Ultimate behaviour of composite floor slabs at ambient and elevated temperature

This paper is concerned with the ultimate behaviour of composite floor slabs under extreme loading situations resembling those occurring during severe building fires. The study focuses on the failure state associated with rupture of the reinforcement in idealised slab elements, which become lightly reinforced in a fire situation due to the early loss of the steel deck. The paper summarises recent studies carried out in order to provide a fundamental approach for assessing the failure limit associated with reinforcement fracture in lightly reinforced beams, representing idealised slab strips. In addition, preliminary results from the first phase of ambient tests on isolated strips are outlined and the main conclusions are discussed. Following the completion of subsequent stages of experiments involving full slab members, this work will enable validation of detailed numerical models which will be used for developing simplified design-oriented guidance

Failure assessment of lightly reinforced floor slabs. II: Analytical studies

This paper describes numerical and analytical assessments of the ultimate response of floor slabs. Simplified analytical models and finite-element simulations are described and validated against the experimental results presented in the companion paper. The simplified analytical model accounts for membrane action and the underlying mechanisms related to failure of floor slabs by either reinforcement rupture or compressive crushing of the concrete. In this respect, the significant influence of material properties, including bond strength, is considered in the model and described in detail. A detailed nonlinear finite-element model is also employed to provide further verification of the simplified approach and to facilitate further understanding of the overall response. The results and observations of this study offer an insight into the key factors that govern the ultimate behavior. Finally, the models are applied under elevated temperature conditions to demonstrate their general applicability and reliability

Failure criteria for composite slabs subject to extreme loading conditions

This paper is concerned with the ultimate behaviour of composite steel/concrete floor slabs under extreme loading situations, particularly those that occur during severe building fires. The study focuses on the failure state associated with rupture of the reinforcement in composite slab members which become lightly reinforced in a fire situation due to the early loss of the steel deck. An account of a series of large scale ambient tests, undertaken on full slab members, is presented in the paper. The experimental arrangements are described together with the details of the specimens. Complementary analytical studies, carried out to assess the salient factors influencing the failure of composite slab members are also summarised. The assessments utilise detailed numerical models which adopt novel finite element formulations including geometric and material nonlinearities, as well as simplified analytical models for the prediction of failure deformations and associated load levels. The results of this investigation offer detailed insights into the key factors that govern the ultimate behaviour of composite floor systems under extreme loading conditions, and provide simplified tools which are suitable for implementation in performance based design procedures

Failure of Unrestrained Lightly Reinforced Concrete Slabs under Fire, Part II: Verification and Application

Accepted versio

Numerical modelling and parametric assessment of hybrid flat slabs with steel shear heads

This investigation examines the performance of hybrid reinforced concrete flat slabs, incorporating fully-integrated shear-heads at connections to steel columns, through a series of numerical evaluations and parametric studies. Validations of the adopted nonlinear finite element procedures, which employ concrete damage plasticity constitutive models, are carried out against experimental results on hybrid members. Complementary verifications on conventional reinforced concrete flat slabs are also undertaken to ensure the reliability of the selected ranges for key modelling parameters. Comparison of the numerical simulations against the test results shows close correlations in terms of ultimate strength, deformations and stress levels in the constituent elements of hybrid members. This is followed by a series of parametric assessments on key structural parameters for hybrid flat slabs with steel shear heads. The results of these investigations enable the identification of three modes of failure as a function of the interaction between the shear-head and surrounding concrete. The findings permit the development of improved analytical models for predicting the response as well as the ultimate strength of such members. In addition, recommendations are given for the determination of shear-head dependent parameters, which are required for practical design purposes, with a particular focus on the embedment length and section size of the shear-head elements. The suggested expressions for assessing the shear-head characteristics offer a more reliable design approach in comparison with existing methods and are suitable for effective practical application and implementation in codified procedures

Ductility considerations for mechanical reinforcement couplers

Mechanical reinforcement couplers can offer considerable constructional and economic advantages in comparison with conventional methods of lap splicing, particularly when the requirements for seismic detailing exacerbates reinforcement congestion problems. However, the lack of specific codified guidance on ductility considerations hinders the application of mechanical couplers under inelastic conditions. To this end, this brief paper provides an overview of various reinforcement coupling systems, as well as a comparative assessment of their ‘in-air’ and ‘in-concrete’ performance, based on results extracted from a collated database. The main behavioural characteristics of different coupler forms are discussed, and their key performance parameters are compared. In addition to strength and ductility, the influence of the coupler size and arrangement on the ductility of structural members is discussed. The comparative assessments presented offer some guidance for the selection and application of mechanical reinforcement couplers in inelastic regions, and highlights areas in which further detailed investigations are required