A tied-arch bridge will connect the U.S. Navy’s existing Naval Support Activity base with its new expansion property on the other side of the Sheikh Khalifa bin Salman Causeway. The navy estimates the bridge will save it approximately $650,000 in annual transportation costs. U.S. Army Corps of Engineers
Engineers overcome challenges to move a 122.5 m long tied-arch bridge into place over a busy causeway for the U.S. Navy in Bahrain.
April 29, 2014—After acquiring land to expand its base in Manama, Bahrain, the U.S. Navy needed a new bridge to connect its existing base with the expansion property across one of the region’s busiest thoroughfares. But disrupting traffic for months of construction was not an option. So the U.S. Army Corps of Engineers developed a plan to construct a steel tied-arch bridge off-site and then move it into place over the causeway—marking the first time the Corps has conducted a bridge move of this type and the first time such a bridge move has been undertaken in Bahrain.
In May 2010 the Navy signed a lease with the Bahrain government for roughly 78 acres of waterfront property across the Sheikh Khalifa bin Salman Causeway from its existing Naval Support Activity (NSA) base. But without a road linking the existing base directly with NSA-2, as the expansion site is known, it can take up to an hour and a half to travel between the two areas on a busy day. So the Navy decided to construct a bridge for vehicles and pedestrians over the causeway—a project it estimates will save $650,000 in annual transportation costs by significantly reducing the time it takes to get from one part of the base to the other, says Mark Wittrock, P.E., an area engineer for the Middle East District of the Corps.
The Corps initially planned to construct a three-span bridge over the six-lane causeway, but that would have required realigning the road and relocating utility lines that serve nearly half of Bahrain. To minimize the impact to the traveling public, utilities, and surrounding community, the Corps analyzed other bridge types and selected a tied-arch bridge because its abutments could be located on NSA property—away from the causeway and utilities—and it could be erected using accelerated construction methods. “The tied-arch bridge gains its structural stability by having the bridge deck, arch, and hangers all combined,” Wittrock explains. The design offered more construction options, he says. “Instead using a traditional method of constructing in-place over the roadway and closing the road for safety, we could construct it off-site and then transport it over the roadway,” Wittrock says.
Four self-propelled modular transporters moved the 122.5 m long
bridge from its temporary location to its permanent site over the
causeway: a six-lane thoroughfare in Manama, Bahrain. U.S.
Army Corps of Engineers
The Corps developed numerous images and computer animations to explain how the bridge would look and how the move would unfold to Bahrain government officials, who had never seen such a bridge move. The Corps proposed closing the causeway for 48 hours to allow enough time to prepare the road for the move by removing the curb and median and then subsequently moving the bridge into place. But Bahrain officials requested that the closure be limited to just seven hours—a time frame the Corps agreed to on the condition that crews could access the site in advance to conduct the preliminary work, Wittrock says. “That turned out to be a good thing because we were able to do minor lane closures to take out the median and the guardrail, put in temporary barriers, and do a lot of the prep work to get the bridge out there,” he notes.
The Omaha-based engineering firm HNTB designed the 122.5 m long and 10.6 m wide tied-arch bridge, which was constructed on the grounds of NSA-2—roughly 460 m away from its permanent location. Once completed, the bridge was jacked up and placed on four self-propelled modular transporters (SPMTs), which together had a total of 96 axels and 192 tires. The plan was to preposition the bridge near the causeway 24 hours prior to the scheduled move but those efforts were abandoned when two hydraulic rams on the SPMTs failed. “We had one seal that broke and another one [that] was leaking pretty badly, so they decided to change those out,” Wittrock says.
The team faced additional challenges the following day when it began to move the bridge toward its permanent location, and a couple of the temporary bracing bolts broke under the stress caused by the turning motion of the SPMTs. As a result, the move was delayed by eight hours while all of the temporary bracing connections were welded into place. “Some of the stresses that we built up popped a couple of the bolts off, so the structural engineers looked at it real quick and came up with the fix,” Wittrock says. Although an analysis indicated that the bolts would adequately handle the turns of the SPMTs, Wittrock notes that challenges on a project of this magnitude are inevitable. “You always have to put in for contingencies,” he says.
Once the welding was completed, the bridge move restarted and hundreds of Bahrain residents and government officials gathered to watch the process. Many expected the weight of the SPMTs and bridge to damage the causeway, Wittrock says. But engineers had conducted a full analysis of the pavement and were confident that it could handle the loads. From that point the move went smoothly and, as expected, the pavement survived unscathed, enabling the team to reopen the causeway in fewer than seven hours from the time the move restarted.
Ramps are now being constructed on either side of the bridge, which is slated to open in late August. Once completed, the bridge will reduce transportation costs while also providing a direct and secure route for emergency-response vehicles and military personnel between the old and new sections of the base. “There are lots and lots of benefits to the bridge,” Wittrock says. The project team also included Tony Gee and Partners, LLP, a consulting engineering firm based in Esher, Surrey, the United Kingdom, that provided modeling services, and the McLean, Virginia-based construction firm Contrack International Inc., which served as the primary contractor.