No description available.

This research study is conducted on one bay-one story non-sway frames where the effects of the rotational restraint and slenderness ratio on the post-buckling strength of the axially restraint column under thermal load are studied. Geometric non-linear analysis of the structures is performed using a research program based on the beam-column theory. A total 32 models are created considering two different bottom end conditions: fixed and hinged, slenderness ratios: 50 and 125, and the beam to column length ratios: 0.5,1,1.5 and 2, to account for the variation in the rotational restraint. All models are subjected to thermal loads and numerical results are obtained to study the post-buckling behavior of the columns of the frames under thermal loads.

The objective of this study is to examine the effect of rotational restraints on thermal post-buckling response of sway columns using geometrically nonlinear analysis. The present design approach considers columns to have failed once they buckle. However, the columns under fire load are found to exhibit significant post-buckling strength which could be utilized for more economical design. The past researchers on the nonlinear thermal analysis used isolated columns with idealized support conditions which mean the columns are assumed to be free or fully restrained in the rotation, lateral and, axial directions. However, that is seldom the case in real structures and the restraint at an end of the column depends upon the members connected at that joint. The restraint provided to the column by the members connected at the joint will be in between the free case and fully restrained case. This study incorporates the variation in rotational restraint due to changes in the properties of members connected at the ends of the column. The columns are assumed to be fully restrained in the axial direction. Since the study is being carried out on sway columns, the restraint in the lateral direction is zero.

Cellular beams (CBs) have become increasingly popular in the UK and other countries over the recent years. However, the research into the behaviour of these beams has not advanced at the same rate. There is still no robust codified guidance available to design cellular beams and cellular composite beams at ambient and elevated temperatures. Meanwhile, numerical simulation approaches, such as Finite Element (FE) analysis, have enabled the researchers to advance their investigations into various behavioural aspects of these beams. In this research, the developed numerical models using the ABAQUS package were able to predict, to a high accuracy, the failure mode and failure load (temperature) of CBs and cellular composite beams at ambient and elevated temperatures.Within the investigations on cellular beams, it was found that predicting the correct failure mode by FE models can be extremely sensitive to the maximum load increment allowed in the software (for elastic-perfectly plastic stress-strain relationship for steel material) and also to the applied boundary conditions. In particular, slight changes in the boundary conditions applied to the top flange of the beam, can change the failure mode from web post buckling to Vierendeel mechanism. The buckling resistance of the web post of cellular composite beams was found to be sensitive to the amplitude of web imperfections at ambient temperature. However, the ultimate resistance of these beams was not affected by the amplitude of web imperfections at elevated temperature. This suggests that the 'Strut' model used in current design method to estimate the buckling resistance of the web post is not reasonable at elevated temperature and needs to be modified. The failure of cellular composite beams under a uniform distributed load (UDL) and at elevated temperatures, was governed by distorsional buckling before the development of web post buckling. Adding full-height web stiffeners to the beam in such cases improved their loading resistance at ambient temperature by up to 15% and prevented the occurrence of distorsional buckling at elevated temperature. Increasing the end-restraints decreased the deflections of CBs which are governed by catenary action at elevated temperature. However, this also critically promoted the occurrence of web post buckling which could be due to the P-∆ effects and instabilities resulting from the restrained expansion of the beam.Asymmetric beams showed a higher sensitivity and vulnerability to the magnitude of the load ratio than symmetric sections. This suggests a more prudent approach for the fire design of asymmetric beams as opposed to symmetric beams.

No description available.

The performance of thin-plate structural systems is known to be greatly influenced by the effect of buckling and post-buckling behaviour. The main factors, which affect the buckling, and post-bucking characteristics and consequently the ultimate performance of thin plate structural components, are noted to be structural geometry, material properties, loading and boundary conditions and geometric imperfections. Present day knowledge and understanding of the buckling and post-buckling behaviour of thin plate structures is at a fairly sophisticated level due to the intensive research that has been carried out over the years in this field of study. This is particularly true for the case of compressive loading whereby the collapse and unloading failure mechanics of thin plate structures has been well documented for this case. The same is not true for the case of shear loading and although much work has been carried out there is a lack of knowledge and in-depth understanding of shear post-ultimate conditions which essentially defines the initiation and progressive development of the plastic failure mechanisms of thin plate structural system. This thesis makes a contribution to the area of study by taking advantage of the developments in recent years of computational technology and computing power to develop finite element modelling strategies and solution procedures using the commercially available FE package PATRAN/NASTRAN to describe in detail the post-buckled shear failure of thin plate structural systems. The work of this thesis provides an in-depth understanding of the complex post-buckled failure mechanics associated with thin-plate structures subjected to in-plane shear displacement and combined shear and compression loading. Simply supported in-plane normal stress free and straight edge boundaries are employed to examine the shear performance as well as the failure mechanisms of thin and stocky web plates. Finite element modelling strategies are developed, which are able to describe the complete loading history from the onset of initial buckling through the nonlinear elastic post-buckling to initial material yielding and its further propagation throughout the structure leading to the development of an appropriate failure mechanism that causes final plastic collapse and subsequent load drop-off. The post-buckled failure response of the thin plate structures is determined with due consideration being given to the effects of geometric and material nonlinearities. The effect of stiffeners on structural performance is detailed for single and multiple asymmetrical and symmetrically attached stiffeners. The degrading influence on the structural performance of cut-outs as well as the considerable redeeming effect due to reinforcements attached at the cut-out boundaries is highlighted in this thesis. The work of the thesis covers the in-plane shear displacement loading of thin web plates, thin web plates with transverse stiffeners, web plates with cut-outs, web plates with stiffened cut-outs and the interactive shear and compressive loading of transversely stiffened web structures. The in-plane shear displacement loading of these structures using the multipoint constraint loading strategy in the finite element modelling procedures has shown to be highly successful in being able to provide an in-depth understanding of the failure mechanics of these structures to a level not to be found in the existing literature.

An ever increasing demand to exploit oil and natural gas reserves has significantly increased extraction activities even in the remotest regions of the Arctic and sub-Arctic regions of the Canadian North. Steel pipelines are the most efficient mode for transporting and distributing these resources. These pipelines, particularly buried in cold region, often subjected to extreme geo-environmental conditions, where significant inelastic deformation may occur resulting in localized wrinkles. Under continued deformation, there is a possibility of excessive cross-sectional deformation at wrinkle locations, eventually leading to fracture or damage in the pipe wall jeopardizing pipeline safety and integrity . Prior research indicated that occurrence of fracture in pipe wrinkle is rare under monotonic load-deformation process. However, a recent field fracture was observed within the wrinkle location of an energy pipeline. Similar failure mode was observed in a laboratory specimen at the University of Alberta. Both field and laboratory observations had indicated that the final failure was a “tearing” failure at the fold of the telescopic wrinkles resulting from monotonic application of axial load not aligned with pipe axis. This research program was designed to study this specific failure mode and to develop design tool for pipeline engineers. This research started with examining the failed field and test specimens. A preliminary investigation was carried out using nonlinear finite element (FE) model to simulate test and field behaviour. Numerical results have indicated that even under monotonic loading, significant strain reversals could occur at the wrinkle fold . Presence of these strain reversals was proposed as the preliminary failure criterion responsible for this unique failure mechanism. In next phase, a full-scale ‘pipe-wrinkling’ test program was carried out concurrent to this research to better understand the loading condition responsible for this type of failure. Results of this test program have shown the presence of tearing fracture or rupture in the pipe walls of several of test specimens. A series of FE analyses was then carried out to predict and verify the behaviour of these test specimens. After successful simulation of the test behaviour, further numerical analyses were carried out using tension coupon model developed herein to simulate the material behaviour using the material test data and hence to formulate the limiting conditions in terms of critical strain responsible for the tearing failure. Based on these numerical results, a double criterion  ‘Strain Reversal’ and ‘Critical Equivalent Plastic Strain Limit’, were proposed to predict tearing fracture of wrinkled pipe under monotonic loading. Results of these numerical analyses have demonstrated that the proposed criteria predict this failure mode with reasonable accuracy. In the final phase of this research, a parametric study was carried out to consider the effect of different parameters on failure modes of wrinkled pipe. Results of this parametric study describe the range of parameters under which the tearing mechanism can/may exhibit. / Structural Engineering

The aim of this thesis is to investigate buckling, post-buckling behaviors and failure characteristics of composite laminated plates under compressive loading with the help of finite element method and experiments. In the finite element analyses, eigen value extraction method is used to determine the critical buckling loads and nonlinear Riks and Newton-Raphson methods are employed to obtain post-buckling behaviors and failure loads. The effects of geometric imperfection amplitude on buckling and post-buckling are discussed. Buckling load, post buckling loaddisplacement relations, out of plane displacements and end shortening of the plates are determined numerically. Furthermore, the numerical results are compared with experimental findings for two different laminates made of woven fabric and unidirectional tapes where buckling, post-buckling behavior and structural failure of laminated plates were determined. The comparisons show that there is a good agreement between numerical and experimental results obtained for buckling load and post-buckling range. However, 15 % - 22 % differences are predicted between the experimental and numerical results for failure of laminates made of woven fabric whereas the laminates with uni-directional tapes show good agreement.

No description available.

The objective of this study was to numerically investigate the effects of slenderness ratios and end rotational restraints on the post-buckling behavior of non-sway columns. To study the effect of end restraints, numerical solutions were generated for three different support conditions, namely, hinged-hinged, fixed-hinged and fixed-fixed. Furthermore, for each of these support conditions, the effects of slenderness ratios on the post-buckling response were analyzed by considering the slenderness ratios of 50,125 and 200. Based on the numerical data presented in this thesis, the following conclusions can be made.  The unrestrained columns under mechanical loads do not exhibit any significant post-buckling strength.  Restrained Columns subjected to thermal loading undergo significantly smaller deformations in contrast to unrestrained columns, where deformations are relatively larger as the loads are increased only slightly above their critical levels.  The mechanical post-buckling response does not seem to depend on the slenderness ratios of the columns ;whereas the thermal post-buckling response depends on the slenderness ratios of the columns with the relative deformation decreasing with slenderness ratio at a given temperature ratio.  Post buckling behavior of columns subjected to mechanical loadings does not seem to change when the rotational restraints are added whereas in case of columns subjected to thermal loading, the post-buckling response depends on the rotational restraints at the ends of the column. o For a constant slenderness ratio, the deflection ratio was found out to be the smallest for the hinged-hinged column and largest for the fixed-fixed column subjected to thermal loads at a given temperature ratio.