Research On Eccentric Load Coefficient And Damage Identification Of Irregular-shaped Girder Bridge

With the rapid growth of China's economy and the process of urbanization,urban traffic demand continues to increase.New challenges were put forward to urban transport.In order to adapt to the continuous growth of urban traffic flow and limitations of terrain space,irregular-shaped bridge as the main line and ramp connection structure has been continuously applied to solve the heavy urban traffic problems.However,the structural spatial stress of the irregular-shaped bridge was complicated,and the existing design specification and calculation theory have not made detailed requirements for the bridge.Therefore,the design theory needs to be improved.Furthermore,the bridge structure was prone to damage under heavy traffic,which brings security risks to the staff and the travel of vehicles.It is very important to improve the design method of irregular-shaped bridge structure and identify the damage of bridge structure timely and effectively,which is of great significance to ensure the safe operation of irregular-shaped bridge.This study was supported by the project of Jilin Provincial Communications Department,two typical irregular-shaped bridges were treated as the objects for investigation.Corresponding theoretical analysis were conducted based on finite element simulation.Moreover,damage location and severity identification methods were proposed for irregular-shaped bridge.The detailed researches are listed as follows:1.The calculation methods of eccentric load coefficient of existing straight bridge were summarized.And the advantages and disadvantages of each method were compared and analyzed.The applicability of finite element numerical simulation method and response surface method in the calculation and analysis of eccentric load coefficient of irregular-shaped bridge was expounded,which provides the theoretical basis for the follow studies.2.The influence of design parameters on the eccentric load coefficient was analyzed.Box-Behnken response surface method was used to calculate and analyze the quantitative relationship between eccentric load factor and design variables of irregular-shaped bridge.With the span,box beam width and height,ramp radius,cross beam rigidity as response input value,eccentric load coefficient as response output value,the analysis scheme for influence of design parameters on eccentric load coefficient was determined.Numerical simulation was carried out on the irregular-shaped bridge with different parameters,the stress and deflection at control points were extracted to calculate the eccentric load coefficient of typical irregular-shaped bridge,and the effects of various design parameters on eccentric load coefficient were obtained.Through the establishment of polynomial function relationship between design variables and eccentric load coefficient,it lays the foundation for the calculation of the partial load factor in the design of the irregular-shaped bridge.3.Based on the modal curvature difference and the fuzzy inference theory,damage identification method of bifurcation section of irregular-shaped bridge was proposed.Modal curvature was calculated by quadratic difference through modal shape data.The damage position was identified by the modal curvature difference before and after damage.On the basis of this,modal curvatures at damage location nodes were used to identify the damage degree of bridge and fuzzy rule base was constructed by the membership function.The damage degree was identified by matching the test sample with the fuzzy rule base.The results of numerical simulation for damage identification revealed that the damage identification method based on modal curvature difference and fuzzy inference can accurately identify the existing damage of irregular-shaped bridge,which presents favorable accuracy.