Dissipation of Axial Load in Continuous Waler

[awatka]

I am looking for a good reference on how to model the dissipation of the axial load in the wale into the wall of a rectangular earth retaining system. Thank you in advance for your help.

 

[csd72]

awatka,

Not sure what exactly you mean.

The axial load is usually assumed to be opposed on opposite ends of the excavation.

 

[awatka]

On deep excavations, the waler is subjected to extremely high axial loads from both the opposing walers and corner braces. ASCE Geotechnical Special Pub No. 74 (Pg. 96 - Guidelines of Engineering Practice for Braced and Tied-Back Excavation) verifies this by stating "Because combined bending-compression is critical to wale design, an important consideration is the dissipation of the axial load in the wale into the wall and thus into the retained soil."

I am trying to find out how to model this dissipation for a sheetpile wall in order to achieve the most economical wale size. If dissipation of load is not considered, the size of the wale can become tremendously large and costly.

 

[PEinc]

I saw this unsuccessfully attempted once in the past. A MAJOR collapse resulted. I have never seen a reference on this dissipation. I don't doubt that some load is dissipated; I just can't say how much. Remember, the steel wale is much stiffer than the soil that may (or may not!) be surrounding the soldier beams or sheet piling. If the wale is stiffer, it will not shed the load so easily.

http://www.PeirceEngineering.com

 

[csd72]

I always tend to disregard this as it relies too much on friction which is not guaranteed.

 

[InDepth]

I agree...I believe the reference is that the waler dissipates axial load into the sheet pile and then through side friction into the soil. You would have to be very careful about your assumptions because you shouldn't consider that the sheet pile wall is always perfectly in contact with the soil and engaging it. Theoretically you could model the sheet pile wall as a shear wall abc the waler as a drag element.

Ultimately, I think the answer is that you balance the axial load with the opposing side by making the waler continuous.

 

[USGeotech]

We always assume the axial load is dissipated into the sheetpile or soldier pile wall then into the soil. The walers must be welded to the walls, particularly near the ends of the wales. A free-body diagram of the wale and load path would show that the end reactions pass must pass through the welds, then into the perpendicular walls, then into the soil. Obviously, the welds must be capable of resisting the reaction load, and the perpendicular walls are treated as if they are diaphragms. The diaphragms must be (and usually are)stiff enough to tranfer the load.

In a one-story building subject to wind load, the wind load is transfered from the walls to the foundation at the bottom and to the roof at the top. The roof diapragm must be stiff enough to transfer the load to the moment resisting frame. AISC has a guide for determining the stiffeness of the roof. Using that guide you'll find that a sheetpile wall has plenty of stiffness to accept the "dissipated" load from the wale end reaction.