Analytical Study on Damping Effect of Building Considering Dynamical Interaction Between Soil and Building

Abstract eng:
It has been pointed out that the damping effect related to building dynamic response characteristics due to the interaction between soil and building is of relatively significant influence. Usually, we want to know the damping effect on the dynamic interaction between the soil and the building taking into consideration the combination of the soil conditions and building dimensions depending on the foundation type. We therefore performed parametric case studies using SDOF building models which have different stories from 2 to 32 stories with a changing natural period, while also taking into consideration the foundation type (direct foundation type or pile foundation type) and surrounding soil conditions (depth and stiffness of surface layer). We divided the combination conditions between the foundation dimensions and building type (divided into 3 types: low, middle and high rise building types according to building stories) and soil conditions (divided into 3 by depth and stiffness of soil layer). The natural period of the building is assumed by the formula used in the Japanese building design code. In the first step, we calculated the impedance between the soil and the building according to the combination conditions with the differences of foundation type by using the results of the impedance analysis. Then, we performed the dynamic response calculation by using Sway-Rocking (S-R) model introducing the spring and damping constants of sway and rocking motion obtained from the impedance in each combination condition. In this calculation process, we assumed two kinds of S-R Model, one being the actual S-R Model (S-R act Model) with actual spring and damping constants obtained from impedance analysis and the building inner damping fixed to 2% (h=0.02) and the other was the revised S-R Model (SR rev Model) which has only the spring constant obtained from the impedance analysis but ignoring the damping constant and the building inner damping h is variably changed. In the second step, we performed the dynamic response calculation using the S-R act Model and the S-R rev Model with all assumed building types from 2 to 32 stories by checking the similarity of the maximum acceleration response values at the top of buildings. Comparing the maximum response value between the S-R act Model and the S-R rev Model, we obtained the building inner damping constant h of the S-R rev Model which gives same effect on the building response due to the interaction between soil and building. In this paper, we performed two analytical studies, one was the case of a building foundation without piles, and the other case was a building foundation with piles. We would like to present the results on the apparent effect of damping due to the interaction between soil and building. In conclusion, in the case of a direct foundation, the result of building inner damping constant decreased according to the number of building stories: and the higher the building, the longer the natural period, t, and the less the interaction combination effect between the soil and the building, and conversely, the higher the building, and the shorter the natural period, and the interaction combination effect increases markedly. Otherwise, in the case of a pile foundation, the results showed a larger damping constant, namely, it showed a greater damping effects due to the dynamic interaction between the soil and the building, namely dispersed damping effects largely appeared in the case of a pile foundation.

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