Development of Procedures for Determination of Yield Lines

This thesis presents methods for determining yield line patterns of isotropic plates that are uniform in thickness and subjected to a uniform loading. The importance of these methods arises from the mathematical complications involved in finding yield line patterns by the present procedures . Since yielding patterns are dependent on the shape of a plate as well as the support conditions, the methods recommended here will be based on assuming a yielding pattern and checking for its correctness. The use of the computer can provide many trial solutions in a very short time. The correct pattern will be that which gives the same value of the yielding moment along all yield lines. The benefit of the recommended methods is that no mathematical complications are involved and a very elementary knowledge of computer programming is sufficient

Comprehensive Load Distribution Model For Wood Truss Roof Assemblies

This study developed and verified a comprehensive structural analysis model to predict the distribution of loads in wood truss roof systems. Experimental testing was performed to provide for model verification and included full-scale tests of individual trusses and a complete roof system.Nine trusses were individually tested to their design load, then placed in a typically constructed and sheathed assembly for roof system testing. The roof assembly tests consisted of loading individual trusses within the roof using various combinations of concentrated vertical loads. Truss reactions, truss loads, and interior bottom chord deflections were electronically measured. The roof assembly was also tested with two types of gable end truss supports.The load distributions within the roof assembly were found to remain constant up to and beyond twice the roof's design load. The load distributed through load sharing was found to vary from 60% of the applied load in stiffer trusses to 80% of the applied load in relatively limber trusses. Gable end truss support significantly influenced the load carried by the trusses near the ends of the roof.By considering the truss members as three-dimensional frame elements with semi-rigid end connections, and by rationally assigning rigidity factors to the connected joints, a model was developed in this study that can accurately predict individual truss stiffness and roof assembly load distributions. Distributions predicted by the model compared closely to those obtained experimentally for both individual truss loadings and for superimposed truss loadings. The model developed does not require experimental connector plate parameters and once fully verified, may prove useful in roof system design procedures

Influence of Truss Plate Connectors on the Analysis of Light Frame Structures

A method of analysis for a plane framed structure with nonrigid connections is studied. The method encompasses the concept of matrix method. Structures are modeled using two types of elements, namely, a beam element and a joint element. Each two-dimensional joint element is composed of three linear springs having no physical dimensions, representing shear, axial, and moment resistance. The mechanical properties of the joint element are obtained experimentally. Two frames and several beams are tested, and results are compared to analytical results. Good correlations are obtained.A solution of a truss with toothed metal plate connectors is presented and a general agreement with available solutions is obtained. A sensitivity study presenting the influence of joint stiffnesses is also presented. It is found that moment and axial spring properties have appreciable influence on members end forces, while the shear spring properties have little effect

Predicting Damping of Semi-Rigid Glued T-Beams

A theoretical model for predicting damping in composite wood T-beam is provided. The formulation is based on energy dissipation due to relative slip at the interface of the flange and joist. A loss factor parameter as obtained from stress-strain relationship of elastomeric adhesive has been introduced into the formulation. Damping computed from experimental tests is found to about 5% to 8% compared to theoretical values of 4.5% to 6.5%

Characteristics Of Wood Diaphragms: Experimental And Parametric Studies

This paper further verifies a previously developed analytical model of sheathed diaphragms. Load-displacement behavior and frequency characteristic are studied, and comparisons are made between analytical and experimental results. An 8- x 8-foot wall with 1/2-inch plywood sheathing was used in sensitivity studies to quantify the effect of the variation of parameters, such as nail spacing, moduli of elasticity of materials, and joint stiffness, on the static load-displacement behavior and frequency of sheathed diaphragms. The major parameters affecting the load-displacement and displacement-frequency relationships of diaphragms were found to be nail spacing and the connection properties between sheathing and frame members. Sheathing arrangements were also found to affect the stiffness of diaphragms. Variations in mechanical properties of sheathing and frame members, however, had only a negligible effect on diaphragm structural behavior

Primary Creep in Douglas-Fir Beams of Commercial Size and Quality

Primary creep of nominal 4- x 4-inch Douglas-fir beams of No. 2 grade was measured at four levels of stress, at 12% wood moisture content.Equations are presented for deflection and relative creep at the four stress levels. Results show relative creep to be nearly independent of stress level, with some evidence that relative creep shows a negative correlation with wood elastic modulus

Influence of Sheathing Gaps on Wood Floor Systems

This paper describes a comparative study of the partial composite action of wood floors with and without sheathing gaps. The beams investigated consist of plywood sheathing bonded to joists with elastomeric adhesive. Beams are considered to be simply supported and subjected to uniformly distributed loading. Results for continuous sheathing, open gaps at third and fourth points are compared and displayed graphically.It is shown that the influence of gaps on the partial composite action is drastic and can increase deflections by as much as 82%, compared to a system with continuous sheathing. Little difference is obtained when comparing a beam with gaps at third and fourth points

Creep of Douglas Fir Beams Due to Cyclic Humidity Fluctuations

This report describes tests of the hypothesis that creep in Douglas fir beams of commercial size is influenced by cyclic humidity fluctuations.Twenty 3.5- x 3.5-inch (89- x 89-mm) beams were creep-tested for a period of approximately 1,200 hours (7 weeks). Deflection data were recorded for loaded beams while the relative humidity of their environment was cycled at 70 F. The environmental EMC was varied from 7 to 20% for periods of 24 and 168 hours, respectively. Three regression models were fitted to the relative creep data. The effect of stress levels and humidity cycles were compared.The study showed that creep for cycled specimens greatly exceeded creep for uncycled specimens

The Effect of Moisture Cycling On Creep of Small Glued Laminated Beams

Creep information for sawn lumber exposed to constant and cyclic humidity environments previously published by the authors is supplemented by this study using glued laminated material of about the same size, tested on the same apparatus, and using the same general procedure.For both sawn and glued laminated material, the relative creep was measured at about 55% of their average ultimate strength. Relative creep was measured for specimens matched with respect of modulus of elasticity (MOE) and exposed to a constant relative humidity (65 F and 65% RH) for about 1,000 hours, and a cyclic relative humidity (65 F and 90% RH for 82 hours followed by 65 F and 40% RH for 82 hours). This 164-hour cycle was repeated six times for about 1,000 hours of cyclic exposure. This is a more severe change in equilibrium moisture content of the environment than is likely to occur in building structures.The result showed relative creep of the glued laminated material increased by 40% to 72% as a result of cycling. One very low MOE pair showed an increase of 167%. The increase for solid sawn lumber previously reported was 200% to 400% due to cycling. Results also showed that the ratio of relative creep for cycled to constant humidity exposure did not change appreciably as time under load was increased. These differences are attributed to permeability differences between glued laminated wood and sawn lumber. The gluelines are believed to retard water vapor movement and reduce the moisture change rate and extremes of wood moisture content in any given cycle