Research On Impact Factor Distribution Characteristics Of Girder Bridges And Its Application In Damage Localization

Vehicle load is an important load by a bridge during its service,and will produce impact effect when running on the bridge deck.This impact effect is generally measured by impact factor.The reasonable value of impact coefficient not only affects the safety and economy of bridge during construction,but also provides the basis for the safety inspection and evaluation of bridge during service.Most current impact factor studies consider only the mid-span position or a very few positions.However,the maximum impact factor is not necessarily in the mid-span of the bridge.It would be more realistic to consider the distribution of the impact factor along the whole bridge.For these reasons,this paper studies the distribution rule of impact factors of simply supported beam and continuous beam under different influencing factors,and proposes a damage localization index based on the deflection impact factor.The effectiveness of the proposed index are verified by numerical and experimental example.The main work and conclusions are as follows:(1)Based on the theory of vehicle-bridge coupled vibration,the finite element model(FEM)of the spring-mass with uniform moving speed is established,and its solving strategy is briefly described.The simulation of road pavement roughness is discussed.(2)Firstly,the analytical expressions for the deflection and strain impact factors of simply supported beams at different locations are derived theoretically.The results prove that the maximum value of impact factor is generally not at the mid-span position;Secondly,numerical examples are used to calculate the deflection and strain impact factors at different positions of the simply supported beam and continuous beam,and the distribution of deflection and strain impact fact along the beam length is investigated considering the influence of vehicle speed,bridge fundamental frequency and road surface roughness.Finally a moving load test model is established in the laboratory to study the variation law of deflection and strain impact factor distribution.Theoretical derivations,numerical simulations and laboratory experiments indicate that,the deflection impact factor distributes more uniformly along the beam,and the strain impact factor is folded along the beam.With the increasing of the vehicle speed and road roughness,the decreasing of the fundamental frequency,the mean and variance of the impact factor variation along the beam increases continuously.(3)Based on the actual situation that the impact factor varies along the full bridge,a damage localization index based on deflection impact factor is proposed for girder bridge.The effects of the number of measurement points,damage location,vehicle speed,road roughness and damage severity on the proposed index are investigated by numeral examples.Besides,the effectiveness of proposed index is verified using single-damage and double-damage beam tests.The results indicate that the increment of deflection impact factor tends to increase and then decrease along the beam,the peak value corresponds to the measurement point near damage element.The effect of the number of measurement points,damage location and damage degree on the effectiveness of the proposed index is not significant,while the vehicle speed has a visible influence on the effectiveness of the proposed index.