Demolition: Construction in Reverse
By Ashlee Peno, PE, SE, Chief Structural Engineer, Special Inspections & Design
As OSHA so articulately points out, demolition is construction in reverse. As such, demolition work involves many of the same hazards that are associated with construction. However, demolition also comes with its own unique set of hazards.
Many of these hazards are due to unknown factors such as changes to the original design intent introduced during construction, undocumented modifications and additions, hazardous materials hidden within structural members, unknown material strengths, and deterioration of structural members hidden by finishes. While it is universally understood that it is necessary to develop structural plans prior to constructing a new building or bridge, it is equally important to have an engineered demolition plan in place prior to deconstructing a structure.
Structures are designed to perform as a unit upon completion of construction. This is why temporary bracing and shoring is required during the construction process until permanent bracing, shear walls, and floor and roof systems are in place and connections are complete. The same concept exists in reverse. Once particular elements are removed or unconnected, the stability and structural integrity of the frame are altered from the original design intent. If not dismantled in the proper order, the structure can become dangerously unstable. Just like with construction, temporary shoring and bracing is often required during demolition.
As with most construction industry activities, proper planning is key to delivering a safe, successful project. Demolition is no exception. The first step in developing an engineered demolition plan is to have a structural inspection performed. The purpose of this inspection is to identify the structural systems used, assess the current condition of the structural framing, and identify potential hazards. If structural design documentation is available, the inspection should be used to confirm the information shown. If structural design documentation is not available, the inspection should be used to layout the structural systems.
Based on the structural inspection, existing documentation review, and discussions between the engineer and demolition contractor, a written demolition plan should be developed. The plan should include detailed guidance on how the structure should be taken apart, what equipment will be required, what safety and environmental protections should be taken, and it should detail any temporary shoring or bracing requirements. Many regulatory agencies, including OSHA, most DOTs, and railroads, require Contractors to submit a demolition plan signed and sealed by a registered Professional Engineer.
The engineered demolition plan should be completed as early in the planning process as possible; however, it is likely that the document will continue to evolve over the course of the project. Often, many of the unknown factors listed above are not discovered until after the actual demolition has begun. It is recommended that the engineer responsible for developing the demolition plan remain involved beyond the planning stages to address hazards discovered in the field.
Contact: Ashlee Peno, PE, SE Chief Structural Engineer
Special Inspections and Design www.sidengineers.com
