擁壁が弾塑性特性を有する場合の簡易評価法への適用

Abstract

We have proposed the simple modeling method for the lateral resistance of elastic retaining wall portion (retaining wall + backfill soil) using fiber model, and we have showed the collision analysis model using the method. This paper aims to confirm the applicability of the method in case of retaining wall with elasto-plastic property. First, we conduct the seismic response collision analysis of a base-isolated structure-soil interaction system using 3D-FEM and estimate the structural behavior and impulse force when it collides uniformly and without twisting into retaining wall. Figure 1 shows 3D-FEM analysis model. Basic specifications and conditions are same as reference No. 11. The thickness of retaining wall is taken as t =300mm, its flexural strength assumes two types of Mu≒145kN·m/m (“flexural strength 1.0 times type”) and Mu≒72.5kN·m/m (“flexural strength 0.5 times type”). Figure 5 shows the time-history response displacement of isolation layer in 3D-FEM collision analysis. The maximum response displacement for both types is the same as approximately 523mm, however their behavior after the maximum displacement is different. Figure 6 shows the time-history response acceleration of superstructure (top floor and 1st floor). With respect to maximum response acceleration (16.5m/s2) at the top floor of elastic retaining wall, flexural strength 1.0 times type is reduced by approximately 12%(14.6m/s2), and flexural strength 0.5 times type is reduced by approximately 23%(13.4m/s2). Meanwhile, with respect to maximum response acceleration (12.4m/s2) at the 1st floor of elastic retaining wall, which values of both types are almost the same. Figure 7 shows the time-history impulse force on lower edge position of girder directly above isolation layer at which maximum impulse force is obtained. Maximum impulse force of both types is reduced approximately 21% against elastic retaining wall. Next, we confirm the applicability of the simple modeling method in case of retaining wall with elasto-plastic property. The verification position is three cases; GL±0m, GL-1.2m, and GL-1.5m. Figure 12 and Figure 13 shows the hysteresis loop of retaining wall portion. In case of GL-1.5m, a difference occurs in the maximum response displacement because the simple modeling method may not accurately reproduce strength of retaining wall portion obtained from 3D-FEM analysis. Also, in case of GL±0m and GL-1.2m, a difference between 3D-FEM result analysis and the simple modeling method is large. This reason is considered to be not conformed the condition of maximum range 3t for the backfill soil considered as added mass because the maximum response displacement of elasto-plastic retaining wall is larger than elastic retaining wall. So, we modify the maximum range from 3t to 6t, and we re-estimate the lateral resistance of retaining wall portion. As a result, hysteresis loop shapes are greatly improved, and it shows relatively good agreement to 3D-FEM analysis result. Finally, we conduct collision analysis using the simple modeling method, and we compare the structure response with the 3D-FEM analysis results. Figure 18 shows the analysis model using the method. In the case of the collision springs taking into account axial stiffness of the girder directly above isolation layer, the method largely captures trends in restoring force characteristics of entire isolation layer (isolation layer + collision spring) from 3D-FEM analysis. The method estimates maximum response acceleration at 1st floor approximately 14% smaller compared to 3D-FEM analysis result. However, it shows relatively good agreement to 3D-FEM. Meanwhile, in the case of the rigid collision springs, the maximum response values are overestimated. This tendency is the same as case of elastic retaining wall.