변위의존형 감쇠장치를 이용한 학교시설 내진보강 연구

Abstract

평가대상 건축물에 대하여 지진을 고려하여 구조해석한 후 이를 바탕으로 하여 변위의존형 감쇠장치를 이용하여 내진보강 방법을 제안하고, 비선형해석을 통한 내진 성능을 확인하여 즉시거주수준(Immediate Occupancy Level, IO) 및 인명안전수준(Life Safety Level, LS)에 대한 기본 목표내진성능 (Basic Safety Objective, BSO)에 대한 검증을 실시하여 기존 구조물의 내진성능을 파악하고 변위의존형 감쇠장치(Displacement-dependent Dampers)를 보강후 비선형해석을 통하여 다음과 같은 결론을 얻었다.

1. 학교시설 내진성능 평가 및 내진보강 가이드라인의 상세평가법을 이용하여 내진성능을 상세 평가한 결과 X방향은 500년 재현주기 지진 시 최종내진등급 C등급, 2400년 재현주기의 2/3 지진(Design Basis Earthquake, DBE) 시 최종내진등급 B등급으로 보강이 필요한 것으로 평가되었으며, Y방향은 500년 재현주기 및 2400년 재현주기의 2/3 지진 시 최종내진등급 A등급으로 평가되어 일상적인 유지관리만 필요한 것으로 평가되었다.

2. 비선형 정적해석을 통하여 기존 구조물과 변위의존형 감쇠장치를 보강하여 검토한 결과, LS레벨(Life Safety Level, LS) X방향, Y방향의 성능점이 보강후 목표성능을 크게 만족하는 수준으로 성능이 향상되었음을 확인할 수 있었다. 또한 CP레벨(Collapse Prevention Level, CP)에서는 X방향의 성능점이 보강전 형성되지 않았지만 보강후 형성되었고, Y방향의 성능점이 보강후 목표성능을 크게 만족하는 수준으로 성능이 향상되었음을 확인 할 수 있었다. 따라서 본 구조물은 규준에서 허용하는 지진에 대하여 충분하게 안정한 거동을 하고 있음을 확인할 수 있다.

3. 비선형 시각이력해석(Nonlinear Time-History Analysis)을 수행하여 변위의존형 감쇠장치로 보강한 구조물에 대하여 층간 변형각은 설계 목표인 LS레벨 1%, CP레벨 1.5%를 크게 하회하는 결과를 나타내어 충분히 구조물이 안정적인 거동을 하고 있음을 확인 할 수 있었다. 각 지진파에 의한 댐퍼의 이력루프를 검토한 결과, 댐퍼가 안정적인 이력거동을 하고 있어, 입력되는 지진에너지가 일부 댐퍼를 통해 소산됨을 확인할 수 있었다. 또한, 전체 댐퍼 중에서 일부는 아직 댐퍼가 작동하지 않고 있는 곳도 있어서 목표로 설정된 지진세기보다 더 큰 지진파에 대하여서도 구조물이 안정적인 거동을 할 수 있는 잉여력을 가지고 있는 것으로 나타났다.

4. 설계지진레벨에서 보강전 X방향은 인명안전(LS LEVEL), Y방향은 즉시거주(I.O LEVEL)였으나, 보강후 X방향 및 Y방향 모두 즉시거주(I.O LEVEL)상태로 평가되었고 최대지진레벨에서 보강전 X방향은 붕괴(Collapse), Y방향은 즉시거주(LS LEVEL)였으나, X방향 및 Y방향 모두 인명안전(LS LEVEL)수준으로 내진성능이 향상되었음을 알 수 있다.

이상에서 살펴본 바와 같이, 본 연구에서 제시한 X방향 변위의존형 감쇠장치 보강공법을 적용함으로써, 지진하중 작용 시 변위의존형 감쇠장치가 충분한 에너지소산능력을 발휘할 수 있었고, 댐퍼의 내진능력으로 기존 구조물의 손상을 최소화하여, 구조물의 내진성능을 향상시키고 있는 것으로 판단된다.

As a result of analyzing the structure of evaluation target buildings considering the earthquake, proposing seismic reinforcement method by using displacement-dependent dampers based on it, confirming seismic performance through non-linear analysis, conducting verification on basic safety objective regarding immediate occupancy level and life safety level, grasping the seismic performance of previous structures, reinforcing displacement-dependent dampers, and carrying out non-linear analysis, following conclusion was made.

1. As a result of conducting detailed evaluation on seismic performance using seismic performance evaluation for school facilities and detailed evaluation method of seismic reinforcement guideline, X direction was evaluated to be in need of reinforcement as final seismic performance category of C during the earthquake with return period of 500 years and final seismic performance category of B during 2/3 earthquake with return period of 2,400 years (design basis earthquake, DBE) were graded. For Y direction, only general maintenance was evaluated to be necessary as final seismic performance category of A was graded for both earthquake with return period of 500 years and 2/3 earthquake with return period of 2,400 years (design basis earthquake, DBE).

2. As a result of examining after reinforcing previous structures and displacement-dependent dampers through non-linear static analysis, it was confirmed that the performance point of X and Y direction for life safety level (LS) were enhanced to very satisfactory level surpassing the target performance after the reinforcement. Also, in case of the collapse prevention level (CP), it was confirmed that the performance point for X direction that wasn't formed before the reinforcement has formed after the reinforcement and the performance point of Y direction was enhance to very satisfactory level surpassing the target performance after the reinforcement. Therefore, it was revealed that the building displays considerably safe movement regarding the earthquake sanctioned in the regulation.

3. As a result of conducting non-linear time-history analysis, the drift angle of structure reinforced with the displacement-dependent dampers was revealed to be considerably lower than design objectives that are LS 1% and CP 1.5% thus it was proven that the structure is displaying considerably stable movement. As a result of examining hysteresis loop of damper in accordance with each seismic wave, the damper displayed stable hysteresis movement thus it was confirmed that input seismic energy is partially dissipated through damper. Also, considering the fact that some of dampers among entire dampers are not being operated, it was revealed that the structure has surplus power to display stable movement for seismic wave bigger than target strength of the earthquake.

4. In regards to designed seismic level, the level of X and Y direction before the reinforcement were LS level and IO level respectively. However, they were both evaluated to be IO level after the reinforcement. In regards to maximum seismic level, the level of X and Y direction before the reinforcement was collapse and IO level respectively. Seismic performance was revealed to be enhanced as the level of both X and Y direction was LS level after the reinforcement.

As seen above, the displacement-dependent dampers displayed sufficient energy dissipation performance with the application of earthquake load when the displacement-dependent dampers reinforcement method in X direction proposed in this study was implemented. Also, it was determined that seismic performance of structure is enhanced as the damage of previous structure is minimized with seismic performance of dampers.