비틀림 비정형을 가지는 저층 RC 필로티 구조물의 강성중심 이동을 고려한 비틀림 모멘트 평가

Abstract

Low-rise RC piloti buildings, which are prevalent in Korea, are particularly vulnerable to seismic load when torsional irregularity is present. Current seismic design codes evaluate torsional moment using static eccentricity based on elastic stiffness. However, this approach does not fully evaluate the actual torsional response once the structure shows the inelastic range, due to translates in the center of rigidity. This study quantitatively investigates the influence of rigidity and strength ratios between wall and column in the soft first story on the nonlinear torsional behavior of irregular piloti buildings. Analytical models with various rigidity and strength ratios are analyzed non-linear static(push-over) analysis. The results of this study show that inelastic behavior was primarily governed by the strength ratio rather than the rigidity ratio. When the wall-to-column strength ratio was low, wall yielded first, causing the center of rigidity to translate toward the center of mass and reducing torsional effects. In such cases, the current codes tended to overestimate torsional moments. Otherwise, with a high strength ratio, weaker columns yielded first, translation the center of rigidity further away from the center of mass and amplifying eccentricity. This led to torsional moments up to 10% higher than those predicted by elastic analysis, suggesting that the current design approach may be unresonable. For the safe seismic designs of torsionally irregular piloti buildings, both rigidity and strength ratios between vertical members should be considered to accurately evaluate torsional moment variations arising from inelastic translates of the center of rigidity.