Seismic Design of Concentrically Braced Steel Frames
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The aim of this project is to develop a robust numerical model that accurately replicates the behaviour of CBFs during earthquakes. This numerical model is then used to validate a codified performance based design approach for CBFs, known as the direct displacement based design (DDBD) procedure. Numerical models and design guidelines have not always been validated using data and findings from real-time physical tests. This research addresses this need. This is carried out in several stages. Firstly, a study of the behaviour of cold-formed square and rectangular structural hollow section brace elements is carried out. These are the main elements in CBF system that dissipates energy during seismic actions. Then, a robust numerical model incorporating a fatigue model for braces is developed with adequate fatigue parameters. A set of pseudo-static cyclic tests is used to calibrate the numerical model for braces, after which another independent set of pseudo-static cyclic tests is used to validate the model for both hot-rolled and cold-formed square and rectangular hollow sections. This numerical model is extended and used to develop a single storey CBF numerical model, which is validated by shake table tests and a large range of nonlinear time history analysis (NLTHA). The comparative assessments presented in this work indicate that these developed numerical models can accurately capture the salient features related to the seismic behaviour of CBFs. Secondly, a DDBD procedure for single storey CBFs is developed. The performance of the DDBD methodology is verified by comparing its design values with experimental results obtained from the shake table tests and a large range of NLTHA. The DDBD procedure is then applied to multi-storey CBFs and it is verified by comparing its design values to predictions obtained from the NLTHA of both 4-storey and 12-storey CBF buildings.