Behavior Of Composite Slabs Research Articles

Advanced Modeling of Composite Slabs with Thin-Walled Steel Sheeting Submitted to Fire

The paper studies the behavior of composite slabs with corrugated steel sheeting at elevated temperatures. Two structural systems are considered: a simply supported composite slab and a continuous composite slab that consists of two equal spans. Both of them are designed according to the respective Eurocodes to have similar strengths at room temperature. In the sequel, sophisticated three-dimensional models of the slabs are developed. Coupled thermo-mechanical analysis is used, which takes into account the various nonlinearities that are present in the physical model (dependence of the thermal and mechanical properties of the material on temperature, nonlinear material behavior, cracking etc.). The results of the thermal analysis are compared with the temperature field that is proposed in Eurocode 4. For both the structural systems, the fire resistance, in time domain, that yields from the coupled analysis is compared with the fire resistance that results following the provisions of Eurocode 4. Another objective is to evaluate the effect of static indeterminacy on the fire resistance of composite slabs.

Damage Mechanics Model for Fracture Process of Steel-Concrete Composite Slabs

Composite slab construction using permanent cold-formed steel decking has become one of the most economical and industrialized forms of flooring systems in modern building structures. Structural performance of the composite slab is affected directly by the horizontal shear bond phenomenon at steel-concrete interface layer. This study utilizes 3D nonlinear finite element quasi-static analysis technique to analyze the shear bond damage and fracture mechanics of the composite slabs. Fracture by opening and sliding modes of the plain concrete over the corrugated steel decking had been modeled with concrete damaged plasticity model available in ABAQUS/Explicit module. The horizontal shear bond was simulated with cohesive element. Cohesive fracture properties such as fracture energy and initiation stress were derived from horizontal shear bond stress versus end slip curves. These curves were extracted from bending tests of narrow width composite slab specimens. Results of the numerical analyses match the experimental results accurately. This study demonstrated that the proposed finite element model and analysis procedure can predict the behavior of composite slabs accurately. The procedure can be used as a cheaper alternative to experimental work for investigating the ultimate strength and actual fracture and damage behavior of steel-concrete composite slab systems.

Experimental and numerical study on restrained composite slab during heating and cooling

In this paper, a series of fire tests on restrained composite slabs, carried out at the University of Manchester, is presented. A total of six composite slabs were tested under different fire scenarios, with different load ratios. The tests were particularly concerned with the variation of internal forces within the slabs during both heating and cooling phases. In addition to the testing programme, two separate nonlinear finite element models have been developed to simulate the thermal and mechanical behaviour of composite slabs during heating and cooling, which is introduced in detail in this paper. In the thermal analysis model, plane elements were adopted to obtain a detailed thermal behaviour. In the structural analysis model, the concrete, steel deck and mesh were simulated by solid elements, shell elements and truss elements respectively. The interaction between the concrete and steel sheet was simplified to spring elements. According to the experimental results and FE modelling, the behaviour of composite slabs was analysed in detail. At last, the parametric study was performed where the effect of concrete strength, steel deck thickness and mesh size was analysed.

Shrinkage Deformations of Composite Slabs with Open Trapezoidal Sheeting

Composite steel-concrete slabs that have integral steel shuttering at the soffit of a reinforced concrete slab are commonplace in building infrastructure. Inevitable shrinkage of the concrete represents an indirect (or non-mechanical) strain that results in deformations of the composite slab, resulting in long-term effects in which creep of the concrete also plays a role. Because the impervious steel sheeting prevents moisture egress at the slab soffit whereas at the top of the slab such moisture egress can occur, there is a variation of the shrinkage strain through the depth of the slab, resulting in warping-type deformations. In addition, the composite action between the steel and concrete results in partial shear interaction between these elements, and this interacts with the shrinkage response. Surprisingly little appears in the published literature on rational modelling of the behaviour of composite slabs incorporating partial interaction that are subjected to shrinkage straining, despite its practical importance and significance. Based on fundamental principles of mechanics, a theoretical model of this shrinkage behaviour that includes partial interaction is developed, and prescriptive equations are derived. These may be used to assess the deflections and stresses in the concrete due to restrained shrinkage which may lead to cracking of the slab. It is also shown that the two effects of partial interaction and shrinkage straining counteract each other when slab deflections are considered.

Experimental behaviour of composite slabs during the heating and cooling fire stages

Most theoretical and experimental research investigating the effect of fire on structures has previously concentrated only on the structural behaviour during the heating stages of the fire, partly due to the fact that internationally accepted standard fire tests only consider this stage of the fire. Evidence from real fires in real buildings has highlighted that the cooling phase of a fire is equally important and it is possible for structures to fail during this stage of the fire even though they have survived the heating stage up to a maximum fire temperature. This paper provides an insight into the behaviour of composite slabs under different fire scenarios considering both the heating and cooling phase of the fire. Extensive test data is presented which shows the redistribution of moments and strains in the deck and steel mesh, together with displacements during the full duration of the fire. The results show that the behaviour of composite slabs is dependent on the heating rate, the maximum temperature reached and the cooling rate. In terms of overall performance, displacements and the temperature on the non-fire side of the slab are important. For the tests presented in this paper it was shown that one fire scenario resulted in the maximum displacement but another fire scenario resulted in the maximum temperature on the unexposed face. In addition the maximum temperature of the unexposed side of the slab and the mesh reinforcement within the slab occurring during the cooling stages of the fire. This highlights the fact that the performance of structures must be checked in design under a range of possible fire scenarios, which must include both the heating and cooling stages of a fire.

Generic modelling of composite steel–concrete slabs subjected to shrinkage, creep and thermal strains including partial interaction

Composite slabs in buildings that comprise permanent and integral thin-walled steel shuttering at the soffit of a reinforced concrete slab are subjected to two types of indirect (or non-mechanical) straining effects: shrinkage straining and thermal straining. Both of these indirect strains result in axial and transverse deformations of the slab, with those caused by concrete shrinkage resulting in long-term effects for which the quasi-viscoelastic properties of the concrete component (including creep and aging) are important. Typical shrinkage and thermal straining of slabs produces warping-type deformations through the slab thickness because indirect strain gradients are induced. For thermal strains, these deformations occur because of the typical temperature gradient through the slab thickness, while for shrinkage straining they occur because of the prevention of free moisture egress through the impervious steel sheeting. Surprisingly, little appears in the published literature on rational modelling of the behaviour of composite slabs subjected to these types of straining, despite its practical importance and significance, and the proliferation of composite slabs in contemporary building structures. This paper presents a model of both of these effects based on fundamental engineering mechanics, and prescriptive equations are derived based on the principle of virtual work. These equations are validated and used to demonstrate their scope by analysing a representative composite slab. The formulation may be used to predict deflections, and stresses in the concrete due to restrained shrinkage which may lead to cracking of the slab.

Experimental and analytical behaviour of composite slabs

The Eurocode 4 presents some negative aspects in the design of composite slabs by the m-k Method or the Partial Connection Method. On one hand, the component chemical adherence is not accounted for in the connection between the profiled steel sheet and the concrete. On the other hand, the application of these methods requires some fitting parameters that must be determined by full scale tests. In this paper, the Eurocode 4 methods are compared with a method developed at the Federal Polytechnic School of Lausanne, based on pullout tests, which can be a valid alternative. Hence, in order to calculate the necessary parameters for the three methods, several tests have been performed such as the full scale test described in Eurocode 4 and pull-out tests. This last type of tests is of small dimensions and implicates lower costs. Finally, a full-scale test of a steelconcrete composite slab with a generic loading is presented, with the goal of verifying the analytical formulation

3D Nonlinear Punching Shear Simulation of Steel-Concrete Composite Slab

In this study, a model for the interface between a concrete slab and a steel plate in composite slabs with studs is developed through a bending test for composite beams. A smeared reinforcing stud model is also implemented to consider the shear-reinforcing effect of taller studs. 3D nonlinear finite element analysis using the model for the interface and the reinforcing stud model developed in this study is found to predict punching shear behavior of composite slabs.

Strength and Performance of Fiber-Reinforced Concrete Composite Slabs

This research aimed to evaluate and compare the influence of 4 types of secondary reinforcement for temperature and shrinkage on the strength and behavior of composite slabs with a variety of loading conditions and span configurations. The 4 types of secondary reinforcement were welded wire fabric (WWF), and 3 types of fibers. The tests included 3-span composite slabs, with the steel deck continuous over the 3 spans but with no negative moment reinforcement used, subjected to a uniformly distributed load, and simple span slabs subjected to point and line loads. In conjunction with the slab tests, the flexural toughness and first-crack strength of the fiber-reinforced concrete mixes were determined using the ASTM C1018 standard test. The performance of the specimens reinforced with fibers is compared with that of the specimens reinforced with WWF. Results indicate that the strength, failure mode, crack initiation, and propagation, and load-deflection behavior are not much influenced by type of secondary reinforcement in the composite slab.

Thermal Behavior of Perfect and Imperfect Contact Composite Slabs Under the Effect of the Hyperbolic Heat Conduction Model

This work studies the heat transfer mechanisms during rapid heating of two-layer composite thin slabs from a macroscopic point of view using the hyperbolic heat conduction model. The composite slabs consist of two thin metal layers which may be in perfect or imperfect thermal contact. The effects of parameters such as the two films' thickness ratio, thermal conductivity ratio, heat capacity ratio, thermal relaxation time, and interfacial heat transfer coefficient on the thermal behavior of the composite slabs are investigated.

Composite Slabs with Corrugated SIMCON Deck as Alternative for Corrugated Metal Sheets

The flexural behavior of composite slabs made of slurry infiltrated mat concrete (SIMCON) deck and plain concrete topping was investigated. The SIMCON deck was fabricated to resemble a corrugated steel deck. Shear studs were used to prevent interfacial bond failure. Two steel fiber volumes were used in the SIMCON deck: 3.5 and 5.0%. The effect of rebar reinforcement of the concrete topping was also studied. Favorable results were achieved in this research effort. Encouraging strength and toughness test results for composite slabs using corrugated SIMCON deck were obtained, revealing potential for field applications of this proposed system.

The longitudinal shear behaviour of a new steel sheeting profile for composite floor slabs

Longitudinal shear failure is the most common failure-type in composite slabs. In this paper, the shear-connection behaviour of composite slabs with a particular profiled steel sheeting having a depth of 153 mm is experimentally studied. Twenty-seven push-out test specimens of different shapes, sizes, locations of embossments and different steel sheeting thicknesses are carried out in two test series. The embossments are first rolled onto the profiled sheeting, then every embossment is punched through along one side. It is found that the shear-connection behaviour of composite slabs is significantly affected by the depth of embossments. For the profiled steel sheeting with penetrated embossments, the reduction of Young's modulus caused by the penetrated embossments is an important factor 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 slabs up to 0.6 N/mm 2, is proposed for further research.

Fatigue behavior of composite beams with pyramidal shear connectors under repeated loading

For the designing of railway bridges with steel-concrete composite slab, it is necessary to estimate fatigue behavior of composite slabs. Regardless of the advancement of structural analytical methods, there still exist many problems in analyzing the composite slab with pyramidal shear connector. In order to clarify the fatigue properties of steel plate-concrete composite slabs, a series of fatigue test was carried out for several types of the TSC beams under various cross-section and loading conditions. The results are as follows: (1) the fatigue failure of TSC beams results from the tensile fracture of bottom steel plate and shear connectors, and (2) the converted fatigue strength of the plate for two million cycles can be estimated at 940kgf/cm2 from the S-N curves. Based on the test results, a simplified method is presented to predict stresses in steel plate and concrete under repeated loads. The calculated values agree well with the test results.

Influence of load arrangement on composite slab behaviour and recommendations for design

A parametric study of the behaviour of composite slabs consisting of profiled steel sheeting and concrete is presented. The FEM program DIANA was used to model the slab as a two-dimensional structure. Non-linear material and interface properties are considered as well as discrete cracking of the concrete. The main parameter is the horizontal shear transfer between the sheeting and the concrete; this is varied with respect to strength, ductility and influence of strain level in the sheeting. The FEM simulations have been validated by comparison with full-scale tests. It is clear from these comparisons that the full-scale behaviour can be described accurately using interface properties determined with small-scale push tests. The results of the simulations show clearly the importance of cracking of the concrete, which has a strong influence on the distribution of horizontal shear between the sheeting and the concrete. The largest slip will be at the so-called governing crack; at such a location the strains in the sheeting are high. For sheeting where the shear transfer relies on indentations, the strains in the sheeting reduce the shear transfer. The partial interaction method for design described in Eurocode 4 part 1 requires a very ductile connection between sheeting and concrete. The purpose of this study was to investigate the distribution of horizontal shear when the connection is less ductile, and to compare results for different load arrangements in order to develop a more general design method. The new method is based on detailed test results and FE analysis. Background information of the proposed method is given.