This thesis investigates the impact of interface surface treatment methods for use in the Virginia Inverted T-Beam bridge system. The specific system consists of precast beams with thin bottom flanges placed next to one another, with a cast-in-place slab on top. Previous research has shown that the strength of this system after cyclic loading is highly dependent upon the shear strength of the interface between the precast and cast-in-place sections, especially for the adhesion-based connection configuration. The approval of this bridge system for use in bridges with high daily traffic volumes hinges on the verification of its strength and durability for a 50-year lifespan. The shear strength of ten different surface textures was tested using push-off tests to determine which interface roughening methods would prove adequate for use in the bridge system. The strength was found to depend on both the amplitude and the geometry of the undulations on the beam-to-slab interface. Using this information, a texture was selected for a new trial of the adhesion-based connection configuration, and a test specimen was constructed. After completing cyclic loading to simulate the design life of the bridge, it was found that the system achieved a strength similar to previous monotonically loaded specimens. It was concluded that the bridge is safe for use in high daily traffic areas provided that a surface roughening with adequate shear strength is used. / Master of Science

The inverted-T bridge system is a rapid bridge construction technique that consists of precast inverted-T girders placed adjacent to one another and covered with a cast-in-place deck. This system was first implemented in the U.S. by the Minnesota Department of Transportation (Mn/DOT). This research focuses on improving the constructability of the Mn/DOT system while maintaining the system's structural performance characteristics. To accomplish this goal, five sub-assemblage specimens were cast and tested in the structures laboratory at Virginia Tech. These tests focused on identifying an improved precast girder geometry and transverse sub-assemblage connection for this system. From this study it was found that all of the proposed specimens behaved adequately at service load and strength. From these results, it is recommended to further evaluate a specimen with a tapered profile and no physical connection between precast girders for use in a Virginia Department of Transportation bridge near Richmond, VA. / Master of Science

Lap splices are used in reinforced concrete structures to transfer tension forces across discontinuous reinforcing bars to allow for continuity of load path in structural elements. Lap splices of straight reinforcing bars present a number of disadvantages when used in connections of large precast concrete elements typical of bridge substructure. Most importantly, lap splices of large (e.g., No. 11) straight bars are substantially long. Since the closure joint connecting two precast elements must be at least long enough to fit the lap splice, traditional lap splices result in impractically large closure joints, offsetting the benefits of using precast concrete elements. To address this problem, bridge designers are using hooked bars in noncontact lap splices to connect precast elements, presuming that hooked bars will allow for shorter required splice lengths. However, there exists neither substantial design guidance nor studies of the behavior of hooked bar lap splices in large precast elements justifying this design philosophy. To develop design guidance permitting the use of noncontact hooked bar lap splices and address the knowledge gap regarding the behavior of such splices, an extensive experimental and computational research program was conducted which is described in this dissertation. Fifty-eight large-scale beam-splice specimens containing hooked bar lap splices were tested to physically study the behavior of hooked bar lap splices and develop a dataset to justify design guidance permitting the use of such splices in practice. Bond variables were parametrically varied among the test specimens to produce guidance applicable over the wide range of geometric configurations and material properties expected in bridge design. The specimens were subjected to monotonic, four-point loading and were designed to fail in a mode related to anchorage to study splice behavior. Nonlinear finite element analyses were conducted to examine the mechanism of force transfer in hooked bar lap splices and numerically assess splice configurations not experimentally studied. A simple approach to modelling hooked reinforcing bars in solid concrete elements which accounts for conditions of imperfect bond was developed and validated using the experimental results. Test results from the 58 specimens were used to assess the appropriateness of using existing guidance for hooked bar anchorages to design hooked bar lap splices. Because the existing guidance was found to be deficient for this application, descriptive and design equations characterizing hooked bar lap splices were developed using power regression analyses. The results demonstrated that all else being equal, a bottom-cast hooked bar lap splice can develop approximately 40% greater stress than contact lap splices of straight bars. Accordingly, hooked bars can be used to splice bars over a substantially shorter length than straight bars. Noncontact hooked bar lap splices without secondary reinforcement (e.g., ties) can fail due to a mode termed "hook side bulging", resulting from eccentricity between the lapped bars. Splices with secondary reinforcement typically fail due to more typical modes observed in the literature, such as side-face blowout and concrete crushing. Unlike as suggested by code authorities and some researchers for noncontact lap splices of straight bars, noncontact hooked bar lap splices were found to exhibit weaker splice strengths than contact splices as the splice spacing increased. The use of steel fibers and increases in lap length, concrete compressive strength, cover depth, amount of secondary reinforcement, or the number of lap splices allowed for greater stress on average to be developed in spliced bars. All else being equal, an increase in either bar size or the number of spliced reinforcement layers decreased the stress that could be developed in the spliced bars. A descriptive equation characterizing splice strength with an average test-to-calculation ratio and coefficient of variation of 6% was developed. The descriptive equation was adapted to develop a design equation for the minimum required lap length of hooked bars which uniformly characterizes the influence of the bond variables over the ranges explored in this study. Design examples and code language facilitating technology transfer of the design equation into immediate practice were developed. / Doctor of Philosophy / Precast concrete is widely used in highway bridges to enable more rapid and economical construction than could be achieved using cast-in-place concrete. However, the connection of two or more precast, prefabricated bridge elements introduces several difficulties which may inhibit construction, thereby reducing overall economy. One of the most significant difficulties is that connections of substructure elements supporting the superstructures are impractically long using a common, code-approved detail―lap splices of straight reinforcing bars. Such splices are quite long (e.g., 5 ft in length) since large bars are typically used in substructure elements, requiring long splice lengths to transfer the large forces in each bar across the connection. Details which would shorten the required splice length would consequently reduce the required connection length, thereby reducing the amount of cast-in-place concrete construction required in the field. Consequently, the speed of construction, economy, and worker safety would increase. This dissertation thus summarizes an extensive experimental and numerical study aimed at validating the use of noncontact hooked bar lap splices to shorten the required splice length of large precast elements. In support of this objective, the anchorage behavior of noncontact hooked bar lap splices was studied through static load testing of 58 large-scale beam-splice specimens and nonlinear finite element models accounting for bond-slip behavior. These efforts revealed that hooked bar lap splices can develop on average approximately 40% more stress over the same lap length than contact splices of straight bars. Existing design provisions which might presently be used to design hooked bar lap splices were evaluated against the experimental results and were found to be deficient in characterizing splice strength. Thus, a design equation was developed for the splice length of hooked bars which accurately characterizes anchorage behavior and allows for significantly shorter splices lengths than what could be achieved with straight bars.

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.

Accelerated bridge construction (ABC) has become a popular alternative to using traditional construction techniques in new bridge construction and existing bridge deck replacement because of the reduction of time spent in field activities. A key feature of bridges built using ABC techniques is the extensive use of prefabricated components. Prefabricated components are joined in the field using small volume closure pours involving high performance materials (steel and concrete) to ensure adequate transfer of forces between components. To date, the materials developed for closure pours have been based on proprietary components, so a need has arisen for development of mixes that use generic components. The goal of this research was to create a method to develop concrete mixtures that are designed using generic constituents and that satisfy performance requirements of accelerated bridge construction closure pours in New England, primarily high early strength and long-term durability. Two concrete mixtures were developed with a primary goal of reaching high-early strength while maintaining constructability. The secondary goal of the concrete mixtures was to be durable; therefore, measures were taken during the development of the concrete mixture to generate a mixture that also had durable properties.