Ultimate behavior of idealized composite floor elements at ambient and elevated temperature

This paper is concerned with the ultimate behavior 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 idealized slab elements, which become lightly reinforced in a fire situation due to the early loss of the steel deck. The paper describes a fundamental approach for assessing the failure limit associated with reinforcement fracture in lightly reinforced beams, representing idealized slab strips. A description of the ambient-temperature tests on isolated restrained elements, carried out to assess the influence of key material parameters on the failure conditions, is firstly presented. The results of a series of material tests, undertaken mainly to examine the effect of elevated temperature on ductility, are also described. A simplified analytical model is employed, in conjunction with the experimental findings, to assess the salient material parameters and their implications on the ultimate response at both ambient and elevated temperature. © 2009 Springer Science+Business Media, LLC

Failure assessment of lightly reinforced floor slabs. I: Experimental investigation

This paper is concerned with the ultimate behavior of lightly reinforced concrete floor slabs under extreme loading conditions. Particular emphasis is given to examining the failure conditions of idealized composite slabs which become lightly reinforced in a fire situation as a result of the early loss of the steel deck. An experimental study is described which focuses on the response of two-way spanning floor slabs with various materials and geometric configurations. The tests enable direct assessment of the influence of a number of key parameters such as the reinforcement type, properties, and ratio on the ultimate response. The results also permit the development of simplified expressions that capture the influence of salient factors such as bond characteristics and reinforcement properties for predicting the ductility of lightly reinforced floor slabs. The companion paper complements the experimental observations with detailed numerical assessments of the ultimate response and proposes analytical models that predict failure of slab members by either reinforcement fracture or compressive crushing of concrete. © 2011 American Society of Civil Engineers

Inelastic displacement ratios for non-structural components in steel framed structures under forward-directivity near-fault strong-ground motion

Funder: University of CambridgeAbstract: This paper describes a detailed numerical investigation into the inelastic displacement ratios of non-structural components mounted within multi-storey steel framed buildings and subjected to ground motions with forward-directivity features which are typical of near-fault events. The study is carried out using detailed multi-degree-of-freedom models of 54 primary steel buildings with different structural characteristics. In conjunction with this, 80 secondary non-structural elements are modelled as single-degree-of-freedom systems and placed at every floor within the primary framed structures, then subsequently analysed through extensive dynamic analysis. The influence of ground motions with forward-directivity effects on the mean response of the inelastic displacement ratios of non-structural components are compared to the results obtained from a reference set of strong-ground motion records representing far-field events. It is shown that the mean demand under near-fault records can be over twice as large as that due to far-fault counterparts, particularly for non-structural components with periods of vibration lower than the fundamental period of the primary building. Based on the results, a prediction model for estimating the inelastic displacement ratios of non-structural components is calibrated for far-field records and near-fault records with directivity features. The model is valid for a wide range of secondary non-structural periods and primary building fundamental periods, as well as for various levels of inelasticity induced within the secondary non-structural elements

Failure of Lightly Reinforced Concrete Floor Slabs with Planar Edge Restraints under Fire

Accepted versio

Assessment of progressive collapse in multi-storey buildings

Accepted versio

Failure of composite steel-concrete slabs under elevated temperatures

The behaviour of composite steel-concrete slabs under fire has attracted considerable attention over recent years and has led researchers to develop performance based models capturing the phenomena observed during fires. However, while the limit load proposed defined corresponds to fracture of the reinforcing mesh, the criterion employed is semi-empirical ignoring fundamental issues such as the bond slip characteristics. A recent model has addressed this issue for lightly reinforced beams, considering the bond slip response of the reinforcement along with other salient problem characteristics, however, it becomes complex for practical application when extended to slabs. In the current work, novel models are developed for the assessment of the failure load of lightly reinforced concrete slabs under fire conditions, considering simply supported rectangular slabs with and without planar edge restraints. In the limit, this load corresponds to the failure load of composite slabs under fire, since fire tests have demonstrated that the steel deck de-bonds leaving a lightly reinforced concrete slab. The developed models account for the temperature effect on the geometric and material properties, and they consider the tensile membrane action developed at large deflections. The deflected shape, used as the basis of model formulation, was observed experimentally to match the failure mode described by yield line theory, and in the developed models, it is assumed that cracks forming along the yield lines, penetrate through the slab depth. The strain concentration in the reinforcement along these cracks is established by considering the bond slip characteristics, and the failure load is determined as that corresponding to a specific rupture mechanical reinforcement strain. Comparisons against the non-linear finite element analysis program ADAPTIC and experimental results are presented along with case studies highlighting the influence of various parameters. Simplified versions of the proposed models are also presented for direct use by designers to assess the failure of composite slabs under elevated temperatures.EThOS - Electronic Theses Online ServiceBuilding Research EstablishmentGBUnited Kingdo

Experimental response of glass-reinforced plastic cylinders under axial compression

This paper presents the results of buckling tests on laminated composite cylinders made from glass fibre reinforced plastic (GFRP). The laminates used are of type 'DF1400' consisting of woven glass fibre roving within a polyester resin matrix. In total, six cylinders constructed from two-ply laminates, in which the main variable is the laminate orientation, were tested under axial compression. The specimen details, experimental set-up and loading arrangements are described, and a detailed account of the test results is given. The results include thickness and imperfection mapping, and displacement, load and strain measurements. Use was made of an automated laser scanning system, which was developed for measuring the initial geometric imperfections as well as buckling deformations during various stages of loading. The results of this experimental study demonstrate the influence of laminate orientation on the buckling strength of composite cylinders, and provide detailed information necessary for analytical and design investigations.This paper presents the results of buckling tests on laminated composite cylinders made from glass fibre reinforced plastic (GFRP). The laminates used are of type `DF1400' consisting of woven glass fibre roving within a polyester resin matrix. In total, six cylinders constructed from two-ply laminates, in which the main variable is the laminate orientation, were tested under axial compression. The specimen details, experimental set-up and loading arrangements are described, and a detailed account of the test results is given. The results include thickness and imperfection mapping, and displacement, load and strain measurements. Use was made of an automated laser scanning system, which was developed for measuring the initial geometric imperfections as well as buckling deformations during various stages of loading. The results of this experimental study demonstrate the influence of laminate orientation on the buckling strength of composite cylinders, and provide detailed information necessary for analytical and design investigations

Experimental in-plane cyclic response of dry and wet masonry walls incorporating lime mortar and clay bricks

This paper investigates the in-plane response of ambient-dry and wet clay-brick/lime-mortar masonry walls under lateral cyclic loading and co-existing compressive gravity load, as well as of square masonry panels under diagonal compression. The properties of the constituent materials were selected to resemble those of existing heritage masonry structures in Historic Cairo. After describing the specimen details and testing arrangements, the main results and observations are provided and discussed. The full load-deformation behaviour of the large-scale wall members is also evaluated , including their ductility and failure modes, and compared with the predictions of available assessment models. It is shown that moisture has a detrimental effect on the main material properties, including the diagonal tension and compression strengths as well as brick-mortar interaction parameters. For the large-scale wall specimens, the wet-to-dry reduction was found to between 8-11% for the lateral strength and around 10% in terms of ductility. The response of diagonal walls was relatively brittle with a reduction between wet-to-dry strengths of around 33%, suggesting that the reduction ratio is dependent on the compression stress level. Provided that the key moisture-dependent masonry properties are appropriately evaluated, it is also shown that analytical assessment methods can be reliably adapted for predicting the response