Q.: I am designing pile caps for 2-, 3-, and 4-pile groups. What reference can I use that covers pile cap design procedures for both flexure and punching shear?
A.: Numerous groups specialize in foundations, such as the Deep Foundations Institute, ASFE, and ASCE's Geo-Institute. But designing the "pile cap" part of a pile foundation seems to fall back into the realm of structural engineering.
As such, one good resource is the American Concrete Institute (ACI). It offers the "Design Handbook in Accordance with the Strength Design Method of ACI 318-97," also known as SP-17 and ACI 340R-97, that deals with such designs and gives some examples and design aids as well.
Pile caps are covered in Volume 1, which includes step-by-step design procedures accompanied by references to the applicable sections of ACI 318. The procedure also has cross-references to design aids provided in the handbook, as well as design examples and a commentary section that explains the basis for the design aids.
Another possible reference would be the book Design of Concrete Structures by Arthur H. Nilson and George Winter. In the 11th edition (1991, McGraw-Hill) the chapter on Footings and Foundations devotes nearly four pages to pile cap design, which only brushes the surface of the topic.