Manual on Use of Self-Propelled Modular Transporters to Remove and Replace Bridges
Chapter 7. Case Studies
This chapter includes case studies for bridge construction projects using SPMTs for the bridge moves. Extensive details are provided for the Florida Department of Transportation (FDOT) project to replace the Graves Avenue Bridge over I-4. Summary information is provided for the other case studies.
7.1. U.S. Bridge Moves with SPMTs
7.1.1. I-4/Graves Avenue, FDOT
188.8.131.52. Project Description
This FDOT project was the first use of SPMTs to move bridge spans that crossed a U.S. Interstate highway. The existing 215-ft (65.5-m) long Graves Avenue Bridge that crossed I-4 in Volusia County northeast of Orlando in Central Florida was replaced to accommodate the widening of I-4 from four to six lanes. The county bridge's four spans of 37, 70.5, 70.5, and 37 ft (11.2, 21.4, 21.4, and 11.2 m) were replaced with two spans, each 143 ft (43.5 m) long, for a new total bridge length of 286 ft (87 m). Graves Avenue was also widened. The 30-ft (9.1-m) width of the existing bridge was increased to 59 ft (17.9 m) to accommodate two 10-ft (3-m) shoulders and two 5-ft (1.5 m) sidewalks in addition to its two traffic lanes.
The cross section of the bridge was changed from the five and four AASHTO Type III beams in each of the two middle and two end spans, respectively, of the existing bridge to eight 78-in (198.1-cm) deep Florida Bulb-T beams with 8-in (20.3-cm) concrete deck in each of the two spans in the new bridge. The weight of each of the previous 70.5-ft (21.4-m) middle spans was 250 tons (226.7 metric tons); the weight of each new span was 1,300 tons (1,179.3 metric tons). Conventional cast-in-place reinforced concrete substructures with pretensioned concrete driven pile foundations completed the new bridge.
The posted speed on I-4 at Graves Avenue during construction was 70 mi/h (112.6 km/h). No I-4 lane closures were allowed from 6 a.m. to 10 p.m., and lane closures were permitted only during active work periods. In Florida, the removal of existing beams, erection of new beams and stay-in-place forms, and pouring of new bridge deck are not allowed over active traffic; lane closures or rolling roadblocks are required for these activities.
The Graves Avenue at I-4 bridge replacement project was awarded using the A+B bidding method with incentives/disincentives and liquidated damages. It specified conventional construction that required night work and rolling roadblocks. A field change was made to use SPMTs to remove the two middle spans of the existing Graves Avenue Bridge and install the two new longer and wider spans. The bridge required a short closure time because it is near a high school and needed to be open in time for the start of school in the fall. Also, a reduced onsite construction timeline minimized disruption to the 67,800 vehicles (13.5 percent trucks) that use I-4 at this location each day. In addition, a staging area for demolition and prefabrication was available about a quarter mile from the bridge.
Minimal structural design changes were required to use SPMTs to move the new spans, which were conventionally designed. The beams were precast, pretensioned concrete beams fabricated offsite, shipped to the staging area, and erected on the temporary supports that were identical in relative elevation to the onsite pier configuration. The beams were designed as simple span for both dead load and live load. Intermediate diaphragms were added at midspan, but were not post-tensioned. The full-depth, cast-in-place concrete deck was designed based on strip analysis and did not include post-tensioning. Because of the upward thrust due to beam rotation, additional longitudinal reinforcement was added across the interior support, as typically done in decks in Florida. Expansion joints were located at each span end of this bridge. Placement of the deck concrete was stopped 5 ft (1.5 m) from each side of the interior support to facilitate installation of the spans; the closure pour provided a continuous deck with good rideability. Bridges in Florida are profiled, ground as needed, and transverse-grooved after the entire deck has been placed.
184.108.40.206. Bridge Removal with SPMTs
Before the bridge removals, the contractor removed the two end spans of the existing bridge using conventional means since they were outside the I-4 traffic lanes. SPMTs with 360-ton (326.5-metric ton) capacity were used to remove the two middle spans over I-4. One six-axle SPMT unit was prepositioned in the median under one end of the existing span over I-4 East. On January 9, 2006, the outside lane of I-4 East was closed from 10 p.m. to midnight to position the second six-axle SPMT unit under the other end of the span. At midnight, a 20-minute rolling roadblock began.
A cross-frame connecting the two SPMT units was attached and the span was lifted 6 in (15.2 cm) off its supports. The span was then moved a short distance down I-4 East to the staging area on the right. From lift-off to arrival at the adjacent site took less than half an hour. The process was repeated two nights later for removal of the existing span over I-4 West. Its removal required two rolling roadblocks. A rolling roadblock on I-4 West provided the time required for the SPMTs to lift the span off its supports (see figure 8), drive it slightly west on I-4 West, and then rotate 90 degrees and drive into the median.
At that point a rolling roadblock on I-4 East began. The span was driven onto I-4 East, rotated 90 degrees, and driven down I-4 East to the staging area while I-4 West traffic was opened. Less than an hour was required from the start of the first rolling roadblock until the span arrived at its demolition site. Although not needed, the contractor had contingency plans for unplanned incidents, including backup equipment in case of mechanical failure, conventional lifting and demolition equipment onsite for timely I-4 clearing, a detour route for extended closure of I-4, and a plan to leave existing lane closures in place until the removed span was off I-4 and at the staging area.
220.127.116.11. Bridge Construction and Erection with SPMTs
Concurrent construction of the substructures onsite and the superstructure at the staging area took place from January to June 2006. Substructures were being cast a month after the superstructure deck was cast. The temporary substructures at the staging area were built on above-ground foundations and negligible settlement occurred. The new spans were built 5 ft (1.5 m) off the ground on the temporary supports at the staging area while I-4 was widened and the abutments and interior bent were built onsite. Several days before the scheduled move, the span to go over I-4 West was lifted off its temporary supports by SPMTs, with each end supported by a set of four six-axle SPMT units.
The centroid of the SPMT supports was about 14 ft (4.2 m) from the end of each span to accommodate the width of two side-by-side SPMT units. The span was then jacked in stages to its setting height and supported on sectional barges atop the SPMTs. The contractor had the sectional barges onsite for other purposes, and they were used to support the span after being checked to ensure adequate strength. Incrementally lifting the span to setting height took 2.5 days, with monitoring to ensure temporary stresses remained within allowable stresses. On June 3, 2006, both directions of I-4 were closed along a 4-mi (6.4-km) length shortly before midnight, and traffic shifted to a 5-mi (8-km) detour.
Figure 8: Removal of FDOT I-4 West Graves Avenue bridge
In about 30 minutes the SPMTs carried the span along I-4 to the bridge site, straddling both directions of I-4 before moving over to the I-4 West lanes for the installation. As the SPMTs approached the substructure, the operator lifted the platforms to provide clearance over the neoprene bearing pads in position on the substructure bearing seats. Proper alignment of the beams onto the bearing seats took about 2 hours. The process was repeated a week later for installation of the new span over I-4 East. The SPMTs again moved the new span to its final location in about half an hour (see figure 9), with proper alignment of the beams onto the bearing seats taking about 1.5 hours.
The standard cast-in-place substructure pier cap construction practice in Florida uses the casting of a beam seat pedestal on top of the pier cap; a neoprene pad is then placed on the beam seat pedestal before beam erection. The construction of the pedestals allows final grade adjustments to the beam seats. For the Graves Avenue spans, the beam elevations at the staging area were carefully surveyed to accurately replicate the onsite pedestal elevations. The onsite pedestal elevations were based on the beam seat elevations in the staging area after casting of the deck to account for any settlements to the temporary supports. FDOT has considered allowing stainless steel shims to adjust for any gaps between the beams and the bearing seats, but careful surveying, pedestal placement, and grinding of pedestals as needed have been adequate to date.
The use of the staging area delayed the excavation of the detention pond required at that location. The contractor started excavation immediately after the second installation.
18.104.22.168. Time Savings
The use of prefabricated construction and SPMTs for the Graves Avenue bridge project reduced the construction time from 12 months for conventional construction to 8 months, a reduction of one-third due to the concurrent activities of offsite superstructure construction and onsite foundation and substructure construction.
Figure 9: Installation of FDOT I-4 East Graves Avenue bridge
In addition, standard demolition and removal with cranes would have taken about 12 nights of lane closures and multiple rolling roadblocks to remove the existing bridge. A total of 20 additional nights of lane closures would have been required to build a conventional bridge onsite. With five beams to be removed in each of the two existing spans over I-4 and eight beams to be erected in each of the two new spans, a number of rolling roadblock operations would have been required for beam moves alone using conventional methods.
The SPMTs removed the two spans crossing I-4 in two nights with three rolling roadblocks of less than 30 minutes each. At the staging area, in less than 48 hours each span was demolished using conventional methods and rubble was removed. SPMTs moved the two new spans into position in one I-4 nighttime closure of a couple hours each. In summary, the 32 nighttime closures of I-4 required for conventional construction were reduced to four nighttime closures of shorter duration.
22.214.171.124. Initial Construction Costs
The 5.5-mi (8.8 km) I-4 widening project was awarded for $27.6 million in 2004 as a conventional construction project. A supplemental agreement for a change order to incorporate the new technology on the Graves Avenue bridge replacement portion of the existing contract was executed in January 2006 between FDOT and the contractor for an additional $568,175. The change order consisted of (1) removal of the two existing spans over I-4 in one piece each and placing them offsite for demolition, (2) simultaneous construction of the substructure onsite and the superstructure offsite, and (3) rapid installation of the two new longer and wider spans by lifting and driving them into position. See "6.8 Prefabrication Plan" and "6.9 Movement Plan" for a breakdown of activities.
The breakdown of the $568,175 additional initial construction cost is as follows:
- $132,178 (23 percent) to contractor
- $345,000 (61 percent) to SPMT subcontractor
- $68,497 (12 percent) to bridge subcontractor
- $22,500 (4 percent) to bridge subcontractor's engineering subcontractor
126.96.36.199. Delay-Related User Cost Savings
Prefabrication of the superstructure and its rapid installation using SPMTs limited the closure of Graves Avenue to the traveling public and limited the traffic disruption to I-4 traffic caused by Graves Avenue bridge construction activities. FDOT determined the delay-related user cost benefit to I-4 motorists by using the Arizona Department of Transportation (ADOT) user cost model, as described below. Because of the six traffic lights on the Graves Avenue detour, the analysis of the delay-related user cost benefit to Graves Avenue motorists did not lend itself well to the Arizona model; therefore, user cost savings due to the reduced closure time of Graves Avenue were calculated manually as described below.
Reduced Closure Time of Graves Avenue
To get actual numbers for length and time to travel the original Graves Avenue route (0.6 mi (0.9 km) and 1.0 minute) and the detour route (2.05 mi (3.2 km) and 5.5 minutes), the routes were driven and measured on a weekday midmorning. Subtracting the original distance and time from the detour distance and time gave 1.45 mi (2.3 km) and 4.5 minutes. The delay-related user cost per vehicle was 1.45 miles x $0.50/mile plus 4.5 minutes/60 minutes x $10.45/hr average user wage = $0.725 + $0.784 = $1.51 per vehicle. The vehicle count on Graves Avenue was 12,010 vehicles per day. Therefore, the cost per day was 12,010 vpd x $1.51/vehicle = $18,135.10 per day of detour. (Note: The $0.50/mile cost is based on cars, trucks, and school buses.)
The delay-related user cost savings for the reduction of 4 months of detour time was $18,135.10/day x 4 months x 30 days/month = $2,176,212. This number is conservative because the times for the six traffic lights on the detour could be longer than at midmorning when the measurements were taken.
Reduced Traffic Disruption on I-4
Conventional construction would have required 32 nights of lane closures for construction operations that include removal of the two old bridge spans (12 nights) and construction of the new bridge spans by erecting the beams, erecting the deck forms and overhang forms, and casting the new deck (20 additional nights). The new technology required only four nights total: two nights to remove the old spans and two nights to set the new spans. The user cost savings per day was determined using the ADOT user cost model spreadsheet, as shown in table 2. The additional user cost savings was 28 nights x $1,774.38 per night = $49,683. (Note: The "Average User Wage" used in the ADOT user cost model spreadsheet for the I-4/Graves Avenue project was updated for subsequent projects, as shown in Appendix A(4), per the latest figures from the U.S. Bureau of Labor Statistics.)
Table 2: ADOT user cost model spreadsheet for disruption to I-4 motorists
188.8.131.52. Net Cost Savings From Use of New Technology
The Graves Avenue detour was reduced from 12 to 8 months for a time savings of 4 months and a delay-related user cost savings of $2,176,212. Lane closures on I-4 were reduced from 32 nights to four nights, for a time savings of 28 nights and a user cost savings of $49,683. Total savings to the traveling public was $2.226 million.
The net benefit was $2.226 million delay-related user cost savings minus $0.568 million initial construction cost, or $1.658 million net delay-related user cost savings. The $568,175 initial construction cost was the net value after reduction for offsetting savings due to the new technology, such as cost savings of traffic control from reduced closures. No time for finishing earlier was given back to FDOT because the bridge was not on the critical path for the overall I-4 widening project. Staged replacement of the bridge using conventional construction would not have been possible without buying right-of-way since the centerline of the existing narrow two-lane bridge without shoulders was the centerline of the new wider two-lane bridge with shoulders and sidewalks.
FDOT administered the project. Volusia County owns the bridge. Metric Engineering, Inc., of Miami, FL, designed the replacement bridge. Ranger Construction Industries, Inc., of West Palm Beach, FL, was the prime contractor. Leware Construction Company of Leesburg, FL, was the bridge subcontractor, and IDA Consulting Engineers, Inc., of Orlando, FL, was Leware's engineering firm. Mammoet was the SPMT subcontractor.
184.108.40.206. Post-Installation Interviews with Contractor and Bridge Subcontractor
Both the contractor and the bridge subcontractor were pleased with the use of SPMTs to move bridges on the project. Comments received include the following:
- Time and money were saved by removing the existing spans and demolishing them at the staging area.
- A fiber optics line kept pile driving for the substructure foundations in limbo for about 6 weeks, but there was no delay because the superstructure was being constructed concurrently at the staging area.
- Saved 4 months but could have saved more time if there had been an incentive.
- Impressed with the speed.
- Allow enough flexibility for installations so that 0.5-in (1.27-cm) variation in placement does not matter; for example, make bearing pads and cap widths wider.
- Day work at staging area is preferable to onsite construction. With uninterrupted and nonrestrictive work hours for superstructure construction at the staging area, no day was missed after beam erection.
- High degree of quality control is required both at staging area and at final location.
- Would have been better if offsite construction had been written into the contract.
- Would prefer that contract specify maximum number of days that work can impact traffic.
- Pull bridge projects such as this one out from I-4 widening and let separately.
- Prefers complete closures to partial lane closures.
220.127.116.11 Lessons Learned
Lessons learned from the FDOT Graves Avenue bridge over I- project are as follows:
- Contractually require the road work to keep pace with the accelerated delivery of the bridge.
- Consider allowing a midspan-supported beam assembly at the staging area for composite dead load design of the prefabricated superstructure to improve cross-section efficiency. Include as an option in the contract documents. This may save a line of beams but would require additional temporary shoring.
- The successful completion of the project made it clear that the use of qualified SPMT companies and the latest equipment and performance specifications were essential to achieving the short onsite construction times and good long-term performance of the new bridge.
- Clearly define who is responsible for providing dimensions and weights of the structures to be moved, including face-to-face distances between obstacles. Based on this information, the SPMT company will develop shop drawings that show lift point locations with distance from face of obstacle to lift point for each lift point.
- Design wider substructure caps and wider clearances to facilitate installation.
- Consider round bearing pads and avoid skewed bearing pads.
- Consider permanently attaching the bearing pads to the bottom of the beams in the plant to avoid setting problems on the substructure.
- The owner should clearly specify the dates and time limits for bridge closure windows in the contract documents, providing adequate bonuses/incentives for early completion and penalties/disincentives for late completion, and including lane rentals and other contracting strategies to achieve the reduced construction timeline.
- The contractor should clearly delineate which construction processes are to be completed by the SPMT company. For example, the contractor should clearly specify that the SPMT subcontractor is to lower a removed span to 5 ft (1.5 m) above the ground at the staging area to facilitate its demolition. The incremental process required to lower the span requires time and additional equipment that the SPMT subcontractor may have to ship to the site.
- The ground at the staging area and along the SPMT path should not be freshly placed, but instead should be compacted early as needed to allow adequate time for settlement.
- Substructures should be built within construction tolerances to ensure proper fit-up with prefabricated superstructures (for example, backwalls should be plumb).
- Set steel plates close to abutment face to provide adequate ground capacity for SPMTs during span-setting operation.
- In span-setting operations, the SPMTs should move closer to the median until in position transversely, if space allows, and then move perpendicularly to set the beams on the abutment bearing seats. Adjustment is needed to accommodate the angle of motion due to the SPMT hinged elbow that moves down during setting operations. To avoid that angle of motion, the contractor should consider using synchronized vertical jacks mounted on the SPMT platform's top cribbing instead of the SPMT hydraulic system to lower the span to set it.
- Spans should be driven into position high during setting operations to accommodate the roadway crown.
- Consider use of laser guidance to line up superstructure with the abutment backwall.
7.1.2. I-10/LA 35, LaDOTD
This Louisiana Department of Transportation and Development (LaDOTD) project was the first use of SPMTs to replace damaged Interstate bridge spans at an intersection. In January 2006 LaDOTD replaced two 60-ft (18.2-m) AASHTO Type III pretensioned concrete beam spans on I-10 after an overheight load traveling under I-10 hit and damaged both the I-10 East and I-10 West bridges over SR 35 at Rayne, near Lafayette. After the September 2005 accident, SR 35 was partially closed and the I-10 bridges were shored while spans identical to the damaged ones were fabricated adjacent to the site. Use of SPMTs to remove the damaged spans and install the new spans was chosen to minimize the closure time of both I-10 and SR 35.
On January 24, 2006, the I-10 East bridge was closed and traffic detoured onto an off-ramp before the bridge and an on-ramp onto I-10 after the bridge. Two sets of six-axle SPMT units were waiting to lift the existing I-10 East span, and another two sets of six-axle SPMT units were loaded with the new I-10 East span. The temporary shoring was removed from under the existing span. The two SPMT units then moved under the bridge, lifted the damaged span, moved it away from the bridge, and rotated it before crossing the median to a nearby demolition site.
As soon as the existing bridge was out of the way, the new span was moved into position. The entire process from moving in the SPMTs to remove the damaged span to final setting of the new span took about half an hour. The process was repeated two nights later to remove the damaged I-10 West span and install the new I-10 West span. For each night, the maximum time of I-10 traffic detour was 10 hours, and the detour time could have been further reduced by doing more of the preparatory work before the closure. See figure 10.
Figure 10: Installation of LaDOTD I-10/LA35 bridge
The emergency replacement cost $1.0 million, including the two new spans, equipment, subcontractors, labor, and Louisiana State Police services. The SPMT subcontractor cost was about 13 percent of the total cost.
7.1.3. Providence River Bridge, RIDOT
The Rhode Island Department of Transportation (RIDOT) Providence River bridge replacement project is part of the reconstruction of I-195 in Providence. The main span is a steel network arch, defined as an arch with inclined cables that cross more than once. The span has three arches to support its 400-ft (121.9-m) length and 160-ft (48.7-m) width that will provide eight traffic lanes. It was assembled at a staging area near the location of barges that moved it up the Providence River for erection.
Mammoet's SPMTs in combination with its strand jack lifting system, shown in figure 2(d), were used to lift the span and move it onto the barges. The contractor requested a field change to use SPMTs to allow erection of the bridge on land and subsequent transfer onto the barges using the SPMTs. In the past, other bridges have been built on barges and transferred to construction sites, but rental cost of the barges is high. The SPMTs allowed a short-term rental of the barges, saving the contractor significant money. In addition, using the SPMTs on barges facilitated final placement of the bridge near a hurricane-barrier site constraint that prevented the use of cranes to erect the span. See figure 11.
Figure 11: SPMTs move RIDOT Providence River bridge span onto barges at staging area
7.1.4. Wells Street Rapid Transit Bridge, City of Chicago
The Wells Street Bridge was an 1899 steel rapid transit bridge crossing Wacker Drive in Chicago, IL. In 2002, the 111-ft (33.8-m) long, 425-ton (385.5-metric ton) prefabricated steel replacement truss span was built near the site as a result of a value-engineering proposal initiated by the contractor, and rolled into place with SPMTs to connect to shorter spans on each end. See figure 12.
The use of SPMTs made it possible for the bridge to be replaced over a weekend. The short closure was needed to minimize disruption in the schedule of the Chicago Transit Authority (CTA) elevated trains. The project was completed on time, avoiding a delay penalty to the contractor of $1,000 per minute. Disruption was significantly shortened for both vehicle and transit users. Conventional construction would have required rebuilding the bridge in sections over several weekends, and the CTA would have had to provide additional shuttle services.
Figure 12: Wells Street bridge installation in Chicago
7.1.5. Lewis and Clark Highway Bridge Deck Replacement, WSDOT
The Lewis and Clark Bridge is on SR 433 crossing the Columbia River between Oregon and Washington. A full-depth, precast concrete deck replacement was completed in 2004 for this 5,500-ft (1,676.4-m) long historic 1929 steel truss bridge. The majority of the existing bridge deck, 3,900 ft (1,188.7 m), was replaced with 103 full-depth, full-width, prefabricated, precast, lightweight concrete deck panels supported by longitudinal steel beams with intermediate transverse beams. SPMTs with a specially designed lifting and transporting frame moved a new panel to the top of the bridge, lifted the old panel that was just cut out, lowered the new panel into place, and moved the old panel off the bridge (see figure 13). The 36-ft (10.9-m) wide panels ranged from 20 to 45 ft (6 to 13.7 m) long, with a maximum panel weight of 96 tons (87 metric tons). One panel was replaced per night within a 6-hour period.
Time constraints allowed full closures from 9:30 p.m. until 5:30 a.m. Monday through Thursday. The deck replacement was completed in only 124 nights plus three weekend closures. Conventional deck replacement would have required replacing the deck lane by lane over a 4-year period, closure for several months, or closure every weekend for 6 months. Use of SPMTs allowed the bridge to remain open for normal weekday operation.
Figure 13: WSDOT Lewis and Clark bridge deck replacement
7.2. European Bridge Moves with SPMTs
7.2.1. A4/A5 Highway Bridge Near Amsterdam's Schipol Airport, Badhoevedorp, Netherlands
This two-span, horizontally curved, post-tensioned concrete bridge is 390 ft (118.8 m) long and weighs more than 3,600 tons (3,265.8 metric tons). The bridge is part of a newly constructed highway that crosses the A4/A5 expressway, one of the Netherlands' busiest highways near Amsterdam's Schipol Airport.
A total of 134 axle lines of SPMTs were coupled together to move the bridge from its nearby temporary supports to its final location. Specifications allowed a maximum deflection of 4 in (10.1 cm) in the bridge from midpoint to end, about 180 ft (54.8 m). Deflections were controlled during the move using a theodolite. A third-party measuring crew continuously monitored a dozen points installed on the bridge and reported them to the owner for calculation of stresses. The project required good ground preparation and level surfaces.
The move took 2 hours. The expressway was closed for only one weekend compared to almost a year that would have been required for conventional construction. See figures 14(a) and 14(b).
Figure 14: (a)SPMTs lift two-span bridge crossing Amsterdam's A4/A5 expressway off temporary supports (courtesy of Mammoet)
Figure 14: (b)SPMTs move bridge crossing Amsterdam's A4/A5 expressway to final location (courtesy of Mammoet)
7.2.2. PRA 13 09 Railway Bridge, France
The 2004 Prefabricated Bridge Elements and Systems Scan team visited the site of the four-span PRA 1309 Railroad Bridge, which crosses a new highway at Nonant Le Pin in France. The bridge was constructed on a concrete slab adjacent to its final location, as shown in the foreground of figure 15.
Figure 15: SPMTs moved four-span PRA 13 09 railway bridge in France
SPMTs moved the bridge, complete with substructure, a distance of 146 ft (44.5 m) to its final location. The average travel speed was 8 in (20.3 cm) per minute. The SPMTs lifted the temporary concrete beams that were cast between the supports to move the bridge. After the bridge was installed, the temporary beams were cut into sections to reduce their hauling size and weight. The protruding end sections shown in the photo were also removed.
The SPMTs moved the bridge into position in 8 hours. The rail line was closed for only 48 hours.