大跨径梁拱组合刚构桥下弦拱梁悬浇施工力学行为分析

Cantilever Casting Construction Mechanical Behavior of Lower Chord Arch Beam of Long-Span Beam-Arch Composite Rigid Frame Bridge

以重庆市快速路二横线西段项目礼嘉嘉陵江特大桥下弦拱梁为研究对象,基于MIDAS⁃FEA软件建立有限元分析模型,建立了4种计算工况,对比分析了有无支撑体系时下弦拱梁的力学状态;在墩拱结合部位、拱梁腹板、支撑体系等关键部位布设应力、应变和变形监测元件,掌握了应力、应变随施工过程变化的规律。研究结果表明:在不采取支撑体系的情况下,墩拱结合部位轴向主拉应力达2.8 MPa,超出C60混凝土抗拉强度设计值(1.96 MPa)的43%,存在拉裂风险;在采取支撑体系主动顶升后,轴向拉应力由1.18 MPa降低至0.26 MPa,主动顶升对拱梁受力状态改善较为显著;悬臂浇筑2#节段时,拱梁塑性区较无支撑体系时有大范围减小。监测数据表明:顶升过程中支撑体系(钢管、托架)应力和位移均随着顶升力呈线性变化规律;顶升完成后钢管轴向应力约为98 MPa,托架剪应力约为89 MPa,托架最大沉降量约6 mm;在挂篮堆载预压阶段,支撑体系应力与位移增长幅度远小于拱梁根部和腹板拉应力,预压阶段荷载主要由下弦拱梁自身承担。

Based on MIDAS-FEA software,a finite element analysis model was established for the lower chord arch beam of Lijia Jialing River Bridge in the west section of the second horizontal line of Chongqing expressway.Four calculation conditions were established to compare and analyze the mechanical state of the lower chord arch beam with or without a support system.Stress,strain and deformation monitoring elements were installed in key parts such as pier arch joints,arch beam webs and support systems to master the law of stress and strain changing with the construction process.The research results show that,without the support system,the axial principal tensile stress of the pier arch joints reaches 2.8 MPa,which is about 43%higher than the designed tensile strength of C60 concrete(1.96 MPa),and there is a risk of tensile cracking.After the active jacking of the support system is adopted,the axial tensile stress decreases from 1.18 MPa to 0.26 MPa.The active jacking significantly improves the stress state of the arch beam.When cantilever casting 2#segment,the plastic zone of the arch beam is greatly reduced compared with that without support system.The monitoring data show that the stress and displacement of the supporting system(steel tube and bracket)change linearly with the lifting force during jacking.After jacking,the axial stress of the steel tube is about 98 MPa,the shear stress of the bracket is about 89 MPa,and the maximum settlement of the bracket is about 6 mm.In the preloading stage of bracket surcharge,the increase amplitude of stress and displacement of the support system is far less than the tensile stress of the root and web of the arch beam,and the load in the preloading stage is mainly borne by the lower chord arch beam itself.