FISHER LANE BRIDGE UPDATE...
Release Date: August 13, 2010
I understand many residents and commuters are concerned about an apparent lack of progress toward repairing the Fisher Lane Bridge. Please be assured this is an active design project and we are working with our consulting engineer to develop the best solution to this problem. As you know, this bridge was closed to westbound traffic this past April after inspection revealed serious structural decay to the steel beams supporting the deck grates. The Town contracted with a local consulting engineering firm, WSP Sells, with expertise in bridge inspection and design services, to inspect the existing conditions, evaluate the bridge and provide design services for the repair and or replacement of the bridge. Under their direction, the Town closed the westbound portion of the bridge after analysis confirmed the steel could not safely support the weight of passing cars. Since that time in April, we have continued to work with WSP Sells to further inspect and evaluate the bridge structure and supporting substructure to determine the condition of all aspects of the bridge so a design can be prepared to restore the bridge to allow traffic to again travel both east and west bound.
While it was first thought the failed steel beams could just be replaced, concerns developed relating to the condition of the existing concrete substructure. To test this system, it was required that the bridge be closed to all traffic. Closure of the bridge involves coordination with the adjacent municipalities, the County and Metro North Railroad and several weeks for advance notice to the commuters that use the lot. On July 19, the bridge was closed overnight as portions of the decking were removed and the concrete substructure was more fully evaluated. The testing verified the integrity of the concrete.
Following this test, design alternatives to the steel beams and deck were evaluated to consider long-term replacement, as the current steel beam and open deck structure is subject to accelerated decay and therefore does not have a long projected lifespan and has high maintenance requirements. The existing bridge failed due to severe rust and corrosion of the steel beams. Also, additional designs to offer improved accessibility along the walkway across the bridge were considered.
Designs evaluated include two different types of pre-cast concrete plank systems and a hybrid system of both steel and poured in place concrete decking. A key design constraint is the bearing capacity of the existing piles supporting the bridge requiring a relatively light deck structure. A second design constraint is the constructability of the new bridge within the restricted time frame of 48-hours over a single weekend to permit access to the lot for commuters.
At this time, WSP-Sells is focusing on a final design alternative that will be strong enough to carry the traffic, light enough not to exceed the capacity of the pile foundation, provide long-life with reasonable maintenance needs and be constructed within a 48-hour window. Our consultant expects a final design by the end of August.
Victor G. Carosi, P.E.
Commissioner of Public Works
Town of Greenburgh