Axial Loads on Sheet Pile Retaining Wall

[bbagar]

Hello:

I am designing a steel sheet pile retaining wall with a 12"
concrete facing on the front face attached via shear studs. I also have a concrete shoulder/barrier shape sitting on the embankment/facing, and these are introduce axial loads and eccentricity.

What formula do you think I should use to evaluate combined bending effects? For soldier piles I have been using AASHTO Formula 10-43 assuming that the pile is braced against buckling. ( which is (fy/0.472Fy) + (fbx/Fbx) + (fby/Fby) < 1.0 ) Do you think this formula also applies for Sheet piles?

Thanks a lot.

 

[Focht3]

Hmmm, this may not be the right forum for this question - this is really more of a geotechnical engineering forum.

I'm not familiar with the AASHTO formula; but the issue of braced vs unbraced buckling is an interesting one. You don't have a lot of eccentricity; what is the vertical force (per foot of wall) and what is the origin of the force?

Because of anchoring issues, most tied-back sheet pile walls do not carry significant axial loads. Is this a cantilever wall? If tied, back, how? Give us some more details -

 

[JoMartins]

Hi,

there is a chapter in the European pre-standard ENV1993, Part5 dealing with the design of steel sheet piles resisting bending moments and axial loads, but it would be too long to write down the formulas here. Buckling, in most of the cases is not a concern, unless you have high axial loads and/or bending moments.
Those equations are based on LRFD, but as far as I know, most of the design of sheet piling retaining structures are still done using the AWS as there is not yet a widely accepted geotechnical code for designing retaining structures with LRFD.
Steel sheet piles with bending and compression loads are quite common, i.e. bulkheads anchored with battered piles or grouted anchors, bulkheads where the sheets bear the vertical loads from cranes, or like in Europe, bridge abutments. For example, a national code in France deals with vertical bearing capacity of deep foundations, steel sheet piling included.
By the way, the concrete facing being quite thick, it would contribute to the stiffness of the steel section (not only a dead load) and might reduce the deflections (depending on when it would be executed). If it is only meant to protect the steel surface from rust, a coating and/or a thicker sheet pile might be as effective, aesthetically as attractive and it would reduce the axial load. If the engineers do it in Europe, why wouldn't it work in the US.

 

[DRC1]

I would certianly investigate the effects of bending and axial load on the sheeting. I don't recall doing this analysis for sheet piling, but I have done it for soldier piles (HP sections). I have used the AISC ASD 9th ed.(green book) formulas for combined bending. They are very similar, but yield a little higher allowable load. For temporary work AISC is ussually fine. For permenant highway work, you may want to check w/ DOT to see which they will want. You will want to be sure your cap design transfer load to both flanges to prevent localized overstessing.

On soldier piles, the lagging ussualy is considered sufficient bracing parrallel to the wall. If the piles are interlocked, I would think that that would constitute sufficent bracing in the y axis. You need to look at x axis bending. A well connected wale can constitute a brace. Counterflexure in the pile occurs a few feet below the surface, and you would need a few feet of embedment to develop suffient resistance perpendicular to the wall.

One additional point to remember is that the inclined tie backs induce lateral load into the sytem.

I would contact a sheeting producer such as L.B Foster and run by what ever design you come up with by their technical support engineer. They can probably provide a lot more information than I can.

GOOD LUCK!