Footing Design in Braced Bays

[waytsh]

I see we have been having quite a few threads on the design of footings for pre-engineered metal buildings. Taking a slightly different angle (no pun intended) I am wondering how most of you are handling the longitudinal reaction from your braced bays in these buildings.

It has been my experience that they can be quite significant and since there is typically not much dead load to speak of in these buildings the footings can become very sizable just trying to resist the sliding and uplift forces.

It can be argued that the grade beam (if you have one) helps provide resistance to longitudinal sliding but could you also consider a portion of it for dead load resistance to uplift? I have typically been designing these as moment footings in most cases and of course they get pretty large.

Does anyone have any tricks to keeping these footings a reasonable size?

 

[msquared48]

Extend the grade beam to load bearing spread footings beyond to increase the overturning resistance.

Mike McCann
McCann Engineering

 

[shin25]

msquared,

doesn't it mean that the grade beam needs to be quite sizeable?

Why not use driven piles when the uplift is that large?

 

[waytsh]

msquared48,

I'm not quite sure I follow. Are you saying that you increase the grade beam with as shin25 described to match the width of the footing?

I'm sure that even a narrow grade beam is going to offer some overturning resistance assuming the reinforcing is tied into the footing. It could get pretty difficult to quantify though since your grade beam would be a continuous beam across the footings.

Thank you for the response.

~waytsh