Rigid pilecap and flexible pilecap

[cstwk]

Which type of pilecap distribute load equally to piles - Rigid pilecap or flexible pilecap?
I came across two conflicting views on the above question:
View A - A rigid pilecap distributes load equally to the piles if the load is applied at the center of the pile group. The reason is that since a rigid pilecap settles uniformly, the load experienced by each pile is the same.
View B - A flexible pilecap distributes load equally to the piles. The reason is that a flexible footing under vertical load has non-uniform settlement but equal load distribution beneath the base of footing.
Hope somebody can enlighten me on this.

 

[dlew]

cstwk,

View "A" seems correct to me. A infinitely rigid pile cap will not deform, but could tilt. So, only if the piles are symmetrically placed about both horizontal axes passing through the column centerline, all the piles will share the load equally and will shorten the same magnitude.

A flexible pile cap will bend, and since the shortening of the piles will be different , the load will be also different. The piles closer to the load will carry more load than the ones located farther. The more flexible the pile cap, the more difference in the load carried by the piles. Only in the case where all the piles are equidistant from the load, would them carry the same load.

Regards

AEF

 

[Ron]

Well....actually I would consider neither to be correct. Load will be transferred to the pile according to its ability to resist it. If the piles are sufficiently strong with adequate reserve capacity, a rigid pile cap will tranfer load more uniformly to the piles. In the event that one or more piles in the group has a greater soil/structure interaction than others in the same group, then load will not be distributed uniformly among the piles, without regard to the stiffness of the cap.