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.
APPLICATION OF THE FINITE ELEMENT METHOD TO ROTARY-WING AEROELASTICITY.
Recent research in rotary-wing aeroelasticity has indicated that all fundamental problems in this area are inherently nonlinear. The non-linearities in this problem are due to the inclusion of finite slopes, due to moderate deflections, in the structural, inertia and aerodynamic operators associated with this aeroelastic problem. In this paper the equations of motion, which are both time and space dependent, for the aeroelastic problem are first formulated in P.D.E. form. Next the equations are linearized about a suitable equilibrium position. The spatial dependence in these equations is discretized using a local Galerkin method of weighted residuals resulting in a finite element formulation of the aeroelastic problem. As an illustration the method is applied to the coupled flap-lag problem of a helicopter rotor blade in hover. Comparison of the solutions with previously published solutions establishes the convergence properties of the method. It is concluded that this formulation is a practical tool for solving rotary-wing aeroelastic stability or response problems.