In early February, a team of Budweiser Clydesdales led the grand opening of the third longest cable-stayed bridge in the U.S., crossing the Mississippi River between Missouri and Illinois. The Stan Musial Veterans Memorial Bridge, initially known as the New Mississippi River Bridge, is part of a $694 million project that involves rerouting St. Louis traffic to alleviate congestion.
Two lanes of Interstate 70 travel over the bridge in each direction, with room to expand to three in the future. Construction of the bridge, featuring a 1500-foot structural steel main span with a concrete deck, 400-foot-tall reinforced concrete piers, and 68 pairs of stay cables, began in January 2010.
From the beginning, contractors at Massman, Traylor, Alberici (MTA) lent their expertise to the project. MTA is a joint venture formed by three construction firms: Massman Construction, Kansas City, Mo.; Traylor Brothers, Evansville, Ind.; and Alberici Constructors, St. Louis.
With generations of combined infrastructure construction experience, the partners each contributed equipment and personnel. “We operated as a team,” says Project Manager Tom Tavernaro. “None of the work was subdivided.” Tavernaro oversaw 24 managers, 12 engineers, seven supervisors, and almost 100 craft workers in constructing the bridge’s four piers and main span.
Forward-thinking policies of the project owner, the Missouri Department of Transportation (MoDOT), allowed MTA to offer design input and take a hands-on approach to quality control, ultimately improving the bridge design and project timeline.
The logistics of spanning a river
The Missouri Department of Transportation (MoDOT) and the Illinois Department of Transportation (IDOT) have a long-standing partnership when it comes to projects involving both states. The two agencies hold an annual Border Bridge meeting to coordinate maintenance on the bridges they share and plan new projects.
The agencies alternate responsibility for each new project and determine financing based on the percentage of the project that falls within each state. MoDOT coordinated construction and managed contracts for Stan Musial Veterans Memorial Bridge, while IDOT was responsible for about two-thirds of the funding because most of the roadwork falls on its side of the Mississippi River. The agencies will split maintenance costs evenly.
To encourage innovation, MoDOT invited designers and contractors to suggest alternative technical concepts (ATC). “We met with contractors during the design phase to see if we could incorporate better ways to complete the work,” says Randy Hitt, MoDOT engineer and project director.
Instead of the original plan for 14 10-foot diameter pylon shafts, MTA recommended six 11 ½-foot diameter shafts with 11-foot diameter rock sockets. Because the contractor had previous experience installing the larger shafts and the cranes and drill equipment to handle the job, MTA was able to save time and material costs. In fact, the contractor submitted a bid that was $45 million lower than the project’s other bidder.
In the process of constructing the footer shafts, MTA set a world record for load testing. An Osterberg Cell (O-Cell) test, designed to determine the concrete base resistance and shaft load resistance, registered a remarkable 36,000 tons of combined resistance. To ensure a strong foundation, each shaft was reinforced with 42 #18 vertical bars.
MTA also persuaded MoDOT to change its 28-day strength requirement to 56 days for the mass concrete elements, to allow for slower strength gain in the bridge piers and footings. The agency also agreed to reduce the bridge footing from 25 to 20 feet thick, which was made possible by increasing the concrete design strength. More importantly, the low heat of hydration mix also helped the contractor meet one of the project’s biggest challenges: staying ahead of springtime floods.
Racing against Mother Nature
Concrete producer Riley Illinois consulted with cement supplier Holcim to develop a 70% slag cement-30% portland cement concrete mix that would help keep construction on schedule. Although the specification for the bridge piers required 6000 psi concrete, Riley’s slag mix achieved up to 8000 psi, consistently exceeding compressive strength requirements.
To meet the unique factors involved in constructing mass concrete elements, MTA also commissioned a thermal control plan from CTLGroup. “We needed to develop and implement a good plan to reduce the thermal control period for the mass concrete elements,” says Tavernaro.
Following CTL’s recommendations, MTA took extra measures to cool the concrete. The contractor assembled a system of cooling tubes by installing more than 1.5 miles of polyethylene pipe in a 5x5-foot grid within the pier footings. Ice cold water from the Mississippi River was pumped through the tubes, then returned to the river.
“With the combination of insulation on the sides of the forms and on top of the footing and using the cold river water, we were able to keep the temperature differential within an acceptable range,” says Tavernaro. The contractor also used maturity meters and temperature sensors embedded in the concrete placements to monitor the concrete’s temperature and performance.
Because the concrete gained strength quickly, the contractors were able to build the piers above the high water level before April 2011, when the Mississippi River crested at record levels in St. Louis. “If the mix hadn’t achieved strength so quickly, the project could have been set back for two or three months,” says Mark Luther, a senior technical service engineer for Holcim (US) Inc.
One of the most time-critical phases was completing the bridge’s two pier footings, founded on the 11 ½-foot diameter drilled shafts. MTA installed a coffer dam and pumped out water to create space for the foundations, and then added modular steel girder forms and 1.4 million pounds of rebar to each footing.
Each 55 x 88 x 20-foot footing took about 40 hours to place, during which Riley’s concrete trucks continuously fed truck-mounted concrete pumps that delivered the material through slick lines to the footings. For bridge elements further from the riverbank, the trucks unloaded onto a barge that delivered the concrete to a crane and bucket setup on the river.
“We worked two shifts throughout the drilled shaft installation, footing construction, and pier shaft construction; roughly the first year of the project,” says Tavernaro. As the piers rose above the water, the contractors scaled back to one shift a day.
Although MoDOT allowed an extension for lost time due to high water, MTA made every effort to keep the project moving. The contractors removed walking access to the piers and used boats instead, and secured barges with ship anchors so they could set structural steel and precast panels on the bridge deck.
“The biggest challenge of building this type of bridge is the linear schedule,” says Tavernaro. “On other projects you can shift work around. But here, everything’s on a critical path.” Amidst the river’s worst flooding in almost 100 years, the contractor received credit for 127 lost days.