Freyssinet, Inc. has been awarded a contract by the Louisiana DOT to act as General Contractor managing and executing the repair of two bridges in New Orleans, Louisiana which span across a channel situated adjacent to Lake Pontchartrain. The repair of 26 deteriorating concrete girders will be achieved by adding external post tensioned 1-1/4” diameter high strength bars and, in one span, by utilizing innovative 7-wire, 11/16” diameter carbon fiber strands.
Due to the relative newness of the use of carbon fiber elements and in order to assess the potential benefit of widespread use of the carbon fiber, a system will be designed by Advitam and put into place to monitor the performance of the girders to compare the effectiveness of each of the two types of external post tensioning over time.
Included in this work will be the installation of two cofferdams which will run just outside of and parallel to each bridge. The water level under the bridges will thereby be able to be drawn down 5’ providing access for the repair crews to install the bars and strands. The cofferdam design will be provided by Aquadam and will consist of large ecologically friendly water filled bags which will rest on the channel bottom and reach from shore to shore at each end of the bridge spans.
Access under the bridges will be from pontoon work barges placed between and under the bridge spans. Also, each bridge will have traffic reduced to one lane to enable the work to be safely accessed and executed.
Another interesting aspect of this work is that the waters of the channel are the known habitat of alligators, some of which have been observed to be 12’ in length. Because of this, and the proximity of workers under the bridge, a special safety plan will be drafted to address this hazard.