The Earthquake Response Study Of Deep-Water Bridges

Nowdays more and more deep-water bridges are built with the devolpment of larg span bridges to cross water areas, and the deepest underwater foundation of deep-water bridges constructed had reached 168m. Under the effect of the earthquake, hydrodynamic pressure of structures will be occurred because of the relative movement between a structure and water induced by radiation wave movement of fluid around the structure. The dynamic characteristics and the dynamic responses of the structures will be changed due to the effects of the hydrodynamic pressure. However, the effects of hydrodynamic pressure induced by the earthquake on the deep water structures, such as underwater foundation of large span bridges have received relatively little attention in exiting literaturea.In this dissertation, the dynamic responses of deep-water bridges under the earthquake are studied based on extensive analysis. The main achievements of this dissertation are as follows:1. Based on the radiation wave theory, an analytical solution of additional hydrodynamic pressure of inner liquid of circular hollow piers is deduced, and by using the characteristic the main axis of a retangle section is coincided with the longitudinal axis and lateral axis of the bridge, and an analytical solution of addditional hydronamic pressure induced by inner and outer waters of the retangle hollow piers is also given. Using displacement-pressure model (u-p) of fluid-solid coupling, the finit element analysis (FEA) is carried out, and comparing with the analytical solution, the accuracy of the semi-analytic approach of additioanl hydrodynamic mass in this dissertation is verified.2. In this dissertation, the hydrodynamic additional pressure is expressed as the hydrodynamic additional mass and the hydrodynamic additional damping. Moreover, a motion equation of deep-water bridges induced by earthquake is presented and its solution method is extensivly investigated. 3. The distribution characteristics of hydrodynamics additional mass along the depth of circle hollow piers and retangle hollow piers are analyzed .The effect of free surface wave, whole depth of submerged water and geometry dimensions on hydrodynamic additional mass are studied and also summarized: a critical depth is found.The hydrodynamic additional mass distributes is a parabola when above the critical depth and the distribution of hydrodynamic additional mass is not effected by the water depth when below the depth. The effect caused by vibration of free-surface wave of structure at a high frequency can be ignored. The hydrodynamic additional mass will increase as the geometry dimensions increase if at the same depth. The shape of piers is the main factor which affects hydrodynamic additional mass.4. According to the preceding thoeries, a time-history analysis of the earthquake responses of long-span continuous rigid frame bridges is carried out and the characteristics of responses of continuous steel frame bridges in deep water under the effect of the longitudinal and lateral earthquake excitation are analyzed. It is indicated that the pier-water coupling vibration increases inner force responses and displacement responses of the main beam and piers, which should be considered in an analysis of earthquake response of continuous steel frame bridges in deep water. The effect of additional mass arising from waters inner and outer piers and whole depth of submerged water on the earthquake responses of piers is invesitigated, and the result shows that the effect of inner water and outer water should be considered. The disadvantages of pier-water coupling vibration increase as the whole depth increases of submerged water. Comparing the results with those calculated according to the Japanese and European criterion, it is found that the results calculated by the European criterion is much too conservative, such as the bridge whose whole depth of submerged water are relative fleet, and it is insecure while the results calculated by Japanese codes such as the bridges whose whole depth of submerged water are relative deep.