| The"5.12"Wenchuan Earthquake has caused damage to 6,140 bridges. Among the first tested 1,657 bridges, there are 80% beam-bridges, such as Miaoziping bridge and Baihua bridge in the Dujiangyan-wenchuan Highway, according to the data released from Sichuan Provincial Communication Department. For these beam-bridges, the middle-bridge-plate may have fallen, and some may have suffered base-deformation and overthrow. As a result, the traffic was broken off and the disaster relief workers and materials were held up in the land routes and this has caused more severe effect significantly. Therefore, the study of beam-bridge seismic behavior under the action of macroseism was to be focused.According to the theoretical analysis and the numerical simulation, the highway-beam-bridges in the meizoseismal area in Wenchuan Earthquake were studied. There are several aspects being studied—failure mechanism, security evaluation and anti-seismic-protection technology. The main results obtained are as follows:1) Based on the data material and site investigation, the beam-bridge damage types were summarized, including support failure, foundation failure and abutment-piece failure. For the support part, the main damage forms include shear failure and shift destruction. For the foundation part, they are bend destruction, shear failure and bent-shear. And for the abutment-piece, the damage forms include: subsidence, craze, rotation and sliding overthrown destruction, etc.2) Assume the pier is ductile and plastic hinge would be produced in the earthquake. For the double column type, the displacement calculation formula for the pier-top damage was deduced, according to the Diagram Multiplication of the structural mechanics. Besides, the earthquake response spectrum is studied. The results show that the pier was affected obviously along the bridge and the bottom stress is the greatest. Based on the Mononobe-Okabe formula, the side-wall active soil pressure calculation formula was deduced when the back-abutment piece being limited. According to the dynamic winkler foundation-beam model, the single-pile horizontal differential equation was solved and verified with one sample.3) For one box girder bridge, the earthquake response spectrum is studied and the result shows that the bending moment and the shearing force are relative higher or change more obviously at the supporting seat, midspan and the cross-section of the pier bottom. They would be the most frail parts. The earthquake has affected the top and bottom of the abutment piece obviously along the bridge, resulting with greater displacement.4) From the aspects of the structural materials, foundation conditions, basis types, seismic forces, the abutment piece filled soil, construction technology and failure mechanism, etc, the security evaluation indices were advanced. For the indices, they are ranked with the different importance according to the degree of membership and the values were modified and confirmed with the Analytic Hierarchy Process(AHP) and expert analysis. Further, the comprehensive evaluation method for the security of the beam-bridge in the earthquake was put forward with the combination of the Fuzzy Mathematical Theory with AHP and verified with the cases in Wenchuan Earthquake. The result is good and fit the actual situation.5) For the beam-bridge, there are two damage phenomena needed to be concerned—abutment piece slippage toward the middle-river and overthrow-slip. Aim to these phenomena, two technologies were presented—Counter-drive beam and anti-seismic reinforce block, and the corresponding methods of calculation, design and construction were raised. |
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