AMPLIFICATION FACTOR OF VERTICAL DISTRIBUTION OF SHEAR FORCE COEFFICIENT FOR SEISMICALLY ISOLATED BUILDINGS CORRESPONDING TO INPUT LEVEL OF DESIGN LONG-PERIOD AND LONG-DURATION GROUND MOTIONS

Abstract

 In June 2016, MLIT (Ministry of Land, Infrastructure, Transport and Tourism) has announced a countermeasure against the Nankai trough long period ground motions (LPGMs). MLIT also announced the region divided by input level of LPGMs in the Kanto (KA1), Chukyo (CH1–3), Shizuoka (SZ1–3), and Osaka (OS1–3) areas. However, the response spectrum method, indicated by the Ministry of Construction notification Vol. 2009, is out of the countermeasure, because this method was considered to be difficult to reflect the influence by LPGMs. Also, we proposed a vertical distribution of design shear force coefficient for seismically isolated buildings (SIBs) using the equivalent isolation ratio which has applicability to various dampers.

 In this paper, we analyze the influence of LPGMs on shear force coefficient distribution of SIBs based on knowledge that response amplification is excited by higher modes. And based on the analytical results, we propose a new equivalent amplification factor and variation correction coefficient. The acquired conclusions are as follows;

 

 1) The equivalent amplification factor of the shear force coefficient changed depending on the region divided by input level of LPGMs. In addition, it was confirmed that the number of cases where the equivalent amplification factor falls within the range of evaluation of Eq. (10) varies depending on the region divided by input level.

 2) Based on the analysis results of nonlinear modal analysis, as region divided by input level of LPGMs decreases, the 1st mode response decreases, and the influence of the higher mode increases relatively.

 3) By quantifying the relationship between the equivalent isolation ratio and the equivalent amplification factor, and the variation of the equivalent amplification factor for each region, it was possible to appropriately evaluate the tendency that the equivalent amplification factor differs depending on the region divided by input level of LPGMs.