Railroad Bridge over Otter Creek
Vermont’s Agency of Transportation was undertaking the rehabilitation of Bridge 219 over Otter Creek. As part of this project, Engineers Construction, Inc. (ECI) needed to replace distressed stone-masonry pier with a new reinforced concrete pier cap supported on drilled shafts. SGH helped them by evaluating an alternate design and construction sequence to allow them to complete the project with limited weekend shutdowns of the railroad operations.
The initial design involved site casting a 55 ft long pier cap adjacent to the bridge and using two cranes to hoist it onto two new 6 ft dia. drilled shafts during a weekend shutdown. SGH designed an alternate layout for the site-casted pier cap with a shorter length, allowing ECI to simplify their erection process compared to that required for the original design. With this revised design and lighter pier cap, ECI was able to erect the pier cap during a single weekend shutdown and later connect it to the drilled shafts without further disrupting the railroad operations. Highlights of SGH’s work include the following:
- Redesigned a 28 ft long, precast concrete pier cap and cast-in-place infill connections to the 6 ft dia. drilled shafts
- Analyzed the stability of the existing stone masonry pier as it temporarily supported a portion of the new reinforced-concrete pier cap until the drilled shafts were installed
- Evaluated the heavy crane lift during placement of the concrete pier cap
In addition to our work related to the redesign, SGH also evaluated compressive strength results for the new concrete pier that were slightly lower than specified. We helped ECI demonstrate to the Vermont Agency of Transportation that the lower compressive strength had negligible effects on the strength of the new pier, helping them keep the project on track and avoid costly reconstruction.