To determine the seismic ground motion for aseismic design after the Hyogoken-Nanbu Earthquake, it is required to take into consideration the earthquakes which occur either at the boundary of intercontinent plate or at the inland faults, although the return period of the latter for every inland fault may be longer than a thousand years. The seismic motion on bedrock with a shear wave speed over 400m/s is determined according to statistical analyses of strong seismic records observed in major earthquakes which occurred both in Japan and in the United States during recent years. In order to reduce deviation of recorded ground motion in statistics, influences of surface soil and topography have been avoided according to the information of the site of observation, and all records have been adjusted with respect to either the Closest Distance to Fault or the Equivalent Hypocentral Distance by attenuation function. Regarding the site where the seismic source can not be located, seismic risk factor is employed to determine the seismic ground motion. The factor is determined by seismic risk analysis based on the data of historical earthquakes as well as inland active faults.

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To determine seismic ground motion for aseismic design, it is necessary to take site effects into account, such as non-linearity of soil and geological irregularities. In this paper, we discuss two aspects of site effects. One is the estimation of nonlinear earthquake response of soil deposits, and the other the estimation of seismic motion on the ground that has topographical and geological irregularities. We propose a new stress-strain model that is applicable to earthquake response analyses of soil deposits under large earthquakes. Next, we develop a practical method to evaluate amplification characteristics of ground motion on the irregularly layered ground.

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This paper focuses on the method of designing structures against liquefaction and a subsequent lateral flow. Shaking table tests and analyses were carried out to clarify the mechanism of pile stresses caused by the liquefaction-induced lateral flow. As a result, it is proved that the design of structure against liquefaction shall reflect changes in the natural frequency while considering the additional inertia force of liquefaction ground. It has also become possible to economically design structures by assuming that the liquefaction-induced lateral flow is a ground displacement force.

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In seismic design of pile foundation, it is important to evaluate the deformation property of soil and the damage process of a pile member suffering large deformation, since the design for earthquake motions in the new design code is larger than those in the old one. Moreover, as stipulated in the new code, dynamic analysis methods should be used for evaluating structure responses induced by earthquakes. This paper outlines the new seismic design method of pile foundation, the model used in push-over analysis for large deformation and the hysteresis rule of soil-pile system.

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Some cut and cover tunnels were damaged by the Hyogoken-Nambu Earthquake in 1995. In most cases, except for important facilities and those constructed in soft subsoil, a seismic resistant design had not been considered. And its design method was not for such large earthquakes. From this viewpoint, a new seismic design method of cut and cover tunnels for larger earthquakes is desired. To investigate the behavior of underground structures at the time of earthquake, damage of three underground structures is first investigated and analytical simulations are carried out. Several model shaking table tests of cut and cover tunnel are then performed and the results are numerically analyzed. Finally, a new seismic design method of cut and cover tunnel is presented based on these test and analysis results.

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The new seismic design code adopted for railway structures in Japan is a system to check whether the response calculated through dynamic analysis satisfies the seismic performance of railway structures. To aim at a new seismic design method, it is necessary to quantitatively evaluate the bearing capacity and ductility of members that compose a structure. Based on the result of cyclic loading tests of members, this paper proposes quantitative evaluation of bearing capacity and ductility correspondent damage degree of reinforced concrete members.

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The new seismic design code adopted for railway structures in Japan is a system to check whether the response calculated through dynamic analysis satisfies the seismic performance of railway structures. To aim at a seismic design method, it is necessary to quantitatively evaluate the bearing capacity and ductility of members that compose a structure. In this paper, the range of application of the quantitative evaluation proposed in the past researches was expanded about the concrete filled tubular steel columns. The quantitative evaluation of bearing capacity and ductility correspondent to the damage degree was re-evaluated.

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To design steel structures more efficiently, it is necessary to appropriately evaluate the earthquake resistance performance of steel structures. In this study, we conducted cyclic loading tests of steel column members and steel frame pier models. Based on the test results, we investigated a quantitative evaluation method of steel members load carrying capacity and ductility and their hysteresis property. In addition, we investigated a method for evaluating earthquake resistance performance of steel rigid frame piers by using a simple analytical model.

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