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Pile Design and Construction Practice, Fifth edition

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45˚<br />

Structural design of piles <strong>and</strong> pile groups 389<br />

Minimum reinforcement<br />

required by Code of<br />

<strong>Practice</strong><br />

Load transferred<br />

to piles over this<br />

area<br />

Figure 7.8 Load transfer from column to deep four-pile cap.<br />

Compressed zone<br />

45°<br />

≥50 mm<br />

Figure 7.9 Distribution of compressive stress from pile head to pile cap.<br />

bottom surface of the cap can be omitted. Also the sides <strong>and</strong> top surfaces of the cap may be<br />

unreinforced if there is no risk of tension developing in these zones (see Figure 7.9). BS 8110<br />

requires minimum percentages of reinforcing steel of 0.24 <strong>and</strong> 0.13 for mild <strong>and</strong> high tensile<br />

steel respectively.<br />

<strong>Pile</strong> caps constructed over large groups of piles as in Figures 7.10 <strong>and</strong> 7.11 can be<br />

designed as solid slabs. The design requirements for these members are set out in Clause 9.3<br />

of EC2.

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