FREQUENCY RESPONSE CHARACTERISTICS OF THE RIGID COLUMN TYPE FOUNDATION

In design, a foundation assumed to be a single whole of columns called the column type foundation. To obtain fundamental data that would help establish seismic design method for the rigid column type foundation during great earthquake, shaking table test of foundation model with different embedded depth Df and height of ground surface H were conducted. The results is the followings: 1) as H/Df increases, the foundation model respond to shaking at their respective natural frequency; 2) a model natural frequency smaller than that of the ground gives rise to a good degree of isolation; 3) as the input acceleration increases, the damping constant increases and thus broadens the frequency range of vibration; 4) the vibration of a model is affected by a phase difference as the input acceleration increases, consequently complicating the vibration mode; 5) the percent reduction of a natural frequency vs. an increased input acceleration tends to be practically equal among the models. We also conducted a modal analysis and verified the nonlinear characteristics of the ground by comparing the results of the modal analysis and those of the bench test