AN EXPERIMENTAL STUDY ON DYNAMIC FLEXURAL BUCKLING FOR REINFORCED CONCRETE PILES IN LIQUEFIED SOIL USING CENTRIFUGE TESTS

Abstract

 In the current Japanese design code of pile foundations, the buckling behavior of pile member is not taken into account. This is because the surrounding ground restrains buckling of the pile member. However, when the ground liquefies, the stiffening force for horizontal deformation of the pile weakens. Therefore, when slender pile is subjected to high axial compression forces as a result of increased vertical loads by overturning moment of superstructure under the strong earthquake, flexural buckling may occur in pile member in soft ground. The buckling behavior of steel pile in liquefied ground has been studied previously. This study investigated the dynamic buckling behavior of reinforced concrete (RC) pile using a centrifuge model.

 This paper investigated the dynamic buckling behavior of reinforced concrete (RC) pile using a centrifuge model. Three specimens with soil densities and input waves as variables were tested by uni-axial shaking. Buckling failure occurred in the pile members of all centrifugal models after the ground were liquefied. All pile members formed three plastic hinges at the pile head, lower side, and middle position. The measured buckling strength of the centrifuge RC pile model was evaluated by extending the tangent modulus theory. In the shaking table test under a 40 G field, the specimen used RC pile models, saturated soil (Toyoura sand) with a relative density of 30%, footing and a superstructure model with a natural period of 0.027 sec (prototype scale: 1.10 sec). Shakings were two Sweep wave (maximum acceleration: 4.19 m/s², 4.44 m/s²) and one Rinkai wave (maximum acceleration: 7.36 m/s²). The lateral displacement of the pile foundation was fully restrained so that the only the vertical load (the sum of the sustained load of the superstructure and the temporary load by overturning moment) acted on the piles.

 Buckling failure occurred in the pile members of the centrifugal model after the ground was liquefied. After the pile buckled, the footing sank, and the seismic response of the superstructure decreased. The measured buckling strength of the centrifuge RC pile model was evaluated by extending the tangent modulus theory (Engesser and Schanley). Since concrete (mortar) is a non-linear material, the tangential stiffness changes according to the acting axial force. Also, even if the ground liquefies, the stiffening force for horizontal deformation of the pile members does not become zero. Therefore, in order to evaluate the buckling strength of RC pile members in liquefied ground, it is necessary to consider the influence of the non-linearity of concrete and the decrease in the stiffening force of the surrounding ground.