The study is a comparative desk study of the application of the vertical earth load, traffic live load and the nominal earth pressure in the design methodology of culverts as outlined in TMH7 – Code of Practice for the design of highways bridges and culverts in South Africa Part 2, AASHTO LRFD Bridge Design specification and the DMRB volume 2 section 2 part 12 - BD31/01. It involves the theoretical design and analysis of five single cell reinforced concrete box culverts ranging from 2.1m to 6.0m under different fill depths ranging from 0 to 8.0m by applying load obtained using the three design manuals. The objective of this study is to analyze the methodology involved in estimating vertical earth load on a culvert as outlined in the design manuals to ascertain relevance of the formulae and procedure in TMH7 or/and to recommend the most effective approach for evaluating the vertical earth load on box culverts specific and appropriate for South Africa. By comparing the load derivation methodology outlined in ASHTO LRFD and BD 31/01 and analyzing the load forces obtained from the analysis. Box culverts are designed as rigid monolithic structures to withstand the maximum bending moment and shear force. The design involves the analysis of the various loads acting on the culvert with the weight of the overhead earth embankment being the most significant. The vertical earth load, live load and the lateral earth pressure acting on the culverts at various fill depth are manually derived from equations as outlined in the three design manuals. The culverts are modelled and analyzed in Prokon as two-dimensional plane frame structures using the frame analysis module by applying this load to determine maximum positive hogging moments, maximum negative sagging moments and maximum positive shear forces for each span for the top slab. The load forces obtained for each span are then plotted against the soil cover depth to illustrate the discrete load effect of the vertical earth load and live load on the culverts at varying fill height and to determine the relationship between the culvert geometry, soil cover depth and the applied load. The result of the analysis shows that an increasing non-linear relationship exists between the load effects, the soil cover depth, and the span length. The dead load effect increases with increasing fill depth and culvert span while the live load effect diminishes with increasing fill height and culvert span i.e., for culverts buried at shallow depths, the traffic live load is the most critical load but as the height of the soil cover increases the dead load becomes more significant until a point is reached where the live load is totally insignificant. The vertical earth loads obtained from TMH7 and BD31/01 are constant at a particular fill depth for each culvert despite the different span length. The vertical earth load for these two manuals is estimated from the soil cover depth and density, the load tabulated clearly is independent of the culvert geometry. The load obtained from AASHTO LFRD is the lowest and less than 20% of the load obtained from the other two design manuals. Unlike TMH7 and BD31/01, AASHTO LFRD considers the effect of the soil-structure interaction to adjust the vertical earth load on the structure which automatically reduces the load value. The vertical earth load values obtained from TMH7 and BD31/01 are generally more conservative as compared to those obtained from AASHTO LFRD.

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No description available.

No description available.

La presente investigación tiene como objetivo principal evaluar la influencia del CBR en el terreno de fundación vial limo arcilloso para determinar espesores de mejoramiento mediante modelos elásticos y la metodología AASHTO 1993. Se evaluaron 21 sectores críticos en la zona de estudio mediante ocho criterios geotécnicos. Se determinó que los materiales evaluados son inadecuados, por lo tanto, no son aptos para asegurar la estabilidad de la estructura del pavimento. Para estabilizar el terreno de fundación se eligió la técnica de reemplazo de material con un CBR de 20%. Se determinaron los espesores razonables de mejoramiento utilizando un enfoque de diseño empírico-mecanicista. Para ello, se utilizó los modelos matemáticos de la teoría elástica propuesto por Boussinesq, Burmister y Odemark para determinar las respuestas mecánicas de la estructura. Estos se han limitado mediante parámetros admisibles para evitar el fallo de la estructura durante el periodo de diseño. Se ha realizado un análisis comparativo entre los espesores de mejoramiento obtenidos según los modelos elásticos y la metodología AASHTO 1993. Se encontró que los espesores de mejoramiento determinados con el modelo de Odemark y la metodología AASHTO son similares para un CBR de 1.9% a 2.2%. Sin embargo, entre la metodología AASHTO con los modelos de Burmister y Boussinesq hay una diferencia que oscila hasta en un 25%. Así mismo, a partir de un CBR>3.5%, los espesores de mejoramiento se van equiparando, evidenciándose una similitud entre las metodologías aplicadas. Los resultados mostraron que el incremento del CBR tiene una influencia significativa en la profundidad de mejoramiento. / The main objective of this research is to assess the influence of CBR in the silty-clayey road foundation ground to determine the improvement depth of subgrade soil using elastic models and AASHTO 1993 methodology. Twenty-one critical sectors in the study area were evaluated using eight geotechnical criteria. It was determined that the materials evaluated are inadequate, therefore, they are not suitable to ensure the stability of the pavement structure. To stabilize the foundation ground, the material replacement technique with a CBR of 20% was chosen. Reasonable improvement depth of subgrade soil were determined using an empirical-mechanistic design approach. For this purpose, the mathematical models of the elastic theory proposed by Boussinesq, Burmister and Odemark were used to determine the mechanical responses of the structure. These have been limited by admissible parameters to avoid failure of the structure during the design period. A comparative analysis has been made between the improvement depth of subgrade soil obtained according to the elastic models and the AASHTO 1993 methodology. It was found that the improvement depth of subgrade soil determined with the Odemark model and the AASHTO methodology are similar for a CBR of 1.9% to 2.2%. However, between the AASHTO methodology and the Burmister and Boussinesq models there is a difference of up to 25%. Also, from a CBR>3.5%, Improvement depth of subgrade soil become equal, showing a similarity between the applied methodologies. The results showed that the increase in CBR has a significant influence on the improvement depth of subgrade soil. / Tesis

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.

The coefficient of thermal expansion (CTE) is one of the major factors responsible for distresses in concrete pavements and structures. Continuously reinforced concrete pavements (CRCPs) in particular are highly susceptible to distresses caused by high CTE in concrete. CRCP is a popular choice across the U.S. and around the world for its long service life and minimal maintenance requirements. CRCP has been built in more than 35 states in the U.S., including Texas. In order to prevent CRCP distresses, the Texas Department of Transportation (TxDOT) has limited the CTE of CRCP concrete to a maximum of 5.5 x10-6 strain/oF (9.9 x10-6 strain/oC). Coarse aggregate sources that produce concrete with CTE higher than the allowable limit are no longer accepted in the TxDOT CRCP projects. Moreover, CTE is an important input in the Mechanistic-Empirical Pavement Design Guide (MEPDG). Small deviations in input CTE can affect the pavement thickness significantly in MEPDG designs. Therefore, accurate determination of concrete CTE is important, as it allows for enhanced concrete structure and pavement design as well as accurate screening of CRCP coarse aggregates. Moreover, optimizing the CTE of concrete according to a structure’s needs can reduce that structure’s cracking potential. This will result in significant savings in repair and rehabilitation costs and will improve the durability and longevity of concrete structures. This study found that the CTEs determined from saturated concrete samples were affected by the internal water pressure. As a result, the TxDOT method yielded higher values than did the American Association of State Highway and Transportation Officials (AASHTO) method. To further investigate the effect of internal water pressure, an analytical model was developed based on the poroelastic phenomenon of concrete. According to the model, porosity, permeability, and the rate of temperature change are the major factors that influence the internal water pressure development. Increasing the permeability of concrete can reduce the internal water pressure development and can thus improve the consistency of measured CTE values. Preconditioning concrete samples by subjecting them to several heating and cooling cycles prior to CTE testing and reducing the rate of temperature change improved the consistency of the CTE test results. Concrete CTE can be reduced by blending low-CTE aggregates with high-CTE aggregates and reducing the cement paste volume. Based on these findings, a concrete CTE optimization technique was developed that provides guidelines for the selection of concrete constituents to achieve target concrete CTE. A concrete proportioning technique was also developed to meet the need for CTE optimization. This concrete proportioning technique can use aggregate from any sources, irrespective of gradation, shape, and texture. The proposed technique has the potential to reduce the cement requirement without sacrificing performance and provides guidelines for multiple coarse and fine aggregate blends. / text

No description available.

AASHTO LRFD requires the use of longitudinal stiffeners in plate girder webs when the web slenderness D/tw is greater than 150. This practice is intended to limit the lateral flexing of the web plate during construction and at service conditions. AASHTO accounts for an increase in the web bend buckling resistance due to the presence of a longitudinal stiffener. However, when the theoretical bend buckling capacity of the stiffened web is exceeded under strength load conditions, the Specifications do not consider any contribution from the longitudinal stiffener to the girder resistance. That is, the AASHTO LRFD web bend buckling strength reduction factor Rb applied in these cases is based on an idealization of the web neglecting the longitudinal stiffener. This deficiency can have significant impact on girder resistance in regions of negative flexure. This research is aimed at evaluating the improvements that may be achieved by fully considering the contribution of web longitudinal stiffeners to the girder flexural resistance. Based on refined FE test simulations, this research establishes that minimum size longitudinal stiffeners, per current AASHTO LRFD requirements, contribute significantly to the post buckling flexural resistance of plate girders, and can bring as much as a 60% increase in the flexural strength of the girder. A simple cross-section Rb model is proposed that can be used to calculate the girder flexural resistance at the yield limit state. This model is developed based on test simulations of straight homogenous girders subjected to pure bending, and is tested extensively and validated for hybrid girders and other limit states. It is found that there is a substantial deviation between the AISC/AASHTO LTB resistance equations and common FE test simulations. Research is conducted to determine the appropriate parameters to use in FE test simulations. Recommended parameters are identified that provide a best fit to the mean of experimental data. Based on FE simulations on unstiffened girders using these recommended parameters, a modified LTB resistance equation is proposed. This equation, used in conjunction with the proposed Rb model also provides an improved handling of combined web buckling and LTB of longitudinally stiffened plate girders. It is observed that the noncompact web slenderness limit in the Specifications, which is an approximation based on nearly rigid edge conditions for the buckling of the web plate in flexure is optimistic for certain cross-sections with narrow flanges. This research establishes that the degree of restraint at the edges of the web depend largely on the relative areas of the adjoining flanges and the area of the web. An improved equation for the noncompact web slenderness limit is proposed which leads to a better understanding and representation of the behavior of these types of members.