View Taking the NEXT Step for information on the first Northeast Extreme Tee Beam, a significant milestone in precast concrete design.
Last fall, hundreds of spectators spent the better part of two evenings watching concrete history in Utah. These hardy souls witnessed the placement of the longest, heaviest concrete bridge ever moved to date.
On Oct. 16-19, crews from the design-build team of Kiewit and W.W. Clyde and Co. slid a massive preconstructed assemblage across I-15 and into place near American Fork's Main Street interchange during the late night and early morning. The first span, with its 192-foot-long concrete girders, was moved from the “bridge farm" construction area southwest of the interchange about 10 p.m. on Friday. The second span was moved Sunday evening and was placed during the early morning hours of Monday, Oct. 19.
The new interchange is part of two Utah DOT projects: Pioneer Crossing and I-15 CORE. Pioneer Crossing will be a new five-to-seven-lane urban arterial road from Redwood Road in Saratoga Springs through Lehi to the American Fork Main Street–I-15 interchange. The road is being built to improve east-west travel to Saratoga Springs and relieve congestion on existing roads in northern Utah County.
The project used accelerated bridge construction techniques. But more importantly, this engineering marvel represents the concrete industry's resolve to not only provide an innovative method of rapid construction, but also an engineered approach to safety.
IN THE ZONE
In 2008, 101 men and women lost their lives while performing their jobs in work zones on our nation's highways. As tragic as this is, the loss of life is even greater for our customers, the driving public. According to the National Work Zone Information Clearinghouse, four out of every five work zone fatalities are motorists traveling through the work zone.
And as more projects start to come online, officials fear more may die. In December 2008, the Federal Highway Administration (FHWA) rule on new, supplemental regulations concerning protection measures between workers and motorized traffic became effective. The regulations apply to all federal highway projects, but state agencies are encouraged to adopt these on other types of projects as well.
This February, a new American National Standards Institute (ANSI) standard, “Work Zone Safety for Highway Construction,” became effective. This comprehensive standard covers flagger safety, runover/backover prevention, equipment operator safety, illumination, and using personal protective equipment, And later this month, DOTs, contractors, and other partners in promoting safety are scheduling events for the 2010 National Work Zone Awareness Week.
All of these efforts are important. One way to reduce work zone fatalities and injuries is to lessen the time it takes to complete construction. For almost a decade, engineers have been working to develop innovative approaches to bridge construction using precast concrete to shorten project length.
In 2000, the American Association of State Highway and Transportation Officials (AASHTO) formed a Technology Implementation group to help organize efforts and encourage acceptance of new technologies. The group selected prefabricated bridge elements and systems as one of its technologies to champion for rapid implementation. Prefabricated bridge elements and systems offer bridge designers and contractors significant advantages in construction time, safety, environmental impact, constructibility, and costs.
Using precast as part of an accelerated bridge project has four important benefits, FHWA says. By precasting bridge elements and systems offsite, time-consuming formwork construction, curing, and other tasks can be done in a controlled environment and reduce traffic interruptions. Worker exposure to traffic, overhead power lines, and elevation drops over water are greatly diminished. Construction activities are less disruptive to the environment as heavy equipment is kept from sensitive environments. Finally, bridge designs are often more constructible, meaning that jobsite constraints can be factored in during the design process.
Concrete producers have been benefiting. Engineers are increasing the use of large assembled concrete systems. Some areas of emphasis are more promising than others.
One area is precast bridge decks. FHWA says prefabrication offers exceptional advantages for deck construction, especially for removing deck placement from the critical path of bridge construction schedules, for the cost to place the deck, and for quality of the deck. The two designs that seem most plausible are partial-depth and full-depth prefabricated deck panels which act as stay-in-place forms and speed construction.
Certain precast substructure elements can also be effective in modulizing bridge projects. Cast-in-place bent caps and horizontal members placed at the top of the columns to support superstructures require extensive form-work and curing times. When cast offsite, curing times are not a factor in onsite project schedules.