On Sept. 18, a little after 5:00 a.m., with lights flashing and horns blowing, the first vehicles rolled across the new St. Anthony Falls Bridge in Minneapolis. The bridge was designed and built in just over 13 months, three months less than the original, extremely tight, schedule. John Chiglo, PE, the Minnesota Department of Transportation (Mn/DOT) project manager for the bridge, estimates that the rapid progress of this design-build project saved about $240 million. The savings to commuters and local businesses was likely another $39 million, as each day the bridge was closed it cost the local economy about $400,000.
Mn/DOT spokesmen have been singing the praises of the design-build team of Flatiron Constructors Inc, in a joint venture with Manson Construction. “The biggest benefits … there’s two — one is the speed of delivery and the other is innovation,” Chiglo said. “We’re able to overlap design and construction activities so that you can take advantage of some of that time that you would normally be just designing the project and start some of the construction activities. We actually started construction right around November 1. We executed the contract on October 8 of last year.
“The other one is innovation and innovation has really been one of the major benefits of using design-build in Mn/DOT, and it brought us a number of different systems on other projects but on this project it’s staging of construction — I mentioned cold weather concrete and mass concreting — these are all things that Mn/DOT is going to take from this job, or will take from this job, and apply to our future projects and not only have benefits for this project, 35W project, but those benefits will carry forward into the future and improve our existing processes and save the taxpayers money ultimately in the long run.”
Jay Hietpas, PE, design-build program manager, Office of Construction and Innovative Contracting, Mn/DOT, commented that on this project cost growth was only 2.5 percent, as opposed to 7 to 10 percent for a typical design-build-bid project.
Community involvement in the bridge, from the initial layout through the before-dawn opening, has made this a popular project. Mn/DOT and Flatiron/Manson held meetings so members of the community could comment on the proposed path of new roadways. The design, intended to blend in with existing structures, was also influenced by community opinions.
Constant communication, alerting the public to road closings and night work, sidewalk superintendent talks, a web cam and web stories on individuals involved in the project all helped local people understand the project and encouraged them with its progress.
Following is a summary of the progress of the project.
August 2007
When the I-35W bridge across the Mississippi collapsed Aug. 1, 2007, it was a devastating event for the Minneapolis area — 13 dead and more injured. Once the shock passed, Mn/DOT took a good look at the situation and moved decisively.
Mn/DOT, in the face of an estimated $400,000 per day in lost revenue and traffic jams on alternate routes, decided to rebuild the bridge as a fast-track design-build project. A week after the initial collapse, Statements of Qualifications from interested firms were due.
Design-build was the project method of choice largely due to its inherent speed, although innovation, flexibility, reduced claims and a single contact point were also factors. On Aug. 17 the city council and Mayor R.T. Rybak unanimously approved a statement of principles for the new bridge.
Another important factor was the decision to involve the community around the bridge site in many of the decisions. This turned out to be a great advantage, since being involved in the decisions made those in the area more tolerant of noise, dust and other annoyances that come with a large construction project. Community meetings, presentations to local groups, a website that included features on the workers and a web cam to follow progress, were all part of this effort. In addition, there was a weekly “sidewalk superintendent” event on Saturdays which became popular enough to require closing a lane of traffic to accommodate those interested.
And, rather than just replacing the old bridge, Mn/DOT decided to expand and improve on it, allowing for future growth and increased traffic.
The new bridge was going to be beautiful as well, fitting in at the site aesthetically and environmentally. Community groups were involved in deciding the final appearance of the bridge, increasing its acceptance. In addition to functional and aesthetic features, the new bridge would also include a memorial to those who died in the initial collapse.
September 2007
The project put the “fast” in fast-track. From the initial collapse on Aug. 1, to a deadline for submitting Statements of Qualifications on Aug. 8, Mn/DOT selected the design-builder on Sept. 19.
Mn/DOT chose Flatiron Constructors Inc. in a joint venture with Manson Construction to design-build the new bridge. In addition to all other factors, the two firms have worked together before and had recently completed the San Francisco Oakland Bay Bridge Skyway together. Design started while the procurement process was being finalized. The contract specified 437 days to get the new bridge designed, built and open for traffic.
During this interim period, Mn/DOT had to develop alternate routes for those who would have used the I-35W bridge. Mn/DOT widened access ramps, converted shoulders to bus-only lanes, added lanes to some roads and added signals, signs and traffic cameras to some roads.
October-December 2007
In order to meet the aggressive schedule, the design-builder planned to have construction taking place on three fronts simultaneously, including in situ construction of the concrete side spans. In order to meet or exceed Mn/DOT’s expectations, the Flatiron/Manson joint venture (F-M) developed a quality management plan and an integrated quality approach. Bimonthly quality evaluation meetings were to keep construction on track for meeting those goals.
In developing preliminary designs for the bridge’s appearance, F-M chose a theme of “Arches, Water, Reflection.” The basic bridge design was to be a concrete box girder variable depth superstructure and a parabolic curve over the Mississippi. A pedestrian walkway underneath the bridge could be added in the future, if needed. The aesthetic features submitted for community and Mn/DOT to choose from included pier shape, railing details, color, textures, gateway monuments and feature lighting. The goal was to have the bridge be modern and elegant and still blend into the surroundings.
In addition to its appearance, the bridge would have multiple levels of redundancy. The design also included a number of innovative materials to minimize life-cycle costs, including high-performance concrete that included a corrosion inhibitor. Extra ducts and anchors allowed for future post-tensioning to increase the live load by up to 10 percent. An integrated sensor and monitoring system would allow Mn/DOT to track the bridge’s status in real time.
Another unique aspect of the bridge project is that it will be the first built under the Federal Highway Administration’s (FHWA) Design-Build Rule. The Rule, Section 1503 of the 2005 Safe, Accountable, Flexible, and Efficient Transportation Equity Act — A Legacy for Users (SAFETEA-LU), requires that FHWA allow state departments of transportation design-build projects to proceed through the preliminary design phase before the National Environmental Policy Act (NEPA) process is complete. This streamlines the preliminary design phase by allowing it to run concurrently with the NEPA review. The final design phase cannot begin until the NEPA review has been concluded. DBIA submitted comments when SAFETEA-LU was being considered.
January-May 2008
Through the winter months, construction continued. F-M’s experience with construction in cold-weather conditions kept workers and materials warm through a tough Minnesota winter. As long as the temperature remained above 20 below zero, footing and pier pours continued. Workers build heated sheds to allow the pre-cast segments to be cast and cured while it was cold outside. They also built the steel falsework for cast-in-place segments at the bridge approaches, built support structures for cranes to lift the pre-cast main span segments into place and shored up retaining walls. A concrete crusher demolished the remains of the old roadway, which were recycled for the base of the new one.
Across the state, extreme weather conditions — including heavy rains and hail — made road repairs necessary and forced state officials to close a number of roads and bridges.
Despite these challenges, Mn/DOT developed a plan to improve state highways and bridges extending through 2018. It specifically addressed bridges that are either “fracture critical” or that have low sufficiency scores.
Crews worked around the clock on both sides of the river and in the casting yard.
By the beginning of April, the majority of the drilled shaft foundations for the bridge supports were complete. Crews continued falsework construction and began pouring concrete. The pours for the sides and bottoms of the south approach spans at the end of March and the road beds in April.
Pre-cast segments were hauled to Bohemian flats, where they were loaded onto barges for the final leg of their journey. “Big Ben,” a barge-mounted crane, lifted the pre-cast segments for the main span into place beginning in May.
At the same time the barrel for a pedestrian tunnel under the south end of the bridge began.
August 2008
Crews began work building the median barriers and installing fencing along the mainline highway. They also worked on paving the “sandbox” area on the north side of the river, between the north abutment and Second Street Southeast, and restoration work on the West River Parkway. Work on installing and testing traffic signals, lighting and the anti-icing system continued.
In late August, construction began on the riverside observation plazas. The median barriers
September 2008
The last concrete for the main span of the bridge was poured, leaving mostly finishing touches to be done — painting, installing signs, landscaping, paving surrounding streets and grinding the surface of the bridge, painting lane stripes on the entrance and exit ramps and so on. Another important final detail was installing application disks for the anti-icing system, which will spray the bridge deck when weather sensors detect the potential for ice forming. And, of special importance to those who lost someone in the initial collapse, the memorial gateway structures were placed.
The last Sidewalk Superintendent Talk was announced for Sept. 6. As has been mentioned, a lane of the 10th Avenue Bridge had to be closed every Saturday in order to accommodate the large number of people who attended. Nearly 5,000 in all had come to see the progress and hear reports from the project managers.
And, finally, on Sept. 18 — three months ahead of schedule and less than a year from initial construction — the bridge opened.