Combined Footing Design

[raleigh0527]

I designed combined footing with the used of Staad Foundation V8i ver 5.3. The size of the footing is 9.7 by 0.9 meter, depth is 0.45meter, I have to limit the width and the depth, because the footings were exposed. Having a larger width, the wheel of the SPMT will clash on the footing. The result Staad Foundations give the size of the footing, the size and spacing of Rebars. But when I checked for the calculation, there is a computation which confused me, on one way shear, the Vu is greater than phiVc but the staad said that result is OK. Thus Staad Reinforced this one way shear with Rebars??

Also I just wanna asked if i can used the formula for Vc=2*sqtrf'c*bw*d for checking for one way shear, if I designed the combined footing with the columns not on the center of the width, I will adjust the 0.9 meter to 1.2 meter, 0.3meter will be added on one side of the footing only.

 

[BAretired]

What code are you using? What is the SPMT? Where will the columns be centered on the 1200 mm wide combined footing?

Offsetting the footing will increase the soil pressure on one edge. It will also result in greater one way shear stress near the same edge.

You don't provide enough information to permit anyone to answer your question. Maybe a sketch would help.

BA

 

[raleigh0527]

thanks Ba.
column would not be on center of 1200mm wide.

SPMT Self Propelled Modular Transporter.

Can one way shear be reinforced?

 

[raleigh0527]

I will provide sketch later. thanks

 

[BAretired]

Where would the columns be centered on the footing, i.e. what is the eccentricity from the center of footing? I assume that the center of column is closer to the edge than 450mm or you would have simply used the 9.7 x 0.9 meter footing with columns centered. If the column is outside the kern of the footing, the additional width will be ineffective.

One way shear can be reinforced. In a 450mm deep member, it would be usual to reinforce with stirrups. With eccentricity of loading, the shear stress will be varying linearly across the footing.

BA

 

[raleigh0527]

if i will use the 900mm width, the center column is in the center of the footing, but the one way shear will fail. staad foundation gave spacing if stirrups, thus the staad foundation already reinforced the one way shear failure.

on the other hand, if i will adjust the width to 1200 for example, the center of the column will remain 450 from one edge and 750 from the other edge.

 

[raleigh0527]

I cant email the pdf file from my office computer to my cellphone, Im using my cellphone for internet. i just took photos, hope it will help

 

[hokie66]

If the 900 wide footing works, why do you want to enlarge it? If you don't know how the Staad program works or how to design the footing manually, you should not be attempting this design without a mentor to work through any issues you have.

 

[raleigh0527]

Thanks hokie, my only concern for the 900 is if it is already reinforced by the stirrups given, because one of my co-engineer told me if the one way shear fails, the only solution is to enlarge the footing.

we dont have a mentor yet, and this is the first time we encounter this problem, so I decided to ask a help on this forum.

your comments were very much appreciated.

 

[raleigh0527]

how to compute allowable soil bearing capacity, if i have to consider settlement, example if i have a 50mm what is the allowable soil bearing capacity. i already have subgrade modulus reaction..