ABSTRACT
CONTENTS 4.1 Introduction ....................................................................................................................... 145 4.2 Design Criteria .................................................................................................................. 146
4.2.1 Conventional Design Method............................................................................. 147 4.2.1.1 Eccentricity Criterion ........................................................................... 147 4.2.1.2 Bearing Capacity Criterion.................................................................. 147 4.2.1.3 Settlement Criterion ............................................................................. 148
4.3 Conventional Design of Rectangular Combined Footings ........................................ 148 4.4 Conventional Design of Mat Footings........................................................................... 152
4.4.1 Bearing Capacity of a Mat Footing .................................................................... 152 4.5 Settlement of Mat Footings ............................................................................................. 154
4.5.1 Immediate Settlement .......................................................................................... 155 4.6 Design of Flexible Combined Footings ......................................................................... 158
4.6.1 Coefficient of Vertical Subgrade Reaction ........................................................ 158 4.6.2 Analysis and Design of Rectangular Combined Footings ............................. 160 4.6.3 Design of Rectangular Combined Footings Based on Beams
on Elastic Foundations......................................................................................... 161 4.6.4 Analysis of Mat Footings Based on Slabs on Elastic Foundations ............... 166
4.7 Structural Matrix Analysis Method for Design of Flexible Combined Footings ... 169 4.8 Finite Difference Method of Flexible Mat Footing Design ........................................ 172 4.9 Additional Design Examples .......................................................................................... 175 References ................................................................................................................................... 178
Combined spread footings can be employed as viable alternatives to isolated spread footings under many circumstances. Some of them are listed below:
1. When the ground bearing capacity is relatively low, the designers have to seek methods of lowering the bearing stress. A larger footing area that provides a common foundation to many columns would distribute the load and reduce the bearing stress. In addition, this modification will also reduce the footing settlement.
