Optimization approach applied to nonlinear analysis of raft-pile foundations

Optimal design of raft-pile foundations is examined by combining finite ele ment technique and the optimization approach. The piles and soil medium are modeled by three dimensional solid elements while the raft is modelled by shell elements. Drucker-Prager criterion is adopted for the soil medium whi le the raft and the piles are assumed to be linear elastic. For the optimiz ation process, the approximate semi-analytical method is used for calculati ng constraint sensitivities and a constraint approximation method which is a combination of the extended Bi-point approximation and Lagrangian polynom ial approximation is used for predicting the behaviour of the constraints. The objective function of the problem is the volume of materials of the fou ndation while the design variables are raft thickness, pile length and pile spacing. The generalized reduced gradient algorithm is chosen for solving the optimization process. It is demonstrated that the method proposed in th is study is promising for obtaining optimal design of raft-pile foundations without carrying out a large number of analyses. The results are also comp ared with those obtained from the previous study in which linear analysis w as carried out.