Deflection influence line analysis and damage diagnosis method for beam bridges considering sectional cracking

To address the accuracy limitations of influence lines in diagnosing section cracking in existing beam bridges, this study investigates a cracking diagnosis method for concrete beam bridges based on nonlinear crack models. By introducing a stiffness damage function to simulate crack effects and incorporating a nonlinear damage function into the analytical solution of the deflection influence line, an analytical method for deflection influence lines considering section cracking is proposed. A crack damage diagnosis method and loading implementation scheme are developed, and the accuracy of the analytical solution derivation is verified through finite element simulations. A simply supported beam model is established in Analysis System (ANSYS) to simulate the nonlinear damage behavior induced by cracks. Comparative analyses of influence lines are conducted using a constant-stiffness torsional spring model, an open crack model, and a breathing crack model. Results indicate that the breathing-crack model more accurately reflects the nonlinear behavior of cracks and is therefore selected as the optimal model for verifying the accuracy of the analytical deflection influence line solution and diagnostic indicators. Finally, case studies of continuous beams validate the precision of the proposed diagnostic indicators from both the influence line and influence surface perspectives, while an in-situ bridge test confirms the practical applicability of the cracking damage diagnosis method. The results demonstrate that the analytical solution of the deflection influence line, considering section cracking, can accurately describe the impact of cracking on bridge influence lines, and the proposed diagnostic indicators can effectively locate and quantify section cracking damage.