Thursday, October 03, 2013

A longview of shortline bridge maintenance

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Bridge B-190 in Madison, Wis., during replacement work.
Bridge B-190 after work was completed.
A temporary steel pier sits around the original masonry pier, which was settling, was replaced with a concrete pier and the work was done under traffic.
Crews perform stringer replacement on bridge B-156 located on WSOR’s Madison Subdivision.
Bridge B-190 in Madison, Wis., during replacement work.

WSOR has developed a long-term structures maintenance program to extend service life where it can, while prioritizing replacement needs.

Wisconsin & Southern Railroad LLC's (WSOR) network grew in part from the abandoned Chicago, Milwaukee, St. Paul and Pacific Railroad. When operations on the Milwaukee Road ended, the state of Wisconsin partnered with several counties to preserve freight rail, ultimately entering into a lease and operations agreement with WSOR.

According to Dave Bierman, bridge structure supervisor at WSOR, the Milwaukee Road kept its bridges in good shape and when WSOR first began operating along the line, the structures could handle the capacity of the day.

"[When the system came out of abandonment] a lot of the subdivisions where we operate had very little traffic. With the investments that have been made with track improvements, we've seen business grow phenomenally," said Bierman.
Part of that business growth means heavier loads traveling along the system and with structures originally built between 1910 and 1950, age was becoming a factor among WSOR structures.

The railroad has 354 total structures on its system, including 157 (45 percent) steel structures, 139 (39 percent) timber structures, 29 (eight percent) stone structures, 21 (six percent) concrete structures and the remainder comprised of miscellaneous material.

"We're getting into bridge rehabilitation mode on our system and we're taking the worst of the worst first to get those either repaired or completely replaced," said Bierman. "Our big ramp up was last year and it carried into this year and will be ongoing as far as our future holds."

According to Bierman, the footprint the railroad is using year-over-year is to identify and prioritize several structures requiring complete replacement, as well as an additional dozen ormore structures that heavy to moderate repairs are economically advantageous to extend their useful life.

"All of our replacement structures are built to AREMA standards, which are qualified for 315k, when we replace a bridge fully, we build a current AREMA structure," said Bierman. "In the structures where we repair, we prioritize our repairs to keep the capacity but operate over it at a slower speed and get that structure to the end of its life. We do this so we can focus on the other structures that we do not have a choice but to replace them."

Bierman said the railroad, which was always committed to bridge inspection, is taking its structures initiative to a new level by working with an outside engineering firm on a bridge management program. He said working with the firm gives WSOR a system wide view to stay ahead of repairs and replacements by allowing for increased inspection and rating efficiencies, as well as prioritization of structures needing work.

"As our traffic increased, we needed a plan to anticipate what was going to happen with some of the structures on our heavier haul corridors, anticipating and trying to eliminate problems ahead of time," said Bierman.

Bierman believes the issue of capacity is at the forefront of most structural engineers in the rail industry.

"AREMA has done massive studies of many span type capacity upgrades and figuring out which remedial course is the best economical fit. We've benefited greatly from many of these studies, as well as learning from what others have accomplished. We've expanded [those lessons] and developed strategies to fit our own bridges. It's an interesting challenge, but we're all in it together," said Bierman. "The solutions that are coming from the railroad engineering world from many different facets are really interesting. To me, it's some of the most interesting engineering since the railroads were built."

Challenges

When asked if there was one particularly exacting bridge, without hesitation, Bierman pointed to F-84, which is a pony truss and deck girder combo with a long timber approach on WSOR's Monroe Subdivision over the Sugar River.

The truss' east abutment and Pier 1 were concrete while Pier 2 was stone masonry. Bierman says Pier 2 was settling and the two concrete elements, while they did not look bad from the outside, still needed work performed.

"We had a fairly extensive project where we completely replaced the timber approach and replaced the masonry pier under traffic, which was an interesting process, because we couldn't shift or realign the bridge, so we had to figure out a way to completely remove the existing pier and construct the new pier in the same position," said Bierman.
WSOR accomplished the replacement by building a temporary steel pier around the masonry pier and on which the existing bridge was placed. Bierman said the contractor was able to dismantle the masonry pier and, using a combination of precast and cast in place concrete, construct a new pier.

"[The project] was designed by a consultant, SW Bridge Engineers LLC. They're outstanding at engineering solutions for the best economic value and structure longevity, as well as cutting edge designs for construction under traffic utilizing small work windows allowing us continue to maintain train schedules. It has been a very valuable working partnership," said Bierman.

While WSOR is primarily concentrating on its lower capacity timber structures with advanced deterioration for total replacement, steel and concrete structures are also garnering attention because many of the concrete sub-structures on the system are composed of monolithic non-reinforced concrete and while the concrete is fairly sound, minor deterioration in load bearing areas is a subtle indicator of advanced shear cracking within the interior of the element.

"We had some concrete sub-structure elements, in F-84 and a number of other structures that were composed of non-reinforced concrete, that didn't exhibit advanced deterioration from the surface until we performed some minor repairs involving removing existing surface concrete and casting it back in place. Well, once the contractor began to expose the loose concrete, we found large shear cracks throughout the element's internal load bearing areas and we had to regroup and remove more of the concrete than we thought. The challenge then was to engineer a repair solution to maintain structural capacity and serviceability while removing and replacing the concrete. What we found was that the outer shell of the concrete was superficially deteriorated, but once we got inside, we discovered that significant areas of the material that felt fairly sound was basically consolidated sand and aggregate with much of the cement missing. These weak areas disrupted the load path causing overloading and uncontrolled fracturing in the adjacent sound concrete," said Bierman. "We used a technique where precast concrete elements were custom produced off site and then employed some short windows where the contractor could go in and chop away the bad concrete and install the precast element. Then, we could continue with the remaining repair work, encasing the element with cast-in-place reinforced concrete. We've had very good luck with that as it allows us to go in and have an effective permanent repair fairly rapidly. In our continuing learning curve, we try to anticipate these potentially deteriorated underlying concrete conditions and have a back up plan in mind as to how we will remediate them if we do encounter them."

While WSOR's structures maintenance program is keeping him busy, Bierman says the diversity of the work is what keeps him motivated.

"You have the known quantity you plan and design for, you spend a lot of time with each individual structure and even though you're working on a lot of them at the same time, it's very personal. As projects evolve and change, you work through the challenges, when you achieve the end goal, it is really satisfying. There is something new, something steady, something rapidly changing and it keeps it really fresh and exciting every day," said Bierman.

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