Baiguera, Marco; (2017) An innovative dual concentrically-braced moment-resisting steel frame for increased seismic resilience. Doctoral thesis (Ph.D), Heriot-Watt University. School of Energy, Geoscience, Infrastructure & Society.

Abstract

Improving seismic resilience of buildings is one of the current challenges in structural engineering. In the context of steel structures, design of conventional systems in accordance to current codes aims at preventing collapse and ensuring life safety under the design earthquake. However, in major seismic events, these systems have experienced extensive damage in the main structural membersand large residual drifts, causing downtime and significant socio-economic losses. This thesis presents the development and validation of an innovative dual steel frame that reduces structural damage and residual drifts for enhanced seismic performance. The proposed system consists of a moment-resisting frame with concentric braces equipped with seismic dampers. These are stainless steel pins with high post-yield stiffness, placed in series with the bracing members. Replaceable elements are inserted in the beams to absorb plastic deformations that would concentrate in the beam-column connections. The seismic performance of the proposed dual frame is evaluated using experimentally-validated finite element models of a prototype steel building. The numerical results show that, under the design and maximum earthquakes, residual storey drifts are minimised due to the high post-yield stiffness of the seismic dampers and the elastic deformation capacity of the moment frame. Structural damage is concentrated in the replaceable seismic devices, indicating the potential for a quick recovery after a strong earthquake. The collapse potential of the proposed frame is also investigated. The fracture capacity of the seismic dampers is experimentally evaluated using two full-scale geometries in a configuration reproducing the damper-brace connection. Criteria for predicting ductile fracture under ultra-low cycle fatigue are calibrated using coupon specimens and complementary finite element analyses, and validated performing explicit simulations of the full-scale tests. The collapse of the dual frame is studied by means of incremental dynamic analyses explicitly simulating the ductile fracture of the seismic dampers. The results show that the dual frame has a superior seismic resistance against collapse as a result of the large energy dissipation and fracture capacities of the seismic dampers.

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