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

Educational Leaders’ Attempts at Holding the Fort: A Transformative Endeavor in Lebanon

Despite its small size, Lebanon has had its fair share of nationwide turbulences that further instigated conflict and instability among the Lebanese population. The crises have weighed heavily on the educational system in Lebanon and has impeded its operations on many fronts. However, educational leaders have attempted to adopt transformative practices in addressing the anticipated and unanticipated challenges. Educational leaders in Lebanon have learned to perceive that ‘the only constant is change,’ and have come to realize and acknowledge that their goals of enhancing educational experiences remain the same but the paths to achieve these goals are nonlinear

Nonlinear Racking Analysis of Nailed Walls

An energy formation of nonlinear analysis of racking resistance of nailed walls is presented. The analysis is dependent on the nonlinear load-slip relationship of nailed connections. The method permits the calculation of the racking force associated with a given horizontal displacement and uses as input data panel geometry, number and spacing of nails, and load distortion relationship of a single connection.Two 4 ft x 8 ft panels with two thicknesses of 1/2 in. and 5/8 in. plywood are analyzed using linear and nonlinear methods, and results of horizontal displacement versus racking force are displayed graphically. It is shown that while the two methods converge at ultimate loads, true representation of wall behavior at low levels of displacement is best described through nonlinear analysis. Good comparison is obtained with a finite element approach

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

Fetal in vivo continuous cardiovascular function during chronic hypoxia.

Although the fetal cardiovascular defence to acute hypoxia and the physiology underlying it have been established for decades, how the fetal cardiovascular system responds to chronic hypoxia has been comparatively understudied. We designed and created isobaric hypoxic chambers able to maintain pregnant sheep for prolonged periods of gestation under controlled significant (10% O2) hypoxia, yielding fetal mean P(aO2) levels (11.5 ± 0.6 mmHg) similar to those measured in human fetuses of hypoxic pregnancy. We also created a wireless data acquisition system able to record fetal blood flow signals in addition to fetal blood pressure and heart rate from free moving ewes as the hypoxic pregnancy is developing. We determined in vivo longitudinal changes in fetal cardiovascular function including parallel measurement of fetal carotid and femoral blood flow and oxygen and glucose delivery during the last third of gestation. The ratio of oxygen (from 2.7 ± 0.2 to 3.8 ± 0.8; P < 0.05) and of glucose (from 2.3 ± 0.1 to 3.3 ± 0.6; P < 0.05) delivery to the fetal carotid, relative to the fetal femoral circulation, increased during and shortly after the period of chronic hypoxia. In contrast, oxygen and glucose delivery remained unchanged from baseline in normoxic fetuses. Fetal plasma urate concentration increased significantly during chronic hypoxia but not during normoxia (Δ: 4.8 ± 1.6 vs. 0.5 ± 1.4 μmol l(-1), P<0.05). The data support the hypotheses tested and show persisting redistribution of substrate delivery away from peripheral and towards essential circulations in the chronically hypoxic fetus, associated with increases in xanthine oxidase-derived reactive oxygen species.This work was supported by the British Heart Foundation.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1113/JP27109