Browsing by Author "Tasnim Hassan, Committee Member"

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Analysis of an Instrumented Jointless Bridge
(2003-04-09) Wing, Kenneth Michael; Mervyn Kowalsky, Committee Chair; Paul Zia, Committee Co-Chair; Tasnim Hassan, Committee Member
Costs of replacement and maintenance of expansion joints are often a large part of the costs associated with bridge maintenance. To replace these expansion joints or eliminate some of them on structures could greatly reduce the costs. Link slab is a new design approach, which could replace the traditional expansion joints. A link slab is the portion of the bridge deck that connects two adjacent simple-span girders. Link slabs also reduce the damage to the substructure of bridges due to water penetration and debris accumulation in the expansion joint. The objective of this research is to validate the design assumptions associated with designing link slabs, investigate a limit states design procedure and develop a program for the long-term monitoring of an instrumented link slab. This thesis provides details about testing and analysis, which were useful in accomplishing the research objectives. It also provides information about the datalogger software that was used in this project and also details the computer program that was written in Microsoft Excel to aid in the data collection and sorting.
Evaluation of Wood Properties of Genetically Modified Trees
(2007-03-14) Saralde, Teofisto Cis Jr.; Ilona Peszlen, Committee Co-Chair; Myron W. Kelly, Committee Member; Perry N. Peralta, Committee Co-Chair; Tasnim Hassan, Committee Member; Bohumil Kasal, Committee Member
Two related studies were conducted for the evaluation of wood properties of genetically modified loblolly pine (Pinus taeda): first in terms of mechanical properties and then for shrinkage properties. Another study focused on the development of methods for the evaluation of the mechanical properties of small young trees. In the first study, the effect associated with genetic modification of loblolly pine was evaluated by comparing the mechanical properties of lumber from trees deficient in cinnamyl alcohol dehydrogenase (CAD) enzyme with those from wild-type trees. Small clear wood specimens were tested in static bending, compression parallel and perpendicular to the grain, tension perpendicular to the grain, and shear parallel to the grain. Results indicated that there was no significant difference between the two genotypes for all mechanical properties measured. Consequently, partially CAD-deficient loblolly pine has no significantly altered mechanical properties. In the second study, partially CAD-deficient and wild-type loblolly pine were studied for shrinkage properties. Pie-shaped samples for the determination of radial and tangential shrinkages were cut from logs. The method allows for the measurement of shrinkage for different wood types and for correction due to the effect of growth ring curvature. Results showed that radial, tangential, and longitudinal shrinkages of juvenile wood were significantly different from the corresponding shrinkages of mature wood. In addition, no significant difference was observed in shrinkage properties between partially CAD-deficient and wild-type loblolly pine. The third study dealt with development of a method for evaluating mechanical properties of small young trees in static bending and compression parallel to the grain utilizing the full cross section of the tree. In the absence of an established test method, the approach was to start from ASTM standard test of small clear wood. The experiment was designed as a replicated 5-level Graeco-Latin square with tree, stem location, dimensional ratio of the test specimen, and test strain rate as factors. Span-to-depth ratio for bending, length-to-diameter ratio for compression, and strain rates were established as test variables based on the analysis of the result. Along the tree height, there was no significant difference in mechanical properties starting from the base to 0.45 of the total height of the tree.
Low Cycle Fatigue Life Prediction of Four Bolt Extended Unstiffened End Plate Moment Connections
(2009-08-10) Lim, Chemin; Sami Rizkalla, Committee Co-Chair; Emmett Sumner, Committee Chair; Jeffrey Eischen, Committee Member; Tasnim Hassan, Committee Member
The end plate moment connection has been studied with various design concepts. However the low cycle fatigue (LCF) analysis was focused after 1994 the Northridge earthquake because the connection failure mode of structure was not matched with the current design concept. This concept has been applied to the design of moment resisting frames and several research studies on the LCF behavior of various connections under cyclic loading have been conducted. While the research on the behavior of end plate moment connections (EPMC) under cyclic loading has been conducted very little information on the LCF behavior is available. To evaluate the accumulation of LCF damage, the LCF life prediction, three phases of experimental tests were conducted. In order to investigate critical geometric parameters for 4E EPMCs in the LCF behavior, parametric study was conducted with pre-qualified FEM model. In the first phase of the experimental test, total 4 reduced EPMCs, T-stub, was tested to verify the elastic range of the connection system and general behavior of the connection. Three different levels of constant peak displacement loadings were applied to three full scale EPMCs for developing a LCF model in second phase of the experimental test. In the last phase, an accumulated damage model was evaluated by one full scale end plate moment connection test using random loading. All of phases were adopted three-dimensional finite element numerical analysis, and theoretical analysis to predict the experimental behavior and it successfully anticipated the behavior of connection. The results of the experimental test developed the LCF model for 4E EPMC and it predicted the LCF life of connection. The parametric study determined the three critical geometry parameters.
Nonlinear Finite Element Analysis of Pavements and Its Application to Performance Evaluation
(2003-07-24) Mun, Sungho; Mansoor Haider, Committee Member; Tasnim Hassan, Committee Member; Murthy N. Guddati, Committee Co-Chair; Y. Richard Kim, Committee Chair
This research documents the findings from the study of failure mechanisms of fatigue cracking in asphalt pavements using the finite element program that employs the viscoelastic continuum damage model for asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables into account, such as asphalt layer thickness, layer stiffnesses, pressure distribution under loading, and load levels applied on the pavement surface. The crack initiations in different pavement structures under different loading conditions are studied by monitoring a damage contour. The developed finite element code, called VECD-FEP++, employs the viscoelastic continuum damage model as the constitutive model of asphalt concrete and the universal model (or so-called Uzan-Witczak resilient modulus model) for unbound materials. The finite element analysis of various pavement-load combinations showed significantly different failure mechanisms. Details on the VECD-FEP++ and the findings are given in the following chapters.
Plate-End Debonding of Longitudinal Near-Surface Mounted Fiber Reinforced Polymer Strips on Reinforced Concrete Flexural Members
(2008-04-22) Vasquez Rayo, Diego; Dr Rudolf Seracino, Committee Chair; Dr Sami Rizkalla, Committee Member; Tasnim Hassan, Committee Member
Seismic Analysis and Design of Type FR Steel Frames Using Displacement-Based Design and Advanced Analysis
(2002-09-17) Harris, John Leroy III; Mervyn Kowalsky, Committee Chair; James Nau, Committee Member; Tasnim Hassan, Committee Member
Current design office methodologies for seismic design of steel moment frames include forced-based methods for calculating equivalent lateral forces and a static elastic analysis. Research has revealed erroneous assumptions in forced-based methods and proposes that displacement-based methods, due to modeling inelastic systems, result in more reasonable lateral force distributions. Additionally, LRFD1 member design interaction equations implicitly account for geometric and material non-linear effects. This philosophy does not satisfy compatibility between the actual inelastic member response and the elastic system as assumed by conventional elastic analysis. Displacement-based lateral force distributions in combination with a second-order inelastic static analysis that sufficiently determines the limit state strength and stability of a structural system, or "Advanced Analysis," is advantageous to the design of steel moment frames. Second-order geometric and inelastic effects are directly accounted for in the analysis. This allows engineers to predict actual frame behavior with greater accuracy and results in a more efficient and economical frame. Another advantage is that force reduction factors outlined in current seismic codes are not required since the frame is designed for inelastic behavior. This approach eliminates discrepancies between initially assumed force reduction factors and final frame ductility capacity. Also, individual member capacity checks outlined in design specifications are similarly not required. The goal of this research is to advance the validity and accuracy of displacement-based design methods and Advanced Analysis for the engineering of seismic resistant steel moment frames. This research will allow the development of alternate seismic analysis and design procedures, as well as refined practical methods that can be incorporated in a design office. 1) Manual of Steel Construction – Load and Resistance Factor Design, American Institute of Steel Construction
The Seismic Behavior of Reinforced Concrete Members at Low Temperatures
(2005-09-28) Sloan, John Elliot; James Nau, Committee Member; Mervyn Kowalsky, Committee Chair; Tasnim Hassan, Committee Member
While reinforced concrete structures depend on ductility for acceptable seismic performance, research on the material behavior of concrete and steel has indicated that the loss of ductility may occur under low temperatures. The current research program investigates the behavior of reinforced concrete column-type members under low temperatures (-20 degrees Celsius, -30 degrees Celsius, and -40 degrees Celsius, approximately) and compares the results to an identical specimen tested at ambient laboratory temperature (23 degrees Celsius). The columns are lightly reinforced, and were loaded in a reversed cyclic manner while inside of an environmental chamber. The results of the experimentation indicate moderate increases in column strength as the temperature decreases, as well as moderate decreases in ultimate displacement capacity as the temperature decreases. The hysteretic damping properties of the columns were not significantly affected by low temperatures, and the specimen tested at -40 degrees Celsius exhibited a shortening of the extent of plasticity.