利用防屈曲支撑提高钢管混凝土肋拱桥抗震性能研究

Ribbed arch bridges have been widely used and been damaged during recent earthquakes. It is found that the lateral braces have high vulnerabilities. The cracking damage of reinforced concrete braces or the buckling of the steel braces can usually be found. The main purpose of the research is that an innovate methods for improving seismic performance of concrete filled steel tube composite ribbed arch bridges by using buckling restrained braces(BRBs) are carried out, especially for the lateral response. The first mode of the concrete filled steel tube composite ribbed arch bridge is usually determined by the lateral bending response and its collapse mode is that the ribs lateral inclined with large displacements，both mean that the method has the feasibility. The new “K” braces with the BRBs will be developed for the arch bridges and can be installed at the foot of the arch or at the peak of the arch. The design parameters are determined by the stability of the arch bridges, the ultimate bearing capacity and the design strength for the earthquakes. The seismic performance of rib arch bridge and the optimization design parameters of new “K” braces with the BRBs will be researched combined with incremental dynamic analysis technology of the whole bridge model and by using parameter sensitivity analysis. The seismic design methods for the new “K” braces with the BRBs and the connected nodes are given and verified by the fine finite element model of the node, the cyclic test of the “K” braces with the BRBs and the time history analysis of the whole bridges. The research results will give an innovate method for seismic isolation design of concrete filled steel tube composite ribbed arch bridges, as well for the seismic design of the reinforced concrete ribbed arch bridges.

肋拱桥为重要的桥梁结构形式，汶川地震安州大桥等国内外震害表明拱肋之间的横向连接系：横撑或横梁易发生开裂(钢筋混凝土)或屈曲(钢)，是肋拱桥抗震的主要薄弱环节。本项目拟以中承式钢管混凝土肋拱桥为例，在拱肋间设置防屈曲支撑(BRB)，形成耗能减震体系以提升其横向抗震能力。现有研究表明这类桥梁基本振型一般为面外侧弯，且其地震倒塌(动力失稳)也以侧向为主，具备可行性。将具体给出拱脚、拱顶处含BRB的K撑构件形式及连接构造；从稳定性分析、极限承载力和小震弹性设计，提出含BRB的K撑构件满足的技术参数范围；结合全桥模型增量动力分析技术及借鉴参数敏感性分析思想，探讨设置BRB后肋拱桥抗震性能及含BRB的K撑构件优化设计参数；建构含BRB的K撑构件及其连接节点设计方法；利用节点精细有限元分析模型和拟静力试验验证。本项目将为钢管混凝土肋拱桥抗震设计提供新颖的技术思路，对普通钢筋混凝土肋拱桥也可提供很好借鉴。

国内外震害表明，肋拱桥拱肋之间的横向连接系：横撑或横梁易发生开裂(钢筋混凝土)或屈曲(钢)，是肋拱桥抗震的主要薄弱环节。本项目侧重于对工程仍较多采用的拱式体系中数量占优的钢筋混凝土拱桥（包括钢管混凝土和钢拱桥）的震害及特征进行研究。从静力角度看，横撑的存在增强了拱桥面外刚度，提高了其横向稳定性，是设计必需的。然而在地震动作用下,横撑的较大刚度也决定其将承受较大的地震力,因此成为易损部位。由于横撑受损，拱圈横桥向刚度遭到削弱，会导致整座肋拱桥（稳定）承载力降低乃至损毁。以山区桥梁的减隔震为研究目标，将防屈曲支撑引入到结构中，引入减震率和残余位移角两个参数，通过增量动力分析方法，进一步验证防屈曲支撑对双柱式桥墩抗震能力的提升作用。将防屈曲支撑用在山区桥梁减隔震的研究可以为其应用于拱桥的横撑提供很好的研究基础。选取近断层和远断层的地震输入对设置横向支撑的背景拱桥进行三向输入地震波下的时程分析。以地震需求/抗震能力方法，判断各构件的抗震性能及抗震薄弱环节。研究发现：中承式悬吊桥面拱桥的横撑在地震作用下首先发生屈服，在强震作用下成为首先破坏点。与汶川地震一些拱桥破坏的认识是一致的；因此增设拱顶斜撑在一定程度上可以降低拱顶内力，提高拱顶横桥向刚度，对拱顶这一敏感截面起到保护作用，而拱脚增设横撑对拱肋横向刚度贡献不大。