UIUC engineers make rail tracks safer, longer-lasting

Trains Magazine
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Now that I think about it, I suspect that some of what I said in my original post is a misunderstanding on my part.

I do specifically remember Prof Andrawes referring to damage that can sometimes occur when the tension is released. In my head I thought that referred to a violent release, but as the video shows, that would be an easily-solvable problem and therefore probably isn’t what he was talking about.

I wonder if the issue has more to do with cracking at the ends of the tie where the confinement is less and the forces have to develop over some distance? One of the obvious differences between the SMA tensioning and traditional is the (proposed) use of non-SMA rebar “hooks” to ensure proper development - all of it happening internal to the tie. Maybe that’s the advantage?

Dan

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We have undertie pads in North America too, although I don’t know if anyone uses them customarily in open track or only in special sensitive situations like on bridges or next to passenger platforms. We don’t have concrete turnouts on BNSF, but I’d bet they’re used there as well.

The reason they’re not used more widely is because they add cost and they wear out relatively quickly. Unlike the pads under the rail seat, they can’t be replaced in track, so it’s just a question of whether they buy you enough benefits to justify the cost before they wear away.

Dan

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Unfortunately, the original article on the ASCE website is behind a paywall.
But one sentence in the freely accessible abstract surprised me:

The issues observed often are related to cracking patterns developed in specific parts of the crossties, such as the central and rail seat regions.

Source: https://ascelibrary.org/doi/pdf/10.1061/JTEPBS.TEENG-8982?download=true#sec-5
Loads: https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTTvJR_ADcobzXv6X8YyGfKnW8WzLJc-eqJDg&s
Acording moments: https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTg7pbkWJjmOgtrXx3lZKWK8Zxjhs4e9SAJWg&s

These are the two areas with the highest bending moments. If cracks occur there, my first conclusion would be to look at the load assumptions and the design procedure. Higher prestressing could solve this problem at first glance.

In Germany, there has also been an increase in damage to concrete ties, but more in the force transmission area of the prestressing due to splitting tensile forces. An inspection of the sleepers has shown that, despite increasing loads, they are over dimensioned in terms of bending compared to the design method from 1982, as improvements in the manufacturing process and further developments in concrete have created reserves. A 20% reduction in prestressing force has been suggested, thereby also reducing the risk of cracks in the head area.

This is the German research: https://mediatum.ub.tum.de/doc/1303754/document.pdf
You find the above load and moments in one graphic on page 19 and the drawing and dimensioning of a B70 tie on page 35.
Regards, Volker

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I took another look at the linked article. I cannot judge whether the drawing linked below is authentic and comes from the study. https://cms.interestingengineering.com/wp-content/uploads/2025/10/IE-Photo-46-1.jpg

If it comes from the study, then it shows that the cracks in the area of the greatest tensile moment at the top are to be counteracted by a local increase in prestressing.

This is not possible in the prestressing bed, as only straight continuous prestressing wires are possible there.

But why not increase the prestressing force over the entire length by adding additional tension wires?

This question can probably only be answered by someone who is familiar with the design of American prestressed concrete sleepers.
Regards, Volker

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I continued to explore the topic of prestressed concrete sleepers. In doing so, I came across two articles.

The first, “Finite Element Models of Prestressed Concrete Sleepers and Fastening Systems in North America,” from the University of Illinois at Urbana-Champaign, Urbana, IL, USA deals with a finite element model for concrete sleepers because, quote:

In North America, the American Railroad Engineering and Maintenance-of-way Association (AREMA)’s Recommended Practices, which has been developed empirically, has been widely adopted as a general design guideline for prestressed concrete sleeper and fastening system design (AREMA, 2012). Therefore, this study focuses on developing a finite element (FE) model of prestressed concrete sleepers and fastening systems to improve the knowledge and understanding of the mechanistic behaviors of the railroad infrastructure.

Source: https://railtec.illinois.edu/wp/wp-content/uploads/pdf-archive/Shin-et-al-2013-WCRR.pdf

Far more interesting is the article by Rail.One, Design of prestressed concrete sleepers, which has also been manufacturing prestressed concrete sleepers for the American market in Clinton, Iowa, since 2014.

The company has developed a new sleeper for the American market. In designing it, they took into account both AREMA and European standards, using the less favorable results in each case.

It was found that AREMA delivers greater moments under the rail seat than European standards (EN), and 17% less in the middle of the sleeper. This could explain the cracking of the sleepers in the middle, as well as the attempt to additionally prestress the middle of the sleeper using the method described in the OP.

The greater moment under the rail seat results from the fact that AREMA specifies the load as point-like, while EN standards provide for a flat introduction over the base area of the rail seat, which leads to a rounding of the moments.
Source: https://www.globalrailwayreview.com/article/2412/prestressed-concrete-sleepers/

Apparently, the problem of cracks can be solved quite normally with the usual prestressing.
Regards, Volker

PS: Rail.One has been producing concrete sleepers for 70 years.

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You need an edit there, don’t you?

What does a cross-section of the tie look like? The strands are parallel straight lines? How far apart? How long?

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While the previously-provided exhibit of a ‘centerbound’ tie is meant to be illustrative rather than dimensionally correct, it shows the tendon alignment reasonably well.

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28

One of the lessons of the 1971 Sylmar earthquake was that bridge columns need hoop (circumferential) reinforcement as well as longitudinal reinforcement. A common technique for retrofitting pre-'71 bridge columns was wrapping with steel or carbon fiber composites.

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As I recall, not just for spalling: the circumferential reinforcement ‘spirals’ up the column.

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Stirrups are primarily needed in centrally loaded concrete columns to prevent buckling of the longitudinal bars and thus spalling. The thinner the longitudinal bar, the closer the stirrup spacing needs to be.

In eccentric loaded columns, they absorb shear forces and increase compressive strength and ductility by restricting elongation in the column surface.

The fact that concrete columns require stirrups is not a discovery from 1971. In Germany, they were first mandated in the early 1950s; before World War II, they were only recommended.

The realization may have been that stirrups in columns must be specifically designed for earthquake resistance. But that realization should also be older. Since we in Germany only experience earthquakes in a few areas, and then only minor ones, I’ve never had to deal with it.
Regards, Volker

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There’s as much rebar in the helical reinforcement as in the longitudinal reinforcement. Another way to look at it is that the wrapping adds a couple more directions of compression on the concrete, whereas pre-stressing only applies it in one direction.

FWIW, I was peripherally involved with a program for using carbon fiber to reinforce bridge columns.

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Here is a Voestalpine catalogue with their different ties: https://www.voestalpine.com/nortrak/static/sites/nortrak/.downloads/Heavy-Haul-Concrete-Crosstie.pdf

When prestressing against a steel formwork, the steel bars can only be straight. In principle, they extend over the entire length, minus the concrete cover for corrosion protection. The number of bars depends on the required prestressing force and the choice of prestressing steel. In Germany, the most commonly used sleeper has four bars. I am not familiar with the practice in the USA.
Regards, Volker

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33

Concrete for us technically challenged

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34

This is purely speculative, but is the actual cement quality or specs of US concrete ties the same as German ones? Our concrete highways seem in much poorer shape.

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My understanding is that US roads are constructed to a ‘lighter’ form of construction with less substantial base and subgrade along with a thinner road layer of paving - concrete or asphalt.

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Germany has 3 huge differences in how they build their roads. First off is the thickness of everything. Here you might get 6 to 8 inches of final pavement. There the minimum is 18 inches thick on a major highway. 2 here the contracts have zero requirements for how long the repairs will last. Germany requires a warranty for all road repairs meaning that if the repairs fail the contractor has to fix it out of their pocket. Lastly is how the bids are awarded. Here it’s the cheapest one there it’s who will guarantee the work the longest and who’s using the best materials for the job.

There’s a stretch of interstate 39 between mile markers 41 to 59 in both directions in Illinois were sections of the road every winter literally come apart due to how poorly they get repaired. I’m talking about car damaging issues with the roadway buckling. It causes wrecks at times. Yet all that gets done to it is band aid repairs. This section also has the Abe Lincoln bridge over the Illinois river on it. We can count on about every 4 years they need to totally replace the bridge decking on the bridge. The currenr one was done in 2020 and it’s starting to fail yet again.

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I was thinking the specs were something like that.

Abc lording to Google AI for a German Autobahn

  • Top layer: A flexible asphalt layer is applied over the concrete slab to provide a smooth riding surface.
  • Concrete slab: A ~400 mm (15.7 inch) reinforced concrete slab provides the main strength and durability for the pavement structure.
  • Base layer: A layer of lean concrete or cement-bound material, typically around 15 cm (6 inches) thick, is placed between the concrete slab and the subbase. This layer is often bonded to the slab and includes pre-notched joints.

Subgrade layers

  • Granular blanket: A granular layer, varying from 30 to 90 cm (12 to 36 inches) thick, is used for drainage and to provide a stable foundation for the base layers.
  • Subgrade: The thickness and composition of the subgrade itself depend on the local soil conditions and frost depth, with plate bearing tests used to ensure adequate support

I think the proportion of bitumen in the asphalt here is much less than in German construction.

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A few comments on concrete roadways in Germany. The following table shows a design for the highest load class Bk100 for highways.

Betonfahrbahn
Betonfahrbahn779×677 45.3 KB

Here are the translations of the terms contained in the table:

  • Belastungsklasse: load class
  • Äquivalente 10 t Achsübergänge [Mio]: Equivalent 10 t axle crossings [million]-
  • Dicke des frostsicheren Oberbaus: Thickness of the frost-proof roadbed
  • Tragschicht mit hydraulischen Bindemitteln auf Frostschutzschicht: Base layer with hydraulic binders on frost protection layer
  • Betondecke: concrete slab
  • Vliesstoff: nonwoven fabric
  • Hydraulisch gebundene Tragschicht: Hydraulically bound base layer
  • Frostschutzschicht: frost protection layer
    All dimensions are in [cm]. 1 in = 2.54 cm

It would be nice if more than just the lowest price were taken into account when awarding highway contracts, but this is extremely rare.

The standard statutory warranty period for highways is five years from the date of acceptance of the structure, in accordance with Section 634a of the German Civil Code (BGB).
Regards, Volker

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That stretch of interstate I’m talking about near me literally every year gets emergency repairs done normally after someone gets injured from the road conditions and instead of fixing it properly which they did with the interstate between El Paso and Bloomington they just keep patching the patches. You can literally see were the patches were cut apart in the concrete and new patches fit into it. Locals call it the patchwork interstate.

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Although there are some differences in the specs from Google vs the official ones Volker provided, German standards do appear to be higher than here.

Harold: There are lots of bad stretches of highway and interstates in northern Illinois and suburbia.