Retaining wall LRFD 5

[precast78]

When you design retaining wall and you have live load surcharge. Do you add the vertical live load surcharge to the heel? Or do you only apply the horizontal? It seems having LL surcharge helps my over turning instead of hurting.

 

[dcarr82775]

I include it. If you have the added lateral from the surcharge you must have the corresponding vertical component.

 

[jayrod12]

I don't include it when checking overturning or sliding but include it when I'm looking at bearing. It's conservative but that's what I do.

 

[msquared48]

The vertical live load surcharge creates a lateral force contributing to overturning. So, if present, it must be included in both the overturning moment and resisting moment calculations.

Mike McCann
MMC Engineering

 

[BadgerPE]

Also, be sure to check the wall for overturning in the absence of all surcharge (vertical and horizontal) forces, to ensure the wall remains stable under just soil forces.

 

[FixedEarth]

I include the lateral load in stem wall design, lateral deflection of the stem, sliding F.S. and overturning F.S. calculations. I use the vertical component in heel bearing pressure, heel shear and heel moment. I don't include it at all if the surcharge begins at a setback greater than 1.5 times the wall height.

http://www.soilstructure.com/

 

[precast78]

So if the heel is shorter than than half the height of the wall, then the worst case scenario would be to have Live Load surcharge at the tip of the heel? That means all you have is horizontal LL surcharge and no vertical LL surcharge?

 

[FixedEarth]

It depends. Draw a 1 horizontal to 2 vertical sloped line from the bottom inside edge of your surcharge and see if it intersects the heel slab. If that lines dives below the heel, then you are right, you have no vertical surcharge. When I have strip load with high intensity or close proximity to the stem wall, I just reverse the footing dimensions - I make the heel very short & the toe the needed width to satisfy eccentricity. Having a high intensity and/or close strip load surcharge can cause a moment reversal on your heel, which is not permissible.

http://www.soilstructure.com/

 

[ztengguy]

Include it, but factor the loads different to produce your max combinations. It could be max lateral/min vertical for eccentricity, or reverse it could be max vertical/ min lateral for bearing or something else. LRFD retaining wall design sucks.

 

[jayrod12]

A clarification on my comment. I include the lateral component of the surcharge in the overturning and sliding but neglect the vertical component. That way I am sure it is conservative.

 

[msquared48]

That is conservative...

Mike McCann
MMC Engineering

 

[RFreund]

In my opinion you need to be cautious including the vertical component. What happens if the surcharge is theoretically positioned so that your wall is being influenced laterally by the surcharge but not over the heal (or withing a 1H:2V as FixedEarth noted? Are you checking this condition?

I find it somewhat surprising that so many use the vertical surcharge to counteract overturning and sliding. I mean some codes will not let you do this as the surcharge is meant to be a de-stabilizing force not a stabilizing force.

It depends on the situation I suppose.



EIT

http://www.HowToEngineer.com

 

[RFreund]

Also your title says LRFD, is there a question about that?

EIT

http://www.HowToEngineer.com

 

[TDIengineer]

This got way more complicated than it needs to be. Review your soil report if you have one.. normally within 10 feet of the wall, the lateral surcharge is approximately 1/2 the vertical pressure. Check the combination with the live load and included this surcharge pressure. Then check the wall/footing without the surcharge.