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Browsing by Author "Widjaja, Budi R."

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    Analysis and Design of Steel Deck-Concrete Composite Slabs
    Widjaja, Budi R. (Virginia Tech, 1997-10-15)
    As cold-formed steel decks are used in virtually every steel-framed structure for composite slab systems, efforts to develop more efficient composite floor systems continues. Efficient composite floor systems can be obtained by optimally utilizing the materials, which includes the possibility of developing long span composite slab systems. For this purpose, new deck profiles that can have a longer span and better interaction with the concrete slab are investigated. Two new mechanical based methods for predicting composite slab strength and behavior are introduced. They are referred to as the iterative and direct methods. These methods, which accurately account for the contribution of parameters affecting the composite action, are used to predict the strength and behavior of composite slabs. Application of the methods in the analytical and experimental study of strength and behavior of composite slabs in general reveals that more accurate predictions are obtained by these methods compared to those of a modified version of the Steel Deck Institute method (SDI-M). A nonlinear finite element model is also developed to provide additional reference. These methods, which are supported by elemental tests of shear bond and end anchorages, offer an alternative solution to performing a large number of full-scale tests as required for the traditional m-k method. Results from 27 composite slab tests are compared with the analytical methods. Four long span composite slab specimens of 20 ft span length, using two different types of deck profiles, were built and tested experimentally. Without significantly increasing the slab depth and weight compared to those of composite slabs with typical span, it was found that these long span slabs showed good performance under the load tests. Some problems with the vibration behavior were encountered, which are thought to be due to the relatively thin layer of concrete cover above the deck rib. Further study on the use of deeper concrete cover to improve the vibrational behavior is suggested. Finally, resistance factors based on the AISI-LRFD approach were established. The resistance factors for flexural design of composite slab systems were found to be f=0.90 for the SDI-M method and f=0.85 for the direct method.
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    Analytical investigation of composite diaphragms strength and behavior
    Widjaja, Budi R. (Virginia Tech, 1993)
    Composite diaphragm strength and behavior were studied using non-linear finite element analysis. A total of 57 three panel diaphragm models were analyzed to failure. Parameters studied included beam size and orientation, panel dimension, connector type and distance, slab opening, yield plateau, and beam connection flexibility. Shear connector, deck-to-concrete interface, and beam connection were the components modeled non-linearly. Orthotropic behavior was used for the deck elements. 2-D and 3-D contours of concrete slab, steel deck and deck-to-concrete interfacial stresses and connector forces are presented to clearly show the behavior of the diaphragm in relation with the component behavior. Complete and incomplete connector force redistributions were observed and an expression of yield plateau length required to develop a complete connector force redistribution was developed. Expressions for diaphragm strength based on beam, beam connection and connector strength for both the complete and incomplete connector force redistribution cases were presented. The diaphragm strength predicted by the expression compared favorably with the finite element results.