Near-fault vertical ground motion effects on the response of balanced cantilever bridges

Post-tensioned balanced cantilever reinforced concrete (RC) bridges allow the economic spanning of wide spans using fewer columns than in more traditional bridges. More and more post-tensioned balanced cantilever bridges are constructed every year all round the world. The aim of this study was to investigate numerically the effects of near-fault vertical ground motions (VGMs) on the seismic behaviour of segmentally constructed, balanced cantilever RC bridges. Two long bridges constructed in Artvin, Turkey - the three-span Budan Bridge and the two-span Sengan Bridge - were selected for the application. Three-dimensional finite-element models (FEMs) of the bridges were created to obtain their dynamic characteristics such as natural frequencies and mode shapes numerically. The frequencies calculated from the FEMs of the bridges were then verified using experimental frequencies measured from ambient vibration tests. Acceleration records of near-fault earthquakes (1992 Erzincan (M=6.69), 1999 Kocaeli (M= 7.51), 1999 Duzce (M=7.14) and 1989 Loma Prieta (M=6.93)) were selected for the seismic analyses. The seismic behaviours of the verified FEMs of the bridges with two and three spans were determined by considering horizontal, vertical and combined horizontal and vertical components of the earthquakes. It was found that near-fault VGM significantly affects the seismic response of segmentally constructed, balanced cantilever bridges.