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3 Rehabilitation and replacement of bridges often include demolition activities as an initial step in project completion, or in some cases, constitute the whole project. The extent of bridge demolition ranges from partial deck and parapet removal to allow bridge deck replacement or widening to full removal of major river crossings. Project delays, traffic disruptions, and injuries, including loss of life, can result from unintended consequences of bridge demolition. Limited published guidance is available on conducting bridge demolition, and state DOTs approach demolition in various manners. The continually changing transportation infrastructure makes updating or replacing bridges a recurring activity. These projects may include partial and total bridge demolition as part of the overall construction. Partial demolition refers to demolition of specific bridge components or portions of the bridge while leaving the remaining structure in place. Examples include deck removal and replacement or total removal of an elevated access ramp no longer needed. Partial demolition is characterized by the requirement that the remaining structure be undamaged by the demolition methods. Phased demolition refers to the sequencing of demolition activities, such as removing two lanes of a bridge deck while the adjacent two lanes remain open; the sequence then has to be reversed. Removing one of a pair of elevated roadways, building the new structure, and then demolishing and rebuilding the other represents phased total demolition. The projectâs design engineer, either in-house DOT staff or consultant, determines the overall limits and phasing of demolition, as well as traffic control requirements. On some projects, the design engineer may also provide either complete or schematic design of anticipated temporary shoring for beams or pier caps that remain during the demolition activity. This information, along with any demolition specifications or special provisions, is given within the contact documents. The contractor uses the contract documents to select appropriate demolition equip- ment and develop a demolition plan. Depending on project complexity or owner requirements, engineering analysis may be required to verify suitability of the proposed demolition scheme. The removal of various bridge components can alter load distribution within the remaining structure and remove sources of lateral bracing for girders and columns. Engineering performed by the contractorâs engineer is specific to the contractorâs chosen means and methods and addresses the effects of any temporary loads applied to the structure during demolition, the stability of the structure at various stages of removal, and the design of all temporary support or bracing that may be required to maintain stability. For partial demolition projects, the shoring may also need to be designed to carry traffic loads and maintain bridge geometry. Various demolition methods are available and are selected based on the bridge configu- ration, location, material type and condition, reuse of the remaining structure, contractor experience and preferences, safety, and other considerations. Demolition techniques, as with other construction technologies, are continually evolving. Mechanical shears, hydrodemolition, C H A P T E R 1 Introduction
4 Bridge Demolition Practices wire sawing, thermal lance cutting, and mechanical and chemical bursting are just a few of the newer technologies that add to more traditional impact breakers and flame cutting. Controlled explosive demolition may be used where total bridge removal is required, particularly for large structures. However, most demolition is limited in its extent, such that explosives are not appropriate. Environmental and safety regulations limit or even preclude its use in some locations. Particularly in cases of accelerated bridge construction, whole bridge spans may be removed as a unit with final demolition undertaken offsite, often under more favorable working conditions. Partial demolition is constrained by the requirement not to damage any portions of the structure that are to remain, hence limiting the techniques that may be used. Environmental considerations can affect selection of demolition procedures and equipment. Noise and dust control, potential vibrations, and containment and removal of debris must be accounted for and are particularly important in urban or built-up areas. Debris must not be allowed to fall into waterways, into wetlands, or onto railroad tracks. Process water used for sawcutting or hydrodemolition must be collected and treated, and lead paint may be present on older steel structures. Restrictions on waste disposal and emphasis on recycling of materials lead to selecting demolition methods that separate removal of bridge components such as bituminous pavement, concrete, and steel, as well as separating concrete from reinforcing steel. Where there are demo- litions of foundations, additional considerations include disposal of contaminated soils and treated timber piles. Advances in design and construction such as prestressed and posttensioned concrete, longer spans and high strength materials, increased use of continuous spans, curved girder, box girder, and cable-stayed bridges yield structures where demolition procedures require careful consideration. The existing structureâs deterioration, accessibility, and lack of as-built infor- mation may also complicate demolition. While for many bridge structures the most critical condition for design occurs during con- struction, similar conditions may occur during demolition or âdeconstruction.â Accidents and collapses have occurred as results of demolition activities with resulting traffic disruptions, project delays, costs, and injuries. Proper management practices such as comprehensive bridge demolition plans, supported by engineering calculations along with field operations oversight, can reduce these occurrences, if not eliminate them. Scope and Approach of the Synthesis The objective of this synthesis was to document practices used by bridge owners to manage and administer bridge demolition in construction projects. The synthesis did not address the specific techniques that contractors may employ for demolition and engineering analysis considerations for structures under demolition. The synthesis presents current practices in the following areas: â¢ The type and extent of information provided in contact documents specifically related to demolition requirements. â¢ Requirements for the content of contractor submittals for demolition activities. â¢ Requirements for engineering calculations to support demolition activities. â¢ Who provides submittal reviews and what are their qualifications. â¢ Owner oversight of demolition activities in the field. â¢ Requirements for contractor contingency plans, including stoppage of work. â¢ Demolition techniques that may be prohibited.
Introduction 5 The synthesis includes a literature review to provide background information and uncover previous research on this topic. Further information was obtained from a survey distributed to voting members of the AASHTO Subcommittee on Bridges and Structures that requested information on their practices for bridge demolition. Forty-two state DOTs responded to the survey, an 84% response rate. The survey responses identified representatives from five DOTs. They were contacted by telephone and e-mail to acquire additional information on practices for administering bridge demolition projects, which are used as case examples. The five DOTs selected for the telephone interviews were chosen based on their expressed willingness to provide additional information, type of demolition activities, and geographic location. Telephone inter- views with seven bridge construction contractors and demolition contractors were conducted to acquire information on their experiences with owner requirements. The contractors for the telephone interviews included five large bridge contractors and two smaller contractors that work for multiple state DOTs. Their demolition experiences include a range of bridge types and sizes as well as project delivery methods. Organization of the Synthesis Report This synthesis report has six chapters: â¢ Chapter 1 introduces the synthesis, providing background information and summarizing the scope and organization of the document. â¢ Chapter 2 presents and summarizes the findings from the literature review. â¢ Chapter 3 presents the results of the state-of-the-practice survey. â¢ Chapter 4 summarizes the results of the contractor interviews. â¢ Chapter 5 summarizes the information provided by the five agencies interviewed for the case examples. â¢ Chapter 6 concludes the synthesis with a summary of key observations from the findings and suggestions for further research and studies. Four appendices are also included in the report. Appendix A provides links to the referenced DOT specifications and standards. Appendix B provides a copy of the questionnaire that was distributed electronically to the state participants, and Appendix C presents the responses by state DOTs to each of the questions posed to the survey participants. Appendix D is the construction contractor questionnaire and lists the questions the contractors were asked.