PILE CAP DESIGN

[voi]

Hi,
I need to understand how to design a pile cap carrying several column loads ( not one column) scattered over the pile cap. All the cases I come across is a single column load supported by 2, 3, 4 etc piles. If I am to assume the total loadings from the columns is at the centroid what column size should i use. Or should i break the pile cap into zones. Then how do i decide which pile is supporting which column load. Please advice,
voi

 

[BAretired]

You need to consider the pile cap as a two way slab with a number of concentrated loads acting upon it. Analysis could be by Yield Line Analysis, Hillerborg Strip Method or Strut and Tie Model, depending on the pile cap thickness and arrangement of piles and columns.

BA

 

[TXStructural]

You could simplify design of the pile group, for capacity concerns, by finding the centroid of loading, and put the centroid of the pile group at that location. This could also be important if there is eccentricity or net uplift concerns.

The cap itself could be designed for shear at sections and for moment demands between piles. Unless there are a large number of these, big-by-stout may be the order of the day, minimizing materials isn't always the economical way to go. It should be acceptable to divide the cap into parts, based on the load and pile configuration, design using the tools you mention (such as the CRSI Design Handbook chapter on pile caps) and make the reinforcement and section continuous into a single pile.

 

[rowingengineer]

a 3D truss model in a analysis program like microstran using strut tie analysis should get you in the right direction. I would start with more struts than required and slowly remove struts until I had my best analysis.

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