db − r1 − 0.5t f ) (3)

whereDb is the depth of the beam;r1 is the distance of the firsrow of bolts below the top of the beam;Dr is the distance ofthe reinforcement above the top of the beam andt f is the flangethickness of the steel beam.

For Rf < Rb + Rr ,

The neutral axis,yc = (Rr +Rb−Rf )

tw Py

where,tw is the web thickness andpy is the design strengthof the steel section.

The moment resistance of the composite connection,Mcc

Mcc = Rr (Db + Dr − 0.5t f )

+ Rb(Db − r1 − 0.5t f ) − Rw

yc

2(4)

whereRw = yctw py.The comparison of the test results and the results f

the proposed method above is shown inTable 8. The resultsshowed that the moment capacity of the semi-rigid composconnections is dependent on the strength and the abilitmobilize the longitudinal reinforcing bars. The influential factoto their mobilization is dependent on the degree of the shconnection between the slabsand the steel beams, whichdetermined by the number and the capacity of the shear sin the hogging moment region. In all five tests carried out,factors but the shear studs were kept constant. All teststhe exception of Test CJ3, theshear connection capacity ilarger than the yield strength of the longitudinal reinforcementtherefore the tensilestrength of the longitudinal bars can bmobilized, and hence adequate moment and rotation capcan be achieved.

7. Conclusions

The behaviour of eight full-scale semi-rigid composconnections with precast hollowcore slabs was examinDifferent levels of shear connection, spacing and positof first studs from the column face have been examinTests showed these joints combine simple and efficienconstruction and yet provide worthwhile levels of momecapacity, rotational stiffness and ductility with the introductiof longitudinal reinforcement across the column. Fromexperimental study of the semi-rigid composite joints w

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ity

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precast hollowcore slabs, the following conclusions canmade:

1. Semi-rigid composite joints with precast hollowcore slcan provide sufficient moment and rotation capacityrequired by the design code as a suitable type of connefor plastic design.

2. Two failure modes are observed from the joint tests. Mof failure was either fracture of the longitudinal rebarsfracture of the headed studs.

3. Adequate shear connection should be provided to enablmobilisation of the longitudinal reinforcement. Partial sheconnection in the hogging moment region will lead to lmoment and rotation capacity as the longitudinal bars cabe fully mobilised. It is recommended that the minimupercentage of shear connection provided should enabllongitudinal reinforcement to develop yield.

4. The ultimate tensile strength of the longitudinal reinforcement should be taken into consideration when calculathe degree of shear connection.

5. Close spacing of the shear stud near to the columnwill affect the crack pattern and demanded high degreelongation from the longitudinal reinforcement to achiethe same rotation capacity with the same joint with larstud spacingbetween the column flange and the first stIt is recommended that the first stud should be placedspacing equivalent to two times the column width.

6. The spacing between other shear studs has little effecthe moment capacity and rotation capacity of the connectioprovided the degree of shear connection is the same.

7. The in situ concrete infill and the precast hollowcore sacted compositely throughout, no separation was obsefrom any of the tests carried out.

8. A simple method to predict the moment and rotatcapacity is proposed and compared with the test resulis found to be acceptable for use to predict the behaviouthis form of composite joints.

Acknowledgements

The authors would like to acknowledge the financial supfrom International Precast Hollowcore Association (IPHA) anOverseas Research Scholarship (ORS), the support proby Severfield—Revee Structures Ltd. for supplying the sspecimens and Bison Concrete Products Ltd. for supplyingprecast hollowcore slabs. The skilled assistance providethe technical staff in the School of Civil Engineering at LeeUniversity is also appreciated.

References

[1] Barnard PR. Innovations of composite floor systems. In: Canastructural engineering conference. Canadian Steel Industries ConstructioCouncil; 1970. p. 13–21.

[2] Johnson RP, Hope-Gill M. Semi-rigid joints in composite frames. InInternational association for bridgeand structural engineering, nincongress. 1972. p. 133–44.


ts,

oftio

tiora

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ast

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st

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[4] Li TQ, Moore DB, Nethercot DA, Choo BS. The experiment behavioura full-scale, semi-rigid connected composite frame: Overall consideraJournal of Constructional Steel Research 1996;39(3):167–91.

[5] Hamilton TR. Composite steel and precast concrete slab construcChartered Membership thesis. UK: The Institution of StructuEngineers; 1989.

[6] Moy SSJ, Tayler C. Composite steel and precast concreteconstruction. Journal of Constructional Steel Research 1996;36(3201–13.

[7] Jolly CK. Long span composite beams for car parks. In: Proceedof the joint IStructE/City university international seminar. London: CUniversity; 1996.

[8] BS5950, Part 3-1, Structural use of steelwork in building: Code of pracfor design of simple and continuous composite beams. London: BrStandards Institution; 1990.

[9] Shim CS, Lee PG, Chung CH. Design of shear connections in compsteel and concrete bridges with precast decks. Journal of Construct

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hollow-cored floor slabs. The Structural Engineer 1998;76(9):167–74[11] Lam D, Elliott KS, Nethercot DA. Experiments on composite st

beams with precast concrete hollow core floor slabs. Proceedings oInstitution of Civil Engineers: Structures and Buildings 2000;140(May127–38.

[12] ABAQUS. Version 6.2. Hibbitt, Karlson and Sorensen, Inc.; 2001.[13] El-Lobody E, Lam D. Modelling of headed stud in steel—prec

composite beams. Steel & Composite Structures 2002;2(5):355–78.[14] BS4449. Specification for carbon steel bars for the reinforcement o

concrete. London: British Standards Institution; 1997.[15] BS EN 10002-1. Metallic materials:Tensile testing—Part 1: Method

of test at ambient temperature. London: British Standards Institu2001.

[16] Lam D. New test for shear connectors in composite constructIn: Composite construction in steel and concrete, IV. American Societyof Civil Engineers; 2000. p. 404–14.

[17] Fu F, Lam D. Modelling semi-rigid composite joints with precahollowcore slabs in hogging moment region (under review).

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