These codes include the AASHTO Guide Specifications for LRFD Seismic Bridge Design (AASHTO 2015), the Canadian Highway Bridge Design Code (CSA 2014), and the Japanese Design Specifications Highway Bridges (PWRI 1998). Accordingly, the small deformation method in conjunction with material nonlinearity is adequate for the seismic analysis of this kind of bridges.ĭespite the numerous related studies, most modern design codes or standards do not provide detailed guidelines for the seismic analysis of cable-stayed bridges under asynchronous excitation. On the other hand, Fleming ( 1979), Fleming and Egeseli ( 1980), and Nazmy and Abdel-Ghaffar ( 1990b) concluded that geometric nonlinearity had a minor effect on the seismic behavior of cable-stayed bridges. The geometric nonlinearity originates from the sag effect of the inclined cables due to their own weight, the nonlinear behavior of bending members, and the geometry changes caused by large displacements. Furthermore, it has been recognized that the overall load–displacement relationship for cable-stayed bridges is nonlinear under design or service loads as reported in Fleming ( 1979) Nazmy and Abdel-Ghaffar ( 1990a). It has been confirmed in several studies that the incoherence effect is less important than the wave passage effect and can be ignored in the seismic analysis of cable-stayed bridges (Abdel-Ghaffar 1991 Priestley et al. As the bridge supports are largely separated in cable-stayed bridges, the lack of the synchronism of the ground motion between the bridge supports is due to the wave passage effect, the incoherence effect, and the local site effect. One of the major discoveries has been that asynchronous excitation should be used as input in the time-history analysis of cable-stayed bridges. 2004).Įxtensive research has been conducted over the last 30 years in order to find ways of protecting cable-stayed bridges from damage caused by earthquakes. 1993) the 3-span cable-stayed Higashi-Kobe Bridge was severely damaged during the 1995 M w 6.9 Kobe earthquake, damage of the connections and wind shoe, as well as buckling of cross beams and pier leg were observed at the west pier of the bridge (Wilson 2003) due to the 1999 M w 7.7 Chi-Chi earthquake, damage to the girder, the cable, the pylon and the pier in the 2-span (199.9 m + 199.9 m) Ji-Ji-Da Bridge occurred (Kosa and Tasaki 2003) and in the same Chi-Chi earthquake, the shear keys, the pylon and one cable were damaged in the 2-span cable-stayed Chi-Lu Bridge (Chang et al. Some notable examples are: the M w 5.9 earthquake that occurred in 1988 in Saguenay, Quebec, Canada, caused a failure of one anchorage plate in the 183-m-long Shipshaw Bridge located about 40 km from the epicenter (Filiatrault et al. Records show that long-span bridges, such as cable-stayed bridges, are vulnerable to earthquakes.
The methodology developed in the study, however, can be applied to any specific bridge to examine the excitation of the deck vertical displacement under the longitudinal seismic ground motion. The proposed C-factor of 0.72 is recommended for use for typical 3-span cable-stayed bridges with a side-to-main span ratio of about 0.48. The two equations and the C-factor are verified through application on two 3-span cable-stayed bridges studied previously by Nazmy and Abdel-Ghaffar. The C-factor in this study is 0.72, which is based on analyzed results from the five selected bridges. The critical wave velocity depends on the total length of the bridge, the fundamental period of the bridge, and the C-factor.
Two equations are proposed in this study to determine a critical seismic wave velocity that would produce the greatest vertical deck displacement. Ten records obtained from earthquakes in US, Japan, and Taiwan are used as input for the seismic excitation in the time-history analysis. The Quincy Bayview Bridge located in Illinois, USA, and four other generic bridges are selected for the study. The purpose of this study is to examine the effects of the seismic wave velocity on vertical displacement of a cable-stayed bridge’s deck under asynchronous excitation.