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Bulb-Tee Sunset

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At 159.5 ft., the Porter Creek Bridge’s Wide-Flange Girders (CA WF78) are the longest non-spliced, monolithic precast members delivered to a California bridge site. Positive results with the Sonoma County and other initial installations have the new generation WF girders rapidly succeeding the legacy California Bulb-Tee.

Consistent with agencies from Florida to the Pacific Northwest who have embraced the cutting edge of precast/prestressed concrete bridge engineering, California Department of Transportation has developed a successor to the state’s Bulb-Tee Girder. The California Wide-Flange Girder suits 70- to 200-ft. lengths and 3- to 10-ft. depths, designated by 6-in. increments from CA WF36 to CA WF120. The WF has 4 ft. and 3 ft. 9 in. top and bottom flanges, respectively, plus a high 0.6-in. diameter strand concentration at the base.

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Taylor Heavy Hauling and KIE-CON staff surveyed every turn and ramp along the route. Near-equal top and bottom sections, plus high strand concentration at the base, make the California Wide-Flange Girder a more stable load than the California Bulb-Tee.

KIE-CON Inc. in Antioch, Calif., proposed a WF-based alternative to a cast-in-place design for the Porter Creek Bridge in Sonoma County, north of San Francisco. Approval ushered a record length, 159.5 ft. (160 ft. span), for precast/prestressed girders delivered over California roads. Leading up to the WF launch in 2012, typical precast/prestressed-suited bridges called for single California Bulb-Tees through 115 ft., with longer spans using two or three spliced Bulb-Tees. KIE-CON enlisted Helser Industries for a new girder form to accommodate the full CA WF36 through CA WF120 series.

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Helser Industries equipped KIE-CON for the California Wide-Flange Girder with a form capable of the series’ full depth and length offerings, respectively: 36- to 120-in. and 70- to 200-ft.

Caltrans officials and many engineers are still discovering the new generation girders’ performance and economy. To reduce costs and shorten schedules, all agency staff, consultants and bridge contractors are being encouraged to use the Wide-Flange in 65-ft. and longer spans on precast/prestressed girder-candidate projects. Bridge producers, in turn, can stick with one cross section and one form, and deliver finished beams of much more stability than California Bulb-Tees.

The Golden State has a substantial of number of concrete bridgeF-KieConIIc-200
projects going design-build; nearly all of their contractors are looking at the Wide-Flange because of cost savings over cast-in-place structures or other prestressed girder profiles. The WF is the leading choice on two major projects under construction: California high speed rail phase 1, requiring an estimated 320 girders, and a State Route 4 crossing with upward of 200 girders. There are approximately 10 projects with WF Girders, in 100- to 165-ft. lengths, nearing completion or under construction in northern California alone. A sizable number of projects are ready to be advertised with spans between 70 ft. (CA WF36) and 180 ft. (CA WF90) for monolithic girders, and up 199 ft. with spliced beams (CA WF102).


VALUE ENGINEERING

F-KieConIVa-200At Porter Creek, KIE-CON showed prospective client Gordon N. Ball, Inc. how seven CA WF78 girders, bearing on cast-in-place abutments, offered a single-span replacement for a five-span, reinforced concrete structure opened in 1935. The contractor and Sonoma County officials noted especially the merits of a solution eliminating much of the crews’ work in the creek area. The producer delivered the structure’s first four girders in August 2013, the final three two months later. Work proceeded through an early-2014 opening for the bridge, presently two lanes—like its predecessor—but expandable to four lanes.

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With little clearance considerations, the single-span, 78-in. deep California Wide-Flange Girder design helped confine the Porter Creek replacement bridge’s cast-in-place concrete requirements to abutments and footings—the original structure’s piers relics of an era pre-dating U.S. adoption of precast/prestressed methods.

The CA WF78 specification called for a 9,000 psi design strength concrete. KIE-CON attained 12,000 psi with a self-consolidating mix using Lehigh Type II modified cement and Sika ViscoCrete high-range water reducers. Crews fabricated the girders with 56 0.6 in. diameter “all straight” strand, its base concentration contributing to hauling stability for the less-than-optimal, 90-mile route between the Antioch plant and Porter Creek site.

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The bridge contract proved the toughest shipping job in company history, requiring drivers to cross seven freeways and negotiate short ramps typical of California highways. During delivery planning, KIE-CON staff surveyed every route ramp, observing 5 to 12 percent slope conditions. It picked the worst slope to analyze the girder haul with a 2:1 safety factor.

A Kiewit-owned company, KIE-CON credits the Porter Creek crossing success to a) quick alternate design approvals by Gordon Ball, Sonoma County officials, and engineer Mark Thomas & Co.; and, b) safety provisions and routing coordination with Taylor Heavy Hauling of Antelope, Calif.