Study On Impact Effects And Overall Impact Factors Of Continuous Concrete Curved Box-Girder Bridges Under Moving Vehicle Load

Concrete curved girder bridge has been widely applied in highway viaducts, approach of long span bridges and large interchanges. However, the study on its impact factor is rare and its measure method has not been specified home and abroad, questions still remain as to the application of straight bridge’s impact factor calculation formula into that of curved bridge. Herein, the widespread concrete curved box-girder bridge is taken in this thesis to study its natural vibration characteristics, impact effect and the calculation method of overall impact factor. The main tasks and conclusions are as follows:1. Based on the design range of each parameter, a finite element model of three-span continuous benchmark bridge is built as the benchmark model. With the variation of parameters like span ratio, span-width ratio, span-depth ratio, curvature radius, diaphragm thickness and so forth, their influence law of characteristic frequency on three-span concrete curved box-girder bridge are analyzed. The results indicate that:span ratio and span-depth ratio have great influence on vertical bending frequency whereas others could be neglected; span ratio, span-width ratio and span-depth ratio have great influence on torsional natural frequency whereas others’ effects are small.2. Pertaining to the 32 in-service bridges collected, their dynamic characteristic analyses are conducted based upon their design data, herein their modal analysis results could be processed with the method of multiple regression analysis. Thus, the simplified formula of vertical bending natural frequency is proposed based on that of straight bridge in current Highway Bridge Design Specification.3. In light of triaxial three-dimensional vehicle model with 12 degrees of freedom, bridge’s simplified model as multi-degree of freedom system, and consideration of road roughness and its effect of derivative term, the analysis program of vehicle-bridge coupling is compiled by APDL language in ANSYS. Factors like bridge deck roughness, radius of curvature, structure’s damping, tyres’stiffness and damping, vehicle’s driving eccentric and so forth are taken into account, then applying the compiled program to parameter analysis. The results show that:road roughness is the main factor affecting impact effect, and with the deterioration of bridge deck, the impact effect of vehicle on bridge will rise significantly, whereas the influences of other parameters are relatively small.4. Through the analysis of the overall impact factor distribution law, it is recommended that:overall impact factor of the superstructure is controlled by longitudinal stress impact factor(which is taken as the superstructure’s representative value) in the center of the bottom-slab across the middle span; that of substructure is measured by the pier column axial force(which is taken as the substructure’s representative value); the study indicates that:neither of them could be covered in the same formula. With the vehicle-bridge coupling analysis results above, its upper bound envelope curve is presented to simplify the calculation formula of overall impact factor under different levels of bridge deck roughness.