NONUNIFORM SEISMIC MOTION OF LONG-SPAN PIPELINE SUSPENSION BRIDGES

The goal of this investigation was to determine the responses of long-span pipeline suspension bridges to nonuniform seismic motion. To achieve this objective, two existing bridges were analyzed: the 457.2 m Missouri River Pipeline Bridge (MORB) in Plattsmouth, Nebraska, and the 655.3 m Mississippi River Pipeline Bridge (MIRB) in Grand Tower, Illinois. Using ground motion records for the 1940 Imperial Valley and 1971 San Fernando earthquakes, time-history analyses were performed on finite element models of both bridges. The inputs were applied to the bridge supports in the longitudinal direction with three different time lags: 0.0 s/km (uniform motion), 0.5 s/km, and 1.0 s/km. The results indicated that the MORB suspended pipes could yield in earthquakes similar to those used in the analyses. Earthquakes with two to three times the studied intensity could cause the MIRB suspended pipes to yield, and under these conditions, the diagonal cable stays in both bridges could break. The stresses in the diagonal cable stays and the vertical translations of the suspended pipes were the most sensitive bridge responses to nonuniform seismic support motions.