The effect of connection flexibility on the seismic performance of industrial racking systems
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Industrial racking systems are load bearing structures for the warehouse storage of goods. They are normally fabricated and assembled from cold-formed perforated open thin-walled vertical members and can be 4 meters to 40 meters high. To resist lateral actions such as seismic loads, racking structures rely typically on flexible boltless beam to upright connections along the storage aisles and braced frames in the transverse cross-aisle direction. Compared to their self weight, industrial racks carry very heavy pallet loads as opposed to other conventional structures. High slenderness ratio, heavy pallet loads, connection flexibility and low degree of redundancy make rack structures very different from conventional steel structures. Therefore, in the racking industry special analysis and design codes are adopted which require specific experimental tests to determine the performance of the key structural components. However the current standards do not give sufficient guidance for seismic design. This PhD research investigates both numerically and experimentally the effect of different connections on the performance of industrial racking systems. The research focus is on three critical connections: (a) Beam-upright connection; (b) Floor connection (Base-plate connection); and (c) Bolted brace connection. Courtesy of Dexion Australia, part of the research was based on test results conducted on their racking components. More than 70 beam to upright connection tests including monotonic and cyclic tests, 15 base plate tests under combined axial and bending loads and 4 full cross aisle shear frame tests were studied. FE models were then developed and verified against the test results. Further FE analyses revealed the behaviour of the aforementioned local connections under monotonic and cyclic actions and as a result simple theoretical models were proposed. After deep investigations on the performance of different connections of a typical rack structure, more than 20 full scaled shake table tests were conducted to reveal the dynamic features of a rack structure and one full scaled static cyclic push over test was performed to evaluate the system deterioration under cyclic actions. Both dynamic and static full scaled tests were accurately modeled using the proposed beam to upright connection model. A new performance based seismic analysis approach was proposed at the end of the thesis which showed much more accurate results compared to the seismic analysis approach in the current racking codes and specifications.
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