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When a concentrated load is introduced perpendicular to the flanges of a steel beam, this condition is referred to as Patch loading (Gozzi, 2007). This occurrence is common in many steel structures, for example at supports or during launching of bridges. Because of the usual slenderness of I-beams and other plated structures, these are sometimes reinforced with stiffeners in order to avoid buckling. Modifications, such as adding stiffeners to a beam, are done to make greater plastic deformations possible before buckling can occur; thereby increasing the resistance against failure. Transverse stiffeners are added in areas where the beam is exposed to concentrated loads (Lagerqvist, 1994). The descriptions of calculating patch loading in the Eurocode are presented for cases of double stiffeners, with the load applied in between two stiffeners with same distance to each of them, or when there is one single stiffener that is acting in line with the load. In the Eurocode there are also descriptions on how to calculate on the resistance against patch loading when there are no stiffeners added. However, the Eurocode lacks descriptions for cases when the stiffeners are misaligned. The purpose of this paper is the evaluation of the impact from transverse stiffeners to the resistance of welded I-beams, when the stiffeners are misaligned and where the length of the beam varies. Because of the complexity of such of problems it is almost impossible to find theoretical solutions (Lagerqvist & Johansson, 1996). Therefore, in this study as well as in almost all studies that aim to predict the ultimate resistances of steel beams subjected to patch loading, the results are gained empirically. The tests herein were done by FE-modeling and the results from the physical experiments done in Lagerkvist’s doctoral thesis were used for validation of the model, as conducting experiments ourselves was not economically possible. 6 The study was made in two steps. In the first step FE-models were produced under the same circumstances as the results obtained by Lagerqvist (1994). Those analyses were not part of the aim of the study; the intention for making the initial analyses was to strengthen the reliability of the results. From there, the final analyses were made with the aim in investigating the influence of stiffeners on the resistance, when these are misaligned. In this step, observations were also made with regards to the impact of the bending moment of the beam on its resistance. The initial analyses, which were made for validation of the modeling, had a satisfying correspondence to the physical experiments; hence the final analyses are assumed valid of acceptance. From observations of the results in the final analyses it is noticed that adding stiffeners is a highly preferred way of increasing the resistance for slender beams. For full utilization it is however important to have the stiffeners optimally placed, because a small deviation from this position gives an unwanted decrease in resistance.

Yes / The impact behavior of deflection-hardening High Performance Fiber Reinforced Cementitious Concretes (HPFRCs) was evaluated herein. During the preparation of HPFRCs, fiber type and amount, fly ash to Portland cement ratio and aggregate to binder ratio were taken into consideration. HPFRC beams were tested for impact resistance using free-fall drop-weight test. Acceleration, displacement and impact load vs. time graphs were constructed and their relationship to the proposed mixture parameters were evaluated. The paper also aims to present and verify a nonlinear finite element analysis, employing the incremental nonlinear dynamic analysis, concrete damage plasticity model and contact surface between the dropped hammer and test specimen available in ABAQUS. The proposed modelling provides extensive and accurate data on structural behavior, including acceleration, displacement profiles and residual displacement results. Experimental results which are further confirmed by numerical studies show that impact resistance of HPFRC mixtures can be significantly improved by a proper mixture proportioning. In the presence of high amounts of coarse aggregates, fly ash and increased volume of hybrid fibers, impact resistance of fiberless reference specimens can be modified in a way to exhibit relatively smaller displacement results after impact loading without risking the basic mechanical properties and deflection-hardening response with multiple cracking.

This study focuses on the response of flat unsymmetric laminates to an inplane compressive loading that for symmetric laminates are of sufficient magnitude to cause bifurcation buckling, postbuckling, and secondary buckling behavior. In particular, the purpose of this study is to investigate whether or not the concept of bifurcation buckling is applicable to unsymmetric laminates. Past work by other researchers has suggested that such a concept is applicable for certain boundary conditions. The study also has as an objective the determination of the response of flat unsymmetric laminates if bifurcation buckling does not occur. The finite-element program ABAQUS is used to obtain results, and a portion of the study is devoted to becoming familiar with the way ABAQUS handles such highly geometrically nonlinear problems, particularly for composite materials and particularly when instabilities and dynamic behavior are involved. Familiarity with the problem, in general, and with the use of ABAQUS, in particular, is partially gained by considering semi-infinite unsymmetrically laminated cross- and angle-ply plates, a one-dimensional problem that can be solve in closed form and with ABAQUS by making the appropriate approximations for the infinite geometry. In this portion of the study it is found that semi-infinite cross-ply laminates with clamped boundary conditions and semi-infinite angle-ply plates with simple-support boundary conditions remain flat under a compressive load until the load magnitude reaches a certain level, at which time the out-of-plane deflection become indeterminate, essentially an eigenvalue problem as encountered with classic bifurcation buckling analyses. Obviously, a linear analysis of such problems would not reveal this behavior and, in fact, there are other revealed significant differences between the predictions of linear and nonlinear analyses. Transversely-loaded and inplane-loaded finite isotropic plates are studied by way of semi-closed form Rayleigh-Ritz-based solutions and ABAQUS in a step to approaching the problem with unsymmetric laminates. A method to investigate the unloading behavior of postbuckled finite isotropic plates is developed that reveal multiple plate configurations in the postbuckled region of the response, and this method is then extended to the study of finite inplane-loaded unsymmetric laminates. To that end, two specific laminates, a symmetric and an unsymmetric cross-ply laminates, and a variety of boundary conditions are used to study the response of inplane-loaded unsymmetric laminates. The symmetric laminate is included to provide a familiar baseline case and a means of comparison. Plates with all four edges clamped and a variety of inplane boundary conditions are studied. Of course the symmetric cross-ply laminate exhibits bifurcation behavior, and when the tangential displacement on the loaded edges and the normal displacement on the unloaded edges are restrained, secondary buckling behavior occurs. For the unsymmetric cross-ply laminate, bifurcation buckling behavior does not occur unless the tangential displacement on the loaded edges and the normal displacement on the unloaded edges are restrained, or the tangential displacement on the loaded edges and the normal displacement on the unloaded edges are free. If either of these conditions are not satisfied, the unsymmetric cross-ply laminate exhibits what could be termed 'near-bifurcation' behavior. In all cases rather complex behavior occurs for high levels of inplane load, including asymmetric postbuckling and secondary buckling behavior. For clamped loaded edges and simply-supported unloaded edges, bifurcation buckling behavior does not occur unless the tangential displacement on the loaded edges and the normal displacement on the unloaded edges are restrained. For this case, rather unusual asymmetric bifurcation and associated limit point behavior occur, as well as secondary buckling. This is a very interesting boundary condition case and is studied further for other unsymmetric cross-ply laminates, including the use of a Rayleigh-Ritz-based solution in attempt to quantify the problem parameters responsible for the asymmetric response. The overall results of the study have led to an increased understanding of the role of laminate asymmetry and boundary conditions on the potential for bifurcation behavior, on the response of the laminate for loads beyond that level. / Ph. D.

The exposure from a localized vehicle fire has been observed to produce excessive damage onto highway bridge structural elements including complete collapse of the infrastructure. The occurrence of a fire beneath a bridge can lead to significant economic expense and loss of service even if the bridge does not collapse. The focus of the current research is to assess and evaluate the effect of realistic localized fire exposures from vehicles on the bridge structural integrity and to guide future development of highway bridge design with improved fire resistance. In this research, the bridge structural element response was predicted through a series of three loosely coupled analyses: fire analysis, thermal analysis, and structural analysis. Two different types of fire modeling methodologies were developed in this research and used to predict the thermo-structural response of bridge structural elements: one to model the non-uniform exposure due to a vehicle fire and another to predict response due to a standard uniform furnace exposure. The vehicle fire scenarios required coupling the computational fluid dynamics (CFD) code Fire Dynamics Simulator (FDS) with Abaqus while the furnace exposure scenarios were all done within Abaqus. Both methodologies were benchmarked against experimental data. Using the developed methodologies, simulations were initially performed to predict the thermo-structural response of a single steel girder-concrete deck composite assembly to different local, non-uniform fires and uniform standard furnace fire exposures. The steel girder-concrete deck composite assembly was selected since it is a common bridge design. Following this, a series of simulations were performed on unprotected highway bridges with multiple steel plate girders and steel tub girders subjected to localized fires. The analyses were used to evaluate the influence of a fire scenario on the bridge element response, identify the factors governing the failure of bridge structural elements subjected to a localized fire exposure, and provide guidance in the design of highway bridge structural elements against fire hazards. This study demonstrates that girder geometry affected both the dynamics of the fire as well as the heat transfer to the bridge structural elements which resulted in a different structural response for the bridge. A heavy goods vehicle (heat release rate of 200 MW) and tanker fires (heat release rate of 300 MW) were predicted to cause the bridge to fail due to collapse, while smaller fires did not. The geometric features of the plate girders caused the girder elements to be exposed to higher heat fluxes from both sides of the girder resulting in collapse when exposed to a HGV fire. Conversely, the closed feature of the box girder does not allow the interior surfaces to be in direct contact with the flames and are only exposed to the internal reradiation from surfaces inside the girder. As a result, the single and double lane tub girder highway bridge structure does not fail due to a heavy goods vehicle fire exposure. / Ph. D.