Contractor Integrates Building with Bridge Using Separate Placing Boom
One of the design challenges of the Station Place Project in Washington DC is to relate a series of new office buildings with historic Union Station on Capital Hill. Besides being a thriving retail and restaurant venue, Union Station is very much a working hub for trains on the busy Eastern Corridor. With trains come tracks and the contractor’s challenge on Phase three of the project is to build a 12-story office building with a notch in it to accommodate an Amtrak line and Union Station service road. An innovative pair of masts and a detachable separate placing boom have been keys to helping cut 36 days from the schedule at the general contractor’s request.
“I just asked management to provide me with a reliable placing system to get this job done,” explains Shawn Gregor, project superintendent for Miller and Long, one of the largest concrete contractors in the United States. The company has offices in Maryland, Virginia and North Carolina. The system chosen incorporates the latest octagonal masts from Schwing with a KVM 39 X truck-mounted concrete pump with Generation Two detachable boom also manufactured by Schwing.
With 44 years in construction, starting as an operator with Miller and Long, equipment superintendent Jerry Wilson chose the system with the help of Dennis Andrews, owner of Schwing dealer Andrews Equipment Company, Inc., Jessup, MD. “The ability to free-stand the masts was a great asset to get the project out of the ground, “according to Wilson, “The fact that we can get maximum utilization from the concrete pump and placing boom is something we always strive for.” Miller and Long own seven Schwing boom pumps with the largest being a new S 45 SX. “Andrews has always been a great source of support with their knowledge of concrete pumps,” adds Wilson. Andrews is the current president of the American Concrete Pumping Association.
By embedding bolts in the floating foundation, the contractor selected two strategic locations for the masts. The masts were pre-mounted on cross frames and bolted down to the slab. The new Schwing designed masts are manufactured in 6-meter sections easing set-up and transport and can be used with any of the company’s separate placing booms from 24 to 37-meters. Sixteen reusable bolts join the sections to allow free-standing to as high as 65-feet without a counterweight. Because the Generation Two design separates the powerpack and hydraulic reservoir from the boom, the 12,890 pound KVM 39 enjoys the lightest weight to reach ratio in the industry.
Using the boom’s 114-feet of horizontal reach the entire site was able to be poured from the two mast locations. Because part of the excavation for the building’s foundation is under an existing bridge, one of the mast locations was located just outside the bridge overhang. The Roll and Fold design on the 4-section boom allowed it to reach under the bridge sections to place foundation walls, some as thick as three-feet which consumed 150 cubic yards for every 40-feet.
The building will accommodate the bridge by being set-back from ground level through the fourth floor before typical decks will be poured to the 12-floor. Structural steel will tie the building to the bridge. “Some of the bridge supports were temporarily reinforced while the below grade portion was pumped,” explains Gregor, “And some steel bridge supports are being replaced by concrete which we are placing.”
Pumping is accomplished from an adjacent roadway with the truck-mounted Schwing pump. “On a busy street like this, you can’t even extend the outriggers, which would have made booming the concrete from the street impossible,” according to Gregor. The closest mast is 100-feet from the pump, the other mast is 115-feet from the street. Two separate lines are employed and the truck shuttles between the pipeline hook-ups. The company flies the boom between masts and truck attaching it with four pins and nine quick-connect hydraulic lines. “The crew can accomplish this in less than 45-minutes,” explains Wilson, “This allows us to use the 39-meter for other pours as a truck-mounted boom for other Miller and Long projects.”
The time consuming task of reinforcing bridge sections and pouring concrete supports to replace steel beams has put the project on a fast track. General contractors Balfour Beatty Construction US with offices in Dallas and Washington DC is attempting to accelerate the building schedule. “We have cut 36 days from the schedule already. Some of that time was saved by this pump and boom combination,” Gregor states.
As the building rises, the octagonal masts will be braced in floor frames located in openings in the decks directly in-line with their free-standing positions. The masts and boom will be raised by the tower crane as floors are completed. “Once we start the typical floors at the fifth level, we expect to pour a floor per week with each deck calling for about 2,000 yards,” according to Gregor.
Wilson in his 44 years has seen the pump emerge as the method of choice for concrete placement. He notes, “The name of the game is equipment utilization and versatility. Attached to the pump this boom does most of our conventional pours, detached from the pump and mounted on a mast it was the perfect tool to access the under-bridge sections. This combination does it all.”
Project: Station Place, Phase III, Washington, D.C.
Owner: Joint venture, Louis Dreyer Property Group , Washington, D.C.
Architects: Kevin Roche John Dinkeloo Associates LLC, Hamden, Connecticut
General Contractor: Balfour Beatty Construction US , Dallas, Texas
Concrete Contractor: Miller and Long, Bethesda, Maryland
Equipment: Schwing KVM 39 X truck-mounted concrete pump with detachable placing boom; two octagonal masts.