Soldier piles using encased steel railroad rail

[Brandon]

I posed this question over in the Structural Engineering forum, but it occurred to me that perhaps the retaining wall guys might have had some first hand experience with this. In short we have a contractor proposing to utilize salvaged steel railroad rail as reinforcement for drilled concrete piers in a soldier pile wall application. They have done this on several projects before with what they claim are barely any deflection, and they assume full composite action of the steel rail & concrete working together. The rail is a 132lb per yard section that is 7-1/8" deep, placed near the tension face of 36" diameter drilled piers spaced at 5' c/c. Maximum retained height above bedrock is 25'.

The biggest concern we have is the assumption of composite action, which may very well be the case, but we have not found sufficient evidence or research to support such behavior for encased steel sections with no shear connectors or reinforcement. In fact, AISC has specifically stated that encased sections in beam applications must have shear connectors (though they disclaim any application of their specifications to non-building applications). We have come across some research and some statements in Handbook of Structural Engineering Second Edition by Chen & Lui which seems to back up this practice, but current codes do not seem to bear witness.

Another way to look at it (perhaps more appropriate?) is to consider the steel rail as reinforcing steel in a traditional reinforced concrete section. However, the concern here is with bond and development length of the steel since it is essentially smooth. The contractor claims that in this case that 50% of the bond strength of deformed bars is appropriate, as studies have shown that "bond" is actually about 50/50 chemical bond & mechanical bond.

Has anyone had any experience with such an application? How have you analyzed such a section? See attached photo for a scale drawing of the proposed section.

 

[dcarr82775]

I wouldn't even dream of cantilevering 25ft with this setup. I would also tend to not believe a contractor that claims they cantilever 25ft with barely any 'deflection'. Unless they are digging in rock. What kind of soils are being retained?

Say you stick with elastic section properties. Calculate what you would need to satisfy the horizontal shear requirement. That would give you a ballpark (Comerica outfield sized ballfield, not a cozy one like Fenway) of a bond stress between concrete and steel. See how that feels to you. It doesn't feel real good to me, but I don't have any numbers. I also don't like the uneven distribution of steel, and the shear strength on unreinforced concrete at that height.

 

[BigHarvey]

Using H or I beams is quite common in soldier piles, therefore why not a rail. It's not a problem. The problem is like dcarr states, it's doubtful you can cantilever 25 feet. You certainly need some anchors.

 

[PEinc]

I agree with BigHarvey. This sounds like a very expensive wall using large diameter (36") holes, drilled into bedrock, at a very close spacing. Twenty-five feet is very (too) high for a cantilevered wall (unless it is an expensive tangent or secant pile wall, which the described wall resembles); but it is not very high for a tiedback soldier beam wall. Is there a reason that tieback anchors cannot be used? Is the wall permanent or temporary? The cost would depend on whether or not the wall is permanent and what type of permanent, finished facing might be required. Drilling soldier beams into rock at 8 to 10 feet on center is a lot cheaper than 5 feet on center. Yes, tiebacks and a permanent facing would add cost if this is a permanent wall. Usually, the key to an economical wall is to reduce drilling for soldier beams, especially rock drilling.

http://www.PeirceEngineering.com

 

[dcarr82775]

A W or H section has real non-composite bending strength. A rail doesn't. I wouldn't consider a W or H shape composite for strength purposes unless they had H.A.S. either

 

[msquared48]

Also, usually the concrete is a very low strength so it can be easily removed for the installation of temporary wood lagging, with the W shape taking ALL the bendng. Is there no lagging here?

Mike McCann
MMC Engineering

 

[Brandon]

msqaured-
This is a tangent wall with plain concrete plug piers, so no lagging.

We have done some additional research and decided to analyze it as a reinforced concrete section, utilizing bond stress for plain bars from the earlier ACI codes (1963 I think) to determine appropriate development length. It doesn't work for all cases the contractor is proposing (i.e. heights over 20' or so) but it works for most. I hope to be able to post more details soon when I get time.

 

[fattdad]

how were the rails legally sourced?

f-d

¡papá gordo ain’t no madre flaca!

 

[Brandon]

fattdad-

Are you referring to made in the US, or legally as in not stolen off some abandoned rail line?

 

[dcarr82775]

Still a terrible idea IMO. Applying a design code in a way clearly not intended while using materials that are clearly not allowed per that Code. Good thing the contractor has your E&O policy to fall back on.

For a 25ft cut, unless you are in some respectable rock at the bottom, you are looking at a rail at least 50 ft long. Do they have single pieces this long?

Do these shafts need casing? I have seen full rebar cages shift significantly in shafts during casing removal. So if these holes are cased, know that your rail WILL be located somewhere other than you want it once the casing is out. I suppose you have a shot at keeping it in the right place without casing.

Is this wall permanent or temporary?

 

[fattdad]

Brandon,

According to CSX, there is no secondary market for railroad materials. You can't recycle it, for example. If there was a secondary market, crooks would take such "free" material at the expense of public safety. The train company is supposed to collect it all and then under chain of custody, melt it down. To see quantities of rail in the secondary market makes me consider the chain of custody of the contractor. Now I'm not suggesting that the contractor is taking his own, but it does raise a red flag to me. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[Brandon]

dcarr- Thanks for your thoughts. The construction issues you mention are certainly things that we will consider in our final response to the contractor. The current design calls for rails as long as 38 ft. I thought I had read somewhere that standard lengths were 39 ft?

f-d - a quick google search yields results of several contractors who specialize in removing rails, and others who keep an inventory of salvaged rail. I also came across an invitation for bids from the Dept. of Energy to remove old rail lines. The request stipulated that the contractor must certify that they will not sell the rail for scrap or smelting, but that they will only sell it in its current physical form. I'm not saying your info is incorrect - just trying to get to the bottom of this. If there are potential legal issues, I would certainly want to know.