Fiber reinforced polymer (FRP) systems have shown great promise in strengthening reinforced concrete structures. These systems are a viable option for use as external reinforcement because of their light weight, resistance to corrosion, and high strength. These systems, externally bonded in the form of sheets or laminates, have shown to increase the flexural and more recently the shear capacity of members. Major concerns of the system are issues related to the bond strength and premature peeling especially when reentrant corners are present. The objectives of this study were to verify the effectiveness of carbon FRP (CFRP) laminates on an I-section beam with no anchorage and to determine the feasibility of using an anchorage system to prevent premature debonding. The two types of anchorage systems used were a horizontal CFRP laminate and glass FRP (GFRP) spikes. These anchorage systems verified that the use of anchorage on I-shaped beams can prevent premature debonding of the laminate and allow the specimens to achieve a higher shear capacity. Recommendations for future research of such systems are also presented.

The current design procedure for steel frame structures is a two-step process including an elastic analysis to determine design actions and a separate member capacity check. This design procedure is unable to trace the full range of load-deflection response and hence the failure modes of the frame structures can not be accurately predicted. In recent years, the development of advanced analysis methods has aimed at solving this problem by combining the analysis and design tasks into one step. Application of the new advanced analysis methods permits a comprehensive assessment of the actual failure modes and ultimate strengths of structural steel systems in practical design situations. One of the advanced analysis methods, the refined plastic hinge method, has shown great potential to become a practical design tool. However, at present, it is only suitable for a special class of steel frame structures that is not subject to lateral torsional buckling effects. The refined plastic hinge analysis can directly account for three types of frame failures, gradual formation of plastic hinges, column buckling and local buckling. However, this precludes most of the steel frame structures whose behaviour is governed by lateral torsional buckling. Therefore, the aim of this research is to develop a practical advanced analysis method suitable for general steel frame structures including the effects of lateral-torsional buckling. Lateral torsional buckling is a complex three dimensional instability phenomenon. Unlike the in-plane buckling of beam-columns, a closed form analytical solution is not available for lateral torsional buckling. The member capacity equations used in design specifications are derived mainly from testing of simply supported beams. Further, there has been very limited research into the behaviour and design of steel frame structures subject to lateral torsional buckling failures. Therefore in order to incorporate lateral torsional buckling effects into an advanced analysis method, a detailed study must be carried out including inelastic beam buckling failures. This thesis contains a detailed description of research on extending the scope of advanced analysis by developing methods that include the effects of lateral torsional buckling in a nonlinear analysis formulation. It has two components. Firstly, distributed plasticity models were developed using the state-of-the-art finite element analysis programs for a range of simply supported beams and rigid frame structures to investigate and fully understand their lateral torsional buckling behavioural characteristics. Nonlinear analyses were conducted to study the load-deflection response of these structures under lateral torsional buckling influences. It was found that the behaviour of simply supported beams and members in rigid frame structures is significantly different. In real frame structures, the connection details are a decisive factor in terms of ultimate frame capacities. Accounting for the connection rigidities in a simplified advanced analysis method is very difficult, but is most critical. Generally, the finite element analysis results of simply supported beams agree very well with the predictions of the current Australian steel structures design code AS4100, but the capacities of rigid frame structures can be significantly higher compared with Australian code predictions. The second part of the thesis concerns the development of a two dimensional refined plastic hinge analysis which is capable of considering lateral torsional buckling effects. The formulation of the new method is based on the observations from the distributed plasticity analyses of both simply supported beams and rigid frame structures. The lateral torsional buckling effects are taken into account implicitly using a flexural stiffness reduction factor in the stiffness matrix formulation based on the member capacities specified by AS4100. Due to the lack of suitable alternatives, concepts of moment modification and effective length factors are still used for determining the member capacities. The effects of connection rigidities and restraints from adjacent members are handled by using appropriate effective length factors in the analysis. Compared with the benchmark solutions for simply supported beams, the new refined plastic hinge analysis is very accurate. For rigid frame structures, the new method is generally more conservative than the finite element models. The accuracy of the new method relies on the user's judgement of beam segment restraints. Overall, the design capacities in the new method are superior to those in the current design procedure, especially for frame structures with less slender members. The new refined plastic hinge analysis is now able to capture four types of failure modes, plastic hinge formation, column buckling, local buckling and lateral torsional buckling. With the inclusion of lateral torsional buckling mode as proposed in this thesis, advanced analysis is one step closer to being used for general design practice.

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The doctoral thesis is focused on evaluation of global sensitivity analysis of load-carrying capacity of steel hot-rolled beams. These beams are subjected to lateral-torsional buckling, weak axis buckling and strong axis buckling. Very comprehensive computational models which were both geometrically and materially nonlinear were created in Ansys software using solid finite elements to calculate the load-carrying capacity. The computational models allowed modelling of random initial imperfections such as initial curvature, deviations of cross-section dimensions and steel properties. Sensitivity analysis quantified their influence on the load-carrying capacity. Simulation runs of random imperfections were generated using the Latin Hypercube Sampling method. Since the evaluation of sensitivity analysis of load-carrying capacity of all finite element models would cost an extreme amount of computer time, the thesis aimed at developing a meta-model (also known as surrogate model) based on approximation of FEM model. The approximation polynomial then facilitated the evaluation of sensitivity indices using a high number of simulation runs. At the end, the relationships between the slenderness and the first and second-order sensitivity indices are plotted in graphs. Those random input imperfections that influence the variability of load-carrying capacity the most are pointed out.

Работа посвящена изучению работы сварных двутавров с гофрированной стенкой в качестве элементов многоэтажных рамных каркасов различного назначения. Проанализированы существующие практические решения таких конструкций, обобщены теоретические подходы и методики расчета изгибаемых и внецентренно-сжатых элементов с гофрированной стенкой. Приведен пример численного расчета многоэтажного рамного каркаса, состоящего из ригелей и колонн с гофрированными стенками. Разработаны узлы крепления элементов каркаса друг к другу и к смежным конструкциям. В рамках исследования установлено, что применение сварных двутавров с гофрированной стенкой позволяет снизить металлоемкость реализации решения как для ригелей, так и для колонн многоэтажных рам зданий без снижения требуемой несущей способности и эксплуатационной надежности конструкции. / Present work is devoted to the study of the operation of welded I-sections with a corrugated web as elements of multi-storey frame structures for various purposes. The existing practical solutions for such structures are analyzed, theoretical approaches and methods for calculating of bending and eccentrically compressed elements with a corrugated web are generalized. An example of a numerical calculation of a multi-storey frame structure consisting of girders and columns with corrugated webs is given. The joints for fastening the frame elements to each other and to adjacent structures have been developed. Within the framework of the study, it was found that the use of welded I-sections with a corrugated webs makes it possible to reduce the metal consumption of the solution as for girders and as columns of multi-storey building frames without reducing the required bearing capacity and operational reliability of the structure.