Study On Damage Symptoms Of Cable-stayed Bridge Model In Laboratory

At present,the damage identification of cable-stayed bridges is mostly based on finite element simulation.There are certain differences between the simulation model and the solid model,which can not fully simulate the real bridge.The design of the test model meets the requirements of multiple working conditions test,and can simulate various damage and abnormal states of the structure.In the damage identification of cable-stayed bridges using monitoring data,the problem of environmental temperature change is often encountered.The influence of temperature change is generally ignored,which brings some damage identification errors.In this paper,the scale model of the laboratory cable-stayed bridge made under the background of Binzhou Yellow River Highway Bridge is taken as the research object,the damage of the cable and main beam of the laboratory cable-stayed bridge model under the influence of temperature is simulated,he response law of different parts of the bridge caused by various damage is studied,the damage symptoms of the cable and main beam based on the cable force and main beam strain are obtained,and the identification method of the damage of the cable and main beam considering the influence of temperature is proposed.The specific research work is as follows:（1）On the basis of the finite element model,the influence of different temperatures on the initial cable force is analyzed,and the cable force of a single cable and two symmetrical cables at different temperatures is analyzed.The results show that the damage of a single cable causes the adjacent cable force to increase,and the change rate of the cable force is proportional to the temperature.When two cables are damaged at the same time,the change of the cable force can be approximately regarded as the superposition of the damage of two single cables.（2）At different temperatures in the laboratory,the relaxation damage of the cable is carried out,and the damage symptoms of the cable are analyzed.The results are basically consistent with the finite element method,which is that the cable force of adjacent cables increases;When the cable is damaged,the change rate of the cable force of the relevant cable generally increases with the increase of temperature;he strain symptoms of the main girder caused by cable damage are analyzed.The results show that the strain of the main girder near the cable damage increases or decreases,and the change of the strain of the main girder has no obvious law with the change of temperature.（3）The main beam of the laboratory cable-stayed bridge model is set up with a damage condition,and the cable force symptoms and the main beam strain symptoms caused by the main beam damage are analyzed.The test results show that when the main beam is damaged,the main beam strain at the damage location and nearby location changes,and the change rate of the main beam strain is greater than that of the cable force.The main beam strain of the damaged main beam under the influence of temperature is analyzed.The results show that there is no obvious law between the damage of the main beam,the change of temperature and the numerical change of the main beam strain.（4）The damage state of the cable and the main beam and the cable force and the main beam strain in the healthy state are described quantitatively.The cable force and the main beam strain in the damaged state and the healthy state are defined.The damage identification of the cable and the main beam is proposed in two steps;Different initial cable forces were changed to verify the reliability of damage symptoms of cables and girders of cable-stayed bridges in the laboratory.A method is proposed to identify the damage position of the cable and the main beam by using the change rate of the cable force and the absolute value of the strain change rate of the main beam at and near the damage position to exceed the upper limit of the healthy state;Based on the existing damage research data at different temperatures,the relevant cable force change rate and damage degree caused by cable and main beam damage are fitted,and the linear damage function "S=kx" is obtained.The identification results show that the theoretical value of damage degree calculated by the damage function has little error with the actual value of the test.