Behaviour of composite floor slabs under fire conditions

This paper is concerned with the ultimate behaviour of composite floor slabs during fire scenarios. Steel/concrete composite structures are increasingly common in the UK and worldwide, particularly for multi-storey construction. The popularity of this construction form is mainly due to the excellent efficiency offered in terms of structural behaviour, construction time and material usage all of which are attractive given the ever-increasing demands for improved sustainability in construction. In this context, the engineering research community has focused considerable effort in recent years towards understanding the response of composite structures during fires. In particular, the contribution made by the floor slab system is of crucial importance as its ability to undergo secondary load-carrying mechanisms (e.g. membrane action) once conventional strength limits have been reached may be the key to preventing disproportionate collapse of the overall structure. Researchers have focused on developing the fundamental understanding of the complex behaviour of floor slabs and also improving the methods of analysis. Building on this work, the current paper describes the development and validation of a finite element model which can simulate the response of floor slab systems until failure, both at ambient and elevated temperature. The model can represent the complexities of the behaviour including the temperature-dependent material and geometric nonlinearities. It is first developed at ambient temperature and validated using a series of experiments on isolated slab elements. The most salient parameters are identified and studied. Thereafter, the model is extended to include the effects of elevated temperature and is employed to investigate the behaviour under these conditions. Comparisons with current design procedures are assessed and discussed

A review of progressive collapse research and regulations

History has demonstrated that buildings designed to conventional design codes can lack the robustness necessary to withstand localised damage, partial or even complete collapse. This variable performance has led governmental organisations to seek ways of ensuring all buildings of significant size possess a minimum level of robustness. The research community has responded by advancing understanding of how structures behave when subjected to localised damage. Regulations and design recommendations have been developed to help ensure more consistent resilience in all framed buildings of significant size, and rigorous design approaches have been specified for buildings deemed potentially vulnerable to extreme loading events. This paper summarises some of the more important progressive collapse events, to identify key attributes that lead to vulnerability to collapse. Current procedures and guidelines for ensuring a minimum level of performance are reviewed and modelling methods for structures subjected to localised damage are described. These include increasingly sophisticated progressive collapse analysis procedures, including linear static and non-linear static analysis, as well as non-linear static pushover and linear dynamic methods. Finally, fully non-linear dynamic methods are considered. Building connections potentially represent the most vulnerable structural elements in steel-framed buildings; their failure can lead to progressive collapses. Steel connections also present difficulties with respect to frame modelling and this paper highlights benefits and drawbacks of some modelling procedures with respect to their treatment of connections

Fire responses and resistance of concrete-filled steel tubular frame structures

This paper presents the results of dynamic responses and fire resistance of concretefilled steel tubular (CFST) frame structures in fire conditions by using non-linear finite element method. Both strength and stability criteria are considered in the collapse analysis. The frame structures are constructed with circular CFST columns and steel beams of I-sections. In order to validate the finite element solutions, the numerical results are compared with those from a fire resistance test on CFST columns. The finite element model is then adopted to simulate the behaviour of frame structures in fire. The structural responses of the frames, including critical temperature and fire-resisting limit time, are obtained for the ISO-834 standard fire. Parametric studies are carried out to show their influence on the load capacity of the frame structures in fire. Suggestions and recommendations are presented for possible adoption in future construction and design of these structures

Experimental Seismic Evaluation of Ceiling-Piping-Partition Nonstructural Systems

The seismic performance of nonstructural components plays a significant role during and after an earthquake. Damage to these systems can leave buildings inoperable, causing economic losses and extensive downtime. Therefore, it is necessary to better understand the response of these systems in order to enhance the seismic resilience of buildings. A series of full-scale system-level experiments conducted at the University of Nevada, Reno Network for Earthquake Engineering Simulation site aimed to investigate the seismic performance of integrated ceiling-piping-partition systems. A full-scale, two-story, two-by-one bay steel braced-frame test-bed structure that spanned over three biaxial shake tables was used to house the nonstructural systems. The test-bed structure was subjected to over 50 generated ground motions in a series of eight tests. The test-bed structure could be constructed into two configurations, one to produce large floor accelerations and the other to produce large inter-story drifts, affecting both acceleration and drift sensitive nonstructural systems. The responses and behaviors of ceiling-piping-partition systems were critically assessed through several design variables, configurations, and materials. The degree of damage observed during testing was used as an evaluation of the performance of nonstructural components.Post processing of experimental data led to results including acceleration amplification factors, seismic fragility analysis, and overall performance of nonstructural systems. Three significant findings from this experiment are as follows: 1) ceiling systems with pop rivet connections have a lower probability of failure compared to seismic clips, 2) pipe joints with 2.0 in. (50.8 mm) diameter pipes have the greatest probability of rotation failure compared to other diameter pipes, and 3) acceleration amplification factors for out-of-plane partition walls are comparable with the recommended amplification suggested by the ASCE 7-10 code for flexible components

Experimental and analytical assessment of ductility in lightly reinforced concrete members

This is the post-print version of the final paper published in Engineering Structures. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.This paper is concerned with the ultimate behaviour of lightly reinforced concrete members under extreme loading conditions. Although the consideration given to the assessment of ductility is of general relevance to various applications, it is of particular importance to conditions resembling those occurring during severe building fires. The main purpose of the investigation is to examine the failure of idealised members representing isolated strips within composite floor slabs which become lightly reinforced in a simulated fire situation due to the early loss of the steel deck. An experimental study, focusing on the failure state associated with rupture of the reinforcement in idealised concrete members, is presented. The tests enable direct assessment of the influence of a number of important parameters such as the reinforcement type, properties and ratio on the ultimate response. The results of several tests also facilitate a detailed examination of the distribution of bond stresses along the length. After describing the experimental arrangements and discussing the main test results, the paper introduces a simplified analytical model that can be used to represent the member response up to failure. The model is validated and calibrated through comparisons against the test results as well as more detailed nonlinear finite element simulations. The results and observations from this investigation offer an insight into the key factors that govern the ultimate behaviour. More importantly, the analytical model permits the development of simple expressions which capture the influence of salient parameters such as bond characteristics and reinforcement properties, for predicting the ductility of this type of member. With due consideration of the findings from other complementary experimental and analytical studies on full slab elements under ambient and elevated temperatures, this work represents a proposed basis for developing quantified failure criteria.Engineering and Physical Sciences Research Council (EPSRC