The purpose of this paper is to experimentally estimate the Dynamical Ground Compliance (DGC) for square reinforced concrete foundations on a stiff soil ground by oscillator tests and to obtain the basic data to apply the theory on DGC to a seismic design of structures. DGC is represented as the ratio of the displacement of a rectangular foundation on a semi-infinite elastic medium to a harmonic disturbing force acting on the foundation. The experimental DGC is compared with the theoretical DGC, and shown in graphical form.
Tests on four kinds of foundation had been conducted three times from December 1978 to March 1979. The site for the experiment is in the suburbs of Ayabe city, Kyoto and consisted of cutting and filling ground as shown in Fig. 1. Tests had been conducted at two locations of the cutting ground, in which the shear wave velocity (Vs,)is different between the two. The measurement of Vs was conducted by refraction survey, and Vs obtained around XA-foundation was 600 m/sec and 250 m/sec around X-, Y- and Z- foundation as shown in Fig. 2. The medium at this Site was divided into two parts; namely' the deposit and the rock. The rock was divided into three parts; namely the strongly weathered rock (Vs=250–700 m/ sec), the weakly weathered rock (Vs= 1000–1200 m/sec) and the hard rock (Vs≥ 1800 m/sec). The unconfined compressive strength of the weathered rock was 99 kg! cm2.
Models for tests are foundations as Shown in Fig. 3 and are made of the spread foundation. X-, Y- and Z-foundation were constructed at the same location in order to estimate the size effect of the foundation. Tests were carried out in the order of X-, Y- and Z-foundation, and each foundation was constructed in the same order for conducting the test. The concrete of Y-foundation was placed around X-foundation and one of Z-foundation was placed around Y-foundation.
Eccentric mass oscillator (weight: 1.3 tons, frequency range: 1–40 Hz, maximum exciting force: 4 tons) was placed on the center at the top of XA-, x-, Y- and Z-foundation. Directions of the exciting force for XA-foundation were the horizontal EW component (east and west), the horizontal NS (north and south) and the vertical one, and those for X-, Y- and Z foundation were the horizontal NE-SW and the vertical one. Responses of foundation were detected by accelerometers (natural frequency: 3 Hz),amplified by amplifiers, integrated into velocity responses and recorded by pen-recorders and data-recorders. Phase signals of oscillator were recorded by data-recorders in order to measure the phase angle between the velocity response and the exciting force. Accelerometers were placed on the top of the foundation or on the surface medium around the foundation. Accelerometers were placed on the foundation as shown in Fig. 3; namely E-, W-, N- and S-point for XA-foundation, NE-, SW-, NW- and SE-point for X-, Y- and Z-foundation. The main eccentric moment(EM)of oscillator was 30 kg' cm. Oscillator was operated by the steady state method.