Study On Dynamic Performance Of New Steel-Concrete Hybrid Continuous Girder Bridge

The application of the steel box girder in the mid-span of the hybrid girder bridge can decrease the height of mid-span girder segment effectively,leading to the lower quantity of the approach span on both sides of the river.This kind of bridge will have a good application prospect for plains and lake districts in Jiangsu and Zhejiang Province in the future.Traditional hybrid girder bridges usually adopt the integral concrete box girder with the integral steel box girder.However,construction quality control is difficult due to the welding operation in a closed space.Meanwhile,it is inconvenient to hoist because the steel box girder is integral.These problems can be solved by replacing the original integral steel box girder with the separated steel box girder.But the separated steel box girder may lead to the uneven distribution of its rigidity and quality,a further study of the dynamic performance of the hybrid girder bridge should be conducted.This thesis will mainly carry out the following studies based on Jinxi Bridge and Changqiao Bridge in Changxing Country:(1)The ABAQUS finite element vehicle-bridge coupling models of single-box concrete-integral steel box girder and single-box concrete-separated steel box are established respectively,which can compare the dynamic response of the steel-concrete hybrid continuous girder bridge under two connection modes by the method of setting different speeds and lanes.(2)Through the field load test,two measurement methods of leveling and photogrammetry have been used to verify each other.On this basis,the long-term monitoring research based on the bridge deflection of the photographic site is carried out.The results indicate that:(1)Through the calculation results of finite element model,the self-vibration frequency of the first-order vibration type in Jinxi Bridge is 2.6273 Hz and the self-vibration frequency of the first-order vibration type in Changqiao Bridge is 1.9201 Hz.The result of impact coefficient of Jinxi Bridge is 0.15498 according to this calculation method of standard impact coefficient,and the impact coefficient of Changqiao Bridge is 0.09956.(2)The low speed(less than 72 km/h)has little effect on the vertical displacement because the hybrid girder bridges are connected in two ways,indicating that the low speed has no significant effect on the impact effect of the hybrid girder bridge and it will not cause resonance.When the vehicle speed is more than 126 km/h,the influence of the vehicle speed on the dynamic displacement is significant.In the field measurement of Jinxi Bridge,the vertical displacement of the side steel box and the mid steel box have reached the maximum under the speed of 40 km/h,but the difference of dynamic displacement is little when the vehicles is driving under the low speed of 20 km/h to 50 km/h.(3)When the vehicle is driving at different speeds,the acceleration of Jinxi Bridge has reached the maximum under the vehicle speed of 108 km/h,but the acceleration of Changqiao Bridge has reached the maximum under the vehicle speed of 90 km/h.The finite element numerical calculation and field measurement data have demonstrated that the structural dynamic properties of single-box concrete to multi-box steel hybrid girder bridge can meet the design specifications.It is necessary to strengthen long-term monitoring for deep understanding of the long-term fatigue performance of the structure because the acceleration amplitude is larger.