关键词: 桥梁工程；梁拱组合刚构桥；下弦拱梁；主动支顶；数值分析；监控量测

Abstract: 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.

Key words: bridge engineering; beam-arch composite rigid frame bridge; lower chord arch beam; active jacking; numerical analysis; monitoring measurement