The ability to rapidly replace deteriorated bridge decks minimizes public inconvenience, travel delays, and financial losses. Methods of bridge-deck replacement that allow repair work to be completed at night or during other periods of low traffic and methods that reduce the total time of reconstruction help to improve public acceptance, reduce accident risk, and yield economic and environmental benefits. This study was conducted to evaluate existing rapid bridge-deck replacement methods and develop better procedures and new superstructure designs for future rapid deck replacement. The three main areas where modifications could be made to make deck systems more suitable for rapid replacement are the demolition process and equipment, the bridge deck system itself, and the bridge girder-to-deck connection. Removing concrete from around steel connectors, without damage to the connectors or the girders, is particularly expensive. The cost of removal has a major influence on the selection of the method of rehabilitation. Also, each method and the equipment used for deck removal have their advantages and disadvantages. Selection of the method and equipment used for deck removal should be made on a job-by-job basis. A set of special provisions is provided to aid owners in the task of deck removal. Because of rapid advancement in equipment technology and the unique abilities of contractors, owners are advised to adopt performance-based specifications that allow for maximum freedom without compromising structural and environmental concerns. The second area of study to improve the speed of deck replacement deals with the deck system itself. Seventy percent of U.S. bridges have cast-in-place (CIP) reinforced concrete decks over steel or concrete girders. A reduction in the amount of reinforcement in CIP systems can enhance deck replacement. Because the most recent `AASHTO LRFD Bridge Design Specifications’ yield a significantly reduced amount of reinforcement in the deck, it should be used wherever applicable. Also, the use of welded wire fabric ) as a replacement for conventional reinforcing bars can considerably reduce the duration of construction. The laboratory time log shows that it took 30 percent less time to place the reinforcement on a deck with WWF than a conventional system. An innovative continuous precast prestressed stay-in-place (SIP) system was developed. The system, shown in Figure 1, extends over the full width of a bridge deck and is continuous both in the transverse and the longitudinal directions to eliminate reflective cracks. The portion over the girder line is kept open to accommodate shear studs, and the overhang form is a part of the SIP system. The construction time for this system was 20 percent less than that for a conventional SIP system and 60 percent less than for a conventional CIP system. Cost estimates show that this system is comparable to the CIP deck system. Also, a full-depth precast system was developed. The system, shown in Figure 2, is transversely pretensioned and longitudinally post-tensioned. This system is about I 0 percent thinner and 20 percent lighter than conventional CIP or precast reinforced concrete sections. The full-depth precast panel system was found to require the least construction time of all systems studied. Further, twoway prestressing controlled the occurrence of transverse and longitudinal cracking. Cost estimates show that this system compares very favourably with other full-depth systems and is ideally suited for new construction as well as renovation. The third area of study to improve the speed of deck replacement examined the connection system of concrete decks to concrete or steel girders. Demolition of bridge decks that are compositely connected with either structural steel I-girders or precast concrete I-girders is one of the major time-consuming tasks in deck replacement. The time required for deck demolition can be reduced by constructing bridges with connections that provide composite action and allow for easier deck removal. Two new connection systems were developed, one for concrete girder-to-concrete deck connections and the other for steel girder-to-concrete deck connections. For concrete girders, a debonded shear key system, shown in Figures 3 and 4, was developed. This system provided excellent results for composite action as well as deck removal. For steel girder-to-concrete deck connections, a 1¼-in. (32-mm) diameter shear stud system, shown in Figure 5, was developed to replace the commonly used ¾-in. (19-mm) and -in. (22-mm) shear studs. The 1¼-in. stud provides approximately twice the capacity of a -in. stud and would allow positioning in a single row over the girder web. Also, the research team found that alternating headed and headless studs was adequate for anchorage to the concrete deck. This further facilitates deck removal. Timelines were produced for different bridge deck systems to compare the speed of construction. Finally, a cost analysis was done to compare the cost-effectiveness of the systems investigated in this project. (A)
Samenvatting