Morenci's East Main Street bridge remains a concern 03.02.2011

Written by David Green.

main_street_bridge_eastBy DAVID GREEN

Morenci’s Main Street bridge on the east side of town remains a problem due to deterioration of the beams and washout around the abutments.

City council is expected to apply for federal bridge replacement funds again this year in hopes of preventing a future detour if the bridge were to be considered unsafe.

Prior to an inspection in 2008, the weight limit was posted at 61 tons, but limits have been reduced more than once since then. Currently, the allowable weight is posted at 15 tons for a one-unit vehicle, 17 tons for a two-unit vehicle and 27 tons for a three-unit vehicle.

The city uses the Brechting Bridge and Engineering firm for bridge inspections. Frank Brechting recently completed a Scour Critical Bridge Action Plan to meet a federal requirement. Scour refers to the washout of soil around bridge abutments from high water events.

“The plan designates a chain of command in case of a high water event,” Brechting explained.

A local official would be designated to monitor the bridge and make a report to the engineering firm. An evaluation of the situation would determine if a detour were needed.

“It’s fairly common that a bridge is scour critical,” Brechting said.

Many of the state’s older bridges that use a spread foundation rather than pilings are subject to washout.

Brechting said the 38-foot bridge was constructed in 1941 and since no construction plans are available, he has to assume that a spread foundation was used. The West Main Street bridge, built in 1949, is supported by pilings driven into the ground.

He estimates a replacement cost of  at least $550,000, including the road approaches. The federal bridge funds—which are funneled through the Michigan Department of Transportation—would cover 95 percent of the cost, leaving the city with a share of around $30,000, plus design and construction engineering costs.

Brechting said a new bridge would likely use different construction materials, such as pre-stressed concrete beams.

“Hopefully it’s going to qualify for bridge funds eventually,” Brechting said. “There’s a lot of need there.”

Applications are rated on factors that include the condition of the bridge and the amount of traffic carried.

City council has discussed in the past the problems that a detour would create, especially since funding for completion of the industrial park road was not received.

At the Feb. 14 meeting, Morenci mayor Keith Pennington asked city supervisor Barney Vanderpool and police chief Larry Weeks to discuss ways of limiting truck traffic on Coomer Street past the school.

The reduced weight limits could lead truck drivers to seek a route that avoids the bridge. Vanderpool said he expects the weight limits to be reduced further in the future.

Chief Weeks pointed out that his department has no means checking the weights of trucks. Pennington said restrictions would probably have to address axles or truck classes.

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