Browsing by Author "Emmett A. Sumner, Ph.D., P.E., Committee Chair"

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    Behavior of Single Plate Shear Connections with Rigid and Flexible Supports
    (2005-07-31) Creech, Dustin Dwayne; James M. Nau, Ph.D., P.E., Committee Member; Mervyn J. Kowalsky, Ph.D., Committee Member; Emmett A. Sumner, Ph.D., P.E., Committee Chair
    Single plate framing connections are a type of shear connection which must sustain both shear and moment transferred from the supported beam. Commonly found in both rigid (beam-to-column flange) and flexible (beam-to-girder web) configurations, the single plate connection has proven to be both economical and easy to erect. A specified design method for single plate connections is presented in the AISC LRFD 3rd Edition Manual (AISC 2003). The design method calculates for associated limit states or failure modes and accounts for eccentric shear created by the moment sustained by the connection. Overly conservative tabulated design strengths, which lead to heavier, more costly, connections, has emphasized the need for research to improve upon the current design procedure. The focus of this research is to address the conservative nature of the currently specified design method. To create a basis for comparison to theoretically calculated design strengths, a total of ten full-scale tests were conducted. Tests incorporated both rigid and flexible support conditions, both standard and short-slotted bolt holes, and connections consisting of various numbers of bolts. Differing from previous research efforts, this series of research incorporated a simulated slab restraint with flexible supported tests. In order to evaluate experimental results and remove unknowns, supplemental tests were conducted to determine the material properties of components used in testing. Major goals accomplished in this research included the investigation of connection limit states and component behavior. Focus was given to qualifying rotational behavior and quantifying the extent that eccentric shear is experienced by the connection as this is felt to be a potential cause of the overly conservative tabulated design values. In addition, comparisons of the AISC design method were made to design methods proposed by other researchers and design methods specified in other countries. All investigations focused upon improving the currently accepted AISC design procedure for single plate framing connections.
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    Full Scale Testing of Overhang Falsework Hangers on NCDOT Modified Bulb Tee (MBT) Girders
    (2006-01-07) Ariyasajjakorn, Donlawit; Emmett A. Sumner, Ph.D., P.E., Committee Chair
    Today's bridges are being constructed with longer spans and higher girder spacing. As a result, the use of precast prestressed concrete modified bulb tee (MBT) girders has significantly increased. The MBT girders have a wider and thinner top flange than other conventional precast concrete cross-sections. The strength of the thin top flange has been identified as a concern for the North Carolina Department Of Transportation when edge of flange falsework hangers are used to support the overhang deck slab falsework system. In response to theses concerns, the NCDOT has funded research project 2005-18 "Full Scale Testing of Overhang Falsework Hangers on NCDOT Modified Bulb Tee (MBT) Girders" to study the behavior of the edge of flange falsework hanger systems. Standard falsework hangers manufactured by Dayton/Richmond and Meadow/Burke were tested as a part of this research. This research consists of two parts, the experimental and analytical investigations. The effects of amount of the shear reinforcement, the effect of the adjacent loaded hangers and the type of hanger were investigated in the experimental investigation. The finite element models were generated to predict the behaviors of the falsework system such as the limit state, ultimate load, and the response of the system. From the experimental result, the ultimate load of both hanger types, Dayton/Richmond and Meadow/Burke did not reach the ultimate strength provided by manufacturer. The Dayton/Richmond and Meadow/Burke hangers failed approximately 75% and 55% of the manufacturer ultimate strength by the spalling of the concrete under the hanger and punching shear failure. There were effects of the shear reinforcement and the adjacent loaded hanger observed. From the results of finite element models, the initial stiffness of the applied hanger load and deflection at mid-span of the model was higher than the experimental results. The models predicted failure by flexural cracking and punching shear for the Dayton/Richmond and Meadow/Burke hangers respectively. When multiple hangers were loaded, the ultimate loads decreased for the Meadow/Burke model. A series of small finite element models were used to gain the better prediction of the local behavior at the hanger. The small finite element models were able to capture the initial stiffness of both hanger types, but only the mode of failure of the Meadow/Burke hanger was captured. It was concluded that the shear reinforcement, number of loaded hanger and the type of hanger affect the ultimate strength and behavior of the structure. The ultimate load of the Dayton/Richmond hanger test is higher than the one from the Meadow/Burke hanger test. However, the observed ultimate loads were less than the manufacturer's ultimate load. The failure of hanger head for Dayton/Richmond hanger occurs because the rotation of hanger head. The bearing failure of Dayton/Richmond hanger test causes the excessive rotation of hanger head. It was recommended that the safe working load of the Dayton/Richmond and Meadow/Burke falsework hanger embedded on the NCDOT modified bulb tee (MBT) girder be reduced, and the use of different type of overhang hanger system such as through flange hanger appears to be necessary to reach the 6,000 lb. safe working load.