Design Example: Piled ground beams with suspended slab

Previously design example  is to be reworked on the assumption that the building is now to be relocated in an area where the  5 m depth of fill is of a much poorer quality, and is con- sidered unsuitable for supporting a floating ground floor slab. The ground floor slab is therefore to be replaced by wide plank precast concrete floors, spanning 8 m parallel to grid lines A–E.

The additional loads due to this suspended floor are shown in Fig. 14.32, and the increased pile loads are indicated.

The increased loads could be catered for by increasing the  number of piles along each load-bearing internal wall  (parallel to grid lines 1–5). In this case however, it has  been decided to maintain the same pile and ground beam layout as in Design Example 3.

Pile capacities
As previously, the pile capacities given in Table 14.9 are derived from previously design Example (Fig. 14.29).

Piles of 450 mm diameter will again be used. Comparison with Design Example 3 indicates increases in length of between 0.5 m and 4.6 m.

Check on strength of pile cross-section
A check on the stresses in the pile cross-section, carried out in a similar manner to Design Example 3, indicates that grade C35 concrete is required.

Ground beam size
The ground beams are designed in a similar manner to previously design example, taking due account of the additional loading from the suspended ground floor.

The calculations will be found to indicate that the 600 mm × 625 mm deep ground beams in previously design example will need to be deepened by approximately 200 mm to accommodate this additional loading.

Fig. 14.29 Pile safe working loads for design examples.

Fig. 14.32 Piled ground beam and suspended slab design example.