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Do edge piles take up same loadings as central piles in rigid cap?

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Due to the effect of interaction of individual piles, the central piles tend to settle more than the edge piles when the pile cap is under a uniform load. For the pile cap to be rigid, the local deformation of central piles would not occur. Instead, the stiff pile cap would transfer the loads from the central piles and redistribute them to the outer piles. Therefore, raking piles at the edge take up a higher fraction of the total loads and are subjected to higher axial and bending loads in case the pile cap is stiff. In the extreme case, the side piles may take up as much as about two to three times the loads in the central piles and this may lead to the failure of these raking edge piles.

There are several choices regarding the design to tackle the uneven distribution of loads. The first one involves the lengthening of side piles to stabilize the piles under high loads. However, the increased length of outer piles tends to attract more loads and this seems not to be a good solution.

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The other way out is to lengthen the central piles aiming at getting more loads and this evens out the load distribution among the piles

Stress bulb effect on load distribution in piles

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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Comments
  • Marcus May 22, 2013 at 1:46 am

    Dear Sir,

    When is a pile head considered as pinned, and when is it considered as fixed? Can I design a slab/pile connection as pinned considering a slab thickness of 1m and pile diameter of 3m.

    Your comment on this would be most appreciated.

    Best Regards,

    Marcus

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