The Dynamic Response Of Long Span CFST Arch Bridge Under Random Traffic Flows

The concrete-filled steel tubular (CFST) arch bridge, as a neotype bridge style, has been widely applied and rapidly developed in our country because of its own merits and the agreement with factual situation of bridge construction in China, and its span is increasing continuously. In recent years, the traffic volume, quantity of vehicle and gross rail load on axle have all increased continuously, causing the problem that the dynamic behavior of CFST arch bridge under random traffic flows becomes projecting in China. The analysis of vehicle-bridge system under deterministic traffic flows was developed to the one under random traffic flows, whose analysis frame was also established. The analysis modular—VB (Vehicle-Bridge system analysis) was written which was encased into the BDANS(Bridge Dynamic ANalysis System). The deflection, endogen force of CFST arch bridge key parts were analyzed adopting the VB.First, basing on the traffic investigation, the master data of vehicle's types, heavers, velocities were obtained by counting and analysing. Making use of Monte-Carlo method and MATLAB program and its toolbox, The RTF (Random Traffic Flow stimulate) program which firstly considered the four parameters including the type, heaver, separation and velocity of vehicles was wrote.Second, the BDANS which programmed by our assignment group and the principle of VB were introduced in this thesis. Then the reliability and validity of VB were proved by the example of sprung mass moving over a beam and the measured values of final completion of XiaBaiShi Bridge. The influences of vehicle suspension system, bridge damping ratio and the barrier on road to the dynamic response and impact coefficient of bridge were researched basing on the XiaBaiShi Bridge. The study indicated the following conclusions: The influences of vehicle suspension's stiffness constant and damping coefficient were significant on deflection and bending moment of bridge when traveling with barrier, but were obscure when traveling is barrier-free. The damping ratio of bridge has a weak effect on the deflection , bending moment and impact coefficient of the bridge. As the height of barrier rising, the peak value and impact coefficient of bridge's vibration were enlarged, but the vibrator frequency was almost invariable. Finally, the effects of random traffic flow samples, road surface roughness and two-way direction on the dynamic response of CFST arch bridge were discussed according to the DaXiHu CFST arch bridge. The analysis indicated: because the randomness of random traffic flow samples was violent, the endogen force and deflection of arch rib and deck and also the impact coefficient fluctuated violently. With the deterioration of road surface roughness, the endogen force of arch rib and suspender expanded notably. In two-way direction case, the axis force of arch rib and the bending moment of arch spring increased quite obviously; the increasing of suspender force was smaller relatively; and the impact coefficient all varied obscurely. In addition, the maximum values of dynamic response in 12 time-intervals were calculated and also the ones within 24 hours with extrapolating method, as the basis of design and maintenance of CFST arch bridge.