Retaining Wall Surcharge Loading

[WBUW]

Hello all,

I've got a 12' retaining wall that I'm working on for a subdevelopment. There will be sidewalk right next to it along with curb and gutter and then a road.

For H20 loading at a 6' distance if one goes through the California Trench and Shore manual, analysis as point loads comes out to about a 300 psf surcharge for an H20 vehicle driving 6' from the wall.

The IBC specifies a live load of...I think its a 250 psf or 200 psf can't recall and don't have my IBC on me right now, for sidewalks, which will be cast right up against the wall. I assume this is for if and when small vehicles happen to drive on the sidewalk, but I'm not 100% clear on the intent.

This will be a cantilevered concrete wall with a fence stuck into the top.

I'm wondering if I need to stack these two surcharges (550 psf) or if using the 300 psf surcharge pretty well covers it.

Thanks in advance!

 

[msquared48]

Just use the 300.

REAL difficult via laws of physics for two bodies to occupy the same space at the same time.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[paddingtongreen]

Mike, they are not in the same space, one is on the sidewalk and one is in the road alongside it. I would think that the construction loads might go as high as the combined load.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[SlideRuleEra]

I agree that you do NOT have to sum the 250 PSF & 300 PSF loads. However, I would simultaneously apply the 300 PSF surcharge load (California Trenching & Shoring Manual, Page 6-22) to the entire width of the sidewalk + curb / gutter + traffic lanes. Don't want the wall to be damaged / collapse just because a truck may happen to jump the curb and wind up on the sidewalk.
This would also cover the (temporary) construction load of 72 PSF (see Page 6-1).

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[WBUW]

Thanks for the replies.

Regarding an H20 truck jumping the sidewalk...the 300 psf load is based on a fixed distance of 6' between the tires and the wall.

If a 16 kip point load is placed 1' away from the wall the load goes up pretty substantially. The 300 psf surcharge will not account for this condition I don't think.

 

[cancmm]

Regarding the point load at 1' away. Yes this does increase the loading substantially. However, the effect is localized to shallow depths and a relatively small width of wall. Research point load surcharges for the equations on how the stress varies with depth and width on a given retaining wall. They can be found in many geotechnical texts. Also remember that the concrete will distribute the stress concentration to a greater area than which it is applied.

 

[SlideRuleEra]

Agree that the 300 PSF load does not account for point loading, it is a simplifying assumption as stated on page 6-22. cancmm's explanation is a good reason why.

Trying to analyze every possible scenario would not only be time consuming but not very practical. For normal situations a surcharge load of 300 psf spread over the width of the traveled way should be sufficient.

Using software a "precise" (not necessary accurate) solution can probably be obtained. However if this is done, then the 300 PSF assumption should NOT be included in the calculations - never mix simple assumptions with exact calcs. A precise solution could include the H20 wheel loads, IBC 250 PSF uniform sidewalk load, and be sure to consider the 8000 lb point load (actually on 20 sq. in.) applied at any location of the sidewalk (IBC 2003, Table 1607.1, Item 32, Note "e")

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[Splitrings]

'96 AASHTO Bridge Specification requires a min. of 250 psf surcharge for the vehicle live load. It also specifys that permanant point load and line surcharges other than vehicle live loads be considered. It lists procedures for calculating these additional surcharges as well.