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Footing design for uplift

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Javier,

 

Regarding the footing uplift question this is a common issue for foundation design with PEMB. For a reference see “Metal Building Systems” by Alexander Newman. In this book he suggests using 20 degrees for cohesionless soil and 30 degrees for cohesive soil. This ref. also has an example. You can also see “Foundation Analysis and Design” by Joseph Bowles 5th edition. If you have a grade wall between exterior columns (common up north) you can design to include this wall, strip footing and associated soil over the strip footing.

 

Best regards,

 

Mark L. Puccio P.E., S.E.

 

 

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From: "Javier Encinas" <jencinas(--nospam--at)asdipsoft.com>

To: <seaint(--nospam--at)seaint.org>

Subject: Footing design for uplift

 

Sometimes in hurricane-prone zones the controlling load in footing design is

uplift. However, the text books are silent about methods to estimate the

self weight to counteract the uplift force. In addition of the concrete

footing we have also the soil cover and the slab on grade. What angle of the

cone is appropriate (45 degrees?), and what is the tributary area of the

slab that helps to keep the footing in place? Any good reference on the

subject, or full scale tests? Thanks in advance,

 

Javier Encinas, PE

 

 

 

 

Mark L. Puccio P.E.,S.E.

Structural Engineer/ Principal

MP-Squared Structural Engineers

mpuccio(--nospam--at)mpsqrd.com