Workers conduct tests on a rural bridge

(Photo: Soy Transportation Coalition)

Iowa Soybean Farmers Partner with Bridge Engineers to Enhance Rural Bridge Evaluation and Management

February 26, 2021

By Mike Steenhoek, STC Executive Director

Iowa farmers depend upon rural bridges to efficiently deliver their soybeans or other commodities to the local elevator or processing facility.  The structural integrity of this infrastructure is essential to farmer profitability.  Unfortunately, a significant number of rural bridges in Iowa are load restricted, requiring vehicles transporting agricultural commodities to detour – often at significant distances.  This results in additional costs being inserted in the nation’s food delivery system and diminished profitability for Iowa farmers.  While the need to maintain and upgrade rural bridges is on the increase, available resources to address this challenge remain insufficient. 

In an effort to promote better evaluation and management of the state’s rural bridges, the Soy Transportation Coalition (STC) has partnered with Kirkham Michael – a civil engineering firm with operations in Iowa, Kansas, and Nebraska – on an innovative project designed to demonstrate the effectiveness of load testing technology when assessing the load carrying capacity of rural bridges. 

“When evaluating and assessing bridges, motorist safety is the number one priority,” says Steve Reneker, P.E., Vice President at Kirkham Michael.  “However, what we have learned is that the sole reliance on visual inspection and theoretical calculations can result in bridges being load restricted or identified for rehabilitation or replacement sooner than necessary.  This not only results in costly detours or limited access, but it prevents our state and local governments from most efficiently targeting taxpayer dollars to those bridges in greatest need of replacement and repair.” 

The focus of the project is to evaluate bridges utilizing load testing sensors attached to the underside of the bridge.  After the sensors are installed, test loads are driven over the various segments of the bridge surface to determine a precise understanding of the capabilities of the bridge.  The up-front costs of the project were provided by the Soy Transportation Coalition and Kirkham Michael.  Client counties and municipalities of Kirkham Michael will subsequently contract with the firm to perform the actual load testing.   

On December 10th, Van Buren County in southeast Iowa contracted with Kirkham Michael to test several rural bridges that had been originally assessed with load restrictions.  Each bridge had been load-limited due to a concern based on the traditional approach of using theoretical calculations to determine a bridge’s load carrying capacity.  However, after evaluating the bridges via load testing sensors, the load restriction on one bridge (25 tons) was able to be safely removed – allowing it to accommodate legal loads.  Two other bridges – one with a seven-ton load restriction and the other with an eleven-ton load restriction – were also evaluated.  After performing the load testing with the sensors, the postings were increased to 17 and 24 tons, respectively.  Additional load testing of bridges in Van Buren and a number of other Iowa counties is being planned for spring and summer of 2021. 

“In my role as a county engineer, I seek to improve the utility and efficiency of the secondary road system without sacrificing the safety of the traveling public,” says Ryne Thornburg, engineer for Van Buren County.  “I was very pleased with the results of the recent bridge load testing since they provided a thorough, objective assessment of the capabilities of the bridges.  As a result, we are able to maintain safety while enhancing access to the road and bridge network Van Buren County residents have paid for.” 

“Given that our families are using these rural bridges on a daily basis, safety is most important,” says Robb Ewoldt, a soybean farmer from Scott County and director on the Iowa Soybean Association and the Soy Transportation Coalition.  “Promoting this technology helps develop a better understanding of which bridges truly need repairs and which ones can safely handle the trucks that transport the soybeans and grain produced in the state.  Iowa soybean farmers are pleased to help partner in this important project.”

“If we have a rural bridge problem in this country, which we do, and if resources to address this problem are scare, which they are, then we should do all we can to ensure we get the diagnosis correct,” explains Mike Steenhoek, executive director of the Soy Transportation Coalition.  “This project is designed to increase clarity of the condition of rural bridges and enhance stewardship of the bridges themselves and scarce taxpayer dollars.  It is our hope that other regions throughout the country will emulate this innovative approach.” 

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