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.
