Concrete Bearing Stress
Concrete Bearing Stress
(OP)
What is the immediate consequence of concrete bearing stress being exceeded in the case of steel column with base plate supported on a pad footing. What is the worst that can happen?
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RE: Concrete Bearing Stress
RE: Concrete Bearing Stress
RE: Concrete Bearing Stress
Can you increase footing depth or bump f'c? What strength concrete are you using?
RE: Concrete Bearing Stress
But, you'd be surprised how far over strength many concretes will reach.
We regularly test all off our pours. Our pours usually require 4 ksi and we routinely test them at 6+ ksi.
This is on a DOT "MS" mix.
RE: Concrete Bearing Stress
RE: Concrete Bearing Stress
You're on thin ice with this one.
RE: Concrete Bearing Stress
40% over is no joke. When you take into account the bump for A2/A1, the bearing capacity is right around the specified concrete strength. If you're 40% over, that means you're approaching f'c for service loads. If you get into a true overload situation, well, I wouldn't be comfortable with being that much over.
The only real remedies (that I can see) are increasing f'c, increasing the footing plan dimensions and/or depth (depending what is controlling the ratio of A2/A1), or a combination of the two.
RE: Concrete Bearing Stress
RE: Concrete Bearing Stress
RE: Concrete Bearing Stress
Yes, they are. An example: Differential settlement of a pad footing induced a moment in the structure that it probably wasn't designed for. Bearing overstress, assuming you really have it, can have a variety of implications, most notably as hokie66 stated...you have other problems you perhaps haven't considered with shear and bending.
If the original concrete design strength (f'c) was 3000 psi and it is 40 percent overstressed in bearing, you now need 4200 psi. Not much of a stretch for most ready mix suppliers, unless the concrete was low strength to begin.
Find out what the actual strength is before you go further....and don't use a Swiss hammer or Windsor probe to check it...take a few cores so that you can visually check the concrete and test its compressive strength.
RE: Concrete Bearing Stress
RE: Concrete Bearing Stress
RE: Concrete Bearing Stress
It is also pertinent to investigate the kind of analysis being performed. Structures redistribute solicitations and as soon as some downwards movement (from initial crushing or sudden increase of settlement) starts, axial load will be transferred elsewhere, to other columns; for fragile concrete not the more envisageable prospective to arrest collapse yet something can do.
On the other hand the on A2/A1 factor resumes what codemakers feel safe to use of 3D constraint at the footing and so you may have found a condition requiring revamping the column at its base.
Respect papers on settlement and differential settlement I would say one should be able to find about the subject in regulatory codes; at least the spanish code is quite somewhat explicit on what must be checked, see attachment at section 2.4.3
RE: Concrete Bearing Stress
www.PeirceEngineering.com
RE: Concrete Bearing Stress
The worst that can happen is that the footing fails in either bending or punching shear. It cannot fail in bearing.
BA
RE: Concrete Bearing Stress