基于场地效应及场地位移的高原大桥落梁破坏研究

Study on Failure Mechanism of Girder Falling of Gaoyuan Bridge Based on Effect and Displacement of Site

地震造成简支梁桥主梁移位甚至落梁破坏的原因不仅与桥梁自身结构有关,还与场地效应和场地位移密切相关。本文以"5·12"汶川地震中发生落梁破坏的高原大桥为研究对象,通过数值模拟软件ABAQUS建立桥梁-场地的整体有限元模型,研究场地效应和场地位移对简支梁桥发生落梁破坏的影响,并结合实际震害特征、地质力学模型试验结果分析高原大桥落梁破坏机理。研究结果表明:简支梁桥桥墩与主梁的相对滑移量受局部场地条件的影响较大,近河岸处的墩-梁滑移量比远河岸处的大;场地软弱程度对桥梁结构的地震反应有明显影响,场地软弱程度越大(即基岩弹性模量越小),墩-梁滑移量呈波动性增加;随场地位移的增加,跨径变化和墩-梁滑移量都逐渐增大;均质基岩条件下的简支梁桥各跨跨径变化值相近,墩-梁滑移量小,各桥墩协调变形能力较好;场地位移方向上各跨跨径变化值逐渐减小,即跨径变化值由小到大依次排列为一跨、二跨、三跨和四跨;高原大桥二跨处出现纵向落梁破坏的主要原因是大桥与宏观震中牛圈沟、龙门山中央主破裂带相距太近,基岩处存在较软的页岩,不利的局部场地条件,板式橡胶支座稳定性较差,且大桥设置了横向挡块。

The reasons of main beam displacement and girder falling of a simply supported beam bridge are related to bridge structure as well as theeffect and displacement of site.In order to study the influence of effect and displacement of site in girder falling and to find the failure mechanism of Gaoyuan bridge,which was a simply supported beam bridge and had girder falling in ＂5·12＂ Wenchuan earthquake,a finite element model ABAQUS was employed to simulate the process.The results showed that the relative slipping between pier and main beam was greatly influenced by the local site condition and the slipping distance near river bank was larger than that far away;The weak degree of filed had an obvious influence on the seismic response of bridge,and the slipping distance was enhanced while the site became weaker.The span change and slipping distance increased with the increase of site displacement.When the base rock was identical,the span change of bridge and slipping distance was small and the ability of adapting toand the deforma- tion of each pier was better.The span change slowly decreased in direction of site displacement,and increased from first span to fourth span.The main reasons for longitudinal failure mechanism of girder falling of Gaoyuan bridge at second span was that the bridge was close to the epicenter and Longmen mountain central main fracture zone,where there exist the soft shale in the bedrock,the unfavor- able local site conditions,the poor stability of laminated rubber bearing,and the use of lateral block in bridge.