Monday, January 28, 2013

Tied and Balanced Foundations.

General Introduction
Tied and balanced foundations are used to combine a number of superstructure loads in order to achieve acceptable bearing pressure. The combined base is used to balance out or tie together difficult eccentricities of loading or horizontal forces. Such foundations usually result from an engineering study of the superstructure loads to be transmitted onto the foundation. The engineer’s aim is to make the best use of the magnitude and direction of such forces in balancing out or tying together eccentric reactions and horizontal thrust to economically achieve the required ground bearing pressures.

Particular problems exist where large lateral forces are transferred at the top edge of a foundation from say portal frames or when large column loads occur at or near site boundaries. Fortunately portal frames tend to have an equal and opposite leg with similar opposing horizontal forces which can be reacted against each other. Buildings with large column loads near to the boundary tend also to have other large column loads either internal to the building or on an opposite boundary. The internal or opposite columns can therefore be used to stabilize the moments produced  by the eccentricity from the outer perimeter frame. Typical examples are given in the following sections.

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