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[jaa046]

Can anyone help me understand why answer to this problem is C?

I have attached the problem in this post. Thanks for your help!

 

[Ble_PE]

I'm not sure how much structural background you have, but when you design a footing for uplift/overturning you always want to look at the worst case scenario. This always means you want to use the least amount of vertical load to counteract whatever force is causing the uplift (in this case wind). This means you would only use the dead load.

To go into more detail, if you can remember your structural analysis or statics class, the wind load applied to the top of the frame can be resolved into a moment by multiplying the force by the height of the frame. You can then resolve that moment into a tension-compression couple, which would give you an uplift force on footing A and a downward force on the other footing. Then you combine that load with the dead load in the column to get the total load on the footing.

Does this help?

 

[sac_engineer]

So the answer would be C, right? You don't use the live load because that would reduce the uplift resistence in Footing A.

 

[PEinVA]

Yes. The OP says the answer right in his post. Is this the depth of structural in the morning?

 

[treyjay]

So the answer would be C, right? You don't use the live load because that would reduce the uplift resistence in Footing A.

the answer is C, but you don't use the live load because you cannot count on the live load being there. if the live was there, it would increase the uplift resistance.

 

[MA_PE]

So the answer would be C, right? You don't use the live load because that would reduce the uplift resistence in Footing A.

the answer is C, but you don't use the live load because you cannot count on the live load being there. if the live was there, it would increase the uplift resistance.

X2 or 3 or 4. what they said.

 

[jaa046]

My understanding was to get worst case scenario you need to take moment about footing A: (Wind load x Height of footing) + ((dead load + live load) x distance between footing).

I thought the answer will be wind + dead + live load, am I doing something wrong?

 

[MA_PE]

The dead load component will always be there so it is always considered. The wind will cause uplift. the live is a temporary load and will resist uplift so it should be ignored.