최근 목조 오층탑의 내진성능에 대한 국외 연구결과, 심주와 탑신이 서로 다른 동적특성을 가져 지진발생시 목조탑의 공진이 감소되는 제진구조의 특성을 갖는 것으로 나타났다. 국내 유일의 목조 오층탑 법주사 팔상전에 대해서도 구조 안전성과 보존을 위하여 공학적인 연구가 필요한 상황으로 본 연구에서는 법주사 팔상전의 내진성능 평가를 위한 상시미동 실험을 수행하였다. 측정대상인 팔상전은 1624년 지어졌고 1968년 해체수리 되었다. 건축 규모는 1층 5칸${\times}$5칸($11.35m{\times}11.35m$), 3층 3칸${\times}$3칸, 5층 1칸${\times}$1칸이고, 팔상전 탑신높이는 17.515 m, 상륜 4.085 m로 전체높이는 21.6 m의 규모이다. 내부 심주는 1층부터 5층까지 이어져 있고 주위에 4개의 기둥과 벽이 심주를 둘러싸고 있다. 상시미동 측정실험 결과, 팔상전의 1차 고유진동수는 X, Y방향 1.22 Hz이고 2.76 Hz, 3.96 Hz 모두 병진모드가 보이고, 1.49Hz에서는 역위상 모드의 동적특성이 나타났다. 인력가진을 이용한 감쇠정수는 X방향 1.9%, Y방향 1.7%를 나타내었다. 기존 1997년 측정결과와 비교하여 1, 2차 고유진동수는 유사하여 구조강성 변화가 거의 없고, 일본 목조탑들과 비교하여 팔상전 높이가 작지만 다른 목조탑의 고유진동수, 감쇠정수 등과 비슷한 경향을 보였다. 국내의 민가, 절, 성문 등 전통 목조 건축물들과 비교하여 고유진동수는 작지만 감쇠정수는 약 2%로 비슷한 것을 알 수 있었다.
According to the result of recent foreign study for seismic performance of 5-story wooden pagoda, it is revealed that damage controlled structure is constituted by central pillar and pagoda body with their respective different dynamic characteristics of reducing resonance of the wooden pagoda during occurrence of earthquake. In conjunction with this discovery, an engineering study is required even for examining structural stability and preservation of the 5-story wooden pagoda of Palsangjeon in Beobju Temple. Accordingly, in order to define seismic performance of Palsangjeon in Beobju Temple, ambient vibration testing was performed as a part of this study. Palsangjeon, which is the subject to be measured, was built in 1624, and was dismantled for repair in 1968. As far as its architectural dimension is concerned, it is constituted with the $1^{st}$ story of $5units{\times}5units$ ($11.35m{\times}11.35m$), the $3^{rd}$ story of $3units{\times}3units$, and the $5^{th}$ story of $1unit{\times}1unit$, and the pagoda body height of Palsangjeon is 17.515 m, and the upper pagoda is 4.085 m, and total height is 21.6 m. Internal central pillar is connected from the $1^{st}$ to the $5^{th}$ story, and it is surrounded by 4 outside pillars and walls. According to the result of ambient vibration testing, it was confirmed that the natural frequency of Palsangjeon is 1.22 Hz for X and Y direction, and the parallel mode is displayed at 2.76 Hz and 3.96 Hz simultaneously, and a reverse-phase mode is indicated at 1.49 Hz. Damping factor with human excitation was 1.9% for X direction and 1.7% for Y direction respectively. Comparing with the existing measurement result tested in 1997, the primary and secondary natural frequency were similar and there is no change of structural rigidity, and comparing with wooden pagodas of Japan, the height of Palsangjeon is smaller, however, its natural frequency, damping factor, and so forth had similar trend with those of the Japanese wooden pagodas. Comparing with the domestic traditional wooden structures such as private house, temple, castle gate, et cetera, it was confirmed that natural frequency was smaller, however, damping factor was similar with the value of around 2%.