E0-190-2008_(4)Chapter_3 - Dynamic Soil Structure...

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Kenji MIURA, Dr. Eng. Professor Graduate School of Engineering Hiroshima University Dynamic Soil Structure Interaction
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Dynamic Soil Structure Interaction Chapter 3 : Effect of SSI on Dynamic Behaviors of Structure Kenji MIURA, Dr. Eng. Professor Graduate School of Engineering Hiroshima University
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3. Effect of SSI on Dynamic Behaviors of Structure The effect of Soil-Structure interaction (SSI) influences strongly the dynamic behaviors of the building. Here, we examine the effects of SSI on dynamic behaviors of a structure. If you will estimate dynamic behaviors of a structure such as the natural frequencies and the damping factors on the assumptions that the basement or the foundation footing is fixed without incorporating the SSI effects, the estimated values will be quite different from these of the actual structure. SSI System Fixed Base System
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3.1 Numerical Condition of SSI System Numerical conditions for the soil, superstructure and foundation described below are employed for examinations of SSI. (1) Soil: Two layered strata shown in the figure: Surface Stratum G.L V S2 =100m/s γ 2 =1.7tf/m 3 ν 2 =0.45 h 2 =0.05 V S1 =400m/s γ 1 =1.9tf/m 3 ν 1 =0.40 h 1 =0.01 20m Bearing Stratum
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(2) Superstructure and foundation (a) Reinforced concrete structure (b) Floor height: 3.0m (c) Weight of each floor and foundation:1,080t and 2,700t (d) Rigidity: Rigidities of each floor are identical, and its value is estimated from the first natural period T 1 as: T 1 =0.025 n , n : number of floors (e) Modeling: Superstructure is modeled by lumped masses model with shear rigidities on the rigid Basement. (f) Basement: embedding depth = 6m.
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(3) Foundations Two types of foundation are considered. (a) spread Foundation (b) Pile Group Foundation One is a spread foundation, the other is a pile group foundation.
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(4) Earthquake Disturbance An earthquake disturbance is assumed to result from an incident SH type wave propagating upward at a right angle to the ground surface. At the time of an earthquake, four kinds of earthquake wave travel to the building. Among them, the S-wave comprises the principal shock of the earthquake motion and it must be incorporated into the seismic design of a structure. As S-wave velocities of strata nearer to the ground surface becomes normally lower, the incident angle of the S-wave gets near a right angle to the ground surface.( Snell’s Law ) φ 1 φ 2 φ 3 φ 4 V 1 V 4 V 3 V 2 3 3 2 2 1 1 V sin V sin V sin ϕ = ϕ = ϕ
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3.2 Response of Soil Let take a look at soil response when a SH type earthquake wave is propagating upward at a right angle to the ground surface. Response of Layered Strata First Natural Frequency f 1 i-th Natural Frequency f i Impedance Ratio α
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