Hoang Dang-Vu

This study evaluated the influence of additional shear walls, constructed on the first floor, as strengthening methods for a piloti-type building subjected to earthquake loadings. Piloti-type buildings are commonly designed as urban structures in many cities of South Korea. The existence of just columns on the first floor of the building is a feature that is advantageous from an architectural viewpoint, and yet has potential structural disadvantages. Such columns usually exhibit shear–axial failure, due to inherent vertical and horizontal irregularities and insufficient seismic reinforcements. Among several retrofitting methods, including additional braces, carbon fiber reinforced polymers, dampers, and so forth, this research considered reinforced concrete shear walls to improve the seismic responses of piloti buildings. A parametric analysis of the location of the retrofitted shear walls in a typical piloti building was implemented using the Zeus-NL program. Nonlinear time history analysis and incremental dynamic analysis were performed to comparatively evaluate the structure’s seismic responses and fragility curves before and after retrofit.

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.

In this research, corner columns of low‐rise residential buildings, which might be unstable and vulnerable to seismic loadings during earthquake due to vertical and horizontal irregularities, are tested under different effects from bending moment and axial force. Here, biaxial loading is focused and developed, representing a rhombus path with 100% force in the main direction, versus 30% force in the perpendicular direction. Two of eight test specimens are subjected to axial compressive force at 30% of column capacity, while other specimens are at 10%. The eight test specimens were constructed with varying transverse reinforcement details, to control the column‐failure mechanism. The objective of this research was to investigate the seismic behavior of the corner columns of low‐rise buildings that used ordinary‐moment‐resisting‐frames (OMRF). The test results were discussed to interpret the effect of biaxial loading on the overall performance of the columns using comparison between global and local responses. It could be very helpful in deeply understanding the seismic behavior of structures which were designed in accordance with OMRF requirements. Furthermore, this information might affect decisions about using intermediate‐moment‐resisting frames or special‐moment‐resisting frames, where more demanding seismic requirements are applied.