Journal of Constructional Steel Research Volume 63 Issue 6 2007 [Doi 10.1016_j.jcsr.2006.07.009] v. Marimuthu; S. Seetharaman; S. Arul Jayachandran; A. Chellappa -- Experimental Studies on Composite

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  Journal of Constructional Steel Research 63 (2007) 791– Experimental studies on composite deck slabs to determine the shear-bondcharacteristic  ( m – k  )  values of the embossed profiled sheet V. Marimuthu a, ∗ , S. Seetharaman a , S. Arul Jayachandran a , A. Chellappan a ,T.K. Bandyopadhyay b , D. Dutta b a Structural Engineering Research Centre, CSIR Campus, Chennai - 600 113, India b  Institute for Steel Development And Growth (INSDAG), Ispat Niketan, 52/1A, Ballygunge Circular Road, Kolkata - 700 019, India Received 15 March 2006; accepted 19 July 2006 Abstract Compositedeckslabfloorsaregainingwideacceptanceinmanycountriesastheylendthemselvestofaster,lighterandeconomicalconstructionin buildings. The cold formed profile sheeting which is an integral part of the deck slab is provided with embossments to improve their shear bondcharacteristics. However, the shear behaviour of composite deck slab is a complex phenomenon and therefore experimental methods are oftenresorted to establish their shear strength under flexural loads. An experimental study has been carried out to investigate primarily the shearbond behaviour of the embossed composite deck slab under simulated imposed loads and to evaluate the  m – k   values. Totally 18 composite slabspecimens were cast using M20 grade concrete. The 18 numbers of specimens were split into six sets of three specimens each in which three setswere tested for shorter shear span loading and the other three sets for longer shear span loading. The specimens were tested as per the generalprovisions in Eurocode 4 [Eurocode 4. Design of composite steel and concrete structures. Part 1.1. General rules and rules for buildings]. Thispaper presents details of the experimental investigations conducted on the composite deck slabs and the evaluation of   m – k   values for the embossedprofiled sheet.c  2006 Elsevier Ltd. All rights reserved. Keywords:  Profiled sheet; Embossments; Composite deck slab; Shear bond failure;  m – k   value 1. Introduction Cold formed profiled steel sheets with embossments arewidely used for composite floor decking wherein they remainpermanently in place as an integral part of the floor system.They perform two functions: they act as the formwork whileconcreting and in the composite slab, they act as the tensionreinforcement. The only additional steel that needs to beprovided is for taking care of shrinkage and temperature. Inthe case of continuous slabs, reinforcing steel is required toresist the negative bending moment at the supports. This typeof flooring results in faster construction, lighter floors andrational use of construction materials. They also provide certainother advantages such as easy handling, a good ceiling surfaceand convenient ducting for routing utility services. Finally, the ∗ Corresponding author. Tel.: +91 044 22549142; fax: +91 044 2254 1508.  E-mail addresses:, mari Marimuthu). thin sheeting is extremely light and hence can be transportedconveniently, and handled and placed easily by the constructionpersonnel. Some of the disadvantages pointed out for thesystem are inadequate fire rating, the need for proper bondingbetween the steel deck and the concrete and also the protectionneeded against damage from high local loads. Even though thesteel deck is galvanized, it is advisable to apply anticorrosivepaints on the exposed side of the sheet. Effects of ponding andedge deformation also need to be taken care of during design.The term ‘composite steel deck floor slab’ means that thereis a provision in the system for bonding between the steel deck and the concrete by some mechanical means. In other words,for the steel deck and concrete to act compositely, a mechanicalinterlocking is needed. This is provided essentially by various‘shear transferring devices’ such as rolled embossments,transverse wires, holes etc. Examples of composite steel deck floor slab systems are illustrated in Fig. 1. One of the efficientways of achieving the interlocking between the steel deck and concrete is by means of embossments on the profiled 0143-974X/$ - see front matter c  2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.jcsr.2006.07.009  792  V. Marimuthu et al. / Journal of Constructional Steel Research 63 (2007) 791–803 List of symbols  A s  Cross sectional area of the profiled sheet  ( mm 2 ) b  Width of the profiled sheet (mm) d   Average depth of the composite deck slab (mm) V  s  Shear force (N)  L s  Shear span (mm)  Lo  Length of overhang of the composite slab fromcentre line of support (mm) ρ  A s bd   f   c ,  f  cm  Cube compressive strength of the concrete ( N / mm 2 ) m  slope of the ultimate shear bond regression line k   Intercept of the ultimate shear bond regressionline Φ   Capacity reduction factor (0.8) s  Parameter denoting supporting condition duringcasting.  N  c ,  N  cf   Compressive force in concrete (N)  N   p  Tensile force in sheeting (N)steel sheeting. The deck profile must provide the resistance tovertical separation and horizontal slippage between the contactsurface of the steel and the concrete. Additional compositeaction may be achieved by attaching studs or similar sheardevices. The shear bond characteristic of the embossed sheetingis rated by two empirical parameters ‘ m ’ and ‘ k  ’, where‘ m ’ represents the mechanical interlocking between steel andconcrete and ‘ k  ’ stands for friction between them.This paper deals with the experimental evaluation of   m – k  values for composite deck slabs using cold formed profiledsheets with rectangular dishing type embossments. Totally 18composite slab specimens were cast using M 20 grade concrete.Using the values of ‘ m ’ and ‘ k  ’ as determined by parametrictests, ultimate load carrying capacity of the composite deck could be calculated. The longitudinal shear strength of thecomposite slab calculated using  m – k   method is verified withthe results obtained by partial shear connection method inEurocode 4 [1, Annex E]. 2. Load carrying mechanism of composite profiled sheetdeck floors In a composite steel floor deck, the hardened concrete slab,acting compositely with the profiled steel decks, spans thesupporting beams and carries the imposed live loads. Thecomposite action depends upon adequate transfer of horizontalshear forces between the concrete slab and the steel deck toenable the deck to act as the tensile reinforcement. In additionto horizontal shearing forces, the bending action also leadsto vertical separation between the steel and the concrete. Theprofiled sheet, therefore, has to be designed to resist verticalseparation, in addition to transferring the horizontal shears.Resistance to vertical separation is achieved by suitable shapein trapezoidal profile and also by the embossments.There are three distinct phases in the structural action of a composite deck system [3]. In the first phase i.e. during the construction phase, the steel sheeting must rigidly supportthe wet concrete during casting. In the composite slab actionphase, the composite steel concrete slab should support theimposed loads on the slab and in the composite beam actionphase, the steel beams, which act compositely with concretethrough the stud shear connectors, must support the imposedloads in the transverse direction. This paper deals with the study Fig. 1. Composite deck slabs using different types of profiled sheets.  V. Marimuthu et al. / Journal of Constructional Steel Research 63 (2007) 791–803  793 of composite slab action phase, wherein the behaviour of thecomposite action of the steel sheet and the overlying concreteis focused.The three primary failure modes important for design of acomposite deck slab are: (1) flexure, (2) shear at support and (3)shear bond mode. Failure of the slab is said to be ductile if thefailure load exceeds the load causing first recorded end slip bymore than 10%. The failure load is taken as the load at midspandeflection of   L / 50 unless failure has already taken place. Oneof the principal modes of failure of steel deck slabs is by theshear bond. The shear bond mode of failure is characterizedby the formation of diagonal tension crack in the concrete ator near the load points, followed by a loss of bond betweenthe steel deck and the concrete. There is a slippage betweenthe steel and concrete causing a loss of composite action in theshear span region, which lies between the support reactions andthe concentrated load. Slippage usually occurs when the loadreaches its ultimate value and this is followed by a significantdrop in loading. 3. Review of literature Crisinel and Marimon [2] have presented a new design approach for the prediction of composite slab behaviour.This new approach combines results from standard materialstests and small-scale tests with a simple calculation model(referred to here as the “New Simplified Method”) to obtainthe moment–curvature relationship at the critical cross-sectionof a composite slab. The New Simplified Method facilitatesthe calculation of the load-carrying capacity of composite slabsby considering three phases of the  M  – θ   behaviour observed incomposite slab critical cross-sections. It requires knowledge of the geometric dimensions of the slab, the material properties(steel and concrete) and the characteristic behaviour of thesteel–concrete connection as determined based on tests onsmall-scale specimen.In order to study the shear-bond action in composite slabs,Chen [3] tested seven simply supported one-span composite slabs and two continuous composite slabs using different endrestraints in the simply supported slabs. The slabs with endanchorage of steel shear connectors were found to bear highershear-bond strength than that of slabs without end anchorage.To enable an effective end anchorage, however, it is the shear-bond slip rather than the strength of anchored studs thatgoverns the contribution of the end restraints to the shear-bondresistance in composite slabs.Burnet and Oehlers [4] presented a new form of push-test that simulates the bond characteristics more accurately andwhich is used in 33 tests to determine the main parametersthat affect both the chemical bond and mechanical bondstrengths of dovetailed and trapezoidal rib shear connectors.The effects of the geometry of the cross-section, embossments,sheet thickness and surface treatment on the bond strengthsare presented in a form that can be used as guidelines in thedevelopment of new forms of profiled sheets for slabs, beamsand walls.Makelainen and Sun [5] studied the shear-connectionbehaviour of composite slabs with a particular profiled steelsheeting having a depth of 153 mm. Twenty-seven push-out testspecimens of different shapes, sizes, locations of embossmentsand different steel sheeting thicknesses are carried out intwo test series. The embossments are first made on theslant faces based on standard design norms. Thereafter, theembossed sheets are profiled as per the requirement suitingto the standards of the manufacturer. It is found that theshear-connection behaviour of composite slabs is significantlyaffected by the depth of embossments. For the profiled steelsheeting with indented embossments, the reduction of Young’smodulus caused by the penetrated embossments is an importantfactor that affects the determination of the depth and width of the embossments. Finally, a new type of profiled steel sheeting,which can offer longitudinal shear strength in composite slabsup to 0 . 6 N / mm 2 , is proposed for further research.Tenhovuori and Leskela [6] studied the behaviour of  composite slabs with profiled steel sheeting as affected by thebond failure in the longitudinal shear connection. The effectof various important parameters is considered and the criticalfactors are reviewed on the basis of numerical data obtainedfrom non-linear calculation by the method of finite elements. Athorough study is carried out to compare the present methods of analysis for the bond failures in the ENV Eurocode 4 [1] Part l-l, and it is shown that they can be improved and simplifiedand finally unified so as to get a clearly comprehensible systemdescribing when the bond failure in a composite slab is possiblein the design and what is to be done for it.Calixto et al. [7] carried out an experimental investigation on the behaviour and strength of full-scale one-way singlespan composite slabs with ribbed decking. Several aspectswere studied, including different steel deck thickness, totalslab height, as well as shear span length. The effect of connectors (stud bolt type) on the end anchorage was alsoinvestigated. Normal procedures for batching and mixing of the concrete were used. Throughout the monotonic loadingtests, midspan deflections, end slips and strains in steeldecking were measured. The test results indicate clearly thebetter performance of the composite slabs built with studbolt connectors. In this study the slabs fabricated with plainsheeting and stud bolts attained in all cases a higher ultimateload when compared to the respective specimens built withribbeddeckingonly.Thefloorsconstructedwithribbeddeckingand stud bolts showed a different behaviour characterizedby no drop in the load during the entire monotonic loadingprocedure. In all cases the failure mode was by shear bondeven in the slabs fabricated with end anchorage and ribbedsheeting. The experimental results are also compared with thepartial interaction design method specified in Eurocode 4 [1]. The current design equations do not separate explicitly theresistance of the mechanical interlocking from the friction atthe concrete-decking interface over the supports. Dependingon the position and shape of the embossments on the ribbeddecking (AXE type II decks for instance), the contribution of each resistance mechanism plays a different role. Thereforea procedure which explicitly takes into consideration the  794  V. Marimuthu et al. / Journal of Constructional Steel Research 63 (2007) 791–803 Fig. 2. Shape, size and frequency of embossments. effects of the mechanical interlocking and friction separately ispresented. The proposed method is compared with the currenttest results and those obtained in other investigations. Thecomparisons show good correlation.Evans and Wright [8] and Wright et al. [9] have carried out more than 200 tests on composite deck slab elements andcompared the results with the available design methods. Theyhave studied the aspects of construction phase, composite slabaction phase and the composite beam action phase in detail.The studies have shown that the variation in concrete strengthhas little effect on the ultimate load capacity. The crucialparameter that has significant effect on the ultimate strengthis the height of the embossment. They have concluded thatthough the present design procedures are safe, they are veryconservative in certain cases. They have recommended thatthe system as a whole, namely, slab span, beam span andstud connectors, should be considered for obtaining maximumeconomy in design.Porter and Ekberg [10] have carried out a large number of  experimental studies on cold formed steel deck floor slabs. Thework primarily involved one way full scale slab elements andtested up to failure, emphasizing the ultimate strength designconcept. Porter et al. [11] have further conducted experimentalstudies on the shear bond failure characteristics of one-way slabelements and reported several observations on the significantparameters influencing the behaviour. They have also reporteda linear regression relationship between  V  u s / bd  √   f   c  and ρ d  /  L s √   f   c  to determine the slope and intercept constantsneeded for design.Design procedures for the design of composite steel deck floor slabs based on the ultimate strength concepts have beenrecommended by Porter and Ekberg [12]. The capacity isbased on the shear bond strength of the deck slab. The designequations for the shear bond capacity are derived from thedata collected from a series of performance tests on theslabs and establishing the linear regression relationship asmentioned above by Porter et al. [11]. A separate regression is recommended for each deck profile, each gauge thickness of the sheeting, steel surface coating and concrete strength. In theconstruction phase the sheeting is designed for the loads due tothe wet concrete and its self weight.The review of literature shows that analysis of the compositedeck slab behaviour is complex. The extent of shear bondachieveddependsuponmanyparameters,liketheheight,shape,orientation and frequency of the embossment pattern and thegeometry and flexibility of the profiled sheet itself. Currentlyan accurate determination of strength is possible only byperformance testing. Performance tests need to be carried outas each steel deck profile has its own unique shear transferringmechanism. The purpose of the tests is to provide data for theultimate strength design equations. Particularly, a series of testsis needed for getting ultimate experimental shears for a linearregression analysis of the parameters that affect the shear bondcapacity. 4. Experimental studies on composite steel deck floor slabs The specimens were split into six sets of three specimenseach in which three sets were tested for shorter shear spanloading and the other three sets for longer shear span loading.The shape, size and frequency of the embossment are givenin Fig. 2. In the shorter shear span loading, shear spans of  320 mm, 350 mm and 380 mm were chosen, while in the longershear span loading, 850 mm, 950 mm and 1150 mm wereadopted. For each set of three specimens, one specimen wastested to failure under monotonic loading, test duration beingnot less than one hour; the other two specimens were tested forcyclic loading for 5000 cycles each for duration of three hours,followed by a static test. The details of the profiled sheet andthe moment carrying capacity of the composite slab worked outas per Eurocode 4 [1] are given in Appendix A. 4.1. Preparation of the composite slab specimen4.1.1. Casting of slab The composite slab was cast with the profiled sheet as thebase. The sheet was thoroughly cleaned before concreting. Thecasting was carried out in a fully supported condition. Mildsteel reinforcing bar meshes (using 6 mm diameter bars) of therequired size with the spacing of bars at 250 mm c / c in bothdirections were prepared. These meshes were placed 25 mmfrom the top surface of the profiled sheet (Fig. 3). The concretemix of M 20 (28 day cube compressive strength of 20 MPa)grade designed as per the relevant Indian Standard [13] code was chosen for concreting. The coarse aggregate size used inthe concrete was 20 mm down. The slabs were cast and curedfor 14 days. Figs. 3 and 4 show the view of embossed sheet with the steel bar mesh and detailing of the composite deck 
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