Pleasant River Bridge undergoes load test - By Stephen Signor

It was just a few days ago drivers in Windham were being encouraged to avoid the bridge over the Pleasant River on Windham Center Road for the purpose of load testing the span. As Scott, a second year research engineer with the University of Maine explained, “This is part of ongoing research being conducted as a result of a multi-year contract with the University of Maine system and the MDOT for the purpose of establishing a bridge’s efficiency.”

The University’s participation stems from its Advanced Structures and Composites Center which provides research, education and economic development encompassing material sciences, manufacturing and engineering of composites and structures. And while a successful test is the obvious goal, the results at this point in the test are not conclusive. “Further analysis of the data takes about a year”, Scott said.

To accomplish this load test, “a full day is needed to carefully and precisely set up sensors that will be located in key point locations underneath the bridge”, said Josh Simpson, E.I.T., a 3-year assistant engineer and bridge inspector for MDOT. What happens next is that on the following day “two fully loaded dump trucks, containing a standard load of sand and gravel and provided by the MDOT, are then parked on predetermined marked locations. These two trucks will then move just inches back and forth in the proximity of where sensors are located the bridge, their wheels stopping periodically on the markers. As a static load this will provide valuable information on structural integrity,” explained Simpson. 

Using a laptop this information is uploaded for immediate review. “If the numbers are within a
certain range, then four trucks will be used to complete the test. If the numbers should not fall within the required results this sends up a red flag,” Simpson continued. He also brought home the point that, “Codes are established initially as conservative for safety reasons. Tests like this one then gives the department a real number to justify the conservative numbers.”

In the planning of the load test motorist considerations were also taken into account. Something as simple as a spray paint was used. Scott indicated, “Using spray paint, marks are made on the road service to indicate the placement of the dump trucks wheels. Since there are several marks for accurate test results doing it this way is time saving as opposed to using a tape measure for each individual mark before moving on to the next spot. 

According to the Maine Department of Transportation website this bridge was built in 1950. The bridge was last inspected in December of 2012, at which time it received a Federal Sufficiency Rating of 66.7 out of a possible 100. Those results were posted in a report dated 07/17/2013.

In the coming months similar tests will be performed statewide to insure that Maine’s infrastructure is maintained to provide safe and worry free traveling.