- Published: Tuesday, 31 July 2012 10:17
- Written by CP Staff
Concrete Tech sets new threshold for bridge beams
Concrete Technology Corp. and heavy-hauler V. Van Dyke Inc. put an exclamation point last month on a contract calling for the longest precast/prestressed concrete girders delivered to date via a U.S. thoroughfare.
Deploying highly stable trailers on post-evening rush hour schedules, the team shipped nine 205-ft.-long, 100-in.-deep beams—the second of two sets—from Concrete Tech’s Port of Tacoma (Wash.) plant to the Alaskan Way Viaduct Replacement site just south of downtown Seattle. The super girders support the northbound lanes of a pier-free crossing within the southern mile of a grade and tunnel project succeeding the viaduct, itself part of SR 99. Phased demolition of the two-level, cast-in-place Alaskan Way structure—deemed structurally obsolete by current seismic standards—will reconnect key portions of downtown Seattle and the Puget Sound.
Concrete Tech and Seattle-based V. Van Dyke shipped an initial set of eight, 205-ft. Wide Flange 100G in mid-2011 (Concrete Products, December, “Take It To The Limit” cover story), this year’s delivery bringing the South Atlantic Street crossing to full width. The producer fabricated the single-piece, 255,000-lb. members according to Washington State Department of Transportation specs for the new generation WF100G girders. WSDOT adopted 10,000-psi design strength concrete mixes and new 0.6-in.-diameter strand patterns to enable single WF100G beams for bridge spans in the 195- to 240-ft. range. Commercial, high strength concrete has been a Seattle fixture for decades thanks to abundant reserves of pristine glacial quartz. Its capacity to develop strength even in lean mix designs suggests some of the highest quality ASTM C33 product on the planet.
Concrete Tech used a high slump mix reaching nearly 13,000-psi compressive strength for the super girders, which contain 74 permanent and eight temporary pretensioned strands. The mix is in lieu of a self consolidating concrete, for which WSDOT has not yet issued a spec. Assessing the hauling prospects along SR 99—providing a direct, 30-mile, at-grade route from the Port of Tacoma—engineers calculated that 10,600-psi strength concrete was required to meet allowable stress limitations and assure lateral stability during girder transfer.
WSDOT, which Concrete Tech credits with helping producers and haulers advance extra-long prestressed girder practice, includes member-to-trailer contact point bunking locations, lifting hardware specs and other trucking parameters on contract documents. The department typically lets longer-span bridge contracts with single-piece or spliced-girder options, contractors opting for the former on jobs where route and site access permit.
Precast/prestressed concrete girders’ strong track record with WSDOT was underscored in the past decade, as Concrete Tech logged record or near-record length road-bound beams—in the 175- to 185-ft. range—for eight bridges under the agency. Besting those projects on the length scale was Salt Lake City’s Hanson Structural Precast, which in 2010 delivered 195-ft. girders for a widened Interstate 15 crossing. Like it, the new Washington SR 99 structure spans a four-lane or wider road with additional rail line clearance requirements. (Calgary-based Con Force Structures maintains the North American record for road-hauled, precast/prestressed members—the Deerfoot Trail at Bow River Bridge’s 211-ft. girders, 2004.)
Concrete Products visits Concrete Tech and V. Van Dyke for some additional perspective on their Alaskan Way WF100G fabrication and delivery feat.
When V. Van Dyke President Cliff Bates crosses any new Washington state bridge, chances are his company had a hand in its construction. “We’re very busy right now,” he affirms, noting how a specialty in oversized loads positions Van Dyke as a hauling candidate whenever larger concrete or steel girders are being transferred in the state. “Contractors know they can count on us to deliver safely and on time.”
Geography and pier placement drove the size of the Alaskan Way super girders, says Bates, “which were the largest we’ve ever seen. [They] represent only part of the project, as we’re working on a half-mile long overpass that takes Highway 99, over railroad tracks, to Atlantic Street and into the tunnel. For the rest of the job, we’re moving 160-foot girders—a bit more pedestrian.”
“We had to develop a new trailer system to handle not so much the [super girders’] length, but the weight,” he adds. All told, an 18-wheel trailer connected to the fifth-wheel cradled the front of the girder, a rear, driveable, 32-wheel trailer maneuvering the back. A driver manned the cockpit of the rear trailer, which looked akin to a vehicle out of a Mad Max movie.
V. Van Dyke used a pair of identically spec’d Kenworth T800s with 550-hp engines driven through 18-speed transmissions. Heavy duty is the name of the game with one pusher and two drive axles, each rated at 46,000 lbs., plus 20,000 lb.-rated front axles. “With minimal hills to navigate and basically a straight shot on Highway 99 from Tacoma to Seattle, the T800 had plenty of power to pull the load,” says Bates. “We were fortunate that the only corner we needed to navigate was near the Port of Tacoma where we picked up the girders. The tricky part was running the 16-foot tall load between traffic signals. There wasn’t a lot of room for error and there was a lot of pressure for the rear driver to navigate a straight line.”
The use of precast/prestressed girders cast with high strength concrete is no accident at a major site like the Alaska Way Replacement southern mile: WSDOT recognizes the long-span, girder line and depth economy 10,000-psi product imparts in bridge members. Agency officials likewise find lower fabrication, transportation and construction costs associated with longer span bridges and optimized pier spacing.
In addition to the 17 record-length WF100G girders (3,485 lineal feet), Concrete Tech and Van Dyke have been coordinating delivery of 114 WF74G girders (16,614 lineal feet) and 34 WF girders, tapering from 74 in. deep at one end to 100 in. deep at the other (4,963 lineal feet), to the Seattle site.
The southern mile of the $3 billion-plus Alaskan Way Viaduct Replacement is scheduled for 2013 completion under lead contractor Skanska USA. Girder erection has continued while Seattle Tunnel Partners, a joint venture of Dragados USA and Tutor Perini Corp., begins boring for a two-level structure running much of the western edge of downtown Seattle. The completed southern mile will remain a feeder route for the existing viaduct leading up to the tunnel’s 2015 completion. The Alaskan Way structure north of the southern mile will then meet a fate similar to viaducts that once carried traffic along prime San Francisco and Boston waterfronts.
Prepared by Don Marsh, Editor, and Siefkis-Petit Communications, Issaquah, Wash., from interviews with Concrete Technology and V. Van Dyke officials, plus Washington State Department of Transportation project profiles.