Uplift force at combine footing

[neaveyoung]

Recently I analysis a combined pad footing. The combine pad footing has two stumps which is the one of the load is greater then another one about 3 times. The lighter load is uplift force. Could anybody help me?

1.Do I need to consider the uplift force in design the combine footing? If need what shall I do?

2.How can I determine the footing size which one load is uplift force?

Thanks.

 

[asixth]

You sure do, if there is two columns supported by one pad footing with unequal loading, there will be an uneven pressure distribution underneath the pad footing.

You can calculate the axial load (Pnet) from column 1 and column 2...

Pnet=Pcol1+Pcol2

Like wise you can calculate the net moment by taking moments about the geometric centre.

Once you know the moment and the axial force, you can calculate the bearing distribution underneath the pad footing.

You must also check the slab for this moment.

 

[neaveyoung]

If the col1 is uplift force then the

Pnet = (-Pcol1)+(Pcol2). Correct?

so can i find out the footing size base on this Pnet? Because i'm not consider the uplift force. I assume it as downward force so i work up the size will be conservative.

If one uplift force and then one downward force so there will be over turning for the footing. Is that the self weight of footing and the weight of soil can resist this overturning?

Please help if i have misleading.Thanks.

 

[lexim]

Remember to check the Bending Moment cased by teh uplift force on the top of your footing and provide appropriate reinforcing there.

Also check for punching shear on teh large load and a pull out resistance on the uplift force.

Lexim