Soldier Pile Design

[smascia87]

Hello,

I am currently trying to check a temporary soldier pile & Lagging Wall design (for estimating purposes). I know how to figure the embedment depth of the piles, but I am having trouble designing the actual soldier pile itself. Should I check LTB? It seems like the SP would be braced by the Wood lagging. Is it as simple as designing a steel beam for a moment and shear? If so, I am trying to use LRFD, what factors should I apply to the moment on the beam?

 

[PEinc]

If the lagging is installed on or just behind the front flange of the soldier beam, the beam is considered fully laterally braced.

For most LRFD soldier beam projects I've done, the load factors are 1.5 for earth loads, 1.0 for water loads, 1.75 for live loads. Resistance factors have been 1.0 on soldier beam bending and passive resistance. I can't remember when shear was ever a controlling factor in one of my soldier beam designs.

If this is a highway project, you should check the DOT and AASHTO soldier beam design requirements.

http://www.PeirceEngineering.com

 

[smascia87]

The front flange would be the flange away from the retained soil correct? In my case, the lagging is held by angles in between both flanges (connected to the web). If I am to consider LTB, would the unbraced length be the wall height (not including embedment depth)?

For the Passive side, do you still use the .08*Phi*Flange Width to determine the tributary area that it takes?

Those load factors would be in addition to the SF. Correct?

Thanks for your helpful comments. I will definitely check DOT/AASHTO.

 

[cntw1953]

As PEinc pointed out, LTB wouldn't be a problem for soldier beams, which have restrain on 3 sides. But, if you would like to check into it, I think the unbraced length shoud be measured from the top to the theoretical inflection point, somewhere below the ground level.

 

[PEinc]

Lagging held by angles connected to the soldier beam web? Why? Sounds expensive.

Never heard of (0.08 x Phi x Flange Width) for calculating the passive resistance width. Usually, the width is just 2 to 3 times the flange width or drill hole diameter if filled with lean concrete or flowable fill. However, 0.08 x phi is usually about 2 to 3.

The load and resistance factors provide the safety factor. You don't need to add another safety factor on top of the load and resistance factors.

Again, USUALLY there is no unbraced soldier beam length to consider.

http://www.PeirceEngineering.com

 

[ishvaaag]

The rationale for embedded piling is that lateral support is provided by the soil, then no buckling can happen and the full section is of use.

For soldier piles you have the soil to 1 side, lagging at 2 sides, and points of support where at the heights the tie back action serves them as reaction point. The only face where buckling is possible is towards the void being made for the basement, and the situation is difficult to model more than anything because of the varying displacements imparted to the piles by the anchors to the ground. Anyway assuming the thing straight you have K factors of about .5 of the difference in height between the anchoring levels, that is not much for quite stout piles, and so scarce reduction in capacity is to be expected by this calculation. With ampler displacements like those caused by failure of anchor points we would see failure of the piles etc at bigger lengths of buckling but would be a secheme of overall failure behaviour of unlikely consideration for normal designs.

 

[smascia87]

Thanks to everyone for helping me out. I think its safe to say LTB is not an issue. The lagging is placed as described earlier because the owner wants to pour concrete in front of the lagging.

The owner has already required a 1.5 SF on the wall by requiring KP to be divided by 1.5. Now my only problem is designing the actual Soldier beam.

For LRFD, I would simply use Mu=.9Mn where Mn is the max moment calculated. Then use Mu=Zx*Fy .

For ASD, I have seen Ma= Sx*Fya where Fya= .66*Fy .

These two methods produce vastly different sections, so I am concerned that something is wrong. Please advise.

 

[cntw1953]

It wouldn't surprise me if LRFD yields a smaller section. Check deflection to see if the section works or not.

 

[PEinc]

When you check deflections, you need to redesign the wall using service loads, not factored loads.

http://www.PeirceEngineering.com