Prefabricated Bridge Elements and Systems Case Studies
Feature Project: Pioneer Crossing Bridge
Prefabricated I-15 bridge at Pioneer Crossing in UT.
Motorists and news crews were curious about the huge concrete structure they’d seen from I-15 at Pioneer Crossing in Utah. It is part of Utah’s Corridor Expansion (CORE) effort aimed at restoring and renovating I-15 in Utah County. As part of this effort, the Utah Department of Transportation is raising the bar in using self-propelled modular transporters (SPMTs) to move bridge spans into place. The south bridge span over the I-15 northbound (NB) lanes for a new diverging diamond interchange was moved into place with SPMTs on Friday night, October 16, 2009. The span over the southbound (SB) lanes was moved into place just 2-days later on Sunday night. Then, the existing four-span bridge was dismantled without reducing the three-lane capacity in each direction on I-15. On the weekend of June 4-6, 2010, the north bridge for the interchange was moved into place from a staging area in the northwest quadrant outside the interchange SB ramp-approximately 1200-feet from the bridge. The span over the SB lanes of I-15 was moved into place on Friday night, and the span over the NB lanes of I-15 was moved into place on Sunday night. These bridges over I-15 are the largest multi-girder spans moved with SPMTs in the United States to date.
The two spans of the north bridge were constructed on temporary support piers in the staging area. On June 3, the SPMTs were moved under the span to be placed over the SB lanes. The 186-foot-long span had nine 96-inch prestressed concrete Washington State bulb tees in the cross section. The span had a 45-degree skew and also weighed 2100 tons. Two lines of SPMTs had to be configured to support the massive span at each end. At acute corners of the spans, two double rows of trailers (one row of 4-axle and one of 6-axle side-by-side) was used and at obtuse corners two double rows of 6-axle trailers were used. Each axle could carry a load of 30 tons. Special tower stand jacks raised and lowered the span off the temporary supports and onto the new substructure elements, respectively. Chains were also used to help control the distance between the double lines of SPMTs. On the top of the bridge, piano-like wire was placed at the diagonals of the span to measure any span distortion. To avoid overstressing the deck concrete, only 3 inches of distortion was allowed.
On Friday night, traffic control for the move got underway. At 8:00 p.m., one lane (of three NB and SB on I-15) in each direction was closed and then at 9:00 p.m. another. While lanes were being closed, the heavy mover subcontractor had workers positioning the span carried by the SPMTs as close to I-15 as possible for the move to begin at 10:00 p.m. A rolling road block was completed by the Utah State Police at that time to allow the SPMTs to move the west span of the north bridge of the interchange out onto I-15 and clear of the SB off-ramp. At approximately 10:15 p.m. the traffic was stopped on the SB lanes and the SPMTs moved onto I-15 SB, turned, and began going SB toward the bridge site. After stopping the traffic for 32 minutes, the one lane of SB traffic was allowed to proceed and was detoured onto the SB ramps around the bridge site. Traffic was released to flow on the ramps at 10:47 p.m. The NB traffic was similarly detoured so that the contractor had all of I-15 both SB and NB to perform operations without traffic influence. By 1:00 a.m. the west span of the north bridge was setting on the bearings, and the SPMTs were being readied for movement back to the staging area. By 6:00 a.m. the traffic was flowing freely on I-15 NB and SB.
On Saturday, the SPMTs were configured to support and move the east span of the north bridge off the span’s temporary construction supports. Cables were installed between the lines of the SPMTs to maintain the geometry of the span being lifted and moved. The span was positioned next to I-15 for the move Sunday night. By approximately 2:40 a.m. the east span of the north bridge was in place on the substructure supports. The contractor’s work was complete and I-15 was opened for the rush-hour traffic on Monday morning.
Case Study Worksheet
The Georgia Department of Transportation (GDOT) used Prefabricated Bridge Elements and Systems (PBES) to radically reduce the time and cost of the I-85 Bridge in Troup County, GA. Using PBES also increased safety and traveler satisfaction.
Case Study: PBES
Access to a Kia Motors manufacturing plant and training facility was a cornerstone of a larger economic development plan in Georgia. Six thousand new jobs were expected to be generated through the new Kia plant and related automotive suppliers.
Though Kia was located near I-85, access to the highway was limited. Existing roads could not accommodate the estimated thousands of additional daily auto and truck trips. A bridge was needed.
To expedite construction and improve safety, GDOT chose PBES. PBES is an innovative solution that substantially reduced the time and costs of the I-85 bridge construction in Troup County, Georgia.
With PBES, innovation could be incorporated into the design without increasing the user costs. Conventional bridge construction, using cast-in-place technology and traditional contracting methods, would have required 30 months. With PBES, the project was completed in only 16.5 months.
Prefabricated Materials for Bridge Installed
Deck Beam arriving on a semitrailier
The I-85 bridge was planned as a four-span concrete structure with eight columns per bent. Prefabricated elements were used for the substructure's columns, pier caps, and deck beams. The bridge components were cast offsite and shipped to the site on conventional semitrailers. Each component was carefully cast to within a 0.25–inch (in) (6.35–millimeter (mm)) tolerance so connections made in the field would fit precisely.
"We're doing some innovative things," said GDOT Third District Engineer Thomas Howell, "using precast, prestressed columns and caps on the bridge in order to expedite the work. It's a first in this district, and I'm pretty sure we haven't done a lot of that in the State. The pieces are actually made at a yard and brought out instead of forming and pouring them on site."
Safety data sets were collected before, during, or after construction to ensure that the innovations did not increase risks. With PBES, no worker injuries were reported. The single motorist incident involved minor vehicle damage with no personal injury.
Cost Savings with Prefabricated Bridges
The cost savings with PBES were equally compelling. GDOT's approach saved approximately $1.98 million, or 45 percent of what the interchange would have cost if it had been built with conventional construction practices.
Choosing PBES also minimized traveler inconvenience. Bridge construction typically causes a lot of highway congestion because of its sequential nature. Foundations for piers and abutments must be built first. Pier columns and caps must be built before beams and decks are placed. Because prefabrication technologies and processes were used, those elements could be constructed offsite and away from traffic, and brought to the project ready to erect.
Whereas conventional construction would have increased trip time by 25 percent, travel delays with PBES were rare. When they did occur, they were typically less than 1.5 hours. Scheduling deliveries for nonpeak traffic hours further minimized inconveniences to the traveling public. Lane closures were minimized.
User Satisfaction with Bridge Construction
I–85 interchange construction
User satisfaction with the bridge construction was also high. The goal was 80 percent or greater satisfaction with the methods used to minimize disruptions during construction. Instead, 91 percent of those surveyed were very to somewhat satisfied with the new I–85 interchange.
Spurring the economy requires new development, including a sound infrastructure of bridges and highways. But the public has lost patience with lengthy and expensive highway and bridge construction. GDOT's use of PBES expedited construction, reduced cost, improved safety, minimized traveler inconvenience, and provided a high quality finished bridge. Using PBES has the potential to transform bridge-building in the 21st century.