AASHTO - Steel box section/ sheet piles

[Useeeer]

Hello everyone!

Does anyone here have worked out example for design of flexural members with box section? I've prepared the design calculations based on the standard but couldn't get any solid examples for box sections. Lot of examples on I section are there. I need something to validate my sheet. Also, have anyone designed standard sheet piles using AASHTO LRFD Bridge design specs. Mostly we refer to Eurocodes which have specific guidelines for sheet piles like AZ, PU, etc. AASHTO was agreed for RC wall design and down the line, concept was changed to sheet pile, and no one wants to change the criteria now. I'm trying to associate with single symmetry box sections in AASHTO. Should I pay any attention to any other particulars while doing so?

 

[BridgeSmith]

Sheet pile loading per AASHTO LRFD would be in accordance with Figure 3.11.5.6-3, -5, or -6, depending on the retained and embedment soil types. Design criteria is in Subsection 11.8.

I'm not sure what you're using the steel box sections for, so I'm not sure how to help you there.

 

[Useeeer]

The above-mentioned figures indicate the force distribution and criteria for evaluating the embedment depth. Basically, geotechnical aspects, I believe. Section 11.8 indicates forces to be considered for structural checks. I'm looking at evaluating the structural capacity (utilization ratio) against the design actions (compression, flexure and shear).

 

[BridgeSmith]

The structural capacity for sheet piling is section modulus (provide by the manufacturer) multiplied by stress limit for the steel. At least that's how I've always evaluated it.

On a typical sheet pile wall, axial compression is negligible, and shear demand is so far below the capacity, that we don't even check it.

The method I use for finding the maximum moment is fairly complicated. It involves finding the point of zero shear by solving a quadratic, and then summing the moments due to loading about that point. I can't remember where it originated.

 

[Useeeer]

That is based on ASD. Isn't it? As per the latest edition, I couldn't find any provisions for ASD. They want to follow LRFD.

 

[BridgeSmith]

The method used is the same as ASD, but LRFD factors the embedment depth needed for stability by 1.2 to get the required embedment. The retained soil and surcharge loads also have load factors.

 

[Useeeer]

Sorry for late response. Design methodology for LRFD is clear. Why I asked for any closed section example is.... The proposed sheet pile is subjected to substantial vertical load from bridge bearing as well. If you look at Eurocodes, we have clear limitation on thickness for a cross section and accordingly the buckling factor will vary (apart from the Euler's bucking load). Currently, I've limited the thicknesses prescribed for box sections in AASHTO to avoid getting beyond the slenderness limit (cross section wise). Regarding design forces, we coordinate with geotechnical team and get them from Plaxis software. But I would like to know about your way of calculating moments to be handy in future. I had a hard time checking the behavior in PLAXIS