Browsing by Subject "Structural engineering"
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Item Shear database for prestressed concrete members(2011-05) Nakamura, Eisuke; Bayrak, Oguzhan, 1969-; Jirsa, James O.Development of shear databases attracted a great deal of attention in the shear research community within the last decade. Although a few shear databases have already been developed by several research groups, there is no comprehensive shear database that is focused on prestressed concrete members. This thesis aims to develop a shear database for prestressed concrete members with an intensive literature review. This literature review resulted in a database that contained a total of 1,696 tests reported in North America, Japan, and Europe from 1954 to 2010. The database was used to evaluate shear design provisions available in North America, Japan, and Europe. The variations in measured versus calculated shear strength using twelve shear design equations were analyzed. The analysis results indicated that design expressions based on the Modified Compression Filed Theory (MCFT) produced the best performance to estimate the shear strength of prestressed concrete members with sufficient shear reinforcement. The MCFT-based design expressions, however, provided unconservative strength estimations for members that failed in shear but exhibited signs of horizontal shear damage and/or anchorage zone distress. The ACI 318-08 detailed method was found to be less conservative than the MCFT-based design expressions. Additionally, on the basis of a careful examination of test results included in the database, a new limit for the minimum shear reinforcement was proposed. The database was also used to investigate the shear behavior of prestressed concrete members. This investigation revealed that there was no evidence of size effect in the shear strength of prestressed concrete members with sufficient shear reinforcement. Additionally, it was found that prestress force and shear reinforcement increased the shear strength although there was an upper limit on the effectiveness of shear reinforcement.Item Simplified modeling of shear tab connections in progressive collapse analysis of steel structures(2010-05) Heumann, Eric Michael, 1985-; Williamson, Eric B., 1968-; Engelhardt, Michael D.Recent tragedies involving the collapse of several large and prominent buildings have brought international attention to the subject of progressive collapse, and the field of structural engineering is actively investigating ways to better protect structures from such catastrophic failures. One focus of these investigations is the behavior and performance of shear tab connections in steel structures during progressive collapse events. The shear tab, a simple connection, is typically modeled as a perfect pin in standard design, but in progressive collapse analysis, a much more accurate model of its true behavior and limits is required. This report documents the development of a simple yet accurate shear tab model and its use in understanding the behavior and limits of shear tab connections in column removal scenarios. Particular attention is paid to the connections’ axial force limit state, an aspect of behavior that is typically unimportant in standard design.Item Stress monitoring and sweep control studies for innovative prestressed precast arches(2012-08) Blok, Joel Phillip; Bayrak, Oguzhan, 1969-; Helwig, Todd Aaron, 1965-The Texas Department of Transportation (TxDOT) has completed the design of a signature bridge in Fort Worth, TX. The proposed structure is comprised of precast, post-tensioned concrete network arches. The arches will be cast on their sides and then rotated into the vertical orientation. Concerns exist about the durability and stability of the arches during stressing, handling, and transportation. The rotation process in particular represents a critical period in the life of the arches. A monitoring system was proposed to track stresses in the arches throughout the construction operations. The primary goals of the project are to install vibrating wire gages (VWGs) in the arches prior to casting to monitor the performance of the arches until the bridge is completed. The instrumentation will be used to provide real-time feedback to TxDOT and the contractor during stressing, handling, and bridge construction. This thesis focuses on the results of a preliminary laboratory study conducted in support of the instrumentation initiative. The purpose of the study was two-fold: to establish the capabilities and limitations of the VWGs and to study the buckling behavior of slender concrete elements with unbonded post-tensioning. More than sixty axial load tests were performed on two slender concrete specimens instrumented with VWGs. Observations are made on the accuracy and reliability of the VWGs. In general, the VWGs were found to be both accurate and reliable in measuring structural parameters and reporting trends in behavior, even at low loads. Some apparent errors were identified, but these were attributed to testing inconsistencies and scale factors rather than to gage error. Observations were also made on the buckling behavior of the elements under a variety of axial loading configurations. The effects of the engagement of the tensioned strand with the duct had a significant impact on the behavior. Strand engagement was shown to increase the buckling capacity of the members through stiffening action, but did not necessarily eliminate the risk of instability. Both the gage resolution study and the stability tests are expected to significantly enhance the ability of the research team to support the arch construction operations.Item The structural mechanics behavior of sealed insulating glass units(Texas Tech University, 1985-05) Anderson, Jon BaxterAesthetically pleasing, glass sheathed buildings and insulating glass (IG) units have formed a combination that is at once attractive and efficient. The use of IG units has increased in all types of buildings construction. Typical IG units consist of two glass plates separated by a perimeter spacer of aluminum. The perimeter is then coated with a polymer sealant which seals the air between the glass plates and holds the unit together. Until recently, most IG units were designed on an experimental basis, primarily by improving the polymer seals that seal the unit and hold it together. Computational tools for examining IG units on a structural mechanics basis were not available. This document introduces a series of working and proposed models designed to meet this need. An examination of the need for research and development in the IG unit field is followed by a discussion of "global" and "local" models designed to examine IG unit behavior from a structural mechanics standpoint. The global model considers the response of the entire IG unit, while the local model focuses on smaller segments of the unit within the seal detail. Specifically, the local model examines the complex response of the boundary of the unit where the materials making up the unit seal (aluminum, glass, sealant) are in contact. Engineering properties of glass and aluminum are well defined, but those of sealants are dependent on polymer type, strain rate and stress relaxation. A method for finding the engineering properties of polymer sealants is presented. Finally, the local model is exercised in a series of parametric studies which examine the effect on component stresses caused by changes in environmental conditions, sealant modulus, spacer cross section, depth of perimeter sealant, and spacer aspect ratio. Potential additional uses of the local model are discussed. These discussions include the effect and modeling method for including the IG unit mounting system such as a mechanical or dry neoprene gasket and a polymer " structural " seal.Item Wind load factors for Atlantic and Gulf Coast hurricane winds(Texas Tech University, 1998-08) McAnulty, John NWith the recent increase of technology and the understanding of wind effects and reliability analysis, studies have begun to re-examine the wind load criteria used in the ASCE 7-95 Standard. In this standard, an unresolved issue about the wind load factor surrounding Load and Resistance Factor Design (LRFD) exists. The current edition of ASCE 7-95 contains a load factor for winds, but the load factor was derived using wind statistics from sites that are generally not subjected to hurricanes. Instead, hurricane wind properties are accounted for in a hurricane coast importance factor. In this research, U.S. Gulf and East coasts hurricane wind loads are considered specifically to develop a partial wind load factor for hurricane winds that may differ from the current wind load factor. The philosophy used to development the wind loads in this research follows that of Ellingwood et al. (1980). This is the same philosophy that is used as the framework for implementing reliability methods into U.S. building codes. This research utilizes the most recent Monte Carlo simulation program along with the model of the analytical-empirical profile model of Holland (1980) in simulating hurricanes. Two different hurricane wind speed distribution types are considered, and the wind loads are calculated based on the most recent values and probability distribution functions of the wind load parameters that were available in 1997