Design rationale for mat foundation based on finite element analysis

Abstract

Recently, mat has become quite popular among foundation engineers. Although there are several methods available for the analysis of mat, none of these is accurate enough to picture the actual behavior of mat. In the current study, two popular methods for the analysis of mat, namely Conventional method and ACI Approximate Flexible method, have been compared with the Finite Element solution of mat using Ahmad's thick shell element. A general computer program, capable of solving any shell type structural problem, has been used for this purpose. Various data generation and result interpretation modules have been added to the original program to convert it into a versatile mat analysis software. The software is capable of analyzing mats with any kind of column and shear wall arrangement as frequently encountered in engineering practice. Also, separate computer programs have been written for analyzing mat using Conventional and ACI methods for the purpose of comparison. In performing the design of mat, the USD method of ACI code of practice has been followed in this study. It has been found that Finite Element method gives the most economic solution and its economy increases sharply with the increase of column loads. It has also been observed that frequently minimum requirements of ACI code govern the design of mat and because of this, Conventional method results in only slightly uneconomic design in comparison to Finite Element method despite its inaccuracy and various drawbacks. For heavy column loads, ACI method has been found to give considerable overdesign in comparison to Finite Element method despite its rigorous nature of analysis. A parametric study has been made in order to identifY the parameters which play the most important roles in defining the behavior of mat. It has been found that mat response is not much sensitive to most of its parameters. The most significant role played in this regard has been identified to be that of mat thickness. Finally, the economic prospect of a reshaping scheme for mat has been examined. Relative performance of mat with non-uniform thickness with respect to mat with uniform thickness, which is the most popular practice so far, has been evaluated. Effects of the new geometric parameters associated with mat with non-uniform thickness have also been investigated in order to find a safe guide line for this redimensioning proposal. It has been found that mat with non-uniform thickness offers about 20 to 30% saving of concrete and reinforcement and its design is not much complicated compared to the design of mat with uniform thickness. In the end, scope for future research has been indicated.