Based On Damage Tolerance Theory Evaluation Of Remaining Life Of Emergency Bridge

The steel truss emergency bridge uses welded integral nodes.The crack defects at the nodes due to the welding process and other reasons will continue to expand under the repeated action of the vehicle moving load.The nodes are prone to fatigue problems,and fatigue damage is the main cause of the steel truss emergency bridge.One of the forms of destruction.It is of great significance for the safety assessment of the emergency bridge to study the initial crack propagation law at the node of the emergency bridge and the remaining life of the structure.In this paper,the damage tolerance method is used to study the crack propagation rule and remaining life of the steel truss emergency bridge node.The specific research contents are as follows:(1)Based on the basic content of the damage tolerance theory,the crack is simplified into a semi-elliptical crack;at the same time,according to the structural characteristics and stress conditions of the emergency bridge,the J integral method is used to calculate the stress intensity factor based on the principles of accuracy,efficiency,and ease of implementation.Choose MTS criterion to calculate the criterion of crack propagation direction,and choose Paris model to calculate the remaining life.(2)According to the load spectrum of the highway bridge and the actual loading situation of the emergency bridge,the method of compiling the load spectrum of the emergency bridge is proposed;the overall rod system model of the 81-meter long-span emergency bridge is established using ANSYS software,and the program is written using APDL to achieve the load spectrum The dynamic response of the node boundary is calculated by the application of the;finally,the node stress amplitude and frequency spectrum are obtained by the MTALAB program based on the rain flow counting method,and the equivalent stress amplitude of the node boundary is obtained by the Miner equivalent stress method.(3)Establish the ANSYS solid model of the typical nodes of the emergency bridge,and use ANSYS sub-model technology and FRANC3 D crack propagation and fatigue life simulation software to simulate the cracks of the bridge bridge connection node and the bridge mid-span node.The remaining life of two typical nodes of the bridge.At the same time,according to the results of FRANC3 D crack propagation analysis,a regression analysis is performed to obtain the calculation formula of the remaining life of the emergency bridge under different depth cracks.(4)The effect of crack shape ratio on the stress intensity factor and remaining life of the crack is studied,which provides a scientific basis for the formulation and safety assessment of the emergency bridge maintenance cycle.