Browsing by Author "Dr. Vernon Matzen, Committee Member"

Now showing 1 - 4 of 4

Bond Behavior of High Performance Reinforcing Bars for Concrete Structures
(2007-05-08) Hosny, Amr; Dr. Sami Rizkalla, Committee Chair; Dr. Emmett Sumner, Committee Member; Dr. Vernon Matzen, Committee Member
Bond between the concrete and the reinforcing steel is a major factor affecting the performance of reinforced concrete structures. Advances in material science led to the production of High Performance Steel that has enhanced corrosion resistance and higher strength compared to conventional Grade 60 steel. Such material can lead to more economical design reducing the material requirements for a particular project and expanding its life span. The objective of this research is to study the bond behavior of High Performance reinforcing bars for concrete structures and to evaluate the effect of different parameters believed to affect the bond characteristics. Twenty-two large scale reinforced concrete splice beams were constructed using No.8 and No.11 reinforcing bars, having different cross-sections with varying concrete compressive strengths and development lengths. The beams were tested using four point bending setup to provide a constant moment region over the splice zone. Test results indicate that stresses up 90 ksi can be achieved in the No.8 bars and up to 70 ksi in the No.11 bars without confinement; however, it is recommended to use transverse reinforcement to confine the High Performance bars in order to ensure ductility. These stresses can be evaluated at failure using a simple proposed equation. Test results were used to extend the current ACI Committee 408 equations to better predict the stresses in the High Performance Steel.
Experimental and Analytical Investigation of Progressive Collapse Through Demolition Scenarios and Computer Modeling
(2008-04-02) Griffin, Joshua Wayne; Dr. James Nau, Committee Member; Dr. Vernon Matzen, Committee Member; Dr. Emmett Sumner, Committee Chair
Within the past 40 years, abnormal loadings resulting from natural hazards, design flaws, construction errors, and man-made threats have induced progressive collapse in structures all over the world. As progressive collapse behavior has become more prominent, it has made the necessity for design and analysis tools evident. In effort to provide one of these tools, Applied Science International, Inc. introduced its Extreme Loading® for Structures (ELS®) software, capable of progressive collapse simulation. This research evaluates the effectiveness of Extreme Loading® for Structures as an emerging, nonlinear dynamic analysis software package in modeling progressive collapse scenarios. The ELS® software utilizes the Applied Element Method (AEM) of numerical analysis, separating it from other available software packages. The software and analysis methodology's accuracy are investigated through simulation of two structural implosions. Comparing the predicted response to the documented response, each scenario is evaluated by analyzing the material models, failure criteria, local structural behavior, and global collapse behavior. The two case studies, Crabtree Sheraton Hotel in Raleigh, North Carolina and Stubbs Tower in Savannah, Georgia, each include an experimental and analytical investigation. The experimental investigations include gathering existing structural information, coordinating with the demolition contractor to simulate the implosion sequence, as well as observing and obtaining documentation from the actual event. The analytical investigation utilizes the Extreme Loading® for Structures software to construct a model for each structure, simulate the implosion sequence, and analyze the predicted behavior. To understand the effects of individual modeling parameters on the model's response, a parametric study was completed. Creation of an evaluation matrix allowed for systematic assessment of the parametric study, as well as the individual model's behavior. For the case studies, a completed evaluation matrix for each iteration can be found in the appendix, providing a rough quantification of the accuracy. Observations from this research show that the software is capable of successfully modeling progressive collapse scenarios. The software allowed for realistic construction of the models and was effective on various levels in predicting the local and global collapse behaviors. Inaccuracies were discovered in each model and were investigated through subsequent iterations of the analysis. A solution was found for some of the inaccurate aspects, while recommendations for future research are proposed to address the others. Allowing for the quick and effective assessment of structures, the Extreme Loading® for Structures software has the potential to become a valuable tool in design and analysis of structures for progressive collapse mitigation. Through continuous validation and verification, modeling techniques and parameters can be established, providing engineers with confidence when venturing into this relatively new realm. Eventually, the advancement in knowledge and computing integrated into this software could provide invaluable benefit to society, in the form of economic cost and life-safety.
Fundamental Behavior of Steel-Concrete Composite Beams Strengthened with High Modulus Carbon Fiber Reinforced Polymer (CFRP) Materials
(2005-06-30) Dawood, Mina Magdy Riad; Dr. Emmett Sumner, Committee Member; Dr. Vernon Matzen, Committee Member; Dr. Sami Rizkalla, Committee Chair
There is a growing need for a cost-effective, durable repair system that can be used for the repair and strengthening of steel bridges. Recently, high modulus carbon fiber reinforced polymers (CFRP) have been developed with a modulus of elasticity approximately two times greater than that of steel. Externally bonded high modulus CFRP materials have successfully been used to increase the elastic stiffness and ultimate capacity of steel-concrete composite beams However, since the technology is relatively new, the detailed behavior of steel bridge members strengthened with high modulus CFRP is not yet well understood. The current research investigates three aspects of the behavior of steel-concrete composite beams in detail. An experimental program was conducted to investigate the behavior of steel-concrete composite beams strengthened with high modulus CFRP materials. In the first phase of the study the behavior under overloading conditions was investigated. In the second phase of the research, the fatigue durability of the system was examined. In the third phase, the possible presence of shear-lag between the steel beam and the CFRP materials was investigated in detail. An analytical model was developed which can be used to determine the ultimate capacity and elastic stiffness increase for steel beams strengthened with high modulus CFRP materials. Additionally, a set of criteria are proposed which can be used to determine the allowable increase in the live load level for steel beams strengthened with high modulus CFRP materials.
Fundamental Characteristics of 3-D GFRP Pultruded Sandwich Panels
(2008-05-10) Patrick, Jason Fredrick; Dr. Paul Zia, Committee Member; Dr. Sami Rizkalla, Committee Chair; Dr. Vernon Matzen, Committee Member
This research presents the behavior of proposed 3-D glass fiber reinforced polymer (GFRP) pultruded sandwich panels designed to enhance the structural efficiency and to overcome delamination problems typically exhibited by traditional FRP panels. The sandwich panels consist of GFRP laminate plates at the top and bottom, separated by a polyurethane foam core, and connected by through-thickness fibers to achieve composite action. The use of the through-thickness fibers prevents delamination-type failures, increases the out-of-plane properties of the panels, allows low cost manufacturing, and ensures full utilization of the individual material strengths. The fundamental material characteristics of the sandwich panels are evaluated in three phases. The first phase evaluates the in-plane tensile properties of the GFRP laminate face sheets to determine the effects, if any, of the through-thickness fiber insertion pattern and test direction. The second phase investigates the shear behavior of the tested panels in order to evaluate the effects of various parameters, including through-thickness fiber insertion pattern, corresponding fiber insertions per square inch (fipsi), and testing direction (parallel and perpendicular to pultrusion direction). The third phase focuses on the flexural behavior of the sandwich panels in order to evaluate the effects of the same parameters in addition to the effects of varying panel widths and span lengths. The analytical phase of the research investigation incorporates the measured tensile and shear material characteristics in conjunction with Elementary and Advanced Sandwich Theories to predict the flexural behavior of the 3-D GFRP panels. Based upon these research findings, recommendations are proposed to the manufacturer and design engineers planning to use these sandwich panels in structural applications. The current research has shown these panels are a viable, cost-effective alternative which can be customized for various applications, such as pedestrian bridge decks, construction and industrial mats, truck trailer or rail car components, and marine environment applications.