Taming Oregon’s Cracked Bridges
Oregon’s epidemic of cracked Interstate-Era bridges was a nightmare come true in 2001. Here’s how the state has dealt with the problem.

by , Contributing Editor

Five years after Oregon learned that it had hundreds of cracked reinforced concrete deck girder bridges in its inventory, the state has diagnosed the problems and is executing an action plan, but the road from then to now has not been easy. There have been multiple inspections, alarmist media coverage, bridge weight restrictions, unwelcome detours, engineering tests, original research, funding challenges, and even a follow-up review by a blue ribbon committee of the Transportation Research Board.

Today — five years after the crisis erupted — bridges are being replaced, weight restrictions removed, and state DOTs across the country have a new understanding of what goes on inside the reinforcing steel of a poured-in-place RCDG concrete bridge constructed with conventional reinforcement.

The state has responded with a vigorous bridge inspection and rating program, lab testing, new funds for bridge work, and hiring of a private sector program management firm to oversee bridge work related to the cracking.

Meanwhile, lab tests at Oregon State University have found that, in general, reinforcing steel within the bridges is not showing signs of fatigue as a result of the cracking, giving the state more time to address the long-term problem of bridge cracking.

An abundance of cracks

During the 1950s and 1960s, Oregon experienced a bridge building boom as the state built its Interstate highways. But there were unseen problems in many of those bridges.

In 2001, the state discovered accelerated cracking in poured-in-place, non-post-tensioned bridges built between 1947 and 1961 on what became the Interstate system. With the discovery came the need to identify, repair and replace several hundreds of bridges all across the state.

Nearly 6,500 bridges are located in the Beaver State, according to the Federal Highway Administration bridge inventory. Of these, 2,680 are state-owned bridges managed by the Oregon DOT, and 3,800 are local bridges owned by cities and counties, according to Oregon’s Economic and Bridge Options Report, April 2005.

Almost half the state-owned bridges, and a third of local bridges, were built prior to 1960. Many of these bridges are of reinforced concrete deck girder bridge design consistent with AASHTO Specifications for Highway Bridges.

In the late 1950s, AASHTO reviewed design specifications for the use of prestressed concrete in bridges, and design specifications appeared in the 1961 edition of the AASHTO Specifications for Highway Bridges. Prestressed and post-tensioned concrete bridges offered greater overall bridge performance at a more economical cost, and Oregon started using these designs instead of RCDG bridge designs in the mid-1960s.

But that still left the pre-1961 bridges in question, and after 2002, Oregon DOT inspections discovered that bridges built from 1947 to 1961 have a high propensity for shear cracking.

“We started getting reports from inspectors of shear cracks in reinforced concrete deck girders,” said Richard Groff, P.E., senior load rating engineer, Oregon DOT.

“We have a large population of that type of bridge compared to the total population of bridges,” Groff told Better Roads. “During the Interstate era, when they were building fast and furious, Oregon stayed with reinforced concrete bridges when a lot of neighbors were starting out with prestressed. These are poured-in-place, reinforced concrete bridges on or over the Interstates, which in retrospect may have been a tactical error, but back then was accepted design practice. But what we know now about shear and how bridges behave under shear conditions is a whole lot different than it was in the 50s. The state-of-the-art on how to detail bridges for shear has progressed since then.”

The fact that municipal and county specifications tend to mirror state specs worked against the lower-level jurisdictions. “Many city and county bridges built in similar time periods using the same designs are also at risk,” the Oregon DOT said in 2005. “Local agency engineers used the same codes and standard drawings that ODOT used, based on the national design code. Many local bridges were probably designed by ODOT staff as federal-aid projects or under the ODOT Local Agency ‘Free Design’ program.”

During a 2001 routine biennial bridge inspection, cracks that were identified on several state bridges in previous inspections had grown, Oregon documents said. “Cracks had progressed to the point that functionality of some of the bridges was at risk,” the state said last year. “In response to the growing problem, ODOT immediately placed load restrictions on these at-risk bridges. By 2001, ODOT had posted weight restrictions on 68 bridges. This number increased to 140 by 2003.”

“In a few of the cases, measurable growth in crack width was reported,” Groff told Better Roads. “At the time, the perception was that crack width was an indicator of shear capacity — that is, the wider the crack width, the less you can count on the concrete to resist shear. The 1994 AASHTO Manual for Condi-tion Evaluation of Bridges stated that if a crack was severe, then the the concrete had no capacity because it was cracked, and therefore only the reinforcement was taking the shear. That resulted in a number of bridge restrictions, which became an economic hardship.”

As the state investigated the accelerated cracking, most of the bridges of concern were found to be reinforced concrete deck girder bridges built in the 1950s. And after all of the 555 state-owned RCDG bridges were evaluated, 487 were found to have varying degrees of problems:

• 178 structures had randomly dispersed low-density cracks — not an urgent concern but could get worse.

• 180 had medium-density cracks, mostly near supports. They need frequent monitoring and must either be restricted or replaced in the near future.

• 129 bridges had widely dispersed high-density cracks. They also need frequent monitoring and must either be restricted or replaced in the near future.

In the meantime, an investigation of the additional 300 RCDG bridges owned by cities and counties showed that a medium to high density of cracks had developed on 122 of these bridges.

Separately, as a result of Oregon’s observations of cracking, the FHWA surveyed other states to determine whether they were experiencing similar problems with their reinforced concrete deck girder bridges. “The FHWA concluded from this survey that the type of cracking observed in Oregon is not unusual, but the large number of bridges in Oregon with such cracks is exceptional,” wrote John E. Breen, P.E., chairman, TRB Committee for Review of the Oregon Department of Transportation Study on Bridge Shear, in a report issued June 2005 (see below).

Cracks disrupt commerce

Nearly 200 bridges identified for repair and replacement were on I-5, the major north-south highway which runs from Washington State to California, connecting every major city in the state. Another 66 bridges were on I-84, which crosses the northeast corner of the state from Washington to Idaho.

Worse, the problem was replicated on state highways throughout Oregon. By the end of 2003, it was estimated that one out of every five state-owned bridges was to require weight restrictions, and truck detours. Without new funding, it was estimated in 2003 that nearly one out of every three state-owned bridges would be weight limited by 2010. The total estimated cost to repair all deficient bridges was $4.7 billion.

Symbolic of the impact on residents was the experience of Riddle, Oregon, one of the first communities to be impacted by the weight restrictions. As described  in Oregon DOT’s Updated Economic and Bridge Options Report, April 2005, for 20 days in March 2001, the communities of Canyonville and Riddle, 30 minutes south of Roseburg, experienced a surge in truck traffic unlike anything they had seen before. Ford’s Bridge, an I-5 bridge several miles away, was closed for emergency repairs, and the truck detours ran through the main streets of these two towns of fewer than 1,500 people.

The streets and bridges of these two small communities were not built to handle the volume of large trucks, resulting in safety concerns and infrastructure damage to city facilities. The detours had a negative effect on local commerce, not to mention lifestyles. For example, Hayes Oil of Medford continued hauling 80 truckloads of gas and oil per week using the detour routes. Depending on which detour they took, Hayes added 100 to 200 miles per trip.

The Oregon DOT put the Ford’s Bridge project on a fast track, making repairs to the bridge that were expected to last three to five years, and got the trucks back on I-5 for the short-term. With funding from the resulting Oregon Transportation Investment Act, the Oregon DOT began construction of a replacement bridge in August 2002.

The funding problem was such that in March 2003, Representative Peter DeFazio (D-Oregon) organized a letter signed by the entire Oregon House delegation, and sent it to the leaders of the House Transportation and Infrastructure Committee, asking that state funding to help repair Oregon’s numerous cracked and crumbling bridges be matched in the future surface transportation bill to replace the existing TEA-21.

“The State of Oregon cannot fix the cracked bridge problem entirely on its own, which is why we are asking for assistance from the federal government to help Oregon meet this need,” DeFazio and the Oregon House delegation said.

Ultimately, DeFazio — the ranking Democrat on the House Highways, Transit and Pipelines Subcommittee — was able to obtain funds when TEA-21’s successor, the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, was passed and signed by President Bush last year.

In SAFETEA-LU, a new funding category was added, dubbed Megaprojects. To receive funding, a Megaproject must have national and regional significance. Under this new category, DeFazio secured $160 million for reconstruction of bridges on I-5 in Oregon and $40 million for reconstruction of bridges across the state.

To further leverage Oregon’s local funds, DeFazio secured language in SAFETEA-LU that lowers the local match for most transportation projects listed in the bill for Oregon. When federal dollars are used for a project, the standard funding split is usually 20% local to 80% federal. But because Oregon supports a large amount of federal lands, and thus has a smaller tax base, DeFazio was able to alter the legislation to cut the local share in half, to 10.27%, with the federal share at 89.73%, applying to all high priority projects and Megaprojects included in the bill.

HB 2041 to rescue

In anticipation of having to repair or replace state bridges, ODOT launched a Statewide Bridge Assessment in February 2003. The purpose of this assessment was to collect environmental and engineering baseline data at each bridge site identified in the 2003 Economic and Bridge Options Report, verify the repair or replacement recommendation for each bridge made in the 2003 report, and refine the scope of work and cost estimates for repairing and replacing bridges, including identification of engineering, construction, and right-of-way costs for each project.

Then, in response to the emerging bridge cracking problem, the Oregon Legislature passed House Bill 2041 in 2003. The bill provided $1.3 billion in funding to repair and replace bridges on Oregon’s state highways. An additional $300 million was earmarked for repair or replacement of county and city bridges, with another $361 million for county and city operations and maintenance.

The package also allocated $500 million in modernization projects, and was promoted as a jobs creator as well as a means to mitigate bridge woes. This is Part III of the Oregon Transportation Investment Act, which the legislature passed in 2001; Part III included a budget note that directed the state to contract with the private sector to assist the agency with the management of the OTIA III State Bridge Delivery Program.

The result was in April 2004, the Oregon DOT contracted with Oregon Bridge Delivery Partners, a private-sector firm that is assisting the agency with managing the $1.3-billion state bridge program.

OBDP is a joint venture formed by HDR Engineering and Fluor Enterprises, and provides day-to-day support to the OTIA III State Bridge Delivery Program, ensures quality projects at least cost, and manages engineering, environmental, financial, safety,  and other aspects of the program.

Detailing beats crack width

The diagonal cracking in beams noted by inspectors has been associated with inadequate shear capacity, a situation engineers design to avoid because it may lead to a sudden failure, reported Oregon DOT’s Research News in late 2005.

But subsequent research funded by Oregon DOT and conducted by Dr. Chris Higgins at Oregon State University at Corvallis at its O.H. Hinsdale Wave Research Laboratory showed that repeated traffic loading — regardless of the condition of the concrete — was not causing the steel reinforcement to gradually deteriorate. This was a critical consideration in deciding whether to replace or repair a bridge.

The research confirmed that Modified Compression Field Theory (MCFT) accurately predicts concrete shear strength.  Based on the research recommendations, ODOT decided to apply the AASHTO Load and Resistance Factor Rating (LRFR) method, which employs MCFT, as a basis for decisions to repair rather than replace many of its cracked bridges that were originally slated for replacement.

“They poured beams of the same reinforcement details and sizes as we had in the 50s, and broke them in the lab,” Groff told Better Roads. “We got great value out of their study. We have implemented a lot of its provisions. We’ve learned, for example, that where the crack looks the biggest, is not where the bridge may fail. It often may fail somewhere else. Dr. Higgins’ tests showed that  the mechanism for failure does not necessarily follow the place where the biggest crack was early on. Crack width is less important than what we used to think it was. What’s more important, Higgins found, was the detailing of the rebar inside, including anchorage of the longitudinal bars, or how far into the support they go. What matters is detailing, not crack width.”

For this research, the OSU Civil, Construction & Environmental Engineering Department was awarded nearly $1.6 million to help the state analyze the severity of cracks.

The research also defined an accurate method to estimate the load capacity of the cracked girders, which was incorporated into a reliability-based procedure to load rate the cracked bridges, the state said. Subsequent efforts have focused on implementing the load rating method for cracked girders, repairing cracked girders, developing an analysis method for cracked bent caps, and deploying bridge monitoring technology.

OSU’s strong floor

The test facility, OSU’s strong floor, is the second largest structural testing floor on the West Coast, and allows researchers to simulate earthquakes and forces up to one million pounds, and frames up to two stories high. The floor, measuring 24-feet wide and 68-feet long, is steel-reinforced concrete, 5-feet thick, with massive bolts and anchors to which materials can be attached and their strength tested.

On the strong floor, researchers can test, at full scale, new high-performance materials, innovative connectors, and seismic energy dissipating devices, as well as different configurations of traditional steel and concrete materials that might be used to provide more efficient or economical structures. The new facility aids research on bridge girders, bridge decks, beam column connections, shear walls, and other structures used in constructing buildings, bridges, and infrastructure.

“Without our new strong floor laboratory, ODOT would have gone out of state to conduct this research,” said Higgins, an associate professor in the College of Engineering.

To be practical, the load rating method developed for the cracked bridges requires automation, the Oregon DOT said in late 2005. “Computer software is being developed at OSU to perform the reliability-based assessment on RCDG bridges,” ODOT said. “An initial load rating software package has been completed and a second generation package is being developed that will provide more flexible analysis capabilities and enhanced visualization modules.”

OSU’s findings are contained in two reports, Remaining Life of Reinforced Concrete Beams with Diagonal-Tension Cracks (SPR 341, Higgins, Yim, et al. 2004), and Assessment Methodology for Diagonally Cracked Reinforced Concrete Deck Girders (SPR 350, Higgins, Miller, et al. 2004).

OSU investigates repair methods

Repair methods for the bridges also are being investigated at OSU, including epoxy injection, supplemental steel stirrups, post-tensioning, and fiber reinforced polymer composites. “Large-scale laboratory specimens cracked and repaired are loaded with increasing amplitude until failure to determine the increase in shear capacity,” the state said in its Fall 2005 Research News publication. “The effect of repeated loading to simulate traffic on the behavior and performance of the different repair methods is [being] evaluated. The research includes investigation of in-service repaired RCDG bridges. This effort will provide accurate methods of predicting the increase in capacity for specific repair types, determine the longevity of repairs, and recommend effective repair approaches optimized for the diagonal cracking prevalent in Oregon’s vintage RCDG bridges.”

In addition, OSU is looking at cracked bent caps. Bent caps are transverse beams that support the main girders. “Though generally more heavily reinforced than girders, bent caps are non-redundant and could potentially cause a bridge to collapse if one were to fail,” Oregon said in 2005. “Many of Oregon’s 1950s-vintage RCDG bridges have cracked bent caps along with cracked girders. Because of the relative dimensions of bent caps, the analytical method for estimating load capacity of cracked girders may not be accurate for bent caps. Consequently, OSU is conducting research on large-scale bent caps in the laboratory to evaluate the capacity and estimate the remaining life of cracked bent caps.”

Monitoring and acoustic analysis

Because monitoring a damaged bridge — in conjunction with reduced load rating — can provide additional comfort that a bridge will perform as expected, Oregon is investigating ways to monitor conditions in real time. The state has contracted with Engineered Monitoring Solutions to install a demonstration structural health monitoring system on four RCDG bridges with cracked girders. The system will send strain and crack size data to DOT personnel, along with alerting engineers to any sudden changes in the condition of the bridge due to an overload.

In addition to bridge monitoring using conventional technology, a joint research project between the Oregon DOT, OSU and Portland State University is investigating acoustic emission testing as another tool for determining the health of bridges. According to the state research group led by Steve Lovejoy, ODOT senior mechanical engineers, in AE monitoring, the sound given off by damage is detected and characterized by the AE system. This research will develop a protocol for applying AE testing to RCDG bridges in order to assist in bridge element rating, setting load restrictions, and predicting the rate of damage progression.

AE testing hears the sound given off by the material when it is damaged, and has been shown to be a highly sensitive method for detecting damage in experiments conducted on reinforced concrete beams, the Oregon DOT said. “This research will develop a protocol for applying AE testing to RCDG bridges with diagonal tension cracks in order to assist in bridge element rating, setting load restrictions, and predicting the rate of damage progression.” A manual for applying AE to reinforced concrete deck girder bridges will be developed.

A critique by TRB

OSU’s work in recreating the bridge components of the 50s and conducting destructive testing on them answered some major questions for the Oregon DOT, but drew some pointed critiques by a Transportation Research Board committee, which issued its opinions in June 2005.

FHWA requested a review of the results of the OSU study by an independent panel of experts, and the Oregon DOT contracted with the Transportation Research Board for an independent peer review of the OSU findings.

The committee found that the OSU analysis, field studies, and laboratory tests that conclusively indicated fatigue of web reinforcement not to be a problem were convincing and followed sound principles. It acknowledged that Oregon obtained a great deal of highly useful documentation and information from OSU, and ODOT officials told the committee that they believed that OSU had satisfied their expectations.

But it also found that OSU did not avail itself of many essential components of basic AASHTO standards for load rating and design, such as load factors and resistance factors, did not treat loads and resistances as time-dependent variables, and did not provide clear guidance for assessing the effects of reinforcement details. “The methodology did not emphasize the use of nondestructive evaluation or invasive materials sampling to enhance assessment of bridge remaining life,” wrote John E. Breen, P.E., committee chairman, Ferguson Structural Engineering Laboratory, University of Texas at Austin.

The Peer Review Panel also concluded that ODOT’s re-evaluation of OTIA III bridges was based on nationally approved methods, and that no bridges would need to be re-evaluated in light of the Peer Review.

“OSU suggested we use Modified Compression Field Theory, which is in use in the newest codes, such as LRFR code. It’s a newer method of assessing shear capacity, and it accounts for the interaction of longitudinal bars along the girder, and transverse bars, or stirrups. It’s more sophisticated than the previous ACI method. You can get more capacity out of the MCFT, and it represents a more realistic approach to capacity.” Groff said.

Regardless of the critique, the OSU study paid off for the Oregon DOT. “We got enormous value out of the OSU study, even though some points of it were criticized,” Groff said.

Research continues in 2006

The Oregon DOT and its Research Unit continued to be focused on bridge conditions in 2005, said Oregon DOT’s Research, Development & Technology Transfer Program in its 2005 annual report, and the work will continue this year.

The focus continues on the remaining life of the generation of the 500 reinforced concrete bridges constructed 45 to 60 years ago, Oregon’s research unit said. “The level of our research effort on topics related to this issue was unprecedented,” the research unit said late last year. “Nearly $1.5 million was spent on research projects in this area in FY 2004 and FY 2005, and we anticipate spending more than $600,000 in Fiscal 2006. That level of investment is approximately one third of our total research effort.”

For More Information

Some of the documents surrounding the Oregon bridge cracking mystery are available off the Internet. Here are some places to start.

The first of the Oregon State University reports — Remaining Life of Reinforced Concrete Beams with Diagonal-Tension Cracks (SPR 341) — may be downloaded at
www.oregon.gov/ODOT/TD/ TP_RES/docs/Reports/SPR341.pdf.

The second report, Assessment Methodology for Diagonally Cracked Reinforced Concrete Deck Girders (SPR 350), does not appear to be available for download at this time.

Oregon DOT’s Research, Development & Technology Transfer Program’s 2005 Report may be obtained at www.oregon.gov/ODOT/TD/TP_ RES/docs/Reports/2005AnnualReport.pdf.

Oregon’s updated Economic and Bridge Options Report is a document detailing Oregon’s aging bridge problem and recommendations for addressing it. In addition, 10 appendices give in-depth information about a variety of topics that are important to understanding and solving the critical bridge problem on Oregon’s highway system. Access them at www.oregon.gov/ODOT/COMM/bridge_options.shtml.

Oregon State University’s strong floor testing lab is described on OSU’s Web site. Visit them at http://ccee.oregonstate.edu/research/strongfloor/.

The June 2005 critique of the OSU studies — Review of Oregon Department of Transportation Study on Bridge Shear — may be viewed at http://trb.org/publications/reports/ORBR_ltr_rpt_june2005.pdf.

Lastly, the Oregon DOT’s research unit lists many practical papers on bridge research, including chloride removal, maintenance, design, and much more.
View them at www.oregon.gov/ODOT/TD/ TP_RES/publications.shtml .

Reprinted from Better Roads Magazine
April 2006

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