Minimum reinforcement in Pile Caps

[Dia10]

I have the following questions regarding pile cap reinforcement

1. In general top reinforcement in pile caps should be provided where tensile stress is anticipated on the top fiber of the pile caps. This will be typically due to net uplift forces on the pile cap from the building structure or due to the fixity conditions of the column base. If the coulmn is a gravity column designed as pinned at the base then there will be no flexural stress and therefore no tensile stresses at the top of pile cap.

2. For a 2-pile group pile cap; there is no flexural stress in the short direction at the bottom of 2-pile cap. The requirement of minimum reinforcement for structural slabs and footings (ACI 10.5.4) applies to the direction of the span (long bars). As I understnad the requirement of shrinkage and temperature reinforcement (ACI 7.12.1) applies to structural slabs only. I could not find in the ACI does the minimum reinforcement requirement in the short direction of one way footings or pile caps. Currently I provided 7#4 bars in the short direction of the 2-pile group pile cap and that follows CRSI Design Handbook 2002.

My question is; does the ACI mandate the top reinforcement in pile caps to meet the temp& shrinkage minimum reinforcement if there are no tensile stresses anticipated at the top of the pile cap? Is there a minimum requirement for the short direction bottom reinforcement in a 2-pile cap?

Dia

 

[civilperson]

The two choices in ACI 7.12 are either: 1) structural slabs ,or 2) soil-supported slab on grade. the pile cap you describe is in category 1, thus shrinkage and temperature reinforcement is required. Place in the bottom on top of the longitudinal flexural steel.

 

[WillisV]

In general, ACI differs to CRSI for pile cap design and reinforcing.

ACI does not require TOP reinforcing be placed in either direction if no flexural tension exists.

Per CRSI it is common practice to provide temperature and shrinkage steel in the short direction of the pile cap. This is generally all placed in the bottom of the cap as you have been doing.