การประเมินความเปราะบางต่อแรงแผ่นดินไหวของอาคารคอนกรีตเสริมเหล็กรูปทรงไม่สม่ำเสมอในแนวระนาบด้วยวิธีการวิเคราะห์ผลตอบสนองเชิงเวลาโดยแยกโหมดเป็นอิสระ

Abstract

The analysis of structural response to seismic waves with accuracy and precision that matches the actual behavior of the structure is called nonlinear response history analysis (NLRHA). However, NLRHA requires a lot of time and computational resources. To deal with this, the Uncoupled Modal Response History Analysis (UMRHA) method has been developed and studied, especially for typical buildings without plan irregularities and in large quantities. The principle of UMRHA is to calculate the time-history response for each mode separately and then combine the results from all modes. The accuracy of this method depends on the hysteretic behavior of each mode, which represents the structural behavior under earthquake loading. This study focuses on the seismic response analysis and fragility assessment of a reinforced concrete building with plan irregularities, characterized by extreme torsional irregularity and reentrant corner irregularity, as defined by ASCE standards and the development of DPT standard 1301/1302-61 (first revision), which can be strongly influenced by rotational modes. The study is conducted in two main parts. First, it compares the accuracy of the UMRHA method using both the bilinear and flag shape models with the NLRHA method when applied to this type of building, the bilinear model and a flag-shaped model are used to represent the hysteretic behavior in each mode, as these models are straightforward to implement and align with the study's goal of reducing structural response computation time. The study will use 30 different seismic waves with varying characteristics. In the second part, fragility curves representing different damage states are developed according to the Hazus methodology (FEMA, 1997), based on the responses of the representative building obtained from the UMRHA method using bilinear and flag shape models. The study will also compare the differences in fragility between the two models by applying 350 seismic waves that correspond to the seismic characteristics of the Chiang Mai region. The selected seismic waves ensure sufficient diversity and comprehensive coverage to the Chiang Mai region The initial part of the study found that the responses of the representative building obtained from the UMRHA method using both models, in terms of overall global responses and story-level responses along the X-axis, closely matched those obtained from the NLRHA method. The strong rotational modes of the building did not significantly affect the accuracy of the UMRHA method. However, the responses derived from the UMRHA method using the bilinear model showed slightly more discrepancies compared to those using the flag shape model. Additionally, the modal contributions to the response in each mode of the representative building indicated that the first mode is the dominant mode, with other modes exhibiting weak coupling. In terms of processing time, the UMRHA method significantly reduced processing time by as much as 35 hours and 30 minutes when compared to the time required for the NLRHA method, using the initial set of 30 seismic waves. In the second part of the study, the development of fragility curves for the representative building is based on responses from the UMRHA method using both models. It was found that the flag shape model results in a higher probability of reaching various damage states compared to the bilinear model.