Ain Shams Engineering Journal (Sep 2021)
Dynamic analysis of combined piled raft system (CPRS)
Abstract
High rise buildings constructed on the combined piled raft system (CPRS) have been rapidly increased in the recent years. Understanding of the load distribution mechanism between the pile and raft especially when these buildings are subjected to the earthquake is the main objective of this research. The kinematic interaction between the pile, soil, and raft is a principally 3-D problem. The main objective of this study is to evaluate the capability of the proposed numerical method by comparing its output with case study data. Further understanding of the raft-soil and pile interaction problem outside the verified case is therefore required by running a series of the parametric studies. These analyses indicate that the interaction mechanism of the raft-soil and pile is based on the inertia and kinematic interaction under seismic and vertical load. These interaction mechanisms are mainly evaluated by considering the load shared by soil beneath the pile tip after the earthquake while the sharing load by either pile or raft is quite stable after the earthquake. Efficiency of CPRS to mitigate the earthquake is demonstrated for the large raft stiffness more than 250 as in cases of (tp = 2 m, & S/D = 3), (tp = 3 m, &S/D = 3 or S/D = 4), and (tp = 2.5 m, &S/D = 3), or by employing long pile (Lp = 25 m). Also, employing the building stiffness to the increase inertia effect is almost not considered dominant in reducing the sharing load carried by CPRS, while the raft lateral displacement, acceleration, and bending moment express a relative increase. Another mitigation technique of the earthquake is adopted by applying the building stiffness assisted with the ductile or rigid base isolator. It proved that the ductile isolator is more effective technique in dissipating the earthquakes more than increasing the inertia of CPRS.
