Contractor uses innovative method for bridge beams on Beltway project
2-foot triangle speeds action of placing beam
Pittsburgh Post-Gazette
Carpenters pass tools and material all the time, whether it’s hand to hand, using a bucket and rope or even by using a pallet.
The crews assembling a bridge last week over Little Raccoon Creek in Washington County as part of the construction of the $800 million Southern Beltway are taking that concept to a larger scale: passing 123foot-long, 75-ton precast concrete beams from one crane to another using a 2-foot welded steel triangle and a couple of Kevlar straps to put them in place.
The innovative process involves two cranes because the beams are too long and heavy to use just one. And the crane-passing isn’t a one-time thing because the bridge in Robinson Township requires 42 beams to build separate spans in each direction.
The load triangle is a relatively new construction tool approved two years ago for use on projects by the state Department of Transportation and the Pennsylvania Turnpike. Alvarez Inc. of Canonsburg became the first company in the state to use this method, which replaced a timeconsuming process that involved sliding beams across a greasy piece of steel.
“That triangle? I personally built that thing,” said Joe Schrecengost, erection supervisor for Alvarez, minutes after he finished guiding a beam into place using little more than the cranes and a 2-by-12 plank of wood.
Mr. Schrecengost, a 33-year construction veteran, said he saw in a trade magazine that an Oregon company was using the load triangle to place beams. For years, the accepted method of placing beams involved sliding the precast concrete across a dummy steel slab placed across the open area and treated with Crisco or a similar slippery substance, then pulling the steel out.
“I thought, ‘If they can do it in Oregon, why can’t we do it here?’ so I made one,” Mr. Schrecengost said, describing the stick-welded steel triangle.
Crane-passing works like this: One crane at the edge of the bridge suspends a cable with a Kevlar strap attached to one corner of the triangle. On the corner of the triangle directly below the strap is a chain with two hooks attached to the beam while the third corner has a second, open Kevlar strap.
The crane lifts one end of the beam and moves it about a third of the way off the tractor-trailer dolly and over the valley the bridge will span. In the valley, midway between the four piers that will support the bridge, is another crane that moves its cable into position adjacent to the triangle.
At that point, Mr. Schrecengost climbs onto the suspended beam, hooks his harness onto safety rigging and scurries to the cable to attach the open strap to the second crane and detach the first strap. That shifts the weight of the beam from the first crane to the second crane. The first crane then moves to the other end of the beam to pick it up, and together the two cranes move it into place, a process that takes about 12 minutes from the first lift.
Using this method allows crews to place as many as six beams in one day, two or three times as many as the Crisco method.
Prelude to the lift
Passing beams from crane to crane is the end of a process that began early last year when crews started clearing brush between Route 22 and Beech Hollow Road and relocating Little Raccoon Creek, a small stream that meanders through a valley so it should have a more permanent path. The bridge is part of a 13-mile toll road under construction by the Pennsylvania Turnpike to link Interstate 79 with Route 22.
Through the summer, crews built four sets of piers for the new bridge, which is being built in an area that seems 12 miles from nowhere. It may have been the end of February, but it was time to begin assembling the framework of the bridge.
“We’re on a pretty tight schedule,” said Tim Mihalek, construction supervisor for subcontractor Greenman-Petersen Inc. “It’s important that we get this done on time.”
That’s because crews will be ready to begin laying pavement in May across this end of the new highway with the bridge scheduled for early June.
The bridge construction site is a good half-mile off Cardiff Road, a half-mile that was left a muddy bog by the historic amount of rainfall in February. It got even muddier approaching the bridge, making it a challenge for trucks to get the beams to the bridge.
Rigs haul the beams to the site one at a time with one end on the bed behind the cab and the other attached to a dolly. The site was so muddy that once a rig arrived on site and tried to back in, a front loader had to scrape the road ahead of it so it could get through.
“I wouldn’t want to drive those trucks on the highway let alone through that mud,” Mr. Mihalek said. “That mud’s like something from ‘The Ten Commandments.’ “
For the truck’s final 30 yards, one member of the crew walked behind the dolly with a remote control device to guide it to the exact location. Nothing is left to chance in bridge erection: Crews have 81 pages of design specifications to follow just for placing the beams.
When the beams arrive at the staging area near the first abutment, a crew of 12 carpenters jumps into action, quickly attaching safety rigging across the top so they can move across the pieces throughout the construction process.
Because of the muddy conditions, the cranes with 113-foot booms have been placed on sets of 12-by-12-inch beams so they won’t sink.
Once the beam is in the air, Mr. Schrecengost uses a combination of a walkietalkie and hand signals to communicate with the crane operators. Third base coaches in baseball could take lessons from him on how he uses one hand to tell the crane operator to move the beam left, right, up and down or to stop.
At the far end, three carpenters are stationed on the pier where the beam will rest. At one point, one leans against the beam to force it to the right place, relatively easy since it is almost weightless suspended in the air.
At the abutment, Mr. Schrecengost uses a wooden plank to make the final adjustment and set the beam in place on a 4-inch-thick rubber composite pad. Immediately, Mr. Mihalek, who had climbed down the hillside under the beam, inspected the placement to make sure the beam was flush on the pad before two men used heavy chains to secure it in place.
The next part of the process involves two carpenters perched on a manlift, who find brackets located at the midpoint of each beam. There, the carpenters attach X-shaped steel braces onto the brackets to tie the adjacent beams together and make sure they will stay in place. When it is constructed, the beam has a camber or curvature of about 4 inches but that goes away almost immediately when it is put in place.
When crews are finished placing beams on one side of the bridge, one crane will be moved to the abutment on the other side so beam placement can be completed on that side.
Over the next few months, crews will finish the preparation for bridge paving by placing two layers of reinforcement bars and preparing the road bed leading up to bridge on both sides for paving.
The whole process was made quicker and easier by a 2-foot steel triangle.
“[Using the triangle] has made such an improvement in how we do this,” Mr. Schrecengost said. “It’s kept the cost down, too.”