Footing Design for House on Piers

[NFExp]

I'm hoping to get some feedback regarding the footing design for houses on piers "Drive Unders". See attached plan. Basically we are designing 1 and 2 story houses on piers for a high wind load area. The piers are masonry and the floor system is wood framing.

Currently our foundation consist of shallow footings 3'x3' connected by grade beams. The grade beams are reinforced with rebar top and bottom and stirrups.

We have gotten a lot of push back from the contractors. The several contractors have mentioned that the standard for the area is to use a 24" wide continuous footing with 3-#5 bottom only. One contractor has even sent us plans from other engineers showing the 24" wide footing.

When I run the numbers, the moments on the grade beam from the lateral wind loads require top steel so I'm not sure how the other engineers are justifying their design.

Please note that the house in the attachment is one of the smaller houses. The houses can get much larger. Typical pier loads are approximately 10k axial and 2k lateral.

I look forward to your comments

 

[SteelPE]

We have designed similar houses in the past.... we have typically used concrete footings with top and bottom steel as well. We have never used grade beams (don't know if there is a reason for that or not). Don't know how others could even justify it as the footings will see both positive and negative bending between the columns.

I'm glad I don't have to deal with your GC as we typically use concrete columns not masonry columns.

 

[boo1]

FEMA P550 Recommended Foundation Types and Construction for COASTAL AREAS Fig 4-6 shows typical detail with top and bottom reinf

http://www.fema.gov/media-library-data/20130726-1517-20490-4124/06_fema_p550_ch4.pdf

http://www.fema.gov/media-library-data/20130726-1516-20490-6981/08_fema_p550_apndxa.pdf

 

[NFExp]

Thanks boo1... I think figure 4-9 is my case Columns with Grade beams (no slab). The figure clearly calls for reinforcement top and bottom. I'll read through the entire document tonight.