Proj Overview

Project Overview


The sweeping lines and glittering lights on the new West Seventh Bridge, in Fort Worth, Tex., have become a focal point of the city, linking downtown with the cultural district across the Trinity River. It is a look that was gracefully achieved thanks to the versatility and high performance features of precast concrete, says Dean Van Landuyt, Engineer of record for the bridge. Before retiring from Texas Department of Transportation (TxDOT) and joining HNTB Corp. as a senior technical advisor Van Landuyt led the team of designers at TxDOT during this selection, design, and construction. Van Landuyt says, “The innovative design provides dramatic flair while blending gracefully into its context and landscape.”

The project required the team to replace an aging 981 ft (299 m) bridge with a new, more durable design, which the project team had to erect with minimal disruption to traffic. “Cost was a factor,” Van Landuyt says, “but aesthetics and inconvenience to motorists were the two biggest challenges.”

Precast concrete arches, floor beams, and stay-in-place deck panels delivered the attractive design while dramatically minimizing on-site construction time and cutting costs.

Precast Solution

To minimize disruption, the drilled shafts and precast concrete columns were constructed outside the existing bridge railings with no need for an interior bent cap, which allowed traffic lanes to remain open.

At a temporary yard near the site, designers cast the 12 arches horizontally, rather than vertically, to simplify the forming system and to improve quality control. The panels and floor beams were cast in plants. The pieces were transported to the site using the existing structure as a haul road, and set into place. Only then was the old bridge dismantled, and the floor beams installed. “An entire span of precast panels could be set in as little as two days, and the topping slab cast after placing reinforcing mats,” Van Landuyt says.

Deck expansion joints at every bent line isolated the spans, making it possible for the contractor to hang floor beams in one span, place panels in another, and cast the deck in a third. The floor beams were made of self-consolidating concrete and the arches had a 9 in. (230 mm) slump, so the surface was dense, he says. “The concrete finish of the floor beams and arches were both fantastic.” This eliminated the need for painting, which further saved time and money.

Designers also had to strike a balance between making the tie and rib cross sections as small as possible to reduce weight while still providing enough room for posttensioning ducts, reinforcing, light fixtures, and other accessories. “The quality control that came with precasting the arches helped ensure proper consolidation between the many items in the slender tie,” he says.

The resulting bridge features six posttensioned network arch-spans, with separate pathways along the outer edges that provide a safe and easy to use space for pedestrians and cyclists, while the public area below offers a shady respite from the sun.

The bridge was completely out of service for four months (instead of the allotted five), with minimal impact to traffic and a final price tag of just $209 per square foot of bridge deck. “Fort Worth and TxDOT took a tremendous leap of faith with a type of bridge that had never been built before,” Van Landuyt says. “It was only through trust and the determination of excellently-skilled contractors and fabricators that something so complex could be built so well and so quickly.”

 

Awards
2015 Design AwardsDesign Award Transportation: Best Bridge with a Main Span More Than 150 Feet
Project Team

Owner

City of Fort Worth Transportation and Public Works, Fort Worth, Tex. 

Engineer

TxDOT, Austin, Tex. 

General Contractor

Sundt Construction Inc., San Antonio, Tex. 

Precaster

Heldenfels Enterprises Inc., San Marcos, Tex. 

Deck Panel Precaster

Austin Prestress, Austin, Tex. 

Photo Credits

City View and River Night: Liam Frederick 
Erection: Texas Department of Transportation

Key Project Attributes

  • The use of a precast concrete design allowed the team to meet aesthetic goals with minimal disruption for just $209 per square foot of bridge deck.
  • Twelve identical 280-ton (2490 kN) arches were cast on their sides in a casting yard just four blocks from the bridge site.
  • To speed construction and increase safety, panels were used continuously from abutment to abutment.

Project/Precast Scope

  • Project size: 12 arches, 102 floor beams, and 77,499 square feet (7199.7 meters squared) of partial depth deck panels.
  • All arches, floor beams, and stay-in-place deck panels were made of precast concrete to reduce cost and minimize on-site construction.
  • The cast-in-place concrete columns were constructed outside the existing bridge with no need for an interior bent cap.
  • Project cost: $25.9 million