A historic project site scores an appealing upgrade

American Bridge (AB) has once again found itself working in a national treasure. Considered the “Grand Canyon of the East” as well as the 2015 winner of the USA TODAY Reader’s Choice Award for Best State Park in the United States, Letchworth State Park is home to one of AB’s latest bridge replacements, the Portageville Bridge.

Over one million people visit this natural beauty annually to take in the stunning views of the three large waterfalls in the Genesee River, as well as the beautiful gorge that the Portageville Bridge traverses. With the scenic views and the historic heritage, creating a safe new crossing for Norfolk Southern Railway Company (NS) has given AB a picture perfect project.

American Bridge (AB) has once again found itself working in a national treasure. Considered the “Grand Canyon of the East” as well as the 2015 winner of the USA TODAY Reader’s Choice Award for Best State Park in the United States, Letchworth State Park is home to one of AB’s latest bridge replacements, the Portageville Bridge.

Over one million people visit this natural beauty annually to take in the stunning views of the three large waterfalls in the Genesee River, as well as the beautiful gorge that the Portageville Bridge traverses. With the scenic views and the historic heritage, creating a safe new crossing for Norfolk Southern Railway Company (NS) has given AB a picture perfect project.

“This popular option would leave no physical footprint in the water below and no obstructions to the scenery, unlike the current structure, ultimately enhancing the views in the park.”

Historical heritage

This historic connection has been the centerpiece of photos for almost two centuries. Over 166 years ago, the first of three Portageville Bridge structures was acting as a vital link for the Erie Railroad across the Genesee River. The 800-foot-long bridge opened in August 1852 after 13 months of construction. It was a massive timber trestle, with the track sitting 234 feet above the river, and it was claimed to be the largest timber bridge ever built. When it burned down unexpectedly in May 1875 due to embers from a passing train, a replacement was needed immediately. In just three months, a new bridge made of iron was constructed on the same alignment. This was an enormous feat—even by today’s standards—and despite the rapid erection, the bridge remains in use over a century later. Local lore has it that the fire may not have been an accident, thus explaining how the new structure could be devised, built, and opened to rail traffic so quickly.

The existing structure has 13 open-deck spans totaling 819 feet carrying a single track across the gorge, 235 feet above the Genesee River. It consists of six towers, four girder spans, and three truss spans. Besides a 1903 strengthening project in which the shorter superstructure spans were replaced with steel deck girder spans and the longer spans were replaced
with pin-connected steel deck truss spans, and some additional maintenance repairs, the structure that remains is largely in part the same from the late 1800s. The existing structure is one of the nation’s oldest iron rail bridges and has become an important connector for NS’s Southern Tier line between Binghamton and Buffalo, New York.
Monthly inspections are performed on the existing bridge, a costly and time-consuming effort for NS. As the last bridge on this route to be replaced or rehabilitated for modern freight loads, it is currently the weakest link and is not able to handle modern transportation needs. The structure is not capable of carrying the 286,000 pound freight cars, therefore weights must be reduced by 13,000 pounds to cross the bridge. Even with the weight restriction, train speed is reduced to 10 miles per hour to prevent overloading the existing bridge. This has created a bottleneck in this main east-west corridor. With anticipated expansion along the Southern Tier Route, the bridge was no longer able to keep up with expectations

A Modernized Improvement

In the late 1990s, Modjeski and Masters (Modjeski) was hired to evaluate both repair and replacement options for the Portageville Bridge. Replacement was deemed the most viable option. This new bridge was essential for NS to operate safe, reliable, and efficient rail operations on the Southern Tier Route. Just under 10 years later, in 2007, Modjeski started design research and provided the best options to complete the enhancement of the route.
Because of the high visibility of the bridge and the large number of visitors to the area, it was required by the National Environmental Policy Act to obtain public input on the design. Both parties agreed on a spandrel-braced arch bridge that would span the entirety of the gorge, framing the beautiful backdrop. This popular option would leave no physical footprint in the water below and no obstructions to the scenery, unlike the current structure, ultimately enhancing the views in the park.

The new arch bridge is a single track railroad crossing with a ballast-filled concrete deck. The main span is a 483-foot-long arch and there are three 80-foot-long girder span approaches on each end, for a total length of 963 feet. The deck sits 235 feet above the Genesee River and contains 7,348,000 pounds of steel. The approach spans consist of 1,231,000 pounds of steel, and the access system has 205,300 pounds. The project also includes 4,030 cubic yards of concrete.

“The Arch Tieback System was an integral part of the cantilever erection and was designed specifically for governing the arch construction stage.”

Construction

In November 2015, just a mere 75 feet south of the existing structure, construction got underway on the new bridge. The proximity to the existing structure made the project site a bit difficult to command. Being a linear project with limited lateral space because of the proximity to the existing structure and surrounding State Park property, the AB team had to overcome obstacles regarding space for materials, construction staging, and housekeeping. Because of these challenges, the construction method had to be carefully considered, but thanks to AB’s talented in-house engineering team, the task seemed effortless. To avoid the need for falsework and to keep the physical footprint in the Genesee River at a minimum, the cantilevered erection method with a tie-back system was implemented for the main part of the project—the arch erection.

To begin arch erection, AB placed a Manitowoc 4100W Ringer Crane with 300-foot boom on each side of the gorge. This allowed each half of the arch to be constructed simultaneously using the cantilevered erection method until each side met in the middle. To support the segments during construction, a temporary tieback system was used.

The first two approach girder spans and the arch span from panel point 0 to panel point 4 were erected using the 4100 Ringers. These cranes then lifted rough terrain cranes onto both cantilevers which were then used to erect the remaining members, lowering each piece into place. This allowed the two cantilevers to be joined together and the bridge to function as a complete arch. The ringer cranes fed material to the rough terrain cranes and erected the final approach span once the arch was completed. The temporary tiebacks were then released upon joining the cantilever halves. This method was possible because a spandrel-braced arch with temporary tiebacks is a self-supporting structure when cantilevered.

The temporary works consisted of two major items: the Stage 1 Support Tower and the Arch Tieback System. The Support Tower on the east side was made up from the falsework towers used on the Puerto Rico Convention Center and U.S. 69 Missouri River Bridge projects (AB Connections Issue #1006). The tight footprint of component rock on which to found the west side support tower required the innovative use of F1 falsework instead of the Puerto Rico falsework.

The towers were used to erect Stage 1, consisting of three arch members. Once they were erected, the arch tieback system was installed and engaged, ultimately releasing the Stage 1 Assembly from the Support Tower, and the Support Tower was removed. Then, the cantilever arch erection continued from both the east and west to eventually close the arch.

The Arch Tieback System was an integral part of the cantilever erection and was designed specifically for governing the arch construction stage. This stage required 900 tons per truss line (1,800 tons total) to hold back the arch. The tieback system consisted of cables that tied into each U0 gusset plate and anchored into a series of guy towers and backstays. The delta plate also served as an erection aid and each tieback cable pinned into a plate which connected to the jacking rod clevis. The jacking rod fed into the tieback tensioning device equipped with one center hole jack and a lock off nut. The tensioning device adjusted the cable lengths and thus the arch geometry during the erection and arch closure. Four guy towers each received three tieback tensioning devices, transferred the demands to the back stay members, and directed the vertical components into the permanent approach span abutment. The backstays were pin connected to a grillage system that was anchored by 140-foot-long pretensioned rock anchors.

As erection progressed, AB’s in-house engineering group monitored the deflection of the arch as well as the tension in the tieback system strands. The engineering group provided the field group with guidelines for the tieback cable tension demands and panel point deflections according to AB’s structural analysis model. The engineering group also provided jacking stroke distances for the adjustment stages. Through a coordinated effort between the east and west tieback system, the arches were adjusted until the bolt holes in the lower panel point were aligned and the field team was able to zip up the mid span panel point connections starting from the bottom, using the tieback system for further adjustment.

AB’s scope of work also included skewback excavation, rock fall protection/fencing, site work, micropile foundations, form/pour concrete and mass concrete, and landscaping and site restoration. AB was working in very close proximity to the original foundations
of the existing structure when performing skewback excavation, so AB had to be extremely diligent.

The new bridge was also required to be built on a parallel alignment in order to maintain rail traffic at all times. AB worked closely with NS to plan operations around their train schedule. Once the structure is complete, waterproofing is applied to the concrete decks, and the approaches leading to the bridge have been final-graded with subballast, AB will hand the bridge and new alignment over to NS. NS will then install the ballast, install the rail, make the tie-ins, and switch the traffic.

Once train service is re-routed, the existing bridge and foundations will be demolished, save one small piece. A portion of one tower will be preserved and given to Letchworth State Park to incorporate into a permanent historical display within the park. Detailed demolition procedures are not yet finalized for the existing structure but AB is working hard to complete the plan. It is likely that the team will perform explosive demolition on two towers and two spans and de-erect the balance of the structure with regular cranes and equipment.

“The bridge will be a beautiful addition to the already appealing scenic views and a complement to what Letchworth State Park is known for. AB is proud to have a hand in continuing this historical narrative.”

Environmental Considerations

As with any project of this size and magnitude, particularly a project through a state park, a large number of permits are required. Two of the more unusual contract permit requirements for this project involved AB compliance with a Bald Eagle Protection Plan, as well as a Timber Rattlesnake Protection Plan.
Approximately 1,200 feet upstream from the Portageville Bridge sits an occupied eagle’s nest. Because eagles return to the same nest every year, NS was required by the U.S. Fish and Wildlife Service to monitor the eagles’ use of the nest as well as their behavioral responses to AB’s construction activities. From mid-January until the eaglets fledged the nest each year, NS engaged an Eagle Monitor to observe and record the raptor’s behavior. This meant that in turn, AB also was required to take some precautions. Concerns with noise disturbances that may cause the eagles to abandon the nest and relocate were raised. One way to alleviate this concern was to install the micropiles via drilling rather than driven piles. The only other restriction made due to the eagle permit was limiting the number of blasts AB could perform each week during the skewback rock blasting and excavations. AB could conduct no more than three blasts per side of the gorge every week. This never impacted the planned schedule and since the project started, the eagle nest has not been abandoned. Eagle chicks have also successfully hatched in both years that AB has occupied the site.

Timber Rattlesnakes are also a concern in the area. Dens within Letchworth State Park are located several miles north of the bridge and the nearest sighting was within a mile. However, some existing or expected site conditions appeared to be a suitable summer migration habitat and because the Timber Rattlesnake is protected, AB also had to comply with the protection of this species. A “rattlesnake barrier” was installed around the project’s perimeter. This barrier is a silt fence titled outward at a 15 degree slope to keep the snakes from climbing over and entering the work zone—much to the contentment of the employees too! Training on the Timber Rattlesnakes is also mandatory for all employees and subcontractors. Training involves instructing employees of what to look for, as well as steps to take if one happens to visit the site. Since the project began, there have been no sightings.

Just under one year away, at the end of 2018, the entirety of the Portageville Bridge project is expected to be complete. The new structure will be operating in late fall 2017, with demolition of the existing structure to follow. AB will wrap up the project with an extensive landscaping component and trail reestablishment.

First published in American Bridge Connections

Contributors
Heather Engbretson, Editor
Kelsey Gooding, Assistant Editor
Bill Felker
Ken Shovlin
Jon Weaver

Special thanks to Norfolk Southern Railway Company