LOAD TRANSFER MECHANISM OF PIER-SUPPORTED-RAFT FOUNDATION SUBJECTED TO VERTICAL LOAD

Open Access
Author:
Wu, Xinli
Graduate Program:
Civil Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 24, 2011
Committee Members:
  • Mian C Wang, Dissertation Advisor
  • Mian C Wang, Committee Chair
  • Derek Elsworth, Committee Member
  • Virendra Puri, Committee Member
  • Andrew Scanlon, Committee Member
Keywords:
  • settlement behavior
  • load transfer mechanism
  • foundation design
  • pile-supported-raft foundation
  • Pier-supported-raft foundation
  • raft load ratio
  • pile load ratio
Abstract:
The pier-supported-raft foundation is a relatively new and effective foundation system commonly used to support high rise buildings. This research investigated the load transfer mechanism and settlement behavior for such a foundation system in order to enhance the existing database that can be used for development of a rational design methodology. Two major tasks were performed: literature review and finite element analysis. The literature review was conducted to update the current state of knowledge on the behavior and design methodology for pier-supported-raft foundation. The finite element analysis was conducted to analyze the load transfer mechanism, foundation settlement, and load distribution between raft and piers for such a foundation subjected to uniformly distributed vertical load. In the finite element analysis, the reinforced concrete raft and pier were characterized as elastic materials, while the foundation soil as an elasto-plastic material that obeys the Drucker-Prager yield criterion. The commercial software ABAQUS was adopted in the analysis. The computer FEA model was verified and validated by comparison of load vs. settlement curve obtained through a published laboratory model test data with that predicted by FEA. The two sets of data agreed fairly well within the reasonable range of error. Therefore, it was concluded that FEA is an effective tool for analyzing the load transfer mechanism and settlement behavior for such type of foundation system. The load transfer mechanism, foundation settlement, and raft load ratio of pier-supported-raft foundation subjected to uniformly distributed vertical loading were analyzed with consideration of influence factors. Influence factors considered were raft thickness and pier diameter, length, spacing, and total number, as well as soil properties. Based upon the results of analysis, the effect of various influence factors on foundation settlement, load transfer mechanism, and raft load ratio was determined. Also, the application to design of an economic foundation was discussed. The research findings should enhance the current database on overall foundation behavior. Furthermore, future studies needed for upgrading and expanding the database for ultimate development of a rational and economical design methodology for pier-supported-raft foundations are recommended.