Precast, prestressed concrete panels (PCPs) and cast-in-place (CIP) concrete slabs are commonly used in Texas and elsewhere. Because PCPs are placed between bridge girders, and CIP concrete slabs are cast over the PCPs, PCPs act as formwork, cost and time for construction can be reduced. However, current designs may be further optimized if it can be shown that the reinforcement in the CIP deck can be reduced. Another issue involves cracking of PCP during fabrication and transportation to the site. The goal of this dissertation is to recommend changes to the CIP-PCP bridge decks that will lead to more cost-effective bridges. The first phase of the research is to suggest an optimized reinforcement layout for cast-in-place (CIP) slabs. Because the capacity of these decks is much greater than the design loads, a decrease in top-mat reinforcement will have minimal effect on the margin of capacity over design loads. Two options were selected, reduced deformed-bar reinforcement; and reduced welded-wire reinforcement. These two options are evaluated through restrained-shrinkage tests and field applications. The second phase of this dissertation is to reduce cracks in precast, prestressed concrete panels (PCPs) which occur during fabrication, handling, and transportation. Most cracks in PCPs are collinear (occur along the strands). They can be reduced in two ways. The first is to reduce initial prestress. The second is to place additional transverse reinforcement at edges. / text

The prestress loss estimation provision in the AASHTO LRFD Bridge Design Specifications was recalibrated in 2005 to be more accurate for "high-strength [conventional] concrete." Greater accuracy may imply less conservatism, the result of which may be flexural cracking of beams under service loads. Concern with a potential lack of conservatism and the degree of complexity of these recalibrated prestress loss estimation provisions prompted the investigation to be discussed in this dissertation. The primary objectives of this investigation were: (1) to assess the conservatism and accuracy of the current prestress loss provisions, (2) to identify the benefits and weaknesses of using the AASHTO LRFD 2004 and 2005 prestress loss provisions, and (3) to make recommendations to simplify the current provisions. These objectives were accomplished through (1) the fabrication, conditioning, and testing of 30 field-representative girders, (2) the assembly and analysis of a prestress loss database unmatched in size and diversity when compared with previously assembled databases, and (3) a parametric study investigating the design implications and sensitivity of the current loss provisions. Based on the database evaluation coupled with the experimental results, it was revealed that the use of the AASHTO LRFD 2005 prestress loss provisions resulted in underestimation of the prestress loss in nearly half of all cases. A loss estimation procedure was developed based on the AASHTO LRFD 2005 provisions to greatly simplify the procedure and provide a reasonable level of conservatism. / text

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An effective, viable design solution for the elevated viaduct guideway for Universal Freight Shuttle (UFS) system championed by Texas Transportation Institute (TTI) is presented. The proposed precast elevated UFS bridge system is analyzed for the operational vehicular loading as provided by TTI and a number of design alternatives for the various bridge components are provided. This includes: the design of the fully precast deck panels for long continuous spans, design of the shear connectors resisting interface shear at bridge deck-girder interface, design of structurally efficient and cost-effective trough girders and its design alternative with I-girders, and economic and long-term serviceable design of bridge piers. A literature review and study of the existing precast bridges is presented for the state-of-the-art and practice, design specifications and publications by AASHTO, State Department of Transportation and other agencies. These existing systems are refined to determine the most appropriate specification for the proposed bridge components by integrating the planning, design, fabrication and construction techniques to ensure high precision freight shuttle movement, construction feasibility, safety, life-cycle cost, durability and serviceability requirements. The design concept presented is a deviation from the conventional railways and highways design. The best practices and specifications of AASHTO and AREMA are combined suitably in this research to suit the major requirements of the project. A combination of the design philosophy with appropriate construction techniques has been blended to devise a system which is efficient for offsite manufacture of components for construction of the bridge and adaptable to the different bridge configurations. Based on the design results, it is found that precast concrete deck panels in combination with precast, prestressed concrete trough girders provides the most efficient superstructure solution for this project. The Damage Avoidance Design for the precast bridge piers along with the precast superstructure provides a system with comparable structural performance along with other benefits such as long term serviceability, economical sections, practically transportable units, modular simplicity for relocation as desired and ability to offer space for commercial usage. The steps for construction of the bridge is schematically presented and sequentially explained.

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