Design of Reinforced Concrete Foundations

INTRODUCTION Structures constructed below the ground level are called substructures. They are generally divided into the following three groups: 

• Foundation structures

 • Retaining structures 

• Other special systems such as tunnels, diaphragm walls, and buried pipes. In this book, we will deal mostly with the first two groups.

 Foundation structures transfer all the loads that come on the superstructure to the ground. These loads can be either vertical loads such as live and dead loads or horizontal loads such as wind loads and earthquake loads. Retaining structures are built to retain earth as inthe case of basement of buildings.

 Foundation structures are themselves divided into the following subdivisions: 

• Shallow foundations • 

Deep foundations • 

Special foundations Shallow foundation can be of two types:

 • Various types of footings

 • Grids and rafts 1

Deep foundation can be of three types (see Chapter 15): 

• Piles

 • Piers

 • Caissons While piles are flexible members that bend under lateral loads, piers are rigid structures that undergo rotation under lateral loads. 

Caissons are usually those piers built under water using pneumatic pressure devices. Special foundations are used for special structures such as transmission towers, cooling towers, and chimneys. The geotechnical design of foundation (e.g. calculation of bearing capacity of soil, and also that of piles, and wells) is usually dealt with in books on Soil Mechanics, which is a part of Foundation Engineering [1]. In this book, we deal mainly with the structural design of commonly used foundations (e.g. footings, rafts, pile caps, and basement) for supporting superstructures. 1.2 

RIGIDAND FLEXIBLEFOUNDATIONS 

Structures such as footings can be assumed to settle uniformly under a central concentrated load. Hence, if we assume that the ground reaction or contact pressure is proportional to deformation (the Winkler theory), the contact pressure will be uniform under the foundation. (However, we know that the elastic stress distribution under a rigid footing in clay or sand is not uniform even though at ultimate stage it tries to even out.) Incertain calculations, we often make the assumption that the shallow foundations are rigid and the contact pressure is, therefore, uniform.