An innovative construction technique — a lateral bridge slide — was employed by the Texas Sterling Construction Company to build a new bridge for the Fred-Med project, a $14.6 million bridge and road project in San Antonio, Texas, with the goa
An innovative construction technique — a lateral bridge slide — was employed by the Texas Sterling Construction Company to build a new bridge for the Fred-Med project, a $14.6 million bridge and road project in San Antonio, Texas, with the goals of establishing a free flow of traffic in and out of the Medical Center, improving the safety of people seeking health care and medical assistance, and reducing critical travel time for those seeking emergency care.
While most of the work for the Texas Department of Transportation was completed last year, the remainder is taking place in the area beneath the bridge with TSC building the future through lanes away from active traffic. There also is some concrete work to be done along pedestrian areas and the completion of permanent traffic signals.
“Most of this work should be complete within the early months of the new year,” said Josh Donat, a TxDOT spokesman, “but a final surface of asphalt won’t be placed until temperatures rise — likely April.”
The seven-lane bridge —three in each direction, with a turn lane in the middle — was installed on Nov. 14, 2014. Work on the project began in late 2013. The bridge, 185 ft. (56 m) wide, 65 ft. (19.8 m) long, is crossed by 33,000 cars daily. The key elements of the work were: adding two through lanes in each direction on Medical Drive, two exit lanes in each direction providing access to Fredericksburg Road, and two entrance lanes in each direction allowing traffic from Fredericksburg Road to reach Medical Drive; along with the construction of improved drain structures, sidewalks and pedestrian features.
The bridge separates two major corridors at an intersection in the South Texas Medical Center — San Antonio’s primary medical care hub and home to The University of Texas Health Sciences Center; and with its completion, gives Medical Drive an unencumbered route into the South Texas Medical Center by passing under the now-bridged Fredericksburg Road.
Jim Reed, president of the south Texas Medical Center Foundation, stresses the importance of the work, which took 15 years of advocacy and studies to become a reality.
“We have 50,000 employees in the Medical Center and do 5.5 million outpatient visits a year,” he said. “You can see where the traffic out here is pretty substantial. This [is] not only a safety measure for them, but for our emergency vehicles.”
TSC crews began forming 90-ft. (27 m) bridge slabs adjacent their final location in the latter part of the summer as the contract held a clause limiting the contractor to having the intersection of Fredericksburg Road and Medical Drive shut down for 14 days or risk facing fees for finishing late.
“We brought this accelerated bridge construction method to TxDOT because it was a limited time frame to complete this milestone in the contract,” said David Griffin, TSC’s project manager. “This is a critical location — you’ve got ambulances coming in and out trying to get off a major interstate, I-10, into the medical center. We felt this type of method needed to be used here.”
Traditional bridge construction techniques would have left the intersection closed about two months. “Even using other accelerated bridge construction techniques familiar to Texas projects,” said Donat, “the intersection could have been closed at least three weeks.”
“Texas Sterling is setting a benchmark with this project,” said Griffin. “We would be more than happy to participate in future bridge slides.”
A lateral bridge slide was employed to install the bridge, a first in Texas.
“It’s been used with increasing frequency in other states,” said Donat. “The process uses a system of Teflon-coated pads and stainless steel plates to slide a bridge deck into place. Two 100-ton hydraulic jacks are used to push the 1,000-ton bridge decks into place. The process was designed by H. Boyle Engineering in Salt Lake City, Utah.
“Texas Sterling completed the milestone in just 190 hours, closing the intersection at 12:01 a.m. on November 7 and reopening the intersection to traffic at 10 p.m. on November 14,” he added. “The work earned TSC the maximum incentive bonus. While we are always careful with how and where we spend the money of Texas taxpayers, bonus checks like this are always nice for us to write.”
This was appreciated by TxDOT.
“Absolutely — to have that bridge deck finished and in use that fast was absolutely our goal from the beginning,” said Donat. “Several of our stakeholders were skeptical we could have the intersection reopened that fast with the amount of work we had to do — TSC exceeded even our own optimistic expectations with this.”
TxDOT will be employing this bridge construction technique on future projects via “the right application,” said Donat. “This technique does tend to cost a little more, and it’s not always practical. It requires quite a bit of space adjacent to the bridge area, so it isn’t something that would be viable everywhere. But state-wide this has started a conversation and our construction engineers are looking for opportunities to implement something like this where it makes sense elsewhere. [The advantages are] the time savings was a huge advantage. That’s really what this technique is all about.”
The bridging technique is used across the country by one of TCS’s sister companies, subsidiaries of Sterling Construction Company, Incorporated.
“The process involves constructing the bridge deck adjacent its final location in advance and then using hydraulic jacks and liquid dish soap to slide the bridge deck into place,” said TxDOT engineer Justin Wiatrek. “Using the method, the time required for major traffic interruptions to demolish the old roadway and have a new road surface in place is cut into a fraction of the time other methods require. It takes the time for forming and all that out of the picture. The only time traffic is actually closed is just for the actual move of the bridge to get it into its final position.”
TSC crews began the work to install the bridge early on Nov. 7, with the intersection excavated in less than 48 hours — 2 large excavators were used to dig 30 ft. (9 m) down to expose bridge supports built underground during the summer. Specialized crews brought in by TSC set each slab — each weighing nearly two million pounds, on Teflon coated steel plates covered with Dawn dish soap. Then hydraulic jacks were used to push the decks individually at a rate of 4 to 6 in. (10 to 15 cm) per-minute.
The entire sliding process took just 27 hours.
“The longest wait of the whole process was for concrete forming the bridge joint supports, poured on the fourth day of the closure, to cure,” said Donat. “By 11:30 p.m. the eighth day the intersection was open for traffic. The early completion will earn Texas Sterling a bonus of about $120,000.”
Griffin and his personnel appreciate the TxDOT’s praise.
“We encountered many challenges on this project,” he said, “including working 24 hours per-day — six days a week for 12 months; multiple utilities being installed — if not in the same alignment, really close; and a really aggressive schedule. But if there was one single most obstacle, it was the bridge slide.
“In Texas there is a lot of earth retaining walls that require drilled shafts and there is a lot of recessed paving that drilled shafts on both sides of them,” he added, “and collectively, with the engineers from RLW Inc., we thought that Texas was an ideal candidate to have a lateral bridge slide because instead of having to set up a bunch of false superstructure, we would just shorten the drill shafts adjacent to the permanent location. Thus the drill shafts run perpendicular, so we shortened the shafts and built a slide pad on them. We then used some pads, and built the new bridge next to its proposed location.”
Planning was crucial and thorough — drawings were produced on AUTOCAD —and approved by engineers. The proposed slide was reviewed several times and TSC’s Project Engineer Christopher Reyes prepared a submittal with the capacities of the jacks and thresholds and other variables that were very important to the execution of the slide given all the hydraulics involved with the slide.
“We had a complete package for internal purposes,” said Griffin, “which TxDOT requested for information only so they could monitor the pressures. We put everything together to have the peace of mind that we got it right. The actual jacking and sliding only took about 24 hours, but we had a 12-hour layover between the two pieces that we installed.
“We moved it in two sections because it was heavy to move — the bridge weighs four million pounds,” he added. “Each section weighs about two million pounds and we had to slide the bridge about 190 feet. But the bridge is wider because of the medians and crosswalks on the outside.”
To slide the bridge, TSC used four 100-ton Enerpac plunger jacks, a Simplex high capacity electric pump to run the jacks, and 44 teflon pads from Scougal Rubber Corporation. To do the excavations for the slide, one 336 Hitachi and one 350 Cat excavator were used. The excavators removed 33,000 tons (29,937 t) of dirt and overall with the demolition of the existing bridges and roads, 1,144 tons (1,037.8 t) of asphalt was moved.
The new bridge consists of 419 cu. yd. (320 cu m) of concrete, and 41 tons (37 t) of rebar.
“We had to build a frontage road on one side to put all the traffic on and another on the other side,” said Griffin, “and then we split traffic and after that was done, we were able to start the construction of the bridge and excavations between the lanes of traffic as the main lanes are recess lanes that go underneath the bridge at the end of the project.”
TSC had a minimum of two shifts per-day — 10 to 15 people per-shift, and at times had three shifts, with each shift between 10 to 12 hours. Only a few subcontractors were brought in, including CP Placers for tieing steel
“We self-performed most of the work,” said Griffin. “Even with the biggest subcontractor that we had, it was about five additional people on site. We did a lot of the drilling ourselves. When we tore the road out, we went down to about 25 feet. It was a road on top of dirt and from the elevation of the bridge, the road was brought down about 25 feet and given a concrete surface.”
TSC rented the plunger jacks from Lifting Gear Hire in Dallas, Texas, and the hydraulic pump from RLW, and it purchased 1,000 linear feet of 1-1/8 in. (2.9 cm) dywidag bar from Dywidag Systems International, a specialized manufacturer of high-strength steel.
“It looks like rebar and it has a ton of nuts and couplers,” said Griffin. “We also purchased a Nelson stud gun from Nelson in Houston, Texas, to help install the wall panel. There were 32,000 square-feet of wall panels — 10 inches thick, big and heavy and sometimes 25 feet tall. They weigh about 1,000 pounds per-vertical foot. And for the salvoes, you had to embed a metal plate into the drill shafts prior to excavating or you had to embed the metal plate into the drill shafts while you were installing the drill shafts; and we had to excavate down in front of the drill shafts and expose the metal plates of the drill shafts and then attach a 5/8 inch stud onto it. The conventional method is to have a welder do it with a welding machine, but to expedite this, we purchased the $25,000 stud gun and we had to get a 200 KVA generator to run the stud gun.”
Other equipment and vehicles used consisted of four foreman heavy duty GMC trucks with trailers, one Cat 416F and one Case 580 rubber tire backhoes, one Volvo L90G wheel loader, one Bobcat loader and one John Deere skid steer loader, one dozer, one 25 KVA generator, two Ingersoll Rand air-compressors, and three Magnum light towers.
TSC had a field office set-up on site and it sent in mechanics as needed for routine maintenance and immediate repairs.
“Our mechanics are sent from job-to-job when needed,” said Griffin. “Our operators do a daily inspection and they turn in their inspection books daily. If there is a problem with equipment, they notify somebody right away. Usually the operator notifies the foreman, who then notifies the superintendent, and if he thinks that it needs to be pushed up the ladder immediately prior to running the equipment, he calls the equipment manager.
“We didn’t have any unexpected repairs,” he added, “but we did have some hydraulic issues when trying to switch attachments onto excavators. For instance, when we were removing the asphalt road so that we could slide the bridge, we had to use a hoe-ram to bust it out and when we were trying to switch attachments — from a bucket to a hoe-ram, we encountered hydraulic leaks and we had to repair them immediately.
“When you are running a bucket on an excavator, you are not using all the hydraulics,” he explained, “but when you attach a hoe to it, you are using hydraulics that are typically not used and that is hard to catch.”
Despite the construction and mechanical difficulties that were encountered, Griffin cited the experience of TSC being involved in many major projects in the past.
Concerning the remaining work on the project, Griffin noted: “we just have to put up some wall panels, pour some coping, and put some asphalt and concrete paving down. It should be completed by the end of March.