Concrete precast units cut bridge cost in half

M. K. Hurd / December 28, 2000

Environmental concerns indirectly turned into a big plus for Erie County, N.Y., last year. To replace a deteriorated bridge on Savage Road, the county's consultant planned a stream relocation and designed a steel girder bridge with a span substantially longer than the existing 1930s steel and concrete bridge over Cazenovia Creek. The estimate of $1,100,000 included a provision for a costly road closing for the entire construction season.

During review of the design, the New York state Department of Environmental Conservation (DEC) expressed concern over disturbing the habitat of trout in the stream, with a strong preference for maintaining the existing bridge location and stream alignment. Joseph Monte, the Erie County bridge engineer, realized that months, maybe even a year or more, would be required to meet their concerns, delaying the project well into the next year's construction season. While considering his options, the scales tipped in favor of replacement at the same site. Monte learned that with in-kind replacement (no site changes), they could design for a flow equal to or slightly in excess of that accommodated by the old bridge, whereas by relocating the bridge and changing the stream flow they would be required to provide for a 100-year flood instead.

But could a replacement bridge be erected fast enough to meet the county's deadline of a road open before school started in September? Guy Puccio of the Erie County purchasing department thought three-sided precast concrete bridge sections might provide the answer. The county's previous experience with precast was limited to four-sided structures accommodating much smaller flows. At about this time Puccio read an advertisement for Con/Span bridges and made inquiries as to what spans were available, and what hydraulic flows they could accommodate. Con/Span was just finalizing its design work on a new bridge section, expanding to a 42-ft span, longer than any previously produced. The county learned that the new span could indeed meet the span and flow requirements at Cazenovia Creek.

Joseph Monte began working out a schedule for using the precast spans in Erie County, and getting the bridge open in time for school bus traffic in September. A fast-track approach was absolutely necessary. The precast had to be ordered as early as possible, without waiting for the consultant to finish all the plans. This meant that the contractor wouldn't be chosen early enough to play the more customary role of ordering and purchasing the precast bridge components.

To take the unorthodox fast-track approach, the county had to purchase the bridge components directly from the precaster. They actually let two contracts: one for the precast, and one for site preparation, installation, and associated road work. "If we would have waited for all plans to be finished before starting the bidding process," Monte says, "we would have fallen far short of our goal of opening the bridge in time for the opening of school."

It was April 21 when Monte set up his tentative schedule, calling for the consultant to prepare general layout drawings for bidding on the precast by May 1. Bids were taken and the precast contract was awarded June 1 to Concrete Pipe & Products Corp. of Cicero, N.Y. By June 25, production was underway at their Rochester, N.Y., plant.

Meanwhile, design consultant Abate Engineering Associates of Buffalo, N.Y., had completed the site work plans in mid-May. Following review by the county and the New York DEC, the job went out for bids on June 22. On July 6 the contract, with a bonus/penalty clause for timely completion, was awarded to Union Concrete and Construction Corp. of West Seneca, N.Y.

Union Concrete began site work in mid-July with road closing and demolition of the old bridge. Because of the stepped-up schedule for bridge replacement made possible by precast concrete, they could project a six-week closing instead of a whole construction season. For this short period, they were allowed to close the bridge without providing an on-site detour. Only a one-lane emergency detour-not open to the public-was required to accommodate fire department vehicles. Union Concrete had built the emergency detour and had the cast-in-place footings ready for the new bridge by the time Concrete Pipe & Products delivered the precast sections in early August.

The eight 42-ft-span concrete arch box sections are believed to be the longest three-sided bridge members cast up to that time, according to the Precast Concrete Association of New York. Designed for AASHTO HS25-44 loading, they were 4 ft wide, had an 11.5-ft rise and weighed approximately 20 tons. They were shipped on their sides and rotated to an upright position when they were unloaded. According to Gary Hill, Union Concrete president, they brought in a Demag 250-ton hydraulic crane to do the heavy work.

The eight arch box sections and four pieces of precast headwalls were all unloaded and installed in a single day. The precast wingwalls were installed the following day. After the joints were sealed with a bituminous membrane, about 1 ft of backfill was placed and compacted in preparation for restoration of the roadway.

Union Concrete completed the job ahead of schedule and collected the bonus, while the county realized its own bonus by saving nearly half of the original cost estimate. The change to a precast structure left a satisfied owner. Joseph Monte says "Everybody did a good job.

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