Jointless bridges are advantageous in removing mechanical joints which are a known cause of bridge deterioration. Elimination of joints provides a smoother riding surface and removes the possibility of de-icing salts penetrating the deck and corroding the deck reinforcing and underlying bridge superstructure. Jointless bridges are traditionally constructed by monolithically casting the entire bridge deck on beams after they have been erected. However, this process requires extensive in-field formwork and lengthy traffic closures. The Texas Department of Transportation proposes a new method of constructing jointless bridges using prefabricated girder-and-deck units connected on-site with cast-in-place closure pours. This new system will expedite construction and reduce disturbances to the traveling public. The objective of this experimental study was to investigate the behavior of the cast-in-place closure pour slab and to determine if it responds to wheel loads in the same way as a traditional monolithic continuous deck. The effects of the cold joints and discontinuous steel details are the focus of the research work.

After 17 years in service, a 3 ft by 3 ft closure pour section of an Interstate 81 (I-81) bridge deck failed by punching through near Marion, Virginia. Visual inspection noted that there was considerable corrosion on some of the reinforcing bars in the vicinity of the construction joint, while other failure bars had little or no corrosion. Sections of the bridge deck were cut and delivered to Virginia Tech for further investigation. It was clear from an initial investigation that shrinkage of the deck concrete had caused the construction joints to open and thereby allow water and chlorides to enter the joint. In addition, it was observed that several bars across the closure pour construction joints had suffered significant section loss due to corrosion, but it was not clear if fatigue and strength failure of the reinforcing bars were also contributing factor in the closure pour failure. To study the problem four fatigue tests and five strength tests performed. The specimens included six slab strips cut from the I-81 bridge deck, with the 3-ft closure pour included, and three additional specimens that were cast in the laboratory to represent a base line for performance. A three-point loading setup was used for both fatigue and strength tests. However, for the final strength and fatigue tests, a jacking system was designed and implemented in an effort to open the closure pour construction joints to simulate the open joints of the I-81 bridge. The objectives of this research program are to provide a better understanding of the closure pour failure mechanism, develop inspection procedures for Virginia Department of Transportation (VDOT) to assess its bridge inventory containing similar construction joints, and to develop recommendations for future construction of similar construction joints. / Master of Science

Continuous longitudinal and transverse U-bar joint connections between flanges of the decked bulb-Ts (DBTs) or between precast panels for accelerated bridge construction are investigated. The procedure for selecting durable closure pour (CP) materials for the connections is discussed firstly. The accelerated construction is quantified as two categories: overnight cure and 7-day cure of CP materials. Candidate materials are selected first based on literature review as well as tests of compressive strength and flow and workability. Then, performance criteria for selecting durable CP materials for both categories are developed based on durability tests of selected candidate materials. These durability tests include freezing-and-thawing durability, shrinkage, bond, and permeability tests. To investigate the longitudinal U-bar joint details, four pairs of full-scale slabs connected by a U-bar detail with one of the selected CP materials, overnight cure and 7-day cure, were tested. The loading demand necessary in the slab testing is determined based on the maximum forces in the longitudinal joint from an analytical parametric study. Static and fatigue tests under four-point flexural loading and three-point flexural-shear loading were conducted. Test results were evaluated based on flexural capacity, curvature behavior, cracking, deflection and steel strain. The transverse U-bar joint details are investigated to provide negative moment continuity in the multi-span bridges. Four full-scale specimens connected by a U-bar detail with one of the selected CP materials, overnight cure and 7-day cure, were tested. Static and fatigue tests under tension loading were conducted. The loading demand necessary in the beam testing is determined based on the maximum forces in the transverse joint from an analytical study. Test results were evaluated based on tension capacity, cracking, displacement and steel strain. Based on the test results, the developed longitudinal and transverse U-bar joint details are viable connection systems.

Accelerated Bridge Construction (ABC) has gained substantial popularity in new bridge construction and bridge deck replacement because it offers innovative construction techniques that result in time and cost savings when compared to traditional bridge construction practice. One technology commonly implemented in ABC to effectively execute its projects is the use of prefabricated bridge components (precast/prestressed bridge components). Precast/prestressed bridge components are fabricated offsite or near the site and then connected on-site using small volume closure pour connections. Diaphragms are also commonly used to strengthen the connection between certain prefabricated components used in ABC, such as beam elements. Bridges containing closure pour connections and diaphragms can be designed using AASHTO LRFD live-load distribution factor formulas under the condition that the bridge must be sufficiently connected. However, these formulas were developed using analytical models that did not account for the effects of closure pours and diaphragms on live-load distribution. This research study investigates live-load distribution characteristics of precast/prestressed concrete bridges with closure pour connections and diaphragms. The investigation was conducted using finite element bridge models with closure pour joints that were calibrated using experimental data and different configuration of diaphragms. The concrete material used for the closure pour connections was developed as part of a larger project intended to develop high early-strength concrete mixtures that specifically reach strength in only 12 hours, a critical requirement for ABC projects.