Microtremor Measurement and Damage Investigation of Historical Timber–masonry Composite Tiered Temples in Nepal

ABSTRACT

Microtremor measurements were performed on four historical timber–masonry composite pagodas (called tiered temples) in Kathmandu Valley. Several measurements were performed between 2009 and 2017. The Gorkha earthquake occurred on April 25, 2015, causing severe damage (collapse, inclination, uplifting of the top tier, and damage to masonry walls) to the temples being monitored. The earthquake damage was assessed, and the results were compared with the structures’ fundamental vibration characteristics, determined using microtremor measurements. The temples, which were surveyed before and after the earthquake, exhibited an increase in the natural period of vibration and a stiffness loss of approximately 10%. For the four temples with multiple tiers investigated, linear idealisation of the natural period of vibration with the height of the structure is proposed. By including microtremor measurements conducted in previous studies, the natural periods of the tiered temples in Nepal were found to be distributed between 0.3 and 0.7 s.

KEYWORDS:

• Gorkha earthquake
• Kathmandu Valley
• timber–brick composite
• traditional structure

Acknowledgments

This research was supported by JSPS KAKENHI, Grant Number 16H01825 (T. Hanazato, K. Fujita et. al). The authors would like to express their sincere gratitude to Director Amod Dixit (NSET), Dr. Narsingh Rajbhandari (Tribhuvan University), Mr. Suman Rajbhandari, Mr. Kuber Bogati (NSET), Prof. Hiroshi Imai, Prof. Syam Kawan, Prof. Yohei Endo, Prof. Kentaro Yamaguchi, Prof. Hidetoshi Saito, Prof. Yasufumi Uekita, Prof. Shoichi Ando, Prof. Nobuko Inaba, Prof. Osamu Goto, Prof. Netra Prakash Bhandary, Prof. Naohiro Kobayashi. The authors extend special thanks to Dr. Shiro Watanabe, Prof. Ayako Maeshima, Prof. Masahiro Watabe, Mr. Hiroki Nakashima, Mr. Daichi Higashi, Mr. Takuya Okamoto, Mr. Kohta Kawashima, and Mr. Yusuke Hosaka and the members of the Fujita Laboratory of the University of Tokyo.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

¹ Measurement of the Nyatapola temple by the authors in 2016 indicated that the natural period was 0.629 s (1.59 Hz) in both directions. The difference observed in the two measurements could be due to a progressive decrease in stiffness or to differences in the measurement and calculation methods.

Additional information

Funding

This work was supported by the Japan Society for the Promotion of Science [16H01825].