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.
Structural Implications of Increased Panel Use in Wood-Frame Buildings
To improve performance and lower cost, conventional wood-frame construction has evolved to incorporate increasing numbers of manufactured components. Through recent work at the Massachusetts Institute of Technology (MIT) to develop a panelized roof system, other, more general observations have been made about the structural implications of panel use, and these observations form the basis for this paper. A partial exploration of structural response in conventional wood-frame construction is included as background, with a particular emphasis on sheathing. Panelized and modularized buildings represent a significant shift from historical practice, with structural implications for floors, walls, and roofs. Without the structural redundancy and load sharing that continuous envelope sheathing provides, panelized wood-frame buildings require more and careful engineering to achieve performance comparable to conventional construction. Floors, walls, and roofs need panel-to-panel joints that resist differential transverse deflection and possess in-plane shear strength and stiffness comparable to site-build, staggered-sheathed assemblies. Wherever structural response includes diaphragm action, the disruption of sheathing and perimeter-chord continuity both have consequences for panelized building systems.
Layered Beam Systems with Interlayer Slip
Layered systems of various materials are used to fabricate beams, plates and shells. The procedures commonly employed to analyze such systems are based on assumption of rigid interconnection between layers. In some widely used systems, however, this assumption is questionable. The basic phenomenon of interlayer slip is considered and a consistent theory for layered beams is developed. The results of experiments with layered wood beams connected with nails, with and without glued ends, are given. Excellent agreement with the general theory is shown. The importance of interlayer slip effect on the deflection of layered beams is demonstrated. The procedures developed can be used for any mechanically-connected beam system.