Experimental and numerical investigation on the complex behaviour of the localised seismic response in a multi-storey plan-asymmetric structure

Under extreme seismic events, earthquakes result in the collapse of structural components. Reinforced concrete (RC) structures are particularly susceptible due to their structural asymmetry. The post-earthquake analysis has highlighted the practical implications of structural irregularities and its contribution to the seismic damage. This requires a thorough understanding of how torsional vibrations influence the response of asymmetric structures. Research findings attribute the high vulnerability of asymmetric structures to earthquakes to coupled torsional vibrations. Unlike in symmetric structures, the vibrations in the asymmetric are high and are as a result if different effects like twisting of the structural floors. Additionally, structural failure under extreme seismic events is governed by many factors, such as structural irregularity, which must be considered to estimate local damage mechanisms accurately.

Even though the global responses are deemed sufficient for studying the overall behavior, it can result in the inaccurate estimation of the component-level damage response, leading to an inaccurate description of the realistic seismic damage mechanism. Moreover, the existing component-level damage studies concentrate on the damaged flexible side of the plan-asymmetric structure with little attention to the potential damage on the flexible edge. Therefore, understanding such damage concentration is of great importance since they can result in global and local seismic failure.

To address the existing research gap, Shenyang Jianzhu University researchers: Professor Zeshan Alam, Professor Li Sun, Professor Chunwei Zhang and Dr. Zhongxin Su, together with Professor Bijan Samali from Qingdao University of Technology, studied in depth the internal damage response behavior of the CCFE of a multi-story plan-asymmetric reinforced concrete structure. Their work is currently published in the journal, Structure and Infrastructure Engineering.

For this research, experimental and numerical investigations were carried out in both elastic and inelastic states. The experiment involved testing a quarter-scaled asymmetric structure with in-plan stiffness eccentricity under progressive seismic excitations. Fibre Bragg grating (FBG) sensors were used to monitor the seismic damage in the critical region of the corner column of the flexible side (CCFE) during the transformation of the structure from elastic to plastic states. Based on a calibrated finite element model developed in ABAQUS, the damage behavior of CCFE was analyzed to determine the influence of the stiffness eccentricity. Finally, the experimental and numerical results were compared and discussed in detail.

The results emphasized the local damage considering the high dependency of the global damage on the local stress concentrations. Identifying the critical regions leading to component-level failure significantly contributed to the robust seismic design considering that an increase in the local seismic effects influences the overall structural response. The abnormal behavior of the local seismic response was observed as the flexible edge of the structure as indicated by the tensile and comprehensive strains. However, this phenomenon was not observed in the stiff edge of the structure because the structural components remained in the elastic state. Unlike the flexible edges that exhibited both tension and compression regarding the stored deformations, corner columns at the stiff edge did not exhibit the variation of the local seismic response.

In summary, the authors investigated the damage concentration of the critical region of the column on the flexible side of the quarter-scaled three-story asymmetric structure with in-plan stiffness eccentricity. Results confirmed the progressive stiffness degradation of the structure under seismic excitations and the significant influence of asymmetry on the local structural response. Most importantly, the authors noted that the CCFE in plan-asymmetric structures requires special seismic detailing and substantial design redundancy to resist seismic events. In a statement to Advances in Engineering, Professor Chunwei Zhang stated that the study provided useful insights that would enable a better understanding and evaluation of the local seismic behavior for developing structural health monitoring guidelines.