Research On Dynamic Behavior Of Stress Ribbon & CFST Arch Bridge

These is a new composition structure bridge of stress ribbons and CFST arch ribs,which make progress at the cable anchor position and arch horizontal thrust issue of traditional suspension bridge.The structure is light,beautiful and competitive in the landscape pedestrian bridge.Taking the suspensory and CFST arch bridge in Fuzhou University as background,the basic dynamic characteristics,dynamic response of pedestrian excitation and seismic loading is analysed for the future application.The main work and conclusions include the following aspects:(1)The ambient vibration of bridge measured,the finite element model is caculatd by the professional software MIDAS/Civil.The result shows that the outside fundamental frequency of brige is symmetrical,2.25 Hz(test)/2.06 Hz(fem);the in-plane fundamental frequency is antisymmetric,3.32 Hz(test)/3.55 Hz(fem).Compared modeling with testing,the first three order in-plane and outside mode of vibration is similar,the frequency difference is less than 8%,which proving correctness of the finite element model.The analysis of main influence parameters shows that the simulation of pile foundation can reduce the natural frequency of bridge significantly;decreasing rise-span ratio of arch ribs can increase outside frequency and reduce in-plane significantly;increasing arch rib stiffness can increase the in-plane and outside stiffness of bridge;the change of outside angle of the main arch has little effect on basic dynamic characteristics of the bridge.(2)The dynamic response of pedestrian excitation is tested,the predominant frequency and vibration amplitude is obtained,in-plane predominant frequency is 3.21 Hz which is close to the testing natural frequency 3.32Hz.The FEM analysis shows that vertical acceleration of bridge deck slab and main arch rib amplifies when the pedestrian stride frequency equals to the in-plane first-order natural frequency of bridge,but the transverse direction acceleration response no obvious amplifies.Along with the increase of pace load amplitude A,the deck slab and main arch rib vertical and horizontal acceleration amplitude increases linearly.The suggested coefficient between walking load amplitude A and weight of pedestrians G is 1.118 for the vertical pedestrian load model of this bridge.The difference of vertical acceleration response calculated values and measured values is no more than 30%,under this suggestion coefficient.Taking speed and acceleration as index to evaluate the pedestrian vibration comfort,the result shows that the comfort of bridge meet the requirements.(3)The response spectrum method is used for the earthquake dynamic response analysis of stress ribbon&CFST arch bridge.The result shows that the responses subjected to earthquake in the out-of-plane direction are larger than those in the longitudinal direction;the increasing of internal force and displacement is less than 4%while the earthquake in both longitudinal and out-of-plane directions.The influence of internal force and displacement of the bridge is less than 5%by vertical seismic.So there is no need to take these situations into consideration in anti-seismic analysis.The bridge is still working elastic under most disadvantaged seismic load,meet the seismic requirements.