Dynamic Elastic-plastic Analysis On Continuous Curved Bridges Under Spatial Seismic Excitation

Prosperous development of highway and urban transportation has significantlyincreased the demands for curved beam bridges in mountainous high-grademotorways and urban viaducts. However, with the bending-torsional coupling effect,curved bridges shows much complicated mechanism compared to straight bridgesunder same loading conditions. Besides in actual cases, typical curved bridges such asBaihua Bridge, Huilan overpass, etc. showed severe damages during WenchuanEarthquake. Therefore intensive studies on curved bridge of its seismic reactionprinciples and characters are indispensable. With relatively large span and toughdomestic topographic site conditions, the wave passage effect and the site effect arealso decisive when analyzing the seismic responses of curved bridges. In existingseismic design codes for bridges, detailed rules are not given for the irregular curvedbridges with relatively small radius, while the consideration on the spatial effects aresketchy. In this paper, dynamic response of curved bridges under spatial seismicexcitation has been specifically studied. Main purposes and achievements are listedbelow:1. The elastic/plastic model of the curved continuous bridge has been establishedwith OpenSees. Plastic hinges on beams and piers, nonlinear bearings are preciselysimulated and the entire structure has been numerically verified.2. Target response spectrum is generated considering the actual site conditionregarding the geotechnical report and the fortification criterion. The according randomvibration time-history acceleration seismogram is hereby adopted for the seismicanalysis on the entire bridge with the wave passage effect involved. The result showsthat under the wave passage effect, with the minishing of the apparent wave velocity,the acceleration response on the pier top decreases while the relative displacement onthe pier top and the forming degree of the plastic hinge at the pier bottom increases.The sliding bearings show increased displacement on the tangential direction undersame condition.3. Based on the PEER-NGA earthquake forecast model, another target responsespectrum has been generated together with its according random vibrationtime-history acceleration seismogram. The analysis on the entire bridge under thesame shows that with site condition varying from A to E, all dynamic response indicesare increased.4. Five curved bridges with identical span length and different radius angles (00,300,600,900,1200) are numerically simulated for the seismic analysis under randomvibration time-history acceleration seismogram based on response spectrums definedby Chinese codes. The results show that when considering uniform excitation insingle plane and single direction, curved bridges with a radius angle within600can be analyzed as regular bridges during dynamic studies. And when the uniform excitationcomes from two directions in single plane, curved bridges with a radius angle within300can be analyzed as regular bridges during dynamic studies.