footing overkill on clay? calculation method


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Old 07-30-12, 11:27 PM
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pier overkill on clay? calculation method

10'x 10' structure
6 4x4x8 Pt Southern Yellow Pine
12'' diameter piers 16'' deep resting on 4'' gravel on clay
min. snow load in Texas 20 psf
roof pitch 1.2/12

Assuming Southern Yellow Pine 2x8 and 4x4 weighs ~ the same as Douglas Fir 2.6 and 2.98 per foot resp. Rounding these up to 3

240 lbs 8 2x8x10
180 lbs 6 2x6x10 (assuming weight is equiv. to 2x8)
241 lbs roofing material
150 lbs 4x4 post
75 lbs 4x4 upper post bracing
200lbs sheet metal screws, zinc bolts, screws, nuts, washers, hangers, base,etc
Total Dead Load ` 1100 lbs


6500 lbs Assuming 1' cubed ice weighing 65 lbs per cubic foot
Total Live Load ` 6500 lbs

Total load ` 7600 lbs



CALCULATION 1
clay is 2000 psf (but assuming it is 1500 psf), then piers should have ` 12.44 '' diameter
used ehow
How to Calculate Concrete Piers | eHow.com

CALCULATION 2

do not know if used correct formula w/ safety factor
(8000x3)/6 = 4,000 lbs per pier
using concrete rated at 4,000 psi


CALCULATION 3

This 10'x10' structure seems overkill , because if the maximum weight that will ever be on the soil is 8,000 lbs over 100 sq ft area , then each square foot of soil only needs to be able to support 80 pounds

do you guys have any opinions or website referals
 

Last edited by flatbread; 07-30-12 at 11:43 PM.
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Old 07-30-12, 11:43 PM
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I am assuming you have run this past your building authority for a permit. They will give their blessings or tell you about local code upgrades needed. Otherwise, the weight should be OK. I question the shallow pitch on the roof, even for rain, much less snow load. What are you spanning across the front and back with at 10'? LVL? You are using PT lumber for posts and setting them on Simpson Strongtie Post Bases, right?
 
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Old 07-31-12, 12:57 AM
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Yes.
Was planning on 2x8 for front and back spans, but 2x8s can not span 10' either? Will consider LVL after saving a 100 . this must be the only way a wooden carport can have beam span of 10',
unless you double up the 2x8s with 3/8'' plywood secured between them?

Right, setting Pt post on Simpson Strong Tie post bases
ZMAX 4x4 Standoff Post Base-ABA44Z at The Home Depot
 
 

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