Numerical analysis of mechanical anchors in hybrid bonded FRP strengthening system

To address the issues of unreasonable torque control and unclear failure modes in concrete anchorage systems with chemical anchors in hybrid bonded Fiber-Reinforced Polymer (FRP) strengthening system, this study focuses on the numerical simulation analysis of bolt-concrete anchorage systems. The mechanical characteristics and concrete failure modes under different anchorage depths, load levels and torque limits are emphatically investigated. Using the finite element numerical simulation method, a three-dimensional model of the bolt-concrete anchorage system is established, in which concrete is modelled with 8-node hexahedral solid elements and bolts with 6-node pentahedral solid elements. A full-bond interface assumption with common nodes is adopted between the two components. Multiple groups of numerical simulations are carried out by varying the parameters of anchorage depth and tightening torque, and the bolt stress, concrete crack propagation and failure patterns are analyzed. The results show that anchorage depth is the dominant factor controlling the ultimate bearing capacity of the anchorage system, and different anchorage depths correspond to different stress attenuation paths. At a medium embedment depth of 50 mm, a mixed failure mode consisting of upper concrete cone failure and lower interfacial bond failure is observed. Based on the simulation results, the recommended limit for bolt tightening torque is determined to be 13 N·m, which can effectively prevent damage to the concrete substrate caused by excessive pre-tightening force. The findings can provide a theoretical reference for the engineering design and torque control of concrete anchorage systems with chemical anchors.