Test On Code Calculation Methods Of Hydrodynamic Effect For Deep-water Bridge Excited By Near-fault Earthquakes

ABSTRACT:Hydrodynamic effect should be highly concerned in seismic design of deep-water bridges. Because of the structural features of high pier and large span, deep-water bridges usually have longer natural vibration period. And these structures will inevitably suffere more serious impact by impulsive long-period ground motions when the bridges are near or cross the active fault region. At present, the study on dynamic response characteristics of deep-water bridges excited by near-fault ground motions with velocity pulse is fairly rare, and the validity and reasonable application scope of related specifications should be tested urgently.In this paper, the hydrodynamic effect calculation methods by typical domestic and foreign codes were summarized systematically, and equivalent single pier and deep-water continuous bridge were introduced as research object respectively. Typical near-fault ground motions were selected as input. By the index of natural vibration characteristics, distributed hydrodynamic pressure, total hydrodynamic pressure and its action location, as well as the dynamic responses of structure, the effectiveness of different codes were tested. And then, groups of pier models were built based on different slenderness ratio to discuss the reasonable application scopes of these codes.The main work is as follows:1. The calculation methods of hydrodynamic effect by representative domestic and foreign codes were selaborated systematically and the main problems or deficiency were analysised comparatively.2. The equivalent single pier model of deep-water bridge was established. With the numerical calculation results of fluid-structure interaction as benchmarks. From the above mentioned indexes, the effectiveness of different codes under impulsive long-period ground motions were tested quantitatively, and the error ratio of above indexes by different codes were specific evaluated.3. Taking a deep-water continuous bridge as research object, the numerical calculation model considering fluid-structure interaction and the semi-analytical model were established respectively. The effectiveness of different codes for the full bridge structure were tested quantitatively, and the error ratio were specificly evaluated. Comparison was taken between the single pier and continuous bridge. And the possible improvement for Chinese railway code were discussed in terms of distributed hydrodynamic pressure.4. From the index of natural vibration characteristics, hydrodynamic pressure and dynamic responses of structure, two groups of pier models were built based on different slendemess ratios. The error rate distribution characteristics with different slendemess ratio were extracted respectively, and the reasonable application scopes of these codes were defined quantitatively.