Innovations Case Study
Bridge Demolition Analysis: PD&E Study for removal of existing bridge of the westbound SR 20 over Apalachicola River Bridge (Old Trammell Bridge)
The purpose of the study is to evaluate multiple alternatives for the future of this bridge while continuing to provide safe and efficient travel for motor vehicles and navigation activities throughout the project area. The future function of the decommissioned bridge and its service to the local community will be assessed.
This project included a PD&E study to evaluate whether to continue expensive maintenance cycles for the 85 year-old steel truss bridge or to take the bridge out of service. The study was led by the prime consultant, Volkert, Inc. The Old Trammell Bridge was constructed in 1938 and is nearing the end of its useful service life. Recent bridge inspections discovered progressive corrosion and deterioration of the structural members resulting in downgrading the load carrying capacity. The Old Trammell Bridge crosses the Apalachicola River between the cities of Blountstown and Bristol (Calhoun and Liberty Counties).
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Serving as a subconsultant to Volkert for this study, FBT provided an evaluation to determine an estimated construction budget and a reasonable method of removing the existing old Westbound SR 20 Bridge over the Apalachicola River. A two-lane eastbound bridge was constructed over the river in 1998. The old westbound bridge consists of five main spans over the river totaling 1,069 feet; three of which form a continuous steel arch truss with the other two spans being simple span steel trusses. The overall bridge has 198 spans and the total bridge length is 8,397 feet. The Trammell Bridge is eligible for listing on the National Register of Historic Places.
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FBT evaluated potential means and methods to remove the approach spans and the main spans. The removal of the approach spans could utilize fairly standard methods of demolition with contractor activities taking place either from the existing bridge deck in a sequential top-down removal method or from equipment located on temporary timber mats and embankment within the floodplain. Removal of the main span sections is more complicated. The center three spans (spans 166, 167 & 168) could be removed first. Span 166 and one-half of span 167 could be removed as one large unit by releasing the pins connecting span 167 together at the center of the arch. In a similar fashion, span 168 and the other one-half of span 167 could also be removed as a separate unit. The total length of each of these truss segments are over 360 feet and varies in height from 27.5 feet at the end to 51 feet high over the channel piers (and 24’-8” at the center of the arch). The weight of each of these truss segments is estimated at 450 kips. Our evaluation concluded two 500-ton cranes working together (Manitowoc 2250 with max ER 2000 counterweights) can handle the reach and lift necessary to remove and lower each of these truss segments down to large barges in the river. In this scenario, the barges could travel south down the Apalachicola River approximately 75 miles down to the Gulf. The height of each of these truss segments, including the height of the barge, is estimated at approximately 68 feet high. These segments on barges can fit under the low member of the existing bridge to the south (US 98) only at certain low water level events.
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The preferred alternative consists of removing the Westbound Old Trammell Bridge and converting the existing eastbound bridge into one travel lane in each direction. The bridge approaches for the westbound Old Trammell Bridge will be removed, stormwater drainage systems will be improved, and a sidewalk will be constructed within the southern right-of-way from the existing eastbound bridge to Bristol.
