Featured Research

from universities, journals, and other organizations

Old And Ugly, Troubled Bridges Can Be Safe

Date:
June 20, 2002
Source:
University Of Arkansas
Summary:
Bridges, both long and short, are a way of life for most Americans, who may cross more than a dozen bridges every day. Recent terrorist threats and a catastrophic accident have put bridges in the spotlight and raised questions concerning their safety. University of Arkansas researchers John Schemmel and Ernie Heymsfield have been trying to find the answers for some well-traveled bridges.

FAYETTEVILLE, Ark. – Bridges, both long and short, are a way of life for most Americans, who may cross more than a dozen bridges every day. Recent terrorist threats and a catastrophic accident have put bridges in the spotlight and raised questions concerning their safety. University of Arkansas researchers John Schemmel and Ernie Heymsfield have been trying to find the answers for some well-traveled bridges.

There are 587,755 bridges in the United States, according to the U.S. Department of Transportation. In 2000, 29 percent of these bridges were rated structurally deficient. In addition, between 1990 and 2000, vehicular traffic across bridges increased by 13 percent – increasing the load on some already stressed structures.

"We are looking at precast concrete bridges, which are very common in some rural areas," explained Heymsfield, assistant professor of civil engineering. "We have identified a dozen states with this type of bridge in use. In Arkansas alone there are 400 precast concrete bridges."

Heymsfield and Schemmel, professor of civil engineering and associate dean of the College of Engineering, studied short-span precast concrete bridges, which might be found crossing small streams or railroad tracks. In addition to examining the bridges in place, they conducted loading tests on beams to determine what is actually happening to the individual beams as traffic passes over the bridge.

States began installing these bridges in 1952 and they continue to be installed. In addition to Arkansas, precast concrete bridges are used in Mississippi, Missouri, Iowa, Nebraska, Indiana, Pennsylvania, Minnesota, North Dakota, South Dakota and Wyoming. Originally designed for a 50-year usage life, many of these bridges are nearing that age.

"In an ideal world, many of these bridges would be replaced, but each state may have several hundred bridges. They simply don’t have the resources to be able to replace them all," Heymsfield said. "We are trying to determine what should be done to maintain their safety."

The precast concrete beams are shaped like an inverted letter "U" and several beams are joined together to form the bridge decking. Because the primary stress occurs at the bottom of the precast beam, steel reinforcing bars are built into each of the "arms," which extend downward when they are installed.

"One of the major problems with these bridges is that the concrete is crumbling away at the bottom, leaving the reinforcing bars exposed. Because they are made of metal, the bars rust," explained Heymsfield. "We wanted to find out if this problem was just cosmetic or presented serious structural issues."

The researchers examined 20 beams from 4 bridges and classified them as either new, good, average, poor or repaired, according to the condition of the concrete and reinforcing bars. Because they were built at different times, some of the precast concrete beams had reinforcing bars with greater concrete cover than others. In those cases, not much of the reinforcing rod was exposed.

"We found that in most cases, the problem may not be as serious as one might initially think from viewing these beams. Shear failure was found to be the typical failure mode for these beams from loading tests," said Heymsfield. "Fortunately, when the beams were manufactured, they were made using a higher concrete material strength than what was initially specified, providing additional shear strength. Our future research will include assuring that the reinforcing steel in these beams is adequately embedded and of sufficient strength."

The researchers are developing guidelines for field evaluation of these precast-concrete channel beams. This will help highway engineers determine the proper load limits for the bridge and its remaining life expectancy, as well as making decisions about on-site remedial improvements or replacement.

The study was conducted for the Arkansas Highway and Transportation Department.


Story Source:

The above story is based on materials provided by University Of Arkansas. Note: Materials may be edited for content and length.


Cite This Page:

University Of Arkansas. "Old And Ugly, Troubled Bridges Can Be Safe." ScienceDaily. ScienceDaily, 20 June 2002. <www.sciencedaily.com/releases/2002/06/020620075737.htm>.
University Of Arkansas. (2002, June 20). Old And Ugly, Troubled Bridges Can Be Safe. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2002/06/020620075737.htm
University Of Arkansas. "Old And Ugly, Troubled Bridges Can Be Safe." ScienceDaily. www.sciencedaily.com/releases/2002/06/020620075737.htm (accessed July 22, 2014).

Share This




More Matter & Energy News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins