Abstract
In a seismic design of embedded foundations, the vertical Subgrade Reaction (SR) acting on a foundation bottom surface and the Rotational Resistance Moment (RRM) generated by the SR are calculated using an SR Modulus (SRM). The SRM and RRM depend on both ground rigidity and Foundation Width (FW). However, the SRM and RRM calculation methods adopted in design codes might not properly consider their FW dependency. In this study, SRM and RRM evaluation methods for embedded foundations subjected to a seismic load were examined by conducting a two-dimensional finite element analysis under the condition where ground rigidity and FW were changed considering the nonlinearity of the ground. The results show that when the seismic load is large and the nonlinearity of the ground appears, the SR distribution is different from the assumption in the design code. The FW dependency of the SRM was lower than the assumption of the design code. Furthermore, methods to calculate the SRM and RRM in accordance with the FW and ground rigidity are proposed.
Highlights
A structure’s foundation must ensure stability by transmitting the applied load to the ground
SR Modulus (SRM) and Rotational Resistance Moment (RRM) evaluation methods for embedded foundations subjected to a seismic load were examined by conducting a two-dimensional finite element analysis under the condition where ground rigidity and Foundation Width (FW) were changed considering the nonlinearity of the ground
The results show that when the seismic load is large and the nonlinearity of the ground appears, the Subgrade Reaction (SR) distribution is different from the assumption in the design code
Summary
A structure’s foundation must ensure stability by transmitting the applied load to the ground. Various design codes, such as the Japanese Specifications for Highway Bridges (JSHB) [4], apply the SRM calculation equation in accordance with the FW. When using the SRM calculation equation adopted in the design code, the SRM significantly decreases as the FW increases, and an increase in the SR proportional to the increase in the FW cannot be expected. The results of the horizontal loading test of pier models where the FW was changed revealed that the seismic resistance becomes extremely high by widening the FW because the vertical SR becomes large [6]. Evaluation methods for the vertical SRM and RRM for embedded foundations subjected to seismic loads are proposed. Since only vertical SR and SRM are considered in this paper, they are described as SR and SRM for simplicity in the following
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