비틀림 비정형을 가지는 저층 RC 필로티 구조물의 비탄성 거동에 관한 강도비 및 평면 형상비의 영향

Abstract

Low-rise reinforced concrete (RC) piloti buildings are highly vulnerable to torsion due to the eccentric placement of core walls, a fact confirmed by numerous failures during the 2017 Pohang earthquake. This study aims to identify the actual inelastic collapse mechanism of piloti buildings and to propose key design parameters for ensuring their seismic safety. To achieve this, a three-dimensional non-linear static analysis (push-over) is performed with the wall-to-column strength ratio (S) and the planar aspect ratio (AR) as the main variables. The results of this study showed that the collapse mechanism was dominantly governed by the strength ratio rather than the initial static eccentricity. When the strength ratio was low (S≤4), a stable, ductile failure was induced by the wall yielding first, which effectively controlled the torsional behavior. In contrast, when the strength ratio was high (S≥6), an unstable, brittle failure occurred due to the premature yielding of weak-side columns, which amplified the torsional response. This difference in collapse mechanisms was clearly identified by the post-yield movement direction of the center of strength (CS). In models with a low strength ratio, the CS moved inward toward the center of mass (CM), indicating a balanced strength distribution. Conversely, in models with a high strength ratio, the CS moved outward, indicating a worsening of the strength imbalance. These models with excessively high strength ratio and aspect ratio failed prematurely without achieving their designed strength. Therefore, it is essential to move beyond static indices like initial eccentricity. Instead the design should focus on controlling the failure sequence by maintaining a wall-to-column strength ratio of 2.0 or less.