Rehabilitating old railway pier 2

[tmalik3156]

Good day.

We are looking into rehabilitating piers of an abandoned rail bridge so that a pedestrian bridge can be installed.
There are no drawings available for the piers. There seems to be no reinforcement in the pier as concrete cover measuring device was not able to detect any rebar.

1. Can anyone please share drawings of a century old concrete rail bridge pier so we can learn how reinforcement was provided those days?

The project is only at brainstorming stage.

 

[BridgeSmith]

The piers may not have been reinforced. The lateral forces on those would have been minimal, so they may not have needed any. Do they work for the ped bridge as plain concrete?

 

[LittleInch]

Are you sure they are concrete and not brick underneath a thick render?

How old exactly?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bugbus]

I recently worked on a very similar project (basically identical). Our piers were about 70 years old, low strength (20 MPa) and unreinforced, although still in decent condition.

Based on what you described, it is quite likely your piers are also unreinforced.

Our calculations showed that the piers had virtually zero reliable overturning capacity under lateral loading (the most severe of which was flood loading), and questionable bending capacity (being unreinforced). (Although clearly they had some capacity since the thing had been standing for 70 years and occasionally going under flood water). Our solution to this was to install a new precast headstock on top of each pier, secured in place by 4x prestressed rock anchors (40 mm DYWIDAG stress bars) installed vertically through the pier and anchored several metres into the underlying bedrock. The anchors provide both stability under lateral load, as well as bending capacity/ductility. We had the benefit that the old deck was still in place, which allowed the drilling rig to be set up directly overhead. I'm not sure if this would work in your case.

Then, a new superstructure was installed onto the new headstocks.

 

[tmalik3156]

Thank you very much for your replies.
I have added photos taken in summer and in winter.

@ BridgeSmith: It is likely that the piers are not reinforced. However, we were told that in old days, they would place some rails vertically inside the pier. If that is the case, then the pier would certainly have significant strength in bending due to lateral load. Moreover, it was also a practice to provide some horizontal rail grillage in order to distribute the concentrated load on top of the pier.
Since we do not have any drawings, we are wondering if such "reinforcements" are provided. That's why I am looking for old pier drawings if anyone has any.

@ LittleInch: That's interesting! We are not sure if there is masonry in the core.

@ bugbus: There is no deck left unfortunately. The height (15.0 m) is also too much to implement the solution that worked for you. Currently, the idea is to chip some (say 100 mm) existing concrete, and then reface with some (say 200 mm) shotcrete or conventional reinforced concrete.

The river freezes in winter. There are some rebars visible at the nosing / cutwater / flared bottom. So likely the pier bottom can withstand ice load or flooding as it has been doing so for probably a century. But the vertical shaft probably has no conventional reinforcement .
The pedestrian bridge will definitely exert a much smaller load than a train.

Please let me know if you are aware of an old practice of putting rails inside a pier as means of reinforcement.

 

[BridgeSmith]

It may have been a common practice to put rails in as reinforcing, but if you can't verify that they did that for these piers, you shouldn't assume anything based on details from something else.

Yes the vertical load of the ped bridge will be much less than it saw as a railroad bridge, but you'll have to watch the moments due to live load eccentricity if the ped bridge is fairly wide. The loading as a railroad bridge would have been centered almost exactly on the piers, so very little live load moment.

 

[LittleInch]

I think you either have to do what bugbus says or chip away y=the base a bit and wrap the exiting pier in say 200mm of reinforced concrete or steel "tube". Use the existing structure for weight bearing and the new outer tube for bending and lateral forces.

Or demolish back to say 10ft off the ground and rebuild in steel or concrete using the existing base which looks pretty solid, as the foundations.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleWheels]

It may be useful to ask some of these questions to railroad historical groups. I have found that, when asked, such groups contain individuals that have unexpected and unlikely information tucked away.

 

[SlideRuleEra]

...please share drawings of a century old concrete rail bridge pier...

1923+, a time of transition. Go back not to many years, likely unreinforced. 1923, could be either reinforced... or not. Here is a "general arrangement" drawing from a 1924 structural engineering handbook. Reinforced (sort of) with 3/4" bars at 2 feet on center:

The entire section of this 1924 book on railway abutment / pier design is attached.

Rails were typically used as horizontal reinforcement for the pile cap or footing, not vertically.

Piers would have been designed for lateral loading from wind (on both the pier and the missing truss) and river current/ice. The way wind design was done (a certain number of psf, maybe 20 psf, or so) this could add up to a significant value.

If you need similar information from and older handbook (more likely to have info on unreinforced piers), I'll be happy to post it.

On another aspect of the project, your photos appear to show "alkali silica reaction". Suggest you investigate, design may have to compensate:

 

[BridgeSmith]

Good catch SRE. Looks like ASR to me, too.

 

[tmalik3156]

Thank you @BridgeSmith, @LittleInch and @LittleWheels for additional information and useful suggestions.

@SlideRuleEra, much appreciated. Please do upload the older handbook you mentioned.

One drawing of the uploaded handbook does show placing old rails horizontally at the bottom. But there are no vertical rails or reinforcements in the shaft.

But the Illinois Bridge does show a grillage of rebars (3/4 inch @ 2') in the shaft. I don't know what a Cor. bar is, but looks like its purpose is to confine the concrete core.

 

[SlideRuleEra]

Thank you, BridgeSmith.

tmalik3156 - Attached is a very short book you may find helpful, "Design of a (Masonry) Bridge Pier" from 1907. Appears to be more about establishing the criteria for design, but that should provide insight into what a vintage pier is (was) capable of doing:

Another book I checked out is the first edition (1914) edition of the same 1924 handbook posted earlier (third edition). The section of the 1914 book on "abutments and piers" shows the same, or very similar, drawing of a reinforced concrete pier. IMHO, the change from masonry to concrete must have started shortly after turn of the century.

About 25 years ago, I worked on early-stage engineering planning for a bridge conversion with a "Rails-to-Trails" group. The "Resource" page of their web site may offer material you could use.

This project was for the "Wateree Passage" of the South Carolina "Palmetto Trail":

One aspect of our involvement was to establish live loading. Pedestrian loading was overridden by the requirement that a 3-axle John Deere Gator be able to travel anywhere on the trail for maintenance purposes. Consider if your project may have a similar need:

The project was conversion of a remote, long abandoned 1900 railroad swing-span over a major river (Wateree River), along with 5 or 6 approach creosoted timber trestles thru the river's adjacent swamp. Note: the photo at the top of "Wateree Passage" link given above shows one of the converted trestles.

FWIW: We also attempted to track down the original Phoenix Bridge Company drawings for the bridge... to our surprise, we were successful. The full set of very large linen drawing, carefully detailed in ink, in pristine condition.

 

[tmalik3156]

@SlideRuleEra thank you again.

The white substance on the pier is likely due to efflorescence (deposit of leached out salt) of concrete. But the cracks may very well be due to alkali-aggregate reaction.

Another photo is attached. There seem to be parallel horizontal lines in concrete. This could be demarcation of each lift of concrete. But it could potentially indicate planes of separation.

Yes, there will be a maintenance vehicle load in addition too the pedestrian load.
Canadian maintenance vehicle loading looks like the following