Lin C.M.CHUNG-CHE CHOUChang Y.W.Jhuang S.J.Lee Z.K.Wu C.L.Chao S.H.Huang J.Y.Mosqueda G.2026-03-122026-03-122024https://www.scopus.com/record/display.uri?eid=2-s2.0-105027854950&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/736257A large earthquake with magnitude MW 6.9 occurred in the Chihshang Township of eastern Taiwan on September 18, 2022, one day after an MW 6.5 foreshock. A large number of small shocks occurred between and after the two major earthquake events. The strong ground motion of the Chihshang earthquake sequence in combination with shallow sources induced a series of ground ruptures, causing one fatality, 171 injuries, two collapsed buildings, two collapsed bridges, and hundreds of partially damaged buildings and bridges across or along the faults around the near-source region of the Longitudinal Valley in eastern Taiwan. After the earthquake, the National Center for Research on Earthquake Engineering (NCREE) immediately analyzed the ground motion data, evaluated the potential losses, and organized reconnaissance teams. On the morning of September 19, several teams headed for eastern Taiwan to survey the damage to buildings, bridges, nonstructural systems, and geotechnical infrastructure. This paper presents the reconnaissance findings on the ground motion characteristics and the damages of old reinforced concrete (RC) buildings and bridges. A near-fault velocity pulse with a maximum value of 132 cm/sec was observed along the fault, destructively impacting the damaged structures. The maximum spectral acceleration of the observed strong motions was about 2.5 times the design response spectra of the 2022 Taiwan seismic code at a short-to-medium period range. The large spectral accelerations caused the shear failure of weak first-story columns in low-rise old RC buildings and the shear failure and toppling of old RC bridge columns with insufficient anchorage of longitudinal reinforcement at the column base, as seen in the Luntian and Gaoliao bridges. A shear key on the cap beam was found effective in preventing a superstructure from falling as seen in the Yuli bridge.falseconference paper2-s2.0-105027854950