Demolition of obsolete structures, from buildings to bridges, brings with it a wide variety of challenges, especially surrounding safety. Unfortunately, accidents have happened, some even resulting in loss of life and many in damage to adjacent property. How can civil engineers involved in bringing down a bridge ensure they’re doing so in the safest and most effective manner?
A new manual of practice from the ASCE Library captures the state of the practice. Bridge Demolition Engineering: Best Practices, MOP 157, offers the latest guidance in one place.
Josh Crain, P.E., S.E., is one of four editors on the manual, produced by the bridge demolition subcommittee of ASCE and its Construction Institute, with input from the American Association of State Highway and Transportation Officials, the National Demolition Association, and the National Steel Bridge Alliance. Crain spoke with Civil Engineering Source about the new MOP and how it will help engineers enhance bridge demolition projects.
Civil Engineering Source: What was the impetus for this manual of practice? What need does it fulfill?
Josh Crain: The demolition MOP was written to fill an industry-wide information gap.
Most engineers acknowledge that additional considerations are required when analyzing a structure as it is being constructed. During bridge erection, engineers consider various stages of partial erection, resulting in potential stability concerns and unique load cases not present once the bridge construction is completed.
Owners, consulting engineers, AASHTO, and other leading technical authorities have focused on bridge construction as an area of concern and have attempted to fill the knowledge gap with numerous technical publications to improve both quality control in the field and the technical review process.
During demolition, the bridge is once again subject to similar concerns related to stability and unique load cases; however, currently, there are limited resources which specially address bridge demolition.
As a result, much of the basis for demolition analysis is left to engineering judgment, which varies widely from state to state and firm to firm. Standardization is needed to establish consensus for those performing and reviewing the engineering analysis for bridge demolition. This first edition of the bridge demolition MOP is a start.
Source: How did the draft come together? What were your primary sources? Was there any kind of theoretical or physical testing done to reach any conclusions and/or recommendations? Were there any considerations that surfaced during the drafting and subsequent reviews that proved challenging to address?
Crain: The demolition MOP was written by a group of contractors and construction engineers who are actively involved in the bridge demolition subcommittee of the ASCE Temporary Works Committee.
In addition to an extensive literature review, one of the first tasks as a committee was to send an industry-wide survey to our peers to establish a reference point for current industry practices. Through this research, we confirmed the need and interest in a document to explain the demolition analysis process and establish a set of best practices for developing or reviewing an engineered demolition plan.
The content published was established based on either the technical committee’s consensus or the industry-wide survey results. One of the significant challenges as a group was deciding what information to leave out. Engineering for demolition is a broad topic, and this document should only be considered a starting point.
Future editions will likely focus on a more detailed analysis section and ideally incorporate testing to develop a more accurate representation of the load effects demolition equipment imparts on a structure.
Source: What advice in the manual might be considered the most dramatic change from what is done commonly in bridge demolition planning and execution?
Crain: The MOP recommends that given the temporary nature of loading imposed on a structure being removed, in certain cases, it is not appropriate to hold the evaluation of the structure to the same design standards as permanent structures.
Source: If nothing else, what is the one thing you hope this manual of practice could transform in the practice of designing and carrying out safe bridge demolitions?
Crain: Our hope with this document is that it helps to level the playing field on both the engineering and construction sides of the demolition process. We’re striving to raise the bar for what constitutes a safe demolition plan on the construction side, while also bringing understanding to designers and reviewing agencies on the differences between the final design of a permanent structure and one that is coming out of service.
Bridge Demolition Engineering: Best Practices, MOP 157, is available in both print and e-book formats in the ASCE Library.
