This thesis introduces a new adjustment factor for the probability-based load and resistance factor (LRFD) design for wood structures. By investigating the empirical data of reaction forces for a wooden house built by the Forest Product Laboratory in 2001, it is found that the reaction values exhibit great variability. To explore the causes of this variability, a 3-D finite element model is built and analyzed using commercial software MSC/Nastran. It is found that differences in member geometry are a major cause of reaction variability. In examining the potential effect the reaction variability might have on the structural safety, reliability is assessed for two different types of wood products under several different situations. Finally, a new adjustment factor Ks, which accounts for the variability in load path, is obtained and validated based on structural reliability theory.

The research presented in this dissertation furthers the state of the art for reliability-based design of composite structures subjected to high cycle variable amplitude (spectrum) fatigue loads. The focus is on fatigue analyses for axially loaded fiber reinforced polymer (FRP) composites that contain a significant proportion of fibers in the loading direction and thus have fiber-direction dominated failure. The four papers presented in this dissertation describe the logical progression used to develop an improved reliability-based methodology for fatigue-critical design. Throughout the analysis extensive experimental fatigue data on several material systems was used to verify the assumptions and suggest the path forward. A comparison of 12 fatigue model approaches from the literature showed that a simple linear residual strength approach (Broutman and Sahu) provides an improvement in fatigue life prediction compared to the Palmgren-Miner rule, while more complex residual strength models did not consistently improve on Broutman and Sahu. Evaluation of the effect of load history randomness on fatigue life was made using experimental results for spectra in terms of the first order autocorrelation of the stress events. For approximately reversed Rayleigh distributed fatigue loading, load sequence was not critical in the material behavior. Based on observations of empirical data and evaluation of the micro-mechanics deterioration and failure phenomena of FRP composites under fatigue loading, a new residual strength model for the tension and compression under any load history was proposed. Then this model was implemented in a stochastic framework and a method was proposed to enable calculation of the load and resistance factor design (LRFD) parameters for realistic reliabilities with relatively few computations. The proposed approach has significant advantages over traditional lifetime-damage-sum-based reliability analysis and provides a significant step toward enabling more accurate reliability-based design with composite materials. / Ph. D.

La presente tesis elabora el diseño de un puente tipo losa y un puente viga losa de 12 metros de luz; específicamente el diseño del tablero, vigas de ser el caso, y los estribos configurados con muros de gravedad. Para el análisis y diseño de ambos puentes se emplea el método de la AASTHO – LRFD (American Associatión of State Highway Transportation Officials) - (Load, Resisten, Factor, Desing) donde se indica los estados límites de diseño y propone un vehículo denominado HL-93 que es un tipo de carga de diseño aplicado al tipo de estructuras de pistas que existe en Estados Unidos y en otros países, como es el caso de Perú.

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

Considerando la variedad de suelos que se encuentran en el territorio peruano, donde la capacidad portante del terreno dependerá de la historia y de la formación del suelo, es importante desarrollar la Ingeniería Geotécnica, más específicamente la estabilización de Taludes en zonas con riesgo de falla en línea con el crecimiento de las ciudades y los proyectos de infraestructura. Además, lo que se busca es solucionar dicha problemática considerando el tiempo, costo, durabilidad y conservación paisajística. Este trabajo de tesis presenta una propuesta para mitigar el riesgo de la falla Global en el acantilado de la costa verde-Chorrillos mediante muro de tierra mecánicamente estabilizado, siendo la característica del suelo un relleno no controlado, conformado por material de desmonte de las épocas en donde se construyeron las principales avenidas de la ciudad de Lima en los años 60. El muro comprende las herramientas necesarias para una propuesta de diseño con sistemas de estabilidad que considere las características geotécnicas, hidráulicas y topográficas de la zona. Es así que se parte del reconocimiento de la zona para definir los parámetros de entrada, además se presenta una descripción teórica de los elementos de la ingeniería geotécnica y su campo de aplicación. También, se hace un enfoque detallado del diseño en este tipo de estructuras a través de la metodología LRFD, con los factores necesarios para garantizar su estabilidad global. Finalmente se presenta un modelo estructural con la comprobación de los principales factores de seguridad mediante herramientas digitales de ingeniería: SOFTWARE MSEW y SLIDE 6.0 / Considering the great variety of soils found in the Peruvian territory, where the bearing capacity of the land will depend on the history and the formation of the soil, it is important to develop Geotechnical Engineering, more specifically the stabilization of Slopes in areas with risk of failure. in line with the growth of cities and infrastructure projects. In addition, what is sought is to solve this problem considering time, cost and durability, in addition to the landscape conservation of certain areas. This thesis work presents a proposal to mitigate the risk of the Global failure in the cliff of the Costa Verde-Chorrillos through a mechanically stabilized earth wall, the characteristic of the soil being an uncontrolled fill, made up of waste material from the times when the main avenues of the city of Lima were built in the 60s. The wall includes the necessary and adequate tools for a proposal for the design of stability systems that considers the geotechnical, hydraulic and topographic characteristics of the area. Thus, it starts with the recognition of the area to define the input parameters, in addition, a theoretical description of the elements of geotechnical engineering and its field of application is presented. Also, a detailed design approach is made in this type of structures through the LRFD methodology, with the necessary factors to guarantee their global stability. Finally, a structural model is presented with the verification of the main safety factors using digital engineering tools: SOFTWARE MSEW and SLIDE 6.0 / Tesis

The aim of this study is designing steel structures with the same geometry, material and soil conditions but in the different countries, and comparing these designs in terms of material savings. According to three steel building codes, namely TS 648, LRFD, Eurocode 3, same structures with various stories (2, 4, 6, 8, and 10) are analyzed and designed. To calculate the design loads, Turkish Earthquake Code 2007 and Turkish Standard 498 (Design Load for Buildings) are utilized when TS 648 is applied. When LRFD is concerned, ASCE Standard 7-05 (Minimum Design Loads for Buildings and Other Structures) and AISC Standard 341-05 (Seismic Provisions for Structural Steel Buildings) are used for calculation of the design loads and earthquake loads. When Eurocode 3 is applied, Eurocode 8 (Earthquake Resistance Code), Eurocode 1 (Actions of Structures) and Eurocode-EN 1990 (Basis of Structural Design) are used in order to determine the design and earthquake loads. Weight of steel used on 1 m&sup2 / is almost the same for procedures of LRFD and EC3. It is important to note that those procedures consider 20 % of material saving compared to TS648.

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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