Showing papers on "Flexural rigidity published in 1971"

The Dimensional Properties of Knitted Wool Fabrics: Part VI: Some Observations of Completely-Relaxed Fabric Geometry

Abstract: Experimental evidence confirms the existence of a fixed knit-cell configuration of completely-relaxed weft-knitted wool fabrics. In this fabric condition, achieved after considerable mechanical agi...

Thin aluminum shear webs

Abstract: The behavior of thin-web girders in shear, when loaded in excess of the buckling value, is studied. The equations and simplified design charts presented take into account the effect of flexural rigidity of the flanges on the strength of the web, stiffeners, and fasteners. The study is directed primarily to aluminum webs, although in theory the concepts should be applicable to webs of other materials. In the development of the ultimate strength equation, it is assumed that the stress distribution in the web is the sum of a component of pure shear equal to the shear buckling value plus two components of tension stresses, one oriented at an angle of 45°, the other oriented at an angle calculated as though the flanges were completely flexible. The relative magnitude of the two tension components depends on flange flexibility. Ultimate failure is assumed to occur when the combined stress state causes yielding of the web. The study also considers the effect of web buckles on the appearance of the girder. The calculated results are compared with experimental data for thin-web aluminum girders.

Behavior of Laterally Reinforced Concrete Columns

Abstract: The results of an experimental and analytical investigation of the effect of non-uniform lateral confinement, such as that produced by closely spaced rectangular ties, on the behavior of concrete columns are presented. The main parameters studied were: flexural rigidity of lateral reinforcement, percentage of lateral reinforcement, concrete shrinkage, and strain rate. The effectiveness of lateral reinforcement, primarily depends on the flexural rigidity of the ties. The confining stress in columns with conventional rectangular ties is concentrated in the vicinity of the column corners and corresponds to the limiting state of confinement with corner forces. The stresses in the ties at maximum load are small and the concrete at some distance from the corners is nearly unconfined. Tie rigidity can be increased by cross bars welded to the ties. The added tie rigidity results in significantly increased ductility and, for small tie spacing in an appreciable strength increase. Comparisons are made with the results of other investigations, and a relation between strength increase due to ties and lateral reinforcement percentage is suggested.

The Bending Behavior of Fabrics at High Curvatures

Abstract: A new experimental method is described that permits the simultaneous determination of bending hysteresis and the flexural rigidity of textile or other flexible materials over a wide range of curvatures. Results are presented that show the variation of these two properties with material, fabric structure, and fabric finish. It is shown that results obtained with this method are in good agreement with those obtained by established methods.

Postcracking stiffness of reinforced concrete beams in torsion and bending

Abstract: THEORETICAL EXPRESSIONS FOR THE POSTRCRACKING STIFFNESS OF RECTANGULAR REINFORCED CONCRETE BEAMS IN TORSION AND BENDING ARE DESCRIBED AND SIMPLIFIED. THEY ARE BASED ON A SPACE TRUSS MODEL. IT IS SHOWN THAT THE POSTRCRACKING TORSIONAL STIFFNESS IS NOT GREATLY INFLUENCED BY BENDING WHILE THE POSTCRACKING FLEXURAL STIFFNESS DEPENDS ON THE AMOUNT OF TORSION. REALIZING THAT THE DROP IN TORSIONAL STIFFNESS AFTER CRACKING IS GREATER THAN THE DROP IN FLEXURAL STIFFNESS, THE TORSIONAL MOMENTS AFTER CRACKING WILL BE SMALLER IN MANY CASES THAN THE ONES PREDICTED BY THE UNCRACKED STIFFNESS VALUES. THE TORSIONAL REINFORCEMENT MAY THUS BE REDUCED BY MEANS OF THE TOOLS PROVIDED IN THIS PAPER. /ACI/

Flexural Rigidity of Concrete Column Sections

Abstract: The examination of theoretical stiffness ratios for reinforced concrete sections under uniaxial bending and axial load has shown that a reasonably simple set of approximate equations can be derived to enable a safe estimate of such stiffnesses to be computed. Due to the quantity of computing involved, the theoretical computations were limited to combinations of concrete strength and steel proportion within the practical ranges of 3,000 psi to 5,000 psi and 0.01 to 0.03 respectively, and to three proportions of cross-section geometry. It is customary to use either the uncracked or fully cracked stiffness in analysis. The method presented has the advantage of a more accurate estimate of stiffness in the middle range, though strain history effects should be incorporated, as wiht other methods.

Out-of-plane buckling of solid rib arches braced with transverse bars

Abstract: The out-of-plane buckling of a circular arch is studied. The arch is composed of two main ribs braced with transverse bars and is subjected to uniformly distributed radial forces (see Fig. 1). The analysis is carried out by means of transfer matrix method and both the field matrix of arched rod and point matrix are presented. Attention is given to the influences of the flexural rigidity, the number and the location of bracing bars on the buckling strength of arches. Buckling coefficients for various types of arch are calculated by trial and error method. Useful suggestions about the bracing method are obtained from the results of computations. The theoretical analysis is followed by model tests in order to verify the results of computation.

Torsion, bending, and shear in prestressed concrete

Abstract: An ultimate strength interaction criterion for web reinforced, prestressed concrete beams under torsion, bending moment and flexural shear is presented. Principal variables considered are the level of prestress and its eccentricity, torque: bending moment ratio, and flexural shear. Test results for 54 rectangular beams include beam properties, ultimate strength, angle of twist at failure, torque-twist curves and typical crack patterns. Bending moment in moderate amounts increases the torsional strength, but the effect of flexural shear is always detrimental. Within limits, the web reinforcement provides a ductile type behavior with ample rotation capacity at failure. The initial torsional stiffness is not affected by the variables considered. Higher levels of prestress and web reinforcement increase the pure torsional strength. Torsion-bending moment interaction is represented by a second degree parabola, and a three-dimensional curved interaction surface is envisaged when flexural shear is also present. Proposed interaction equations indicate good correlation with test data.

Continuous Beams with Prestressed Reinforcement

Abstract: TEST DATA FROM FOUR CONTINOUS RECTANGULAR BEAMS, SIMPLY SUPPORTED OVER TWO 15-FT SPANS ARE REPORTED. THE ONLY VARIABLE IN THE TEST IS THE RELATIVE AMOUNT OF DEFORMED STEEL BARS AND PRECAST PRESTRESSED CONCRETE PRISMS USED AS TENSION REINFORCEMENT OVER THE INTERMEDIATE SUPPORT. USE OF PRESTRESSED REINFORCEMENT AT INTERMEDIATE SUPPORT REGIONS OF BEAMS CONTROLS CRACK DEVELOPMENT AND PROPAGATION AT THOSE LOCATIONS AND IMPROVES THE OVERALL FLEXURAL RIGIDITY. OPTIMUM RESULTS ARE OBTAINED WHEN PRESTRESSED REINFORCEMENT IS USED SHORTLY AFTER THEY ARE CAST, WHEN THEY ARE PLACED AS CLOSE AS POSSIBLE TO THE EXTREME TENSION FIBER, AND WHEN THEY ARE ACCOMPANIED BY A SMALL AMOUNT OF NONPRESTRESSED REINFORCEMENT. PLASTIC CURVATURES AT A HINGING REGION MAY BE CONSIDERED TO EXTEND OVER A DISTANCE EQUAL TO THE EFFECTIVE DEPTH OF THE BEAM PLUS THE WIDTH OF THE DISTRIBUTING PLATE. HINGE ROTATIONS AND MOMENT REDISTRIBUTION ARE NOT INFLUENCED BY THE RELATIVE PRESTRESSING INDEX RATIO. BECAUSE OF THEIR BETTER SERVICEABILITY CRITERIA, BEAMS WITH PRESTRESSED REINFORCEMENT COULD BE ALLOWED HIGHER DESIGN PERCENTAGE MOMENT REDISTRIBUTION. /AUTHOR/

Transverse vibrations of a rotating counterweighted cable of small flexural rigidity.

Abstract: This paper presents an analysis of the transverse vibration of a rotating cable-connected spacecraft in which the flexural rigidity of the connecting cable is retained in the analysis. The method of matched asymptotic expansions is used to solve the singular perturbation problem, which must be solved for the determination of the mode shapes and natural frequencies. The problem is complicated by the presence of the eigenvalues and the perturbation parameter (which is a measure of the cable slenderness) in the boundary conditions. The effects of flexural rigidity on the mode shapes are shown to be confined to boundarylayer regions near the cable ends, and the effects on natural frequencies are shown to grow rapidly with increasing mode number.

Study on Viscoelastic Behavior of Carpet

Abstract: The bending properties of several pile yarns, which were made by different kinds of fiber and textured process were investigated in terms of bending rigidity and bending force-deflection curve by using specially designed apparatuses.When a circular looped pile yarn is deflected so as to increasing and decreasing its diameter uniaxially, the bending force-deflection curves differ with the direction of applied deflection. In the case of looped pile yarn made of different ratios of loop spacing S to length H, the bending force-deflection curve in the direction to decreasing H under the same applied deflection shifts to higher bending force side with decreasing S/H.Apparent values of complex dynamic bending rigidity of a looped pile yarn measured by means of Hysteresis loop method were almost independent of the observed frequency within 0.001 to 1 Hz and were not affected by degree of applied inicial deflection. But these values were affected by degree of applied amplitude.Apparent values of bending rigidity of a straight pile yarn measured by means of Vibrating reed method decrease with decreasing the sample length. Also, when these values compared with calculated results, as the pile yarn is a flitch beam or a built-up beam constructed with m fibers, the observed values represent intermediate one between the two calculated results.

Bending of prestressed glass-reinforced plastic beams

Abstract: Initial waviness of the fibers and prestressing are investigated in relation to their effect on flexural stiffness and strength for beams with low shear strength. It is shown that prestressing the reinforcement increases the flexural stiffness but at the same time adds to the shear correction as a result of an increase in the modulus of elasticity Ex in the direction of reinforcement and the insensitivity of the shear modulus Gxz to prestress. It is established that prestressing increases the shear strength and the degree of anisotropy β. Materials of two types are investigated: unidirectional (AG-4S) and cloth-reinforced (SKT-11).