PREDICTING THE STRENGTH OF WOOD-JOIST FLOORS.
Abstract : This study was intended to explore the relationships between strengths at first rupture predicted by linear and nonlinear models for wood-joist floors of a given configuration but having various combinations of joist material properties. The study produced two ways of altering linear models to account for the nonlinear behavior of nails in floors loaded to failure. The strength at first joist failure of 72 floors was analyzed using linear and nonlinear finite-element models and statistical comparisons. The results of the study are presented in two forms. The first is recommended factors by which the predicted failure loads from the linear analysis can be scaled to give failure loads consistent with the nonlinear analysis. The second is recommended substitute nail stiffness which can be used in a linear analysis to predict floor responses with near-equivalent accuracy as provided by a nonlinear analysis. The results presented are specific to the floor design used in this study, but similar techniques could be used to derive equivalent information for other floor designs.
Stiffness and Strength of Uniformly Loaded Floors with In-Grade Lumber.
Abstract : To implement more efficient design techniques for wood joist floor systems, existing systems with a history of satisfactory service must be characterized. Such a procedure, known as calibration, is necessary to ensure that new design techniques and construction materials do not change the overall acceptability of wood floor systems. To characterize such performance, a structural analysis model and computer program for floors, FEAFLO, was used with data on numerous samples of lumber from sawmill inventory. Over 500 floor analyses yielded estimates of the distributions of floor stiffness and strength that will be useful to designers and code agencies in establishing or revising acceptance criteria for floors. (Author)
Ground Fault Protection for Electric Utility Generating Station Medium Voltage Auxiliary Power Systems
Most generating station designs have medium voltage auxiliary power systems with low resistance grounded neutrals.1 In order to provide even higher reliability, the auxiliary power distribution system configurations supply increasingly redundant process equipment.