|M.Sc Student||Menahem Avishur|
|Subject||Physical Models for Soil-Pile Interaction under Seismic|
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Emeritus Frydman Sam|
Due to increasing awareness to earthquake hazards, the National Building Research Institute of Israel (NBRI) carried out a research investigation, financed by the Ministry of Construction and Housing, to study the behavior of piles under seismic loading conditions.
The bending stresses along a single pile subjected to seismic activity are affected by several mechanisms, including the inertia of the superstructure (Inertial response), the shear wave propagation through the soil (Kinematic response), gapping, etc...
In the present research, an experimental system was developed, which enables the testing of the behavior of small-scale models of piles driven into sand, under earthquake conditions. The system is centered around a small-scale model of a pile driven into sand, and attached to a shaking table. In order to establish dimensional similitude between the small model and the large prototype, water is flowed vertically downward through the model under a preset hydraulic gradient, creating downward drag forces and resulting in increased body forces, equal to the gravity forces in the prototype.
A preliminary set of tests on a single pile with a head mass driven into sand was conducted in this research. The following observations were made:
· For free field condition, the base acceleration was amplified through the soil up to a factor of 1.6 at the surface. Reasonable agreement was achieved in the majority of the tests, with analysis results obtained using SHAKE software.
· For free-headed pile driven into sand, the maximum bending moment along the pile can develop below the mid-point of the pile during base shaking. This finding is contrary to the common assumption that the maximum moment develops near the top of the pile. A lack of reinforcement in the lower part of a real pile could lead to severe damage.
Several phenomena observed in the present study justify further investigation, and a broader research should throw light on the behavior of piles under various seismic conditions.