Fundamentals of Highway Bridge Demolition

摘要

As the transportation infrastructure in the United States is aging and expanding rapidly, demolition and replacement of the existing systems has increasing importance. Highway bridge demolition has become increasingly significant as the bridges reaching their service design life require rehabilitation or replacement. Highway widening to meet capacity increase also involves partial or total removal of highway bridges. This paper presents the fundamentals of highway bridge demolition by explaining the systematic deconstruction, crane usage, and the engineering involved with this process. Systematic deconstruction is the art and science of preventing unplanned potential energy release during a demolition process. Engineering is needed for the deconstruction process in order to protect the lives of the workers and in order not to damage any other structure in the close proximity of the structure to be demolished. In addition, the expensive machinery used for the deconstruction process needs to be protected. As a result, nearly as much engineering analysis is needed to demolish a structure than to initially build it. While the stereotypical image of demolition is a wrecking ball or an explosive event, these are not typically used in highway bridge demolition. Explosive demolition is rare, and is used occasionally for very large bridges (as well as other large structures outside of this scope). For a typical highway overpass bridge hydraulic excavators sit on the deck removing concrete with a hydraulic hammer or shear, and then excavators or cranes placed on grade remove the girders. The bridge structure is analyzed for different excavator positions and different stages of the demolition. The excavator body weight and the hammer tip weights are considered separately for different cases of demolition sequence. The engineering work required for cranes involves support design for crane bases (tracks or outriggers), pick plan and pick weights (pick sequence, radii, clearances, center of mass, lay-down area), and rigging design (wire rope slings, stability of structure while being picked, local failures of the object being picked or the rigging components).