Abstract- Uçkan PhD
IMPACT TABLE SIMULATION OF NONLINEAR SOIL STRUCTURE INTERACTION
M. Eren Uçkan
(Thesis Supervisor: Mustafa Erdik)
The nonlinear response of a soil-structure interaction (SSI) system is simulated by performing impact table tests. The test setup consists of a suspended platform and a cylindrical tank filled with dry sand on which a rigid rocking cylindrical structure is founded. Tank rests on the rigid concrete platfom and has a diameter of 1m, height of 50 cm and a thickness of 1 mm. In order to provide good bonding at the bottom surface bottom plate of the tank is glued before the sand is poured. Side wall of the tank is soft in order not to cause any interaction with soil. Hammer impacts with short pulse widths ranging from 0.1ms to 1 ms were applied to the platform in the horizontal direction. Load pulses are assumed to be transferred from concrete platfom to soil causing vertically propogating shear waves in the test setup.
Analog to Digital (A/D) data acquisition was performed through a code which is specially developed to run at high sampling rates (5-20 kHz) via the Direct Memory Access (DMA) option. Six mini capacitive accelerometers were installed in the model to take measurements at various depths of the soil and structural points.
A series of pulses with varying intensities are applied to the model. Dynamic properties and natural frequencies of the soil and soil-structure interaction (SSI) system in low strains are identified through FFT and spectral ratios of the acceleration records. The acceleration time histories at the bottom and top of the structure clearly demonstrated rocking motion. As the loading intensity increased, the SSI model behaved nonlinearly, causing an increase in the hysterestic damping and decrease in the predominant frequencies.