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Inspection finds locally maintained bridges to be structurally deficient

September 21st, 2013 8:44 pm by Gary B. Gray

Inspection finds locally maintained bridges to be structurally deficient


Nothing lasts forever. 


The latest inspection of 289 bridges revealed that 16 locally maintained bridges and three state-maintained bridges in Washington County are “structurally deficient,” according to the Tennessee Inventory and Appraisal Report, an account compiled by the Tennessee Department of Transportation as required by the Federal Highway Administration. 


“We have replaced about 100 bridges in the past 30 years,” said Johnny Deakins, Washington County Highway Department superintendent. “We don’t have any that are critical, but we do have some that are in poor condition.”  Take a deep breath. Relax. Exhale.


Bridge identity


The news does mean some aging, as well as some relatively new, structures need attention, but it does not mean they are ready to crumble when a leaf floats down and touches their decks, girders or sidewalks.


States must inspect all bridges every two years and hand over their analyses to help the federal agency compile a “bridge dictionary,” if you will. Besides TDOT’s finding that some locally maintained bridges in the county are structurally deficient, 15 others have “sufficiency ratings” below 50, as measured on a scale of 0 to 100. All the bridges were last visually inspected in June 2012.


Four of these were built prior to 1930. The oldest are a roughly half-mile steel structure running across Limestone Creek, and a very short steel bridge over Little Limestone Creek, both built in 1920. The other very dated bridges on this short list include small structures over Little Cherokee Creek and Little Limestone Creek, both built in 1930. 


The bridge on Milligan Highway at Legion and King streets, which supports a healthy amount of traffic over a CSX Railroad line, has the lowest of all sufficiency ratings in the county at 8.4.


Meanwhile, three state-maintained concrete bridges in Washington County were found structurally deficient, including bridges over Big Limestone Creek, Little Limestone Creek and a portion of the CSX railroad not immediately identified. 


“On-System” bridges are those maintained, owned and operated by the state. They are found on the interstate system, the National Highway System and the State Route System. “Off-System” bridges are those found on roads owned, maintained and operated by local governments that include counties, cities and towns in Tennessee. That number was 11,449 as of February.


County sets priorities


Deakins said the main focus now is on three bridges. The County Commission approved about $500,000 in bonds that will help pay for repairs on one bridge and the replacement of another. The concrete bridge that washed out over Dry Creek in the August 2012 flood is set for replacement. This concrete slab bridge, which remains closed, will be rebuilt using a state grant that requires a 20 percent local match.  


“The first is the one over Watauga River on Austin Springs Road,” he said. “That will be repaired using the bond money, and it will cost between $250,000 and $300,000. The other bridge to be funded by the bonds also in on Austin Springs and runs over Cobb Creek about a half-mile outside the Johnson City limits. That will be replaced and cost about $200,000. If I need more money to do it, I’ll probably have to take it out of our fund balance. We also have several small bridges that are not on the (TDOT) list.” 


The 607-foot-long bridge over the Watauga, originally built in 1985, is classified by the state as a city street and has a sufficiency rating of 41.1. The state report recommends the bridge be replaced and lengthened and estimates the roadway improvement cost at $411,000, the bridge improvement cost at $4.1 million and a total project cost of $6.2 million.


It was last inspected by the state in June 2012. 


Recommendations and funding


This bridge likely will be the first to get attention. Bids will be let this winter and the county hopes to begin repairs next spring. The bridge on Austin Springs over Cobb Creek will not be replaced for a while. Deakins said he is “starting from scratch” and a basic design has not yet been developed. Once complete, it will be at least one year before that project is bid.


Meanwhile, the replacement of the bridge on Rock House Road over Dry Creek is funded with a state grant requiring the county to pitch in 20 percent. However, Deakins said he’s still waiting for TDOT to approve the plans.


“Every bridge inspected has recommended improvements,” he said. “They may recommend railings be replaced, but it’s not really a requirement. They will rate things like decks and traffic safety features from a zero, which means a failed condition, to 9, which is excellent condition.”


Most of the ratings on the bridge over the Watauga are fair to good. Deakins said he plans to contract a company to repair cracking that has occurred in the bridge’s concrete beams with a special epoxy, as well as making other structural repairs. 


“If you have a sufficiency rating of, say, 25, a part of the structure is deficient,” he said. “Also, you can be rated higher and still have a number of very minor things included in the equation, like a missing sign.”


He also said the bridge on Austin Springs over Cobb Creek would have taken quite a few years to replace were it not for the bonds.


“When we get grants, they are an 80-20 match with the state paying the state paying the larger portion,” he said. “The General Assembly designates a certain amount for bridges each year in its annual spending plan. They take 50 percent of that and divide it by population. 


“I get about $50,000 a year. So if I have a bridge that needs $300,000 to be repaired, it’s going to take about five years to accumulate enough money from the state to repair that one bridge. A lot of counties with small populations have no money for bridge repair; they have to use what they get from gasoline tax revenue to make bridge repairs.”   


How do they rate?


To be structurally deficient, which is particular to this bridge in Washington County over the Watauga River, it basically must have some component that has been rated poor or obsolete, said Terry Leatherwood, TDOT’s Structures Division engineer, who oversees all state bridge inspections. 


Leatherwood said bridges are appraised by using several methods. Basically, a sufficiency rating is used to identify the defects using a numbering system. These numbers are then run through a very complicated set of equations, which in turn results in a 0 to 100 rating. 


“Even bridges that are brand new don’t rate 100,” he said.


Structural deficiency is determined by another rating system, and it is much simpler. In general, a bridge’s main components are rated from 0 to 9. Ratings of 7 and above are good; ratings of 4 and below equate to poor or critical.


“It’s kind of confusing, but a bridge with a lower sufficiency rating may just need a new deck; it may otherwise be fine,” he said. “But a structurally deficient bridge is considered worse, because it’s super-structure, the beams, girders and other systems — whatever holds it up — has a component that is obsolete. To qualify for federal funding, you look at both. Generally, if the sufficiency rating is below 80, you qualify for federal funding.”


Leatherwood also explained why the recommended improvement amounts are so much higher than what repairs a local government plans to spend.


“The feds want us to tell them what it would cost to replace the entire structure,” he said. “In the case of this bridge over the Watauga, it qualifies as structurally deficient. But it sounds like they have looked at it and said, ‘we don’t want to replace the entire bridge.’ The recommendations are not requirements. All (Washington County has) to do is improve the super-structure, and that bridge would come off the structurally deficient list.”


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