The composite action of a bridge deck and girder is essential to the optimization of the superstructure. The transfer of forces in the deck to the girders is done across a shear interface between the two elements. The transfer occurs through the cohesion of the concrete at the interface and then through the shear reinforcement across the interface. Adequate shear strength is essential to the success of the superstructure. A collection of 537 horizontal shear tests comprised the database for the study of various concrete types and interface surface treatments. The predicted horizontal shear strength calculated from the AASHTO LFRD bridge design code was compared to the measured shear strength. The professional bias was computed for each specimen. The professional biases, standard deviations, and coefficients of variation for each category were calculated. The material properties factor along with fabrication factor was researched. The loading factors were researched and calculated for use in calculating the reliability index. The final step was to compute the reliability index for each category. The process was repeated to learn the reliability of the equation proposed by Wallenfelsz. The results showed that the reliability index for the AASHTO LRFD horizontal shear strength equation wash much lower than the desired target reliability index of 3.5. The reliability index for the Wallenfelsz equation was higher but still not close to the target reliability index. / Master of Science

Ultra high performance concrete, specifically Ductal® concrete, has begun to revolutionize the bridge design industry. This extremely high strength material has given smaller composite sections the ability to carry larger loads. As the forces being transferred through composite members are increasing in magnitude, it is vital that the equations being used for design are applicable for use with the new materials. Of particular importance is the design of the horizontal shear reinforcement connecting the bridge deck to the top flange of the beams. Without adequate shear transfer, the flexural and shearing capacities will be greatly diminished. The current design equations from ACI and AASHTO were not developed for use in designing sections composed of Ductal® and Lightweight concrete. Twenty-four push-off tests were performed to determine if the current horizontal shear design equations could accurately predict the horizontal shear strength of composite Ductal® and Lightweight concrete sections. Effects from various surface treatments, reinforcement ratios, and aspect ratios, were determined. The results predicted by the current design equations were compared to the actual results found during testing. The current design equations were all found to be conservative. For its ability to incorporate various cohesion and friction factors, it is recommended that the equation from AASHTO LRFD Specification (2004) be used for design. / Master of Science

Full-depth precast panels are used in concrete bridges to provide several benefits such as faster construction, lower cost and reduced constructional hazard. However, one construction drawback is that connectors are required to transmit horizontal shear across the interface between the girder and deck. Shear connector performance is characterized by a series of experiments performed on part of a bridge system that mimics a full-depth precast deck on concrete girder with a pocket-connector-haunch system. Following initial breakaway of the adhesive bond within the haunch region, the specimens slide with frictional resistance provided by the clamping force of the anchor bolt. This leads to bolt yield with an observed sliding friction coefficient of 0.8 (+/- 20%) with lower values occurring at higher displacements. It is concluded that for a viable connector system to be developed a key feature is to have sufficient stirrups in the neighborhood of the anchor bolt to form a non-contact splice and to ensure the high pull-out force can be sustained without leading to premature beam failure. The successful implementation of a full-depth precast deck-panel system requires the use of a viable design methodology that properly accounts for system behavior. The design of a deck-haunch-girder system uses a truss modeling approach to design for the shear forces created by service loading. The truss model approach is considered more suitable for a concrete member due to the premise that the member will be substantially cracked at an ultimate limit state and that traditional beam theory does not account for the decreased ability of shear stresses to transfer across open cracks. Experimental results from Chapter II, such as the friction coefficient mu, are used along with a previously developed crack angle model to layout the geometry of the truss within a deck-panel span. Design solutions are presented utilizing the Rock Creek Bridge in Parker County, Texas as an example structure.

The full-width, full-depth precast panel system is very convenient for rehabilitation of deteriorated decks as well as for new bridge construction. The horizontal shear strength at the interface between the two interconnected elements is of primary importance in order to provide composite action. The strength of the bond between the two precast members should be high enough to prevent any progressive slip from taking place. Flexural strength, shear strength and deflection characteristics all depend on the satisfactory performance of the interface to provide composite action. However, the case when both of the interconnected elements are precast members bonded by means of grout, is not currently addressed by ACI or AASHTO. This is the main impetus for this project. A total of 36 push-off tests were performed to develop a method for quantifying horizontal shear strength and to recommend the best practice for the system. Test parameters included different haunch heights, different grout types, different amount and different type of shear connectors. Two equations, for uncracked and cracked concrete interfaces, are proposed to be used in horizontal shear design when the precast panels are used. Predictive equations are compared with available methods for the horizontal shear strength of the precast panel system. Conclusions and recommendations for the optimum system are made. / Master of Science

The Texas U-Beam standard designs were released in the 1990’s and have been used increasingly in bridges across the state since. While prototypes of the 54-in. deep prestressed concrete beam were built during the design phase, no full-scale load tests were performed. This study of the U-Beam had five goals: (i) determine the magnitude and location of stresses induced in reinforcing bars in the end region of the beam at prestress transfer, (ii) measure concrete curing temperatures in square and skewed end blocks, (iii) establish the vertical shear capacity of the standard section, (iv) evaluate interaction between behavior at prestress transfer and performance under shear-critical loads, and (v) identify design and detailing improvements and make recommendations. Eight full-scale Texas U54 prestressed concrete beams were fabricated to achieve these goals. Load testing of the first four of these beams revealed a critical weakness along the bottom flange-to-web interface of the beam. The weakness caused failures that occurred at loads well below the calculated shear capacity. Given the horizontal sliding observed, the failure mode was called horizontal shear. The next two beams were fabricated to test three modifications to the end-region design, two of which were deemed successful. The final two beam sections tested contained the recommended new standard reinforcement and concrete geometry. A method to evaluate the horizontal shear demand on and capacity of the bottom flange-to-web interface of prestressed concrete beams was developed. The calculations were formulated using the theories of beam bending and shear friction. This method was calibrated and verified using the U-Beam test data, a series of small-scale specimens, and results of shear tests in the literature. Stresses induced in reinforcing bars at prestress transfer met expectations set by existing codified equations. No modifications to the current U-Beam standard design are needed to manage these stresses. The induced stresses did not influence vertical shear behavior, and no interaction between the two is believed to exist for U-Beams. This dissertation contains the specifics of the beams tested and the data collected, and provides the details of recommended changes to the Texas U-Beam standard drawings. / text

Full-depth precast deck panels are a promising alternative to the conventional cast-in-place concrete deck. They afford reduced construction time and fewer burdens on the motoring public. In order to provide designers guidance on the design of full-depth precast slab systems with their full composite strength, the horizontal shear resistance provided at the slab-to-beam interface must be quantified through further investigation. Currently, all design equations, both in the AASHTO Specifications and the ACI code, are based upon research for cast-in-place slabs. The introduction of a grouted interface between the slab and beam can result in different shear resistances than those predicted by current equations. A total of 29 push off tests were performed to quantify peak and post-peak shear stresses at the failure interface. The different series of tests investigated the surface treatment of the bottom of the slab, the type and amount of shear connector and a viable alternative pocket detail. Based on the research performed changes to the principles of the shear friction theory as presented in the AASHTO LRFD specifications are proposed. The proposal is to break the current equation into two equation that separate coulomb friction and cohesion. Along with these changes, values for the coefficient of friction and cohesion for the precast deck panel system are proposed. / Master of Science

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 horizontal shear strength of the interface between prestressed concrete hollow core slabs and cast-in-place concrete topping slabs was evaluated through a set of 24 push-off experiments. The push-off test specimens featured segments of dry-mix and wet-mix hollow core slabs with a variety of surface treatments including machine finished, sandblasted, broom roughened, rake roughened and grouted. A cast-in-place slab was poured on top of the hollow core specimens to form a 15 inch by 15 inch interface between the two materials. Results indicate the average horizontal shear strength of the push-off specimens was 227 psi. Higher shear strength and slip capacity was observed in specimens that were broom roughened in the direction transverse to the applied shear force and in grouted dry-mix specimens. Specimens with machine finished surfaces had lower average horizontal shear strength than those with intentionally roughened surfaces, but still exceeded the shear strength of 80 psi specified in the ACI 318-08 code. A method to comparatively quantify the surface roughness of the hollow core slabs with different surface treatments was adapted from an existing ASTM standard for pavements. This standard specifies the procedure to determine mean texture depth that can be correlated to horizontal shear strength of the push-off specimens. Analytical studies were also performed to estimate the maximum horizontal shear stresses that can be expected in composite hollow core slabs under normal construction conditions. A finite element model was developed to observe the behavior of the horizontal shear failure mode for composite hollow core slabs.

Precast girders and cast-in-place decks are a typical type of concrete bridge construction. A key part of this type of construction is developing composite action between the girder and deck. In order to develop composite action, adequate horizontal shear resistance must be provided at the interface. As lightweight concrete is increasingly being used in bridge designs, it is important to understand the horizontal shear behavior of lightweight concrete. The current AASHTO LRFD Specification provides design equations for horizontal shear strength of both lightweight and normal weight concrete. Thirty-six push-off tests were performed to determine if the current code equations accurately predict the horizontal shear strength of precast girders and cast-in-place decks for both normal weight and lightweight concrete. The different test series investigated effects from lightweight and normal weight concrete used for the girder/slab combination and the quantity of shear reinforcement provided across the interface. The test results were compared to the results predicted by current design equations. A structural reliability analysis was performed and the test-to-predicted statistics were used to define LRFD resistance factors and quantify the probability of failure. The current design equations were found to be conservative and more conservative for lightweight concrete than for normal weight concrete. / Master of Science

Knots are usually regarded as defects when grading lumber. In order to evaluate a member under out-of-plane loading, shear strength is one of the major mechanical properties, specifically, rolling shear (RS) strength is one of the critical mechanical properties of Cross-Laminated Timber (CLT), which determines the flexural strength of CLT under short-span bending loads. Lower grade lumber with a higher percentage of knots is recommended to be utilized for the cross-layer laminations which are mainly responsible for resisting shear stresses. Firstly, shear tests were performed in order to evaluate the effect of knots on longitudinal shear strength using shear blocks. After that, the effect of knots on the RS strength of 3-ply southern yellow pine CLT were investigated by experimental tests and an analytical model. Center-point bending tests with a span-to-depth ratio of 6 and two-plate shear tests with a loading angle of 14° were conducted on six CLT configurations composed of different types of cross layer laminations: clear flatsawn lumber with/without pith, lumber with sound knots with/without pith, and lumber with decayed knots with/without pith. The shear analogy method was implemented to evaluate the RS strength values from the bending test results, which were also compared against the results from the two-plate shear tests. It was found that: (1) The shear blocks containing sound knots had higher shear strength than matched clear shear blocks, the shear blocks containing unsound knots had lower shear strength than the matched clear shear blocks. (2) CLT specimens with cross-layer laminations with either sound knots or decayed knots had higher RS strength. (3) In general, the shear analogy method underestimated the RS strength of CLT specimens containing knots and pith.