9 Mile to go

July 15, 2010

On an otherwise typical summer evening in Detroit, a chain of fateful events took place which would ultimately cause a bridge to come crashing to the freeway below.

On an otherwise typical summer evening in Detroit, a chain of fateful events took place which would ultimately cause a bridge to come crashing to the freeway below.

Around 8 p.m. on July 15, 2009, a crash occurred along a winding stretch of northbound I-75 near the 9 Mile Road overpass involving a passenger vehicle, a semi truck and a tanker truck carrying 13,000 gal of fuel. The tanker truck crashed and ignited under the bridge, melting the steel bridge beams, which caused the span over northbound I-75 to collapse. Amazingly, only three minor injuries were reported, and no fatalities resulted from the incident, despite the fact that I-75 carries 100,000 vehicles per day and 9 Mile Road sees over 12,000 vehicles per day.

The community of Hazel Park, split in two by I-75 during the construction of the nation’s freeway system in the 1960s, relies heavily on all of the I-75 freeway overpasses in the area. When the 9 Mile Road bridge collapsed last summer, the local residents and business owners immediately felt the impact on their commute times and commerce. The collapse came just a year after the local residents experienced delays caused by the rehabilitation of the very same bridge.

The Michigan Department of Transportation (MDOT) immediately recognized the importance of this overpass and the freeway below by quickly beginning cleanup and planning the reconstruction efforts. Prior to the accident, MDOT had developed and initiated a design-build program that they elected to use as an expedited project delivery method for replacing this bridge. In addition to a new bridge, MDOT added I-75 improvements to the project, including superelevation correction and vertical profile adjustments to improve the safety through the curve. With the contracting method in place, the table was set for a design-build project that would replace the bridge in just seven weeks from the start of construction and have it open to traffic only five months after the collapse, reconnecting the community of Hazel Park.

On Sept. 30, 2009, the team of Walter Toebe Construction Co.; Fishbeck, Thompson, Carr & Huber (road design); Bergmann Associates (bridge design); and Soil and Materials Engineers (geotechnical design) was announced as the apparent low bidder for the project with a construction bid of $11.8 million, $1.4 million less than the next lowest bidder. The total bid, including lane and bridge rentals (the actual bid used in determining the winner), was $16.2 million, approximately $200,000 less than the next lowest bidder. Award of the project was completed on Oct. 7, 2009, marking the official start of the project.

Eye on the present, future
On Oct. 1, Bergmann Associates immediately began work with High Steel Structures, Lancaster, Pa., the structural steel fabricator on the project, to provide a design of the 36-in.-deep steel-plate girders for the project. The design had to accommodate the existing geometry of the I-75 freeway, the proposed geometry of the freeway and the future geometry that would be required as a result of I-75 being widened and realigned, which was currently being studied by MDOT. The future geometry requirements included a median pier that would be built at a different skew and approximately 15 ft to the east of the median pier being built as part of this project. The design of the plate girders and the preparation of shop drawings were done concurrently by Bergmann and High Steel Structures to ensure an expeditious review process and to utilize materials that were on inventory at High Steel's facility.

On Oct. 5, a preconstruction meeting was held to discuss the project and the design-build plan to construct the bridge within the aggressive schedule bid. During the meeting it was understood by MDOT that the design-build team would be performing much of the work “at-risk” by ordering materials and constructing portions of the bridge prior to plans being released for construction. Due in large part to MDOT’s early coordination during the advertisement period and the one-on-one meetings held during that period, MDOT, the contractor and the designers already were on the same page with respect to the design of the new bridge.

Furthermore, the design-build team utilized over-the-shoulder meetings extensively throughout the project. These meetings allowed the team to meet directly with MDOT staff to review the plans and discuss any issues they had with direction of the design or construction methods. These meetings also allowed the design-build team to progress with the at-risk work with some level of comfort.

The proposed bridge utilized a two-span continuous arrangement with tall wall-type abutments and a cap-and-column median pier. The plate-girder design was complicated by the requirement for the future median pier shift, which stretches the negative moment area that the beams needed to be designed for. The benefits of composite-beam design were diminished because shear connectors were not permitted in these regions. As a result, the challenge of meeting vertical clearance requirements was further complicated with constraints to 9 Mile Road profile adjustments.

Preliminary abutment and pier foundation design called for conservative loading to be utilized along with conservative lap splices and bar length to allow the contractor to order re-steel ahead of MDOT’s review of the substructure details to allow adjustments, if necessary.

Spread footings were designed at the abutments and the proposed pier location to take advantage of the stiff clays onsite and to expedite construction. Differential settlement controlled the size of the individual footings, and consideration also was required for the changing superstructure reactions at the abutments as a result of a potential future shift of the median pier. A pile-supported foundation was designed for the future median pier to minimize potential differential settlement in the future condition.

The west abutment was designed as a full-height wall for both proposed and future conditions and set near the edge of the proposed I-75 outside shoulder behind freeway barrier. The east abutment is unique in that a sloped embankment was constructed in front of it as part of this project, and will allow for the future shift and widening of I-75, which will require a wall-type abutment behind barrier. Both abutments utilize footing keyways to help resist sliding forces, as well as geofoam as a portion of the backfill to reduce lateral pressures on the abutment walls.

Just 14 days after the project was let and eight days after project award, design and detailing for the structural steel was complete. Additionally, load-rating calculations were submitted for the new bridge, which included analysis for both the proposed span arrangement and the future span arrangement with a shift of the median pier accounted for. The load rating included Michigan’s 28 legal loads and 20 overload vehicles, with two different analyses required for each to evaluate positive and negative moments in the girders and proposed and future conditions.

A 20-ft cut was required at the abutments to install the new footing below the existing and future freeway elevations. Temporary sheeting was used at the median pier to excavate and install the new pier footing to minimize I-75 lane closures.

The abutment foundation areas were prepared and the footing keyway was cast. The keyway was formed into the stiff clays and immediately filled with concrete to ensure the existing soils were not disturbed.

On Oct. 28 the contractor began installing the future pier sheet piling to be left in place, which will allow for construction of the future pier footing without disruption to I-75 traffic. The sheeting was installed assuming that the future work will need to be completed with the bridge superstructure in place.

Like the sheet piling for the future pier, it is assumed that construction of the new pier will have overhead constraints and, as a result, the foundation piling was installed. Pile driving continued for over 24 hours straight in cold rain and was completed the following day.

The following week columns for the proposed pier were formed and concrete was cast. Forming of the abutment walls also was initiated at the same time, and they were cast on Nov. 4. Several pours were required due to the large height and length of each.

On Nov. 9, the pier cap was cast and began to cure as the last remaining step prior to setting the new steel beams. Meanwhile, structural steel was on schedule, with the painting of the beams being completed in Pennsylvania. Permits for driving the beams to the site were secured, and arrangements were made for closing the I-75 freeway at night, one direction at a time, in order to erect the structural steel. The contract documents allowed for five nighttime closures of I-75 without lane-rental costs to erect the beams.

The geofoam backfill was then placed behind the abutment walls, along with foundation drainage and the remaining sand backfill.

The first of the steel-plate girders arrived on-site on Nov. 17. Southbound I-75 was closed for two consecutive nights while erection of the steel girders took place. The plate girders were fabricated and shipped in three pieces with one field splice made on the ground prior to setting the beams over southbound I-75. The second splice was made in the air over northbound I-75 on the third night. The steel girders were completely erected on-site only 44 days after award. False decking was installed for work to proceed on the superstructure without disrupting I-75 traffic below.

The first of three deck pours took place on Nov. 29, which was followed by the remaining pours in the designated sequence shown on the plans. The deck was heated from below utilizing forced warm air from the abutment ends of the bridge in between the deck forms and the falsework supported by the lower flanges of the steel beams. The weather was cool but unseasonably warm for the time of year, which played in the project’s favor.

Over the remaining days, sidewalks were cast and work progressed on the approaches, which included the abutment slopewalls, curb and gutter and service-drive drainage features. The bridge barrier also was formed and the concrete cast. On Dec. 5 the approach slabs were cast at each end of the structure, and steel railing tubes and pedestrian fencing also were installed prior to the bridge being opened to traffic on Dec. 11, just 65 calendar days from the official award of the contract and just five months after the collapse of the old bridge.

Staying put
Construction on the project was expected to continue through early summer 2010 to reconstruct approximately 1 mile of I-75, relocate and lower a siphon sewer under I-75 and reconstruct a portion of a median pier on a structure located south of the 9 Mile Road overpass that straddles the siphon sewer.

The remaining 9 Mile Road bridge work will be completed during the freeway reconstruction activities by placing slope paving in front of the new abutments and surface coating all of the exposed substructure concrete and superstructure fascias. Once planning of the future reconstruction of I-75 is complete, the 9 Mile Road bridge built today will be able to remain in place, saving time and money, thanks to the accelerated efforts of all involved.

Faced with many complex challenges, MDOT and the design-build team came together on this project in a positive team atmosphere to reopen two important arterials in Detroit. MDOT’s recent experience with design-build transportation projects allowed it to apply the same contracting mechanism to this emergency bridge replacement project. The public responded to the speed of MDOT’s response with great appreciation, and the local businesses repeatedly expressed their relief for a quick reopening of the bridge.

About The Author: Hedden and Quagliata are with Bergmann Associates.

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