This paper summarizes the development of a precast concrete bent-cap system, which can connect precast concrete bent caps to cast-in-place concrete columns or precast concrete trestle piles in nonseismic regions. The primary focus of this paper is the anchorage of reinforcing bars connecting the column or pile to the bent cap. Four connection types were explored, including grout pockets, grouted ducts, grouted sleeve couplers, and bolted connections. Reinforcing-bar-anchorage failure modes and capacities for grouted ducts and grout pockets developed during the first phase of a three-phase test program are presented based on 32 pullout test of no. 6 to no. 11 (19M to 36M) epoxy-coated reinforcing bars. Anchorage capacity for headed reinforcing bars in grout pockets was found to be accurately determined using the concrete-capacity-designequation reduced by a factor of 0.75 to account for grout-pocket cracking. Based on a uniform bond-stress model, development-length equations for straight reinforcing bars in grout pockets and straight and headed reinforcing bars in grouted ducts were conservatively established for design. Grout-pocket specimens using neat grout achieved the same capacity as similar specimens using grout extended with pea gravel. Spiral confining reinforcement enhanced ductility and capacity more effectively than welded-wire reinforcement. Phase 2 and 3 test results, the design methodology, and a precast concrete construction connection specification will be presented in a future publication.

This report is the last technical report from a comprehensive research program started in 1993 under TxDOT Project 0-1405. The objectives were to examine the use of post-tensioning in bridge substructures, identify durability concerns and existing technology, develop and carry out an experimental testing program, and conclude with durability design guidelines. Four experimental programs were developed: improved and high-performance grout studies, to develop grout with desirable fresh properties to provide good corrosion protection to the prestressing strands; a long-term macrocell corrosion test series, to investigate corrosion protection for internal tendons in precast segmental construction; a long-term beam corrosion test series, to examine the effects of post-tensioning on corrosion protection as affected by crack width; and, a long-term column corrosion test series, to examine corrosion protection in vertical elements. This report includes the final results after completion of exposure testing, performing comprehensive autopsies and updating the durability design guidelines to reduce the corrosion risk of the post-tensioning system.

A research project was conducted to assess the feasibility of reducing the current ACI Building Code and AASHTO Bridge Specification requirements for minimum longitudinal reinforcing steel in columns. The current code requirement is based primarily on research conducted in the 1920s and 1930s on concrete with a compressive strength generally less than 34.5 MPa (5000 psi).The investigation was conducted to determine the effects of present-day construction materials on minimum reinforcement requirements. A research program was carried out that included: 1) fabrication and long-term loading and monitoring of 24, 8-in. diameter by 4-ft long reinforced concrete column specimens; 2) fabrication of reduced-humidity enclosures for storage of all specimens throughout the test program; and 3) long-term monitoring of 14 unloaded companion specimens. Test variables included concrete strength and reinforcement ratio. All loaded specimens were subjected to a nominal compressive force of 0.40f(c)'/A(g). The long-term response of concentrically loaded and unloaded specimens is presented in this paper, and measured responses are compared with predicted long-term responses based on recommendations from ACI Committee 209.

A series of fresh property tests and accelerated corrosion tests were used to develop grouts that combine favorable grouting properties with good corrosion protection. The grouts were then pumped into a clear duct with multiple drapes to observe their behavior under simulated field conditions. Two high performance grouts for post-tensioning applications are recommended from this testing. For horizontal applications, a low water-cement ratio grout with fly ash (Class C) is recommended. For vertical applications (such as tall bridge piers), a low water-cement ratio grout containing antibleed admixture is recommended.

A large portion of the off-system bridges and some on-system bridges in Texas were constructed in the 1950s using vehicle loads that are less than the current design standards. As a result, the legal load that is permitted to cross these bridges is often limited and many are scheduled for replacement. The use of carbon fiber reinforced polymer (CFRP) composites to increase the flexural capacity of reinforced concrete bridges was investigated in this research project. The overall goal was to develop design procedures for strengthening existing bridges using CFRP to avoid replacement of bridges that have been functioning satisfactorily for many years. The third phase of the research project is described in this report. Four full-scale specimens representative of bridge construction during the 1950s in Texas were constructed, strengthened, and tested in the laboratory to assess the effectiveness of the CFRP composites for increasing the flexural capacity. Results from the laboratory tests indicate that the composite materials may be used successfully to strengthen existing bridges. The strength of all specimens was controlled by debonding of the CFRP composites from the surface of the concrete. An analytical model was verified using the measured response of the laboratory specimens. The model was able to reproduce the overall response of the specimens, but did not reproduce the local modes of failure. Therefore, the model may be used to design strengthening systems for reinforced concrete bridges, but the maximum strain in the CFRP composites must be limited to reflect the observed modes of failure. Design guidelines for CFRP systems are presented.

External posttensioning tendons in concrete box girder bridges are usually anchored in very massive end diaphragms. Several incidences of distress of such diaphragms have been reported in the literature. This paper presents the results of an analytical and experimental research program on design and behavior of end diaphragms when used for the anchorage of external tendons. Finite-element analysis results, strut-and-tie models, and results of a physical test series of half-scale specimens are included. The strut-and-tie model approach is shown to be an effective method to describe the flow of forces in the structure and for design. Ultimate strength predictions based on simple strut-and-tie models were safe but quite conservative. Refined strut-and-tie models based on finite-element analysis results were required to arrive at satisfactory reinforcement arrangements for crack control.

This report documents a series of accelerated corrosion tests on small-sized specimens typical of bonded internal post-tensioning tendons in segmentally constructed box girder concrete bridges. Thirty-eight macrocell specimens were subjected to a highly aggressive exposure and observed for 4 1/2 years. At that time, 19 of the specimens were opened for detailed examination and all corrosion behavior recorded. The variables included were joint type (dry or epoxy), duct type (galvanized steel or plastic), grout type (3 grouts with differing additives) and level of joint compression (3 different levels). Half-cell potentials and macrocell corrosion currents were measured throughout exposure. While some substantial corrosion was found in dry joint specimens, the corrosion resistance of epoxy joint specimens was excellent.

Durability design requires an understanding of the factors influencing durability and the measures necessary to improve durability of concrete structures. The objectives of this report are to: (1) survey the condition of bridge substructures in Texas; (2) provide background material on bridge substructure durability; and (3) review durability research and field experience for post-tensioned bridges. A condition survey of existing bridges in Texas was used to identify trends in exposure conditions and common durability problems. The forms of attack on durability for bridge substructures in Texas are reviewed. Basic theory for corrosion of steel in concrete is presented, including the effect of cracking. Corrosion protection measures for post-tensioned concrete are presented. Literature on sulfate attack, freeze-thaw damage, and alkali-aggregate reaction is summarized. Literature on the field performance of prestressed concrete bridges and relevant experimental studies of corrosion in prestressed concrete is included. Crack prediction methods for prestressed concrete members are presented.