A.Y. Elghazouli

Numerical modelling of the structural fire behaviour of composite buildings

This paper describes numerical models constructed to simulate the response of composite steel/concrete building floors under fire conditions. In particular, this study deals with two of the fire tests recently undertaken on a full-scale multi-storey building at Cardington, UK. The analysis is carried out using a structural analysis program which accounts for both geometric and material nonlinearities, and which includes temperature-dependent constitutive models for steel and concrete materials. The approaches used to represent the various structural details are discussed, and the procedure employed for incorporating the experimentally measured temperature profiles and histories is outlined. For the two tests considered in this investigation, the numerical results are in general agreement with the experimental data, particularly in terms of the magnitude of vertical deformations induced in the floors at elevated temperatures. Close examination of the numerical and experimental findings provides an insight into the complex interactions that occur in the structure at elevated temperatures. Most significantly, the influence of the restraint to thermal expansion of the heated floor area, which is provided by the surrounding parts of the structure, is shown to be of paramount importance. The increasing confidence that can be placed in numerical models as well as the improved understanding of the structural fire response may be used in developing more realistic and cost-effective design methods which are based on the actual structural response rather than that of isolated members.

Numerical simulation of glass-reinforced plastic cylinders under axial compression

Abstract The results of a numerical simulation study for the buckling behaviour of laminated composite cylinders are presented in this paper. The laminates are made from glass-reinforced plastic (GFRP) of type ‘DF 1400’ consisting of woven glass fibre roving within a polyester resin matrix. Two-ply cylinders with various laminate orientations, subjected to axial compression, are considered. The numerical simulations are compared to the results of a previous experimental investigation which is briefly described. The finite element model, used to carry out the numerical simulations, is presented and associated limitations are discussed. Linear eigenvalue analysis as well as geometrically non-linear simulations are undertaken using a general purpose finite element program. Detailed measurements of thickness variations and geometric imperfections, carried out within the experimental study, are directly introduced in the analysis. Several thickness representations are considered and their influence on the results is assessed. The correlation between numerical and experimental results is also discussed in terms of buckling strength, axial stiffness, buckling modes and surface strains. In addition to demonstrating the influence of various modelling idealisations on the results, this numerical study highlights the effect of the specific material and laminate construction detail on the buckling behaviour of composite cylinders.

Validation of FE models for buckling analysis of woven GFRP shells

Abstract This paper gives the details of a numerical finite element validation study for laminated GFRP cylinders subjected to concentric and eccentric compression. The laminates are of type ‘Rovimat 1200’ consisting of woven glass fibre roving, with a chopped mat on one side, within a polyester resin matrix. Two and three-ply cylinders with various orthogonal orientations are considered, for which the nominal radius-to-thickness ratio is about 108 and 72, respectively. The numerical results are compared to findings from a previous experimental investigation in which detailed measurements were obtained. Following a brief description of the experimental work, details of the development of suitable finite element models are presented and associated limitations are highlighted. Careful attention is given to thickness idealisation as well as the introduction of geometric imperfections into the numerical models. Both linear eigenvalue analysis and geometrically nonlinear simulations are undertaken using a general purpose finite element program. The correlation between numerical and experimental results is discussed in terms of buckling strength, axial stiffness, buckling deformations and surface strains. The analysis is shown to give a good representation of the buckling behaviour of GFRP cylinders of the type examined. It is also concluded that whereas the cylinders appear to be less sensitive to the effects of initial geometric imperfections than their isotropic counterparts, including such imperfections in a geometrically nonlinear analysis does improve the comparison between tests and finite element results, and is considered essential for the derivation of numerical ‘knockdown’ factors.

Compression tests on anti-symmetric two-ply GFRP cylinders

Abstract This article deals with the experimental buckling behaviour of glass fibre-reinforced plastic (GFRP) cylinders under concentric and eccentric compression. The laminates are of type ‘Rovimat 1200’ consisting of woven glass-fibre roving within a polyester resin matrix. Two-ply cylinders, for which the nominal radius-to-thickness ratio is about 108, with anti-symmetric lay-up of different orientation and overlapping procedure, are examined. In particular, the comparative response of cross-ply and angle-ply configurations is investigated and discussed. The results of experiments on eight models are presented including thickness and imperfection mapping, load and strain measurements as well as salient observations regarding the behaviour of each model. Systematic and automated data acquisition techniques using a laser scanning system and computer-controlled loading procedures were used in order to provide the experimental measurements in a form that can be readily used for further analytical and design studies. The results demonstrate the significant influence of laminate orientation and loading eccentricity on the buckling strength of anti-symmetric cross-ply and angle-ply GFRP cylinders.

Buckling of woven GFRP cylinders under concentric and eccentric compression

Abstract The experimental behaviour of laminated glass fibre-reinforced plastic (GFRP) cylinders under compression and bending is examined in this paper. The laminates are of type `Rovimat 1200 consisting of woven glass fibre roving, with a chopped mat on one side, within a polyester resin matrix. Two and three-ply cylinders with various orthogonal orientations were considered, for which the nominal radius-to-thickness ratio was about 108 and 72, respectively. Use was made of an automated laser scanning system for measuring geometric imperfections and progressive buckling deformations of the models. Following a description of the specimen and loading details, the results of experiments on ten models are presented. The results include thickness and imperfection mapping, displacement and load measurements as well as important observations regarding the failure mode and overall behaviour of each model. The findings highlight the effects of laminate construction and loading eccentricity on the buckling strength of cylinders within the range examined. Both elastic buckling and material-dominated failure modes were observed, depending on the slenderness and load type considered. The tests also provide detailed experimental data, which are necessary for further analytical and design studies.

Experimental response of glass-reinforced plastic cylinders under axial compression

Abstract 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.

Long-Term Performance and Assessment of Circular Reinforced Concrete Silos

Abstract This paper presents an investigation into specific aspects related to the performance of reinforced concrete circular silos. Firstly, two case studies of recent failures in circular silos in the UK are described and significant observations are highlighted. Methods used for estimating internal horizontal pressures acting on silo walls are discussed, and recommended values of design parameters are compared. A brief account of the results of an analytical investigation, on typical silo configurations selected from the case studies, is also given. The study reflects the level of uncertainty in calculating internal pressures considering possible variability in the properties of stored material and silo walls. Additionally, an assessment of stresses induced in steel reinforcement and associated cracking in concrete within critical wall sections is summarized. Finally, the expected causes of observed damage in this type of structure are outlined. In particular, it is concluded that inadequate consideration of crack control and durability requirements increases the vulnerability of the structure and may lead to premature failures especially in the long term.