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Rapid Removal and Replacement of the 4500 South Bridge over I-215 in Salt Lake City
The 4500 South Bridge on SR 266 over I-215 in Salt Lake City, designated as structure F-156 in UDOT's bridge management system, is the focus of this infrastructure renewal project. The four-span structure, originally built in 1971, was 244 ft (74.3 m) long and 77.2 ft (23.5 m) wide, including a driving lane, turn lane, shoulders, curbs, gutters, and sidewalks.
Figure 1 shows the typical section for the existing bridge.
The average daily traffic (ADT) for I-215 and SR 266 is 66,085 and 14,815 vehicles, respectively.
By 2007, the structure was in poor condition, with delaminated, distressed concrete columns, pier caps, girders, and decks, as well as badly exposed and corroded reinforcing steel. On a scale of 0 to 100, the overall sufficiency rating for this structure was 40.3, indicating an unsafe condition requiring immediate mitigation. The deck, superstructure, and substructure were rated at 4, 4, and 3 on a 0-to-10 scale, respectively, causing it to be categorized as "structurally deficient." Some of the columns of the bridge were in such poor condition that UDOT had to shore up the bent caps for extra support (see Figure 2 and Figure 3). The poor overall condition of the bridge prompted UDOT to expedite the removal and replacement of the bridge.
Using a combination of innovative bidding and construction approaches centered on ABC methods, UDOT replaced the existing 4500 South Bridge with a new single-span structure. The main goal was to reduce traffic impacts on I-215 and minimize impacts on residents who use the 4500 South Bridge. The selected reconstruction approach represents the core principles of the HfL program and UDOT's modern approach to bridge construction: to deliver projects expeditiously, safely, economically, and with minimal impact on the environment and highway users.
A plan view of the proposed new structure is shown in Figure 4. The innovative elements of the project include the following:
These innovative elements are described in the following subsections.
Construction Manager General Contacting
CMGC is a construction delivery method in which the construction manager acts as a general contractor, bringing the contractor and designer together to meet the owner's goals for the project. In general, the CMGC method uses an integrated team approach, applying modern management techniques that allow the designer and contractor to collaborate during the design process to control time, cost, and quality. This process was used effectively on this project, and some major design and construction decisions were processed together by the teams. This ultimately saved time and expensive change orders on the project. In terms of time savings, UDOT noted that the traditional design-bid-build approach would have taken 12 months longer from preliminary design to construction completion than the CMGC approach adopted.
One of the major decisions made to accelerate the replacement of the existing structure was to construct the superstructure offsite, next to the existing bridge. The girders were assembled on a 9 percent slope3 over temporary abutments (see Figure 5). After assembling the girders, the deck was cast in place over the girders and painted. Figure 6 shows the built superstructure resting on the temporary abutments about 50 ft (15.3 m) from the existing bridge on a specially constructed staging area. The benefits of constructing the superstructure offsite include the following:
Concurrent with the superstructure construction, substructures were constructed below the bridge with little or no impact on I-215 traffic. Portions of the I-215 shoulders were used during construction of the substructures, but the shoulder and traffic lane were separated using Jersey barriers. The substructure construction consisted of building abutments with aesthetic murals on CIP spread footing foundations with extended wingwalls (see Figure 7, Figure 8, and Figure 9). Abutments were cast in place by pouring concrete through the holes drilled into the existing bridge deck.
To facilitate construction of the abutments and wingwalls, the approach embankments were stabilized by inserting tiebacks ranging from 27 to 37 ft (8.2 to 11.2 m) long in a grid system of 5 by 7 ft (1.5 by 2.1 m) using a technique called soil nailing. After the tiebacks were inserted, shotcrete was applied to the entire exposed face of the approach embankments (Figure 10).
Use of Free-Draining Backfill Materials
Free-draining backfill material conforming to American Association of State Highway and Transportation Officials (AASHTO) No. 57 stone was placed behind the abutments to minimize the need for compaction and to expedite the construction, as shown in Figure 11 and Figure 12. AASHTO 57 stone requires very little compactive effort and is a highly drainable aggregate with a coefficient of permeability, k, greater than 10,000 feet per day. A small hand-operated vibratory plate compactor was used to seat the aggregate (Figure 13).
Prefabricated Bridge Components
Interlocking bridge approach panels (weighing 40,000 pounds (lb) (18,143 kilograms (kg)) and measuring 25 by 12 ft (7.6 by 3.6 m)) and sleeper slabs were precast next to the bridge, as shown in Figure 14 and Figure 15.
Removal and Replacement of 4500 South Bridge Using an SPMT
The 4500 South Bridge was removed and replaced successfully in a 53-hour time span during and immediately before the weekend of October 27 and 28, 2007. To make such a rapid removal and replacement possible, UDOT used an SPMT for the first time in its history. The SPMT greatly reduced construction time, minimized inconvenience to the traveling public, improved worker and motorist safety, and maintained a normal workweek traffic flow.
An SPMT is a computer-controlled platform vehicle with a large array of articulating wheels on the bottom. It is used for transporting massive objects such as bridges, buildings, heavy and oversized equipment, and other objects too large or too heavy for normal trucks. The SPMT deployed on this job was equipped with two sets of 16 axles, each with eight independent, fully articulated, computer-controlled wheels (256 wheels total) and a hydraulic system capable of moving up and down within a vertical range of 24 inches (in) (25.4 millimeters (mm)). It was operated remotely by a single operator using a joystick control.
Although UDOT decided early to use an SPMT to remove and replace the bridge, this project presented unique challenges. One of the most challenging factors was the weight and size of the superstructure, estimated at about 3.2 million lb (1.4 million kg) and 172 ft (52.4 m), respectively. This was the longest bridge ever moved by SPMT in the United States. Another challenge included the various slopes on the project—5- to 7-ft (1.5- to 2.1-m) elevation differential between the north- and southbound lanes, 4 percent roadway longitudinal grade, 2 percent pavement cross slope on I-215, and 12 percent slope of the superstructure longitudinally along SR 266.
On the afternoon of October 26, UDOT closed both I-215 and the 4500 South Bridge and began final preparation for the removal of the existing bridge. To facilitate removal of the superstructure, preliminary work had to be performed on the bridge surface, including sawing and removal of the asphalt overlay, rubblization, and removal of the bridge railings, concrete median, and approach slabs (Figure 16 and Figure 17). On October 27, the SPMT was used to lift and move the two-span superstructure of the 4500 South Bridge to a demolition area alongside I-215 (Figure 18). It took the SPMT two trips (one per span) to complete the removal of the superstructure.
The supports for the superstructure at the demolition site were built to mimic the existing alignment, which facilitated the rapid placement of each span (see Figure 19).
The entire removal process took about 4 hours. After moving both parts of the existing superstructure to the demolition area, work on rubblizing the existing columns and bent caps began over I-215, as shown in Figure 20. The remaining time on Saturday was spent removing the rubblized materials and preparing the abutments (Figure 21) for placement of the new superstructure.
On Sunday, October 28, the SPMT moved the new superstructure to its final location to rest on the newly built abutments. Because of the considerable length of the superstructure, the SPMT used both the north- and southbound lanes of I-215 to transport the structure (Figure 22 and Figure 23). One glitch was encountered in placing the superstructure on the abutments. As the superstructure approached the abutments it was discovered that the incline at which the superstructure was held by the SPMT (i.e., its cross-slope) did not match the incline of the abutments (see Figure 24). As a consequence, halfway into transporting the superstructure over the abutments, the southeastern corner of the superstructure came close to touching the eastern abutment. To prevent the superstructure from coming into contact with the abutments prematurely and to ensure correct placement, the contractor had to implement a contingency that they had considered for this scenario. The superstructure was jacked up as high as possible using the 16 hydraulic jacks that the SPMT was equipped with. In addition, using the materials on-site, the contractor built a temporary ramp on I-215 that the SPMT could climb over to ensure enough clearance between the superstructure and the highest point of the abutment. The SPMT used the ramp and was able to then precisely install the superstructure. This entire adjustment only added approximately 1 hour to the entire operation and I-215 was opened to traffic on Monday morning as scheduled.
Many members of the public, as well as representatives from UDOT and other Federal and State transportation agencies, witnessed the entire removal and replacement process (Figure 25). Local and national news outlets, including CNN, covered the proceedings at the construction site.
I-215 reopened to traffic on Monday, October 29, at 1 a.m. The 4500 South Bridge reopened to traffic about 10 days later. Overall, despite the minor glitch associated with the placement of the superstructure, the removal and replacement of the 4500 South Bridge project was a great success. Arguably, the biggest payoff from this project is the change in bridge construction practice in Utah. As a result of the success of this project, UDOT has developed implementation plans to use ABC technologies on all future structural projects in the State.
Figure 26 and Figure 27 show views of the 4500 South Bridge after it opened to traffic and during postconstruction HfL data collection activities on December 5, 2007.
3 At the time of bridge placement, the superstructure was inclined longitudinally by another 3 percent to a final position of 12 percent grade.
This page last modified on 04/04/11