Monday, January 7, 2013

Pier and Beam Foundations.

In a similar manner to pile foundations, pier and beam foundations are used as a means of transferring load down through unsuitable bearing strata into a firm layer at depth.

The piers are constructed in brick, mass concrete or reinforced concrete. The spacing of the piers is determined on economic considerations based upon the depth of the piers, the sub-strata conditions, the load to be carried and site conditions. The beams on top of the piers can be precast concrete, in situ concrete, timber or steel; a few typical pier and beam forms are shown in Fig. 9.48.

The choice between the use of piles or piers is usually made on the basis of economy. When the site works are relatively large, the depths to suitable load-bearing strata great  and the site access reasonable, then piles are usually the most economic. In situations where pier excavations are relatively easy, not too deep and/or of small numbers,  then piers and beam foundations are usually the more  economic. The spacing of the piers and the type of ground beam is chosen from the loading and site conditions. The typical economic range is 3–5 m. Figure 9.49 indicates some typical forms.

The beams supporting the walls can be designed as composite with the masonry, in a similar manner to the ground beams for the pile solution. If composite action is exploited then the possible future adaptation of the building should be considered.

Fig. 9.48 Pier and beam foundation.

Fig. 9.49 Typical pile/pier and ground beam arrangement.

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