Research On Generation Mechanism Of Impact Coefficient And Reliability Assessment Of Highway Bridges In Oversize Transport

The research on dynamic response and reliability of highway bridges is the foundation of bridge safety assessment in oversize transport.In this paper, the research on dynamic response of bridge structures under the action of heavy vehicle with low speed fill in the blank in the research of vehicle-bridge coupled vibration and break the conventional understanding from the past. Based on the study of the impact coefficient of bridge structures in oversize transport, the safety assessment of bridge structure become more accurate.The main work and research results of the paper are as follows:(1) The vibration differential equations of the monomer vehicle with super multi degree of freedom and the joint vehicle were established utilizing the generalized virtual work principle.The improved pseudo static method,namely β-θ method,was introduced to solve the vibration equations of the vehicle and then the solution of vehicle-bridge coupling vibration was realized based on multi point restart function of ANSYS using the APDL language.(2) A real-time monitoring of bridge dynamic responses and numerical simulation based on vehicle-bridge coupled vibration was carried out to study the displacement, velocity, acceleration of the bridge, taking the over-size transportation of absorption tower as the background. The calculation results are in good agreement with the measured results. The results show that vehicle-bridge coupling vibration effect is obvious and the impact factor is large when the absorption tower crosses the bridge with low speed. For the middle and smaller span bridges, the effect of speed on the impact coefficient is smaller than that of road roughness. And treatment of deck is an effective method to reduce vehicle impact effect. Combined with orthogonal test, support vector regression machine significantly improves the efficiency of parameter inversion and the precision of the prediction model can satisfy the need of engineering.(3) Through the analysis of the relationship between IRI and vehicle speed, there can be seen that IRI grows with the increasement of vehicle speed and the IRI reaches the peak when the vehicle speed reaches 20km/h and IRI decreases with the further increasement of vehicle speed.The IRI increases when the road surface conditions deteriorate.Based on the Wiener-Khintchine theorem, the relationship between IRI and PSD can be theoretically established.And using the trigonometric series method, the reconstruction formula of one-dimensional and two-dimensional road surface can be derived which are applicable to the oversize transport with low speed.(4) The main influence factors of impact coefficient of highway bridges in oversize transport are recognized based on the orthogonal test. With the vehicle-bridge coupling force as the breakthrough point, the production mechanism and the action mode of the main influence factors were analyzed.The concrete elastic modulus and Rayleigh damping constant are the internal causes which mainly influence the dynamic properties of bridge structures. The deck roughness grade and vehicle speed are external causes which mainly influence the vehicle-bridge coupling force.(5) The influence of distribution form of deck roughness on bridge impact coefficient can not be ignored.For definite bridge structure, different sequences of deck roughness can be obtained according to IRI through reconstruction,which can be considered to obey normal distribution. Through the value analysis of relations between the standard value of impact coefficient and IRI, the two can be fitted to a linear relationship.(6) For definite bridge structure, different international roughness index corresponds to different random variable of impact coefficient, which then influences the reliability of bridge structure. The bridge reliability will be decreased considering the impact coefficient in oversize transport.The reliability index of bridge structure gradually becomes smaller as the IRI increases, but the degree of influence is different for bending reliability and shear reliability.(7) The practical safety assessment method and flow chart were proposed for highway bridges in oversize transport.Different processes and steps can be adopted to evaluate the reliability of bridge structures in different stages of assessment and for different requirements and such suggestions as structure reinforcement,vehicle layout optimization can also be proposed.