jut out from the edges of the bridge to provide support during deck construction. “The conventional alternative to using bridge brackets,” he continues, “is fraught with wasted money and materials.” Dinmore spent 20 years working on high-profile infrastructure proj - ects in Metropolitan New York, the last 6 years as Chief Engineer for a Fortune 500 heavy civil contractor. He saw money wasted on transportation, unnecessary tasks, and the disposal of plywood after bridge brackets were disassembled. Most contractors don’t own bridge brackets that conform to the requirements of today’s construction and those that do often spend time digging them up in the yard for the next project only to find that they have fallen into disrepair. “Every time I would find an area where we were losing money, it traced back to these bridge brackets,” Dinmore says passionately. “The money was going everywhere except into the structural deck where it belonged.” The closer spacing of these costly brackets has exacerbated the prob- lem, according to Dinmore. Contractors used to set them around 36 to 48 inches apart. “They are now putting them much closer and that gets very, very expensive,” he says. “Precasteel eliminates the need for brackets altogether.” Bridge brackets can also impact paving quality. The proximity of the bridge paver screed rail to the brackets causes them to deflect during paving and creates a wave, or a washboard effect, in the concrete deck along the barrier that often collects water and eventually scales. The damage is often discovered after the project is completed but the war - ranty has not expired, leaving the contractor with the unexpected cost of diamond grinding or deck replacement depending upon available concrete cover over the deck reinforcing steel. Precasteel is not subject to this issue since the paver screed rail is located along the centerline of the fascia beam as opposed to the panel itself. Precasting and Installing Precasteel J&R Slaw produced the panels at its Lehighton plant with Precasteel performing periodic quality inspections for quality assurance, espe- cially on the first bridge known as the Frontage Road Structure (FRS). No plant inspectors were present from PANYNJ; although the author - ity did station an inspector at the plant for ramp L29, the second of the structures. All Precasteel sections were five feet long and 1,000 pounds on average. “It was shown in the design that soffit widths varied, requiring each panel to be custom,” Dinmore recalls. “At the end of the day Slaw did a really good job, especially on the geometry, because everything fit like a glove.” There was no specification for Precasteel so guidelines from the Archi - tectural Precast Association (APA) were adopted early on. The recom - mended slender ratio dictated an increase in thickness from 2 ½ to 3 inches and a minimum concrete compression strength of 6,500 psi to avoid shrinkage and stress cracks. All Precasteel sections were palletized, stacked on a flatbed trailer, and shipped off to LaGuardia. Upon arrival, Skanska-Walsh crews
The gap also eliminated rework and scheduling issues for Skanska- Walsh. In one instance, a panel was damaged prior to installation and needed to be replaced. The crew was able to continue setting panels, butting them tightly together, and skipping over the damaged panel location until a new one could be installed. They used a flat bar to make some minor adjustments to adjacent panels and the final panel fit perfectly. “You don’t have to stop just because you don’t have one piece of the puzzle,” says Dinmore. “That ¼-inch gap helped. It gave the contractor plenty of room to drop it in without banging against the other panels.” Deviating from the Original Design Precasteel was originally designed with a 90-degree angle. The archi - tect at LaGuardia; however, was going for a different aesthetic. The vertical axis tilts back as a result, which Dinmore dubbed the “lazy L.” Aesthetics are, in fact, what drove the specification of Precasteel over conventional methods at LaGuardia. The tilted back panel would have required extra bracing, whereas precast concrete was able to be formed without additional costs. The architect discussed the use of white concrete for the facade, but Precasteel suggested that standard concrete would be a close match. They worked with its precast supplier J&R Slaw to provide samples and it was approved. The Problem with Bridge Brackets “There are inherent problems with bridge brackets,” said Dinmore. These triangular brackets, consisting of steel and heavy-duty plywood, Precasteel was originally designed with a 90-degree angle. The architect at LaGuardia wanted to achieve a different aesthetic so the vertical axis tilts back as a result.
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csengineermag.com
August 2022
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