模数式桥梁伸缩缝疲劳寿命分析与结构优化

为提高伸缩缝结构的强度和疲劳寿命，提出了一种考虑移动车轮荷载的伸缩缝结构动力响应计算方法，该方法同时考虑了车轮的竖向与水平冲击荷载，这些冲击荷载作用在内力影响线分析得到的最不利作用点上。在动力分析基础上，采用包含有效缺口应力、雨流计数和线性累计损伤理论的结构疲劳寿命分析方法，评估了模数式伸缩缝的疲劳寿命。针对伸缩缝结构强度与疲劳寿命的不足，依次提出了4种结构优化方法：①优化焊趾结构，减小应力集中。②增设单中梁支撑肋板，提高局部抗弯刚度。③增设双中梁支撑肋板，均匀提高抗弯刚度。④增设带横向连接的双中梁支撑肋板，同时提高局部抗弯和抗扭刚度。研究结果表明：中梁与横梁的连接焊缝和中梁跨中是典型的双缝模数式伸缩缝的易损位置。中梁与横梁的连接焊缝上的最大Mises应力超过了Q345级钢材的屈服应力，疲劳寿命远小于中国桥梁规范要求的200万次。优化焊趾结构无法满足强度要求；增设单中梁或双中梁支撑肋板能够能使结构满足强度要求，但无法达到规范要求的疲劳寿命；增设带横向连接的双中梁支撑肋板，可以达到强度和疲劳寿命要求。

Fatigue Life Analysis and Structural Optimization of Modular Bridge Expansion Joint

To improve the strength and fatigue life of Modular bridge expansion joints(MBEJ),a computational method is presented for the dynamic response of the structure under the moving wheel loads,in which both the horizontal and vertical impact loads are considered.These impact loads are applied on the most adverse positions from the analysis of the influence line of the internal forces.Based on the dynamic analysis,the analytical method for the fatigue analysis is proposed including the effective notch stress,rain flow counting,and linear cumulative damage theory.Subsequently,the fatigue life of the MBEJ is calculated.In view of the deficiency of the strength and fatigue life of the expansion joint structure,four structural optimization methods are put forward step by step:①optimizing the weld structure to decrease the stress concentration;②adding a single-rib reinforcement for the center beam to improve the local bending stiffness;③adding a double-rib reinforcement for the center beam to evenly improve the local bending stiffness;and④adding a double-rib reinforcement with transverse connections for the center beam to improve both the bending and torsion stiffness.The analyses of practical examples show that the welded connection between the center and cross beams,and the mid-span of the center beam are vulnerable positions in the typical double-span modular bridge expansion joint.The maximum Mises stress at the welded connection between the center and cross beams exceeds the yield stress of steel Q345,and the fatigue life is considerably less than the 2million required in the Chinese bridge codes.The optimization of weld structure cannot satisfy the strength requirement.The single-and double-rib reinforcement for the center beam can contribute to the MBEJ satisfying the strength requirements;however,it cannot achieve the fatigue life required by the specification.The double-rib reinforcement with transverse connections can satisfy both the strength and fatigue life requirements.