Eccentric Pad Footing with Tie Bars? 1

[Jfet]

Hi,

I’m working on a warehouse project in Australia involving a pad footing that supports precast concrete panels located on the site boundary. Since the panel is positioned right on the boundary, the footing is highly eccentric, resulting in bearing pressures that exceed the allowable limits.

I was given an example from a previous project by another engineer facing a similar situation. From the calculations, the bearing pressure reached 380 kPa, which is above the allowable limit of 250 kPa. Then the engineer simply added a note stating: “Provide N16-500 tie bars to the slab on ground.”



Apparently a lot of warehouses with eccentric pads like this have been built. I’m trying to understand how the tie bars helps here. Could someone please explain? Some detailed calcs will be really helpful. Thanks in advance.

 

[DaveAtkins]

There is a moment which must be resisted by the slab-on-grade. There will be an upward reaction at the center of the footing, not lined up with the downward wall load. The wall load times this eccentricity is a moment which must be resisted by the slab. The slab will need to be reinforced, and must be heavy enough, to accept the moment.

 

[Nick6781]

You can justify using a uniform bearing pressure if the slab is engaged to tie the footing. The dowel will act as a shear-friction bar to transfer the load.

My diagram shows the balanced horizontal force at the bottom of the footing, though there may be horizontal pressure distributed along the height of the footing. In any case, you’ll also need to check the shear and moment within the footing.

 

[Greenalleycat]

You can justify using a uniform bearing pressure if the slab is engaged to tie the footing. The dowel will act as a shear-friction bar to transfer the load.

My diagram shows the balanced horizontal force at the bottom of the footing, though there may be horizontal pressure distributed along the height of the footing. In any case, you’ll also need to check the shear and moment within the footing.




View attachment 14478

This is my guess as well, though I'm dubious of this detailing in practice
That said, I've seen similar (and worse) detailing here in NZ and haven't observed issues yet...