基于模态挠度的斜交桥静载试验数值方法

Numerical Method of Static Load Test for Skew Bridge Based on Modal Deflection

为了探讨不中断交通情况下进行桥梁静载试验的可行性,以斜交简支空心板桥龙山桥为研究对象,研究基于模态挠度的静载试验应用于斜交板桥承载力评估的计算精度问题。首先利用环境激励获得桥梁在运营状态下的模态参数,再采用附加质量法对桥梁模态振型进行质量归一化,计算桥梁的位移柔度矩阵,最后利用位移柔度矩阵和等效荷载分配的方法计算桥梁的模态挠度。建立龙山桥的有限元梁格计算模型,根据荷载试验规程设计了静载试验中载和偏载2个加载工况,利用龙山桥的前5阶模态参数计算位移柔度矩阵,预测桥梁在2个加载工况下各控制截面的模态挠度,并与有限元模型计算挠度和实测挠度相对比。结果表明:中载工况下模态挠度与计算挠度相比,相对误差均小于5%,控制截面最大计算相对误差为3.55%;偏载工况下模态挠度与计算挠度相比,相对误差均小于6%,控制截面最大相对误差为5.15%,能够满足工程精度要求;模态挠度能够有效代替桥梁静载试验的实测静载挠度,利用模态挠度评估桥梁承载力具有较强的有效性和可行性。

In order to explore the feasibility of carrying out bridge static load test under traffic excitation, taking the Longshan bridge,a skew simply supported hollow slab bridge, as the study object, the calculation accuracy of applying static load test based on modal deflection method to the bearing capacity evaluation of skew slab bridge was studied. Firstly, the modal parameters of the bridge under the operation state were obtained by using environmental excitation. Then the modal shapes of the bridge were normalized by using the additional mass method, and the displacement compliance matrix of the bridge was calculated. Finally the modal deflection of the bridge was calculated by using the displacement compliance matrix and the equivalent load distribution method. The finite element beam lattice calculation model of Longshan bridge was established. According to the load test method, two loading conditions of static load test and eccentric load were designed. The displacement flexibility matrix was calculated by using the first fifth modal parameters of Longshan bridge. The modal deflections of each control section of the bridge under the two loading conditions were predicted, and compared with the calculated deflection of the finite element model and measured deflection. The results show that, compared with the calculated deflection, the error of the medium load condition is less than 5% and the maximum calculation error of the control section is 3.55%. Compared with the calculated deflection, the error of the partial load condition is less than 6%, and the maximum error of the control section is 5.15%, which can meet the engineering precision requirements. The modal deflection can effectively replace the measured static deflection of bridge static load test,and it is effective and feasible to use modal deflection to evaluate bridge bearing capacity.