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I think AASHTO and ASCE are divergent when it comes to the gust effect factor. ASCE allows the 0.85 for a rigid structure. AASHTO considers everything a wind sensitive structure and defaults to the 1.14 G value. So instead of decreasing the force by 15% the value is increasing by 14%. Not as...

I like this approach JoshPlumSE. I'll run some numbers using this approach and see where the design lands.

Thanks ZiggyKS....I think the AASTHO LTS is based on ASCE 7 but I was not aware of the 10, 25, 50, and 100yr MRI tables. This will be helpful in the analysis. Thanks for pointing these out. You are correct on the design approach as well....it's kind of a one (or two or three) size fits all...

yes...i'm in CA but registered in CA and FL. The design is somewhat generic in nature and is intended to be applied in multiple areas....am looking at worst case scenarios. The wind seems to be the controlling factor. Seismic force is high but the moment created by it is similar to thw wind...

yeah....AASHTO LTS and ASCE 7 have all of the coastal regions pretty much at that level or higher for the 300yr MRI which is the lowest risk category.

in agreement with you milkshake....have a client though that is wanting to make this footing as small as possible and is using the design of a prior engineer as justification to use the Pp in order to do that. I'd rather not use it but am having a hard time arguing against it....was looking for...

thanks everyone....to milkshakes point.... Wind Pressure Pz = 0.00256KzKdGV^2Cd With a wind velocity of 150mph and all other factors per AASHTO LTS the wind pressure on an 8ft tall by 3ft wide sign is approx 125psf. This creates an Mo of about 18000lb-ft. A Pp of 800lb-ft is supplying 4.5% of...

Thanks for the replies. I think there's always a chance of loss of passive pressure with shallow spread type footings...flood, scour, landscaper moving dirt, critters, kegger down the street :) For that reason I typically discount it. The client being a precaster though wants the foundation to...

thread507-367772 I have a client wanting a design for a shallow precast sign foundation. A prior engineer on the project utilized soil pressure (from the backfill) to resist sliding and overturning from wind, seismic, and impact. This is contrary to what I know is correct (for overturning at...