F basement embedding depth 6m 3 foundations two types

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Unformatted text preview: t: embedding depth = 6m. (3) Foundations Two types of foundation are considered. One is a spread foundation, (a) spread Foundation the other is a pile group foundation. (b) Pile Group Foundation (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. φ4 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) V4 φ3 φ2 φ1 V3 V2 V1 sin ϕ1 sin ϕ 2 sin ϕ3 = = V1 V2 V3 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 f1 i-th Natural Frequency fi Impedance Ratio α The figure shows magnification factor(M.F) US/2EO of the ground surface response to the amplitude of the incident wave EO. A denominator 2EO of M.F denotes the amplitude of response at the surface of the bearing stratum when the surface stratum is removed. 1.25Hz 3.75Hz Two resonance peaks are observed. The lower peak corresponds to a first natural frequency 1.25Hz of the surface stratum, while the higher to a second 3.75Hz. The i-th natural frequency fi of the surface stratum is formularized by : (3-1) When the surface stratum consists of multi-layered strata, the natural frequency is similarly calculated using an equivalent shear wave velocity Vse given by: (3-2) where m is number of layers over the bearing stratum, and VSj is shear wave velocity and dj thickness of the j-th stratum. Subst...
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