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The robustness of a seismically-designed steel self-centering moment-resisting frame (SC-MRF) under a column loss scenario is numerically assessed. The prototype SC-MRF is equipped with post-tensioned bars and optimised stainless steel energy dissipation devices. The SC-MRF was modelled in full detail using solid finite elements. The numerical model was calibrated using results from previous tests on post-tensioned beam-column connections and isolated component tests on the energy dissipation devices. Quasi-static analyses were carried out to identify the failure modes of the SC-MRF under a column loss scenario. Nonlinear dynamic analyses were also performed to evaluate the dynamic response of the frame and to assess the acceptance criteria against progressive collapse according to current formalised procedures. The results show that the SC-MRF has superior robustness and it can guarantee a high level of safety under a sudden column loss scenario due to the high fracture capacity of the stainless steel energy dissipation devices and the tie force resistance provided by the post-tensioned bars.

This paper investigates the behavior of a typical Chilean reinforced concrete wall building under sequential earthquake and tsunami actions using a double pushover analysis approach. A real concrete wall structure that was damaged after the M w = 8.8 2010 Maule earthquake is considered as a case study building and a simplified nonlinear finite element model of a fictitious slice of the building is subjected to earthquake and tsunami loading in sequence. The analysis of the building under these loadings consists of three stages: the structure is first subjected to seismic loading by means of a pushover analysis until a specific damage state is reached; then a pushover with the same load pattern but in the opposite direction is applied until the shear at the base is zero; and finally, the building is subjected to tsunami loading by means of a variable depth pushover analysis until the maximum capacity is reached. Different tsunami load cases are considered in this study, varying the Froude number and the direction of the tsunami loading. The results show that the tsunami response of the building is mainly dependent on the Froude number of the tsunami flow; however, when the seismic damage is severe, the tsunami capacity of the building is found to be reduced. This is more likely to occur when the effect of the tsunami increases the damage previously induced by the earthquake in the same direction.

A dual seismic-resistant steel frame, which consists of a moment-resisting frame equipped with high post-yield stiffness energy-dissipative braces, is proposed and numerically evaluated. Replaceable hourglass shape pins made of duplex stainless steel with high post-yield stiffness and large energy dissipation and fracture capacity are in series connected to conventional steel braces. Moreover, replaceable fuses are introduced in the beams at the locations where plastic hinges are expected to develop. A performance-based seismic design procedure and appropriate capacity design rules are used to design the dual frame, while its seismic performance is evaluated with advanced numerical simulations using experimentally validated shell–solid finite element models and simplified beam element models. The numerical results show that the dual frame has adequate stiffness and energy dissipation capacity to control peak storey drifts (i.e. non-structural damage), while plastic deformations (i.e. structural damage) are isolated within the replaceable pins of the braces and the beam fuses. In addition, the high post-yield stiffness of the pins, combined with the appreciable elastic deformation capacity of the moment-resisting frame, results in significant reduction of residual storey drifts, which are found to have a mean value of 0.06% under the design earthquake and a mean value of 0.12% under the maximum considered earthquake. These values indicate a superior residual storey drift performance compared to steel frames equipped with buckling restrained braces, and highlight the potential of the proposed dual frame to help steel buildings to return to service within an acceptable short time in the aftermath of a strong earthquake.

Many coastal regions lying on subduction zones are likely to experience the catastrophic effects of cascading earthquake and tsunami observed in recent events, e.g., 2011 Tohoku Earthquake and Tsunami. The influence of earthquake on the response of the structure to tsunami is difficult to quantify through damage observations from past events, since they only provide information on the combined effects of both perils. Hence, the use of analytical methodologies is fundamental. This paper investigates the response of a reinforced concrete frame subjected to realistic ground motion and tsunami inundation time histories that have been simulated considering a seismic source representative of the M9 2011 Tohoku earthquake event. The structure is analysed via nonlinear time-history analyses under (a) tsunami inundation only and (b) earthquake ground motion and tsunami inundation in sequence. Comparison of these analyses shows that there is a small impact of the preceding earthquake ground shaking on the tsunami fragility. The fragility curves constructed for the cascading hazards show less than 15% reduction in the median estimate of tsunami capacity compared to the fragility functions for tsunami only. This outcome reflects the fundamentally different response of the structure to the two perils: while the ground motion response of the structure is governed by its strength, ductility and stiffness, the tsunami performance of the structure is dominated by its strength. It is found that the ground shaking influences the tsunami displacement response of the considered structure due to the stiffness degradation induced in the ground motion cyclic response, but this effect decreases with increasing tsunami force.