National Academies Press: OpenBook

Bridge Demolition Practices (2019)

Chapter: Chapter 6 - Conclusions

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Page 46
Suggested Citation:"Chapter 6 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Bridge Demolition Practices. Washington, DC: The National Academies Press. doi: 10.17226/25478.
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Page 46
Page 47
Suggested Citation:"Chapter 6 - Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Bridge Demolition Practices. Washington, DC: The National Academies Press. doi: 10.17226/25478.
×
Page 47

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46 The objective of this synthesis was to document practices used by bridge owners to manage and administer bridge demolition in construction projects. Information gathered during this synthesis included the type of information for demolition provided by bridge owners in the contract documents, contractor submittal contents, and owner processes for submittal reviews and demolition field oversight. Advances in design and construction, such as prestressed and posttensioned concrete, high strength materials, long span and continuous structures, curved bridges, and cable-stayed bridges are but a few cases that can complicate demolition. Docu- mented accidents and collapses have occurred during demolition. Research on demolition practices is limited. What is available deals primarily with individual demolition techniques or particular types of equipment. Articles presenting projects are general overviews that provide minimal technical information, particularly related to project processes. AASHTO specifications for bridge design and construction provide limited information. State DOT standard specifications provide a range of requirements for demolition, including structural removal as well as deck removal. Some states provide only a paragraph covering demolition, while other states include detailed provisions, both for submittals and execution. Special provisions addressing demolition are provided for large or complex projects. While most states require the contractor to submit a demolition plan, specific requirements for the content or for any supporting calculations were not found in the standard specifications. Literature articles on demolition collapses that were reviewed, as well as OSHA reports, stress the importance of thorough demolition plans and supporting engineering calculations. OSHA also identified knowledgeable field oversight as important in preventing incidents. Those observations are supported by comments received during interviews with demolition contractors. To understand better current DOT practices in managing and administering demolition projects, a survey of the practice was conducted through NCHRP in cooperation with AASHTO. The survey was distributed to AASHTO’s Subcommittee on Bridges and Structures voting members, who were encouraged to forward it to the person most familiar with the agency’s demolition practices. Eighty-eight percent of the 42 responding agencies have specification provisions that address bridge demolition. Fifty-seven percent provide special provisions for demolition work. In addition to standard specifications, special provisions, and design plans, 90% also provide existing structure plans, when available, when demolition is required. Sixty percent stated that they prohibit some types of demolition methods such as limits on equipment sizes or use with explosives. Thirty-five responding agencies require submittal of a demolition plan for phased, partial, or total demolition. Those requirements did not vary based on project delivery methods. The C H A P T E R 6 Conclusions

Conclusions 47 contractor prepares the demolition plans, and most agencies require them to be signed and sealed by a licensed design professional. The literature review found that some agencies do not require an engineer’s seal for small structures or shorter simple span bridges. For those requiring demolition plan submittals, the required contents were consistent, including a work sequence and narrative, types and locations of equipment, temporary structure support or bracing requirements, and supporting calculations and drawings. Approximately one-half of the agencies require calculations for demolition to conform to the AASHTO LRFD specification, while the primary alternate specification is the AASHTO standard specification. Two-thirds of the agencies review the demolition plan submittals with bridge design engineers who are either in house or consulting. The remaining agencies use construction staff. A quarter of the agencies require the reviewers to have on-the-job training or experience in demolition activities. Review comments are provided to the contractors and must be resolved prior to start of field activities. All but one agency provides field oversight of demolition activities either by in-house staff or a combination of in-house staff and consultants. Only 40% of agencies indicated that they pro- vide any special staff training related to demolition. Just over one-half of the agencies conduct a predemolition site meeting, but only two agencies have a standard meeting agenda. Ten agencies require contingency plans identifying specific responses to unanticipated events. Ninety-three percent reported using daily reports to document field activities, with one-half also using photographic logs. Just over one-half of the agencies provide full-time oversight, while all but 10% provide at least 75% oversight. The five case examples presented a variety of contract bid documents, plan submittal require- ments and processes for demolition, and field oversight procedures. Two of the five case examples were projects that had unintended events, while the other three case examples were completed as planned. The types of documents provided to bidders did not vary significantly from agency to agency. All five agencies provided field oversight. Three agencies provided both agency staff and a consultant to oversee the project, while one agency required only an agency representative, and one agency required just a consultant inspector. All the agencies had differing requirements for a bridge demolition submittal, though all of them did require one. States that viewed their projects as a more common bridge demolition typically required less in their submittal while, Alaska, for example, required more extensive information due to the complexity of the project and use of explosives. The seven demolition contractors interviewed all commented that the owner requires a demolition plan submittal and that detailed plan requirements are generally only specified for large or complex projects. They did not report any significant difference in demolition require- ments for delivery of accelerated bridge construction projects. They also commented that the degree of field oversight is largely dependent on the individual resident engineer and on project complexity. The results of the synthesis indicate some knowledge gaps in the current practices that can be addressed through future research or studies. They are • Identifying design criteria and guidance applicable to analysis of structures under demolition. • Identifying critical steps for field oversight of demolition activities. • Establishing load distribution criteria for equipment operating on structures during demolition activities.

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TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 536: Bridge Demolition Practices documents practices used by bridge owners to manage and administer bridge demolition in construction projects.

Each year hundreds of bridges are rebuilt or are entirely replaced as part of highway construction projects. Bridge reconstruction or replacement work often entails demolition of part or all of the bridge structure.

Unintended events resulting in injury, project delays, and traffic disruptions can occur and have occurred during bridge demolition activities. The intention of this synthesis report is to assist in better understanding how to reduce risk associated with bridge demolition.

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