Browsing by Author "Dr. Emmett Sumner, Committee Chair"

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    Analytical Evaluation of Concrete Penetration Modeling Techniques
    (2010-02-22) Bush, Blake Marshall; Dr. Sami Rizkalla, Committee Member; Dr. Murthy Guddati, Committee Member; Dr. Emmett Sumner, Committee Chair
    The resistance of concrete targets to penetration of high speed projectiles is a topic of high value in the national security and catastrophic design fields. Many methods have been developed to effectively analyze these types of problems. Currently there are a number of numerical codes and constitutive models used to analyze concrete impact and penetration with new methods developed continuously. This research evaluates the accuracy of four analysis codes and five concrete constitutive models. Two Lagrangian analysis programs, EPIC and LS-DYNA, as well as an Eulerian code, CTH, are compared in this work. A developmental version of the Material Point Method is also evaluated in order to study the effectiveness of Arbitrary Lagrangian Eulerian (ALE) modeling methods for concrete impact and penetration. The concrete models evaluated in this research include Holmquist Johnson Cook, Brittle Failure Kinetics, Osborn, Karagozian and Case, and Drucker-Prager. The modeling programs and constitutive models are evaluated by comparing simulation results to a series of concrete impact and penetration experiments. The experimental test data, provided by Sandia National Laboratories, comprises concrete targets of two compressive strengths (3.3 and 5.7 ksi) and two thicknesses and projectiles of two nose shapes. Extensive material testing of the experimental concrete is used to calibrate the constitutive models in each analysis package. An additional parametric study investigates the influence of experimental variables on the most promising analytical configuration. Observations from this research show that the EPIC and LS-DYNA analysis codes are currently best suited for concrete impact and penetration problems. Both codes contain features which allow for realistic modeling and produce accurate results for the experimental impact tests. Recommendations for improving analysis methods specific to concrete impact and penetration are presented.
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    Experimental and Analytical Investigation of an Innovative Composite Shallow Floor Framing System
    (2009-12-08) Willis, Meade Hanes; Dr. James Nau, Committee Member; Dr. Emmett Sumner, Committee Chair; Dr. Rudolf Seracino, Committee Member
    Since the early 1950’s, composite concrete-steel systems have been a popular and economic choice for floor construction in the United States. The conventional composite floor system comprised of a concrete slab with light gauge steel deck form supported by wide flange structural steel girders has been widely used in construction. In recent years, modifications to the conventional system have been made to meet a market need for floor systems with reduced structural depth to be used in a variety of building types including office buildings, hotels, and hospitals. In 2007, Diversakore® LLC developed the Versa :T:TM beam, an innovative shallow floor composite framing system that utilizes a small structural depth and also makes improvements in the ease and speed of construction. The system includes a u-shaped steel plate which supports hollow core plank flooring during construction and serves as a stay-in-place form for a cast-in-place reinforced concrete girder. The concrete girder is cast monolithically with a topping slab to engage the hollow core planks and the u-shaped steel section into a composite t-beam. A research program to evaluate the performance of this innovative floor system has been developed and is currently ongoing at the Constructed Facilities Laboratory at North Carolina State University in Raleigh, NC. The experimental and analytical program includes full-scale tests of representative sub-assemblages and utilizes a layered sectional analysis to predict the behavior. The results of the analytical model and the experimental investigation are presented along with conclusions drawn from the initial phase of the research program.
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    Experimental and Analytical Investigation of Optimized Cold-Formed Steel Compression Members
    (2009-12-02) Klingshirn, Daniel J; Dr. Nabil A. Rahman, Committee Co-Chair; Dr. Emmett Sumner, Committee Chair; Dr. James Nau, Committee Member
    In recent years, load-bearing light steel framing (LSF) systems have become popular in the low to mid-rise construction market in the United States. This construction market covers a wide range of building usage, including apartment and office buildings, hotels, and schools. In the past, standard C-shaped metal studs have been the only option for designers and contractors when selecting a cross section for load bearing studs. An alternative cross section, which has primarily been used as a roof purlin in Europe and is seldom found in the U.S., is the sigma-shaped section. Recognizing the potential of this section for use within a LSF system, a research program was completed at North Carolina State University’s Constructed Facilities Laboratory (CFL) to evaluate the axial compression capacity for the proprietary stud product SigmaStud®. The experimental test program, which includes fifty-eight sigma-shaped stud tests and forty-eight comparable C-stud tests, was developed with the ultimate goal of adding the SigmaStud® to the pre-qualified column set of the relatively new Direct Strength Method (DSM) design method. Studs were tested at various lengths to force global, distortional, and local buckling failure modes. Additionally, the test program contained studs with and without web holes. Comparisons of experimental results with the AISI design methods, Effective Width (EWM) and Direct Strength (DSM), are discussed. Based on the results of this research program, the SigmaStud® section is recommended to be added to the pre-qualified member set of the DSM. Both design methods are shown to produce accurate strength predictions. Another important conclusion from this test program is that the optimized sigma-shaped stud is shown to be a much more efficient use of material than a comparable C-stud. Strength increases ranged from 30-175% for 24†studs and 45-450% for 120†studs. Web holes were shown to decrease stud capacity in most cases, although strength increases were observed in both short and long studs. Additionally, long studs are shown to be very sensitive to loading eccentricity, while short studs are not.
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    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.
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    An Investigation of Bridge Deck Overhang Falsework Systems Installed onto Modified Bulb Tee Girders
    (2007-04-27) Lackey, Paul Ellis; Dr. Sami Rizkalla, Committee Member; Dr. James Nau, Committee Member; Dr. Emmett Sumner, Committee Chair
    Bulb Tee girders provide a practical, efficient means of spanning the large distances required in today's bridge designs by utilizing large moments of inertia to withstand the massive moments created in the spans. A bulb tee girder possesses a wider, thinner top flange than conventional precast concrete cross-sections. Previous research suggests the thin top flange of an exterior bulb tee girder in the bridge deck overhang falsework system to fail in punching shear and concrete bearing/spalling at premature loads. Meadow Burke Products, Inc. has manufactured an innovative falsework hanger for use with thin flange girders such as the bulb tee. The hanger utilizes a bearing plate to distribute the vertical loads on the top flange. Experimental full scale testing of the innovative hanger on a bulb tee girder was completed as the first phase of this study. The hangers were installed onto a 63 in. North Carolina Department of Transportation (NCDOT) Modified Bulb Tee (MBT) girder and loaded by a hydraulic load cylinder at a 45 degree angle. The behavior and ultimate strength of the hanger and top flange of the girder were recorded. Phase two of the experimental study consisted of testing the overhang falsework system with support brackets attached to the Meadow Burke hangers. The support brackets were loaded vertically utilizing hydraulic load cylinders. The load distribution behavior of the bracket and ultimate loading capacity of the system were recorded. Both phases of the experimental study concluded that a punching shear failure will occur in the top flange of the girder at a consistent loading. Subsequent analytical studies were carried out in an attempt to predict and emulate the results seen in the experimental testing. The analytical study consisted of finite element models and ACI code provisional analysis for punching shear. The finite element models developed are able to accurately predict the behavior and ultimate strength of the system. ACI code for punching shear does not accurately predict the punching shear capacity of the MBT girder flange.
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    Web Crippling Strength of Sigma-Shaped Cold-Formed Steel Studs Subjected to Axial Load
    (2006-10-16) Boylan, Matthew Aaron; Dr. Emmett Sumner, Committee Chair; Dr. Sami Rizkalla, Committee Member; Dr. James Nau, Committee Member
    Load-bearing light steel framing (LSF) systems have gained good acceptance to the low to mid-rise construction market in the U.S. in recent years. This construction market covers a wide range of building usage, including apartment and office buildings, hotels, and schools. For years, standard C-shaped metal studs have been the only option for designers and contractors when selecting a cross-section for load bearing studs. As design loads for the studs get larger with heavier floor systems or at lower levels of mid-rise buildings, designers have been required to either use multiple (built-up) C-shaped studs or switch to structural steel members. An alternative to the standard shapes, although seldom found in the U.S., is the sigma-shaped section, but this shape is primarily used as a roof purlin in Europe. The Steel Network, Inc. of Raleigh, North Carolina recognized the potential of this section for use within a LSF system and developed the SigmaStud. A testing program was developed for the SigmaStud and testing was conducted at North Carolina State University's Constructed Facilities Laboratory (CFL). Presented are the results of a series of tests to evaluate the web crippling behavior of a new sigma-shaped metal stud when subjected to lateral load in addition to axial load. Also presented is an analytical study that results in proposed modifications to the AISI web crippling equation to account for sigma-shaped sections with or without axial load.