wood/steel stake capacities in the ground

[hawkinjc]

Does anyone have capacities or methods for obtaining capacities for 2x4 wood or round steel stakes into the ground for wall bracing against horizontal loads (wind). We currently brace our wall forms to concrete deadmen and use the friction between the deadman and the ground to arrest our force. Thanks in advance for any help.

Jon

 

[jdonville]

Assuming the ground will hold, the limiting factor is the flexural and shear capacity of the dowel/stake. However, relatively thin elements like rebar would be expected to plow through the near-surface soil material to some extent.

Figure on a rough estimate of allowable lateral resistance of about 100 lb per foot of width and per foot of embedment of the dowel. Dowels should be spaced C-C no closer than 3 times the width of the dowel.

The problem is essentially the lateral response of a single pile. Reese and van Impe have a pretty good book on the subject, and many of the methods that can be used are documented in the COM624P documentation.

Your mileage may vary, and it sounds like the deadmen are a good way to go without involved engineering.

You may also want to look into an engineered product, although I don't know of any offhand.

Jeff

 

[msquared48]

If you drive the stake deep enough, the stake will fail rather than the soil. You might be able to approximate the resisting force using the pole footing equations in the IBC, realizing though that these equations are for drilled and placed poles (stakes), not driven.

Mike McCann
MMC Engineering

 

[RHTPE]

In an application such as this, it first helps to define "failure". It has been my experience that excessive movement can occur before a stake actually fails. Depending upon the angle of the brace, form movement away from the stake can pull the stake from the ground. That movement can be the cause of an out-of-tolerance wall, which can result in costly repair or replacement.

Concrete deadman can be an excellent brace-to point, but depending upon the ground surface properties, they can slide on the ground due to brace loads. I have found that deadmen behave better when "shimmed" with a rough surfaced block at all four corners. This concentrates the load applied to the ground, increasing the frictional resistance and reducing any tendency to slide.

I know of no way to quantify a safe working load for a 2x4 stake driven into the ground. It would be very dependant upon the soil and compaction properties at each location of a stake.


Ralph
Structures Consulting
Northeast USA

 

[csd72]

treat it as a slender pile.