LEBANON, Ind. — In Lebanon last week, an underutilized sensor technology

was put to use in a weight limit test on a county bridge, to demonstrate its

usefulness in more accurately estimating weight load limits on crossings used

by heavy farm equipment.

 

Members of the Indiana Soybean Alliance (ISA), a local farmer and a Purdue

University civil engineering researcher stood by while a heavy truck ran over a

county bridge that had been fitted with sensors. They were attached underneath

the bridge at certain pressure points to determine if its current load limit was

accurate.

 

Such limits are placed by bridge designers and inspectors to prevent the disaster

of a bridge collapsing under the weight of heavy loads. Inspections are

conducted visually and usually rated conservatively to prevent such disasters;

however, some farmers rely on these bridges to carry such loads of agricultural

product as grain or livestock.

 

Should a farmer’s load be heavier than the limit, they must use detours that can

cost precious time and money in seasons which depend on those factors to prevent

losses. Donnie Lawson, a local farmer and county commissioner in Boone County,

believes the technology will be a great help.

 

“We have these bridges inspected every two years and we never know if that’s exactly

what they can handle or not,” he said. “We know they are probably rated

conservatively. Information like this can help us determine whether a weight limit

is underrated, and we can go to a higher weight limit – not only for agriculture,

but also for emergency vehicles.”

 

Patrick Conner, research manager for the Indiana Local Technical Assistance

Program based at Purdue, is overseeing research to make the sensors more available

to Indiana counties. He said though the sensor test would never replace visual

bridge inspection, it is a helpful tool to verify and possibly adjust bridge load

ratings.

 

“It’s old technology, but it’s never really been well-implemented,” Conner explained.

“It is a costly process, so that’s one of the purposes of what we’re doing:

To demonstrate the potential that it has, when needed in special circumstances.”

 

Special circumstances would include a bridge near a grain elevator that has a

load rating lighter than what is needed to get fully-loaded semis over it during

harvest.

 

If it is not legal to have loads go across the bridge due to the load rating, counties

could have the sensor test done to show that properly planning and designing

a budget to repair the bridge can wait until after harvest.

 

Conner explained that doing emergency repairs on a bridge usually requires a

higher premium of cost to fix, so raising the load rating for a short period would

prevent the county from incurring that cost. The bridge test results can be obtained

within a couple weeks to a month. 

 

Jonathan Olson, a professional engineer and bridge inspector with Butler

Fairman and Seufert civil engineering firm in Indianapolis, said the sensors

may be useful in situations in which the materials of a bridge are unknown due to

its age or lack of bridge plans.

 

“When a bridge has unknown material properties, an inspector may be overly

conservative when performing load rating calculations,” he said. “Many times,

this results in load restrictions for bridges that may not actually need them.”

Olson said the sensors can measure how much weight a bridge can safely

handle with a great deal of accuracy, regardless of whether the bridge materials

are known. However, the test may be costly for counties.

 

“Using these sensors will end up costing the counties additional money,” Olson

noted. “That is money above and beyond what they are required to spend on

typical inspections. Therefore, the use of these sensors and this technology may

be limited to a select number of bridges that hurt local commerce.”

 

Ed Ebert, senior director of grain production and utilization for the ISA, said

some farmers currently must go out of their way to avoid certain bridges.

 

“The majority of our farmers do report that they have problems with access

around bridges,” he said. “So, over time, they make allowances to go different directions, but that adds to time and cost, and with farm prices and commodity prices

the way they have been in recent years, obviously being efficient and being able to

get from farm to market is important.”