Millions of square feet of mechanically stabilized earth retaining wall are constructed annually in the United States. When used in highway fill applications in conjunction with bridges, these MSE walls are typically constructed with a roadside barrier system supported on the edge of the wall. This barrier system generally consists of a traffic barrier or bridge rail placed on a continuous footing or structural slab. The footing is intended to reduce the influence of barrier impact loads on the retaining wall system by distributing the load over a wide area and to provide stability for the barrier against sliding or overturning. The proper design of the roadside barrier, the structural slab, and the MSE wall system requires a good understanding of relevant failure modes, how barrier impact loads are transferred into the wall system, and the magnitude and distribution of these loads. In this study, a procedure is developed that provides guidance for designing: 1. the barrier-moment slab, 2. the wall reinforcement, and 3. the wall panels. These design guidelines are developed in terms of AASHTO LRFD procedures. The research approach consisted of engineering analyses, finite element analyses, static load tests, full-scale dynamic impact tests, and a full-scale vehicle crash test. It was concluded that a 44.5 kN (10 kips) equivalent static load is appropriate for the stability design of the barrier-moment slab system. This will result in much more economical design than systems developed using the 240 kN (54 kips) load that some user agencies are using. Design loads for the wall reinforcement and wall panels are also presented.

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

Self-consolidating concrete (SCC) is a new, innovative construction material that can be placed into forms without the need for mechanical vibration. The mixture proportions are critical for producing quality SCC and require an optimized combination of coarse and fine aggregates, cement, water, and chemical and mineral admixtures. The required mixture constituents and proportions may affect the mechanical properties, bond characteristics, and long-term behavior, and SCC may not provide the same inservice performance as conventional concrete (CC). Different SCC mixture constituents and proportions were evaluated for mechanical properties, shear characteristics, bond characteristics, creep, and durability. Variables evaluated included mixture type (CC or SCC), coarse aggregate type (river gravel or limestone), and coarse aggregate volume. To correlate these results with full-scale samples and investigate structural behavior related to strand bond properties, four girder-deck systems, 40 ft (12 m) long, with CC and SCC pretensioned girders were fabricated and tested. Results from the research indicate that the American Association of State Highway Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) Specifications can be used to estimate the mechanical properties of SCC for a concrete compressive strength range of 5 to 10 ksi (34 to 70 MPa). In addition, the research team developed prediction equations for concrete compressive strength ranges from 5 to 16 ksi (34 to 110 MPa). With respect to shear characteristics, a more appropriate expression is proposed to estimate the concrete shear strength for CC and SCC girders with a compressive strength greater than 10 ksi (70 MPa). The author found that girder-deck systems with Type A SCC girders exhibit similar flexural performance as deck-systems with CC girders. The AASHTO LRFD (2006) equations for computing the cracking moment, nominal moment, transfer length, development length, and prestress losses may be used for SCC girder-deck systems similar to those tested in this study. For environments exhibiting freeze-thaw cycles, a minimum 16-hour release strength of 7 ksi (48 MPa) is recommended for SCC mixtures.

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Master of Science / Department of Civil Engineering / Asadollah Esmaeily / The shear and combined shear and torsion provisions of the AASHTO LRFD (2008) Bridge Design Specifications, as well as simplified AASHTO procedure for prestressed and non-prestressed reinforced concrete members were investigated and compared to their equivalent ACI 318-08 provisions. Response-2000, an analytical tool developed based on the Modified Compression Field Theory (MCFT), was first validated against the existing experimental data and then used to generate the required data for cases where no experimental data was available. Several normal and prestressed beams, either simply supported or continuous were used to evaluate the AASHTO and ACI shear design provisions In addition, the AASHTO LRFD provisions for combined shear and torsion were investigated and their accuracy was validated against the available experimental data. These provisions were also compared to their equivalent ACI code requirements. The latest design procedures in both codes propose exact shear-torsion interaction equations that can directly be compared to the experimental results by considering all ϕ factors as one. In this comprehensive study, different over-reinforced, moderately-reinforced, and under-reinforced sections with high-strength and normal-strength concrete for both solid and hollow sections were analyzed. The main objectives of this study were to: • Evaluate the shear and the shear-torsion procedures proposed by AASHTO LRFD (2008) and ACI 318-08 • Validate the code procedures against the experimental results by mapping the experimental points on the code-based exact interaction diagrams • Develop a MathCAD program as a design tool for sections subjected to shear or combined shear and torsion

Current seismic design approach of bridge structures can be categorized into two distinctive methods: (i) force based and (ii) performance based. AASHTO LRFD seismic design specification is a typical example of force based design approach especially used in Turkey. Three different importance categories are presented as &ldquo / Critical Bridges&rdquo / , &ldquo / Essential Bridges&rdquo / and &ldquo / Other Bridges&rdquo / in AASHTO LRFD. These classifications are mainly based on the serviceability requirement of bridges after a design earthquake. The bridge&rsquo / s overall performance during a given seismic event cannot be clearly described. Serviceability requirements specified for a given importance category are assumed to be assured by using different response modification factors. Although response modification factor is directly related with strength provided to resisting column, it might be correlated with selected performance levels including different engineering response measures. Within the scope of this study, 27216 single circular bridge column bent models designed according to AASHTO LRFD and having varying column aspect ratio, column diameter, axial load ratio, response modification factor and elastic design spectrum data are investigated through a series of analyses such as response spectrum analysis and push-over analysis. Three performance levels such as &ldquo / Fully Functional&rdquo / , &ldquo / Operational&rdquo / and &ldquo / Delayed Operational&rdquo / are defined in which their criteria are selected in terms of column drift measure corresponding to several damage states obtained from column tests. Using the results of analyses, performance categorization of single bridge column bents is conducted. Seismic responses of investigated cases are identified with several measures such as capacity over inelastic demand displacement and response modification factor.

El concepto moderno de la técnica de suelo reforzado data de inicios de la década de los 60. En el tiempo en que esta práctica viene siendo empleada y estudiada, ha gozado de gran popularidad debido a sus relativos bajos costos en comparación con sistemas tradicionales equivalentes, el grado de fiabilidad del sistema, su aspecto y su diversidad arquitectónicos. En el año 2001, la Federal Highway Administration de Estados Unidos desarrolló el manual de diseño y construcción de muros TEM, actualmente FHWA-NHI-10-024 y FHWA-NHI-10-25, los cuales brindan instrucciones y recomendaciones para el diseño y construcción de estas estructuras, basados en las instrucciones de la norma AASHTO LRFD. Estas fuentes incluyen una serie de supuestos, entre los cuales se encuentra el asumir la base del muro como una cimentación equivalente. La norma AASHTO LRFD lo establece de la siguiente manera: “(…) se deberá asumir una cimentación equivalente cuya longitud sea la longitud del muro y cuyo ancho sea la longitud de la cinta de refuerzo al nivel de la fundación. Las presiones a soportar deberán ser modeladas empleando una distribución uniforme de carga en la base, aplicado en un ancho efectivo (B’= L-2e)”. AASHTO LRFD (2010). La presente investigación pretende analizar el modo como se realiza la transferencia de esfuerzos al suelo de fundación de un muro de suelo reforzado con el fin de verificar en que modo dicho supuesto es técnicamente correcto, así como analizar la posibilidad de reducir la extensión del refuerzo empleado por medio de una optimización del cálculo a través de un modelo más cercano a la realidad. Para ello, se pretende realizar un Análisis por Elementos Finitos empleando un Modelo Constitutivo que incorpore al modelo el comportamiento no-lineal del suelo, tanto para el material de relleno como para el suelo de fundación. / The modern concept of the reinforced earth technique dates to the early 1960s. In the time this practice has been used and studied, it has enjoyed great popularity due to its relatively low costs compared to equivalent traditional systems, the degree of reliability of the system, its architectural appearance and diversity. In 2001, the United States Federal Highway Administration developed the MSE wall design and construction manual, currently FHWA-NHI-10-024 and FHWA-NHI-10-25, which provide instructions and recommendations for the design and construction of these structures, based on the instructions of the AASHTO LRFD standard. These sources include a series of assumptions, among which is the assumption of the base of the wall as an equivalent foundation. The AASHTO LRFD standard states it as follows: “(…) An equivalent footing shall be assumed whose length is the length of the wall, and whose width is the length of the reinforcement strip at the foundation level. Bearing pressures shall be computed using a uniform base pressure distribution over an effective width (B ’= L-2e)”. AASHTO LRFD (2010). The present research aims to analyze the way in which stresses are transferred to the foundation soil of a reinforced soil wall to verify in which way that assumption is technically correct. As well as to analyze the possibility of reducing the extension of the reinforcement used, by means of an optimization of the calculation through a model closer to reality. To do this, it is intended to carry out a Finite Element Analysis using a Constitutive Model that incorporates the non-linear behavior of the soil into the model, both for the filling material and for the foundation soil. / Tesis

<p dir="ltr">Reinforced concrete elements are vulnerable to sliding against each other when shear forces are transmitted between them. Shear-friction is the mechanism by which shear is transferred between concrete surfaces. It develops by aggregate interlock between the concrete interfaces while reinforcement crossing the shear interface or normal force due to external loads contributes to the shear resistance. Current design provisions used in the United States (ACI 318-19, AASHTO LRFD (2020), and the PCI Design Handbook (2017)) include design expression for shear-friction capacity. However, the value of the reinforcement yield strength input into the expressions is limited to a maximum of 60 ksi. Furthermore, the concrete strength is not incorporated into the primary design expressions. These limits cause the potential contribution of high-strength reinforcement and high-strength concrete in shear-friction applications from being considered. Therefore, a research program was developed to investigate the possibility of improving current shear-friction design practice and addressing these current limits.</p><p dir="ltr">Specifically, an experimental program was conducted to evaluate the influence of high-strength reinforcement and high-strength concrete on shear-friction strength. In addition, a statistical analysis was performed using a comprehensive shear-frication database comprised of past tests available in the literature. The experimental program consisted of two phases. Phase I included 24 push-off specimens to study the influence of the yield strength of the interface reinforcement (Grade 60 and Grade 100) and the number and size of interface reinforcing bars (6-No.4 and 4-No. 5 bars) with three different interface conditions (rough, smooth, and shear-key). Phase II included 20 push-off specimens with rough interfaces to investigate the influence of the yield strength of the interface reinforcement (Grade 60 and Grade 100) and concrete strength (target strengths of 4000 psi and 8000 psi). The influence of these two variables was observed over a range of reinforcement ratios (ρ = 0.55%, 0.83%, 1.11%, and 1.38%).</p><p dir="ltr">The test results showed that the overall shear-friction strength was the greatest for rough interface specimens, followed by specimens detailed with shear keys. The smooth interface specimens had the lowest strengths. The results of both phases of the experimental program indicated that the use of high-strength reinforcement did not improve shear-friction capacity.</p><p dir="ltr">Furthermore, the results from the Phase II tests showed that increasing the concrete compressive strength led to increased shear-friction capacity. The test results from the experimental program were analyzed and compared with current design provisions, which demonstrated room for improvement of current design practice.</p><p dir="ltr">Following the experimental program, a comprehensive shear-friction database was analyzed, and multilinear regression was used to create a model to predict shear-friction strength. Factors were then applied to the model to provide acceptable design expressions for shear-friction strength (less than 5% unconservative estimates). The database was used to evaluate the factored model and current design provisions.</p><p dir="ltr">The research outcomes, especially the expressions for shear-friction strength that were developed and that include consideration of the concrete compression strength, along with the shear-friction tests demonstrating the lack of strength gain with the use of Grade 100 reinforcement, provide valuable information for the concrete community to help direct efforts toward improving current shear-friction design practice.</p>