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This study aims to investigate the influence of shear‐axial force interaction on the seismic performance of a piloti‐type building subjected to the Pohang earthquake. For this purpose, a four‐story piloti‐type building in Pohang, Korea whose columns were brutally damaged by the 2017 Pohang earthquake, one of this country's strongest earthquakes in modern history, was chosen as the object of the study. Columns of this piloti‐type building were designed with insufficient transverse reinforcement, resulting in an increased potential for shear‐axial failure. The piloti‐type building was simulated using Zeus‐NL, an efficient analysis and simulation platform developed for earthquake engineering applications to perform nonlinear time history analysis. A hysteretic shear model in Zeus‐NL capable of accounting for the variation in column axial force was adopted to capture the effect of the shear‐axial force interaction, caused by a combination of horizontal and vertical ground motions. The shear model was validated by comparing the simulated and experimental results. The seismic performance of the piloti‐type building under the effect of the shear‐axial force interaction was compared with that under the shear effect only. Results have indicated that shear effect and shear‐axial force interaction effect significantly reduce column maximum shear force and increase column drift demand. The influence is more intense considering shear‐axial interaction. The seismic response in terms of hysteretic behavior, energy dissipation, and stiffness degradation is presented and discussed. [ABSTRACT FROM AUTHOR]

In building design codes, buildings having less than 3 stories and a floor area less than 1000 m 2 are generally defined as small-scale buildings, and these are generally exempted from seismic requirements. To prevent potential loss of life and economic damage in the event of an earthquake, such buildings should be retrofitted so as to conform to current seismic design codes. In this study, a seismic retrofit scheme using buckling-restrained knee brace (BRKBs) was developed for a 2-story non-seismic gravity-designed steel frame building using the fragility contour method. To develop an effective retrofit scheme using BRKB for this building, 75 types of BRKB analytical models were used to achieve the desired performance levels and analyzed. Then, the seismic performance of the building before and after the retrofit was evaluated using the fragility contour method, and the improvement in the performance level of the probability against the structural limit state, such as component failures and structural collapse, was investigated. Based on the analytical studies, the most effective BRKB model for the retrofit scheme was proposed based on various scenarios in terms of the weight of the developed BRKB models. This study shows that the fragility contour method can be used for rapid evaluations and should be an effective tool for structural engineers to perform the seismic retrofit of buildings. [ABSTRACT FROM AUTHOR]

• A new rapid tool to determine multi-hazard performance and retrofit scheme. • Artificial neural network models developed for rapid performance evaluation. • A framework for combining seismic and blast performance limits using the ANN models. • Demonstration of the rapid tool to select an effective retrofit scheme under multi-hazards. Non-ductile reinforced concrete building frames have seismic and blast vulnerabilities due to inadequate reinforcement detailing resulting in premature failure. One option to mitigate these vulnerabilities is the installation of a retrofit system on susceptible structures. However, differences in code-defined performance limits depending on loading type may result in a non-conservative retrofit design under multi-hazard loads. This paper presents a rapid tool for multi-hazard assessment and mitigation for the seismically-vulnerable building frames using artificial neural network models, which can rapidly generate large datasets. Using the models, energy-based performance limits for multi-hazard loading are derived, and a rapid decision-making approach for the retrofit design is developed under seismic and blast loads. [ABSTRACT FROM AUTHOR]