Showing papers on "Flexural rigidity published in 1980"

1—the initial load–extension behaviour of plain-woven fabrics

Abstract: An analysis of the initial load–extension behaviour of plain-woven fabrics is presented, Castigliano's theorem being used as the principal method of attack. Yarn compression and extension are taken into account in addition to yarn bending rigidity. The theory is compared with some experimental data.

Practical formulas for estimation of cable tension by vibration method

Abstract: The vibration method is usually used for field measurement of cable tension during the construc­ tion of cable system bridges such as an arch bridge stiffened with inclined cables or a cable-stayed bridge. Practical formulas for the vibration method are proposed herein taking the effects of flexural rigidity and sag of a cable into account. The formulas are based on the approximate solutions of high accuracy for the equation of inclined cable with flexural rigidity. Cable tensions are easily estimated by these formulas using measured natural frequencies of low-order modes. The practical formulas presented herein are applicable to various cables, regardless of length and tension as far as the vibration of first- or second-order mode is measurable. As to a very long cable that cannot be easily excited artificially, a formula is presented by using natural frequencies of high-order modes obtained from stationary microvibrations. The accuracy is confirmed through comparison of the values obtained by practical formulas with measured values and calculated values by the finite element method.

The measurement of flexural stiffness of multistranded electrical conductors while under tension

Abstract: The ACSR Electrical conductor is a complex structure composed of layers of aluminum wires wrapped around one another over a steel-wire core. Three different test arrangements were considered for testing the static flexural stiffness. The cross-load method was easiest to implement and avoided the problems with load-spacing sensitivity of the couple method which used two forcesQ. However, the maximum usable value of λ for test method one was around 6 or 7. This meant that the test spant had to be changed to satisty this requirement.

Steel-polypropylene-steel laminate: a new weight reduction material

Abstract: The dent resistance, flexural stiffness, fatigue strength, and formability are characterized for a steel-polypropylene-steel (S-P-S) laminate for automotive applications. Many of these physical properties are comparable to those of steel. The S-P-S laminate takes advantage of the I-beam principle in bending. The highest stress is in the surface, with the lowest stress at the neutral axis. The material has a high stiffness-to-weight ratio, with the potential to reduce component weight by 50% with no loss in flexural stiffness. Applications where bending stiffness is the major design criterion include: seat backs, load floors, covers, narrow body panels, truck trailer sides, and interior trim. One disadvantage of S-P-S is loss of bolt torque due to creep by the polypropylene core. This loss is a function of the applied stress level, core thickness and temperature.

Relationship between modulus and density for high-density closed-cell thermoplastic foams

Abstract: It is necessary to establish a relationship between Young's modulus and density for a closed-cell plastic foam in order to predict the flexural stiffness properties of integral skinned foamed thermoplastics. It has been shown experimentally that there exists a square-power relationship between modulus and density for high-density closed-cell thermoplastic foams, but this has not been confirmed by existing theoretical models for foams. These models are reviewed and finite element analyses of “circular hole in square plate” and “spherical hole in solid cube” models are presented which give close agreement with the empirical results.

Shear-Lag Effect in Sandwich Panels With Stiffeners Under Three-Point Bending

Abstract: In this paper, a modified theory based upon Reissner’s procedure for the shear-lag effect of the sandwich panel is presented, which includes the effects of the anisotropy of the faces and the shearing rigidity of the core. In order to verify this theory, bending experiments were performed with sandwich panels composed of a soft core, stiffeners, and orthotropic faces. It was found that the effective bending rigidity calculated from this theory was lower than that derived from the classical bending theory and that the theoretical strain distribution on the faces agreed well with the experimental results.

The influence of bar spacing on tension stiffening in reinforced concrete slabs

Abstract: The concrete between the cracks in the tension zone of a cracked flexural member makes a significant contribution to the flexural stiffness of the member. This paper describes tests which provide data on the tension stiffening effect and, in particular, the influence of bar spacing on tension stiffening in slabs. It is concluded that the tension stiffening can be calculated on the basis of an average tensile stress equal to a fraction of the tensile strength of the concrete acting over an effective area of concrete surrounding the bars in the tension zone. The tension stiffening reduces, with an increase in strain, at a rate which depends upon the bar spacing.

Theoretical Study on Anisotropy of Bending Rigidity of Woven Fabrics

Abstract: In order to analyse the bending rigidity of woven fabrics in any direction, the authors have theoretically derived a versatile equation (19) without neglecting twist effects of constituent yarns. Assuming that yarns are elastic and homogeneous and no interaction exists in yarns, the twist effects could be described as a function of flexural rigidities in principal directions of woven fabrics, and Poisson's ratio of yarns (eq. (25)). However, because observed values do not always agree with theoretical values, the authors have introduced a parameter n (eq. (27)) which relates to V introduced by Cooper (eq. (28)).

Effect of Openings on Lateral Buckling of Beams

Abstract: The present paper describes a series of test on slender model cantilever beams containing a set of rectangular or circular openings along the center line of the beam, in which the size and spacing of the opening were varied. The beams were subjected to tip shear loads, and results are given to illustrate the influence of the relative size of the openings on the buckling loads which were determined by a modified Southwell Plot. The experimental results have been compared with approximate theoretical values based on an equivalent beam flexural rigidity.

Frame-Wall Systems with Rigidly Jointed Link Beams

Abstract: A new continuum model for the lateral load analysis of frame-wall systems with rigidly jointed link beams is presented. It consists of a vertical shear element with infinite flexural rigidity and a restraint-free wall having infinite shearing rigidity. The stiffness of the rotational restraints provided by the link beams to the wall is included in the rigidity of the shear beam. The validity of the proposed model is demonstrated with an example of a 15-story system. The present results are in excellent agreement with those obtained by analyzing the structure as a frame, in which the wall is treated as a wide column and the members are taken as inextensible. For the same structure the top deflection found by employing the conventional model was found to be more than three times the correct value, where the conventional model is one in which the link beams are assumed to provide rotational restraints equal to 12 times their flexural stiffness only to the adjacent column.

Method and device for measuring flexural rigidity of filamenttlike material

Abstract: PURPOSE:To make it possible to measure flexural rigidity of a thin filament-like material with simplicity and high precision by detecting buckling stress of a test piece held by projecting at a specific length out of a clamping plate for securing the test piece, when the test piece is pressed in its axial direction. CONSTITUTION:A bar 3 is fixed to a stress pickup 2 of a stress meter 1, and a plate 4 is fitted to the tip of the bar 3. Directly below the plate 4 there are provided clamping plates 6 for clamping test piece such as fibers, filaments or the like and a movable part 7 fixing the clamping plates 6 and capable of moving in the direction of the axis of the test piece. In the measuring process, the test piece 5 is held by clamping plates 6 so that the test piece is projected at a length l defined by formula, 0.5<=l<=100 D, where D represents an apparent diameter (mm) of the test piece, from the clamping plate, and thereafter the movable part 7 is lifted to press the sample in the axial direction and to measure the buclking stress generated thereby. As the movable part 7, there is utilized a conventional tension testing machine, for example, and as the defor meter 1 there is utilized a load cell or the like of a small capacity used in the tension tester.

Analytical studies of the effects of movements on steel and concrete bridges

Abstract: An analysis of the effects of support settlement on steel highway bridges and member stresses is presented. Design equations are given to determine tolerable limits for such movements. The structural performance of several concrete systems is also evaluated for differential settlements. A simple but approximate method of analysis (relaxation method) was used in the analysis. The flexural rigidity, span length, creep and shrinkage coefficients of concrete, and rate of the foundation settlement were found to be the most important parameters in accurately determining the settlement stresses.

Buckling of elastically supported continuous columns, including hand design of grids of columns and supporting beams

Abstract: Exact methods are given for finding the lowest elastic critical load of a continuous column with elastic supports, and for finding stiffness to represent the out of plane support which the columns of a grid of beams and columns receive from the beams. The beams and columns of the grid need not be identical, uniform or evenly spaced. However, the flexural rigidity distribution for one beam must follow from that of any other beam by scaling, and the column flexural rigidities (and axial forces) must be similarly interrelated. The exact methods require a computer. Therefore design curves and approximate methods are also given. Hence hand calculations can be used to obtain out of plane grid buckling loads or to design grids with required buckling loads. The column methods apply regardless of the source of the elastic supports, and the beam methods apply when the supported columns are replaced by suitably interrelated structures. (Author/TRRL)

Plastomer mfr. with improved physical properties - by stretch deformation in rolling mill gap at raised temp.

Abstract: Slabs, plates, profiles and other sections, made of a plastomer are passed through the gap between pairs of rolls which reduces their cross-section by a combined compressive and shear stress. A sandwich type of structuring is produced thereby, with a grain orientation which is governed by the process temperature, velocity and friction of the rolls, and by the set gap width. To achieve permanent compressive stretch deformation in amorphous plastomers, the temperature is held below the glazing temperature, and in the case of partly crystalline plastomers the crystallite fusion temperature is the upper temperature threshold. This imparts to plastomers improved properties, specially as regards flexural rigidity, without having to add reinforcement, for example, by glass fibres. The complex machinery, required for biaxial stretch deformation of plastomers, is saved and standard rolling mills can be used.

Method of winding linear material

Abstract: PURPOSE:To enable winding with enough reverse tension without damaging the surface of a linear material, by providing a forcibly bending section in a fore position to pass the material through the beinding section while curving the linear material. CONSTITUTION:A forcibly bending section 3, which comprises two pairs of guide rollers 5, 6 separated from each other in the direction of reception toward a receiving machine 1 and intermediate guide rollers 7 vertically displaced from the direction of reception, resists the movement of a linear material 2. The tension T2 of the material already passed through the bending section 3 is equal to the sum of the tension T1 between the section 3 and the receiving machine 1 and a tension increment due to the resistance. Therefore, the tension T2 is stronger than the other T1. A necessary reverse tensile force is applied to the material by the bending section 3 within such limits that the reverse tensile force due to the receiving machine 1 is not applied to the surface of the linear material. As a result, the material can be wound without slipping even if the material has a high flexural rigidity and requires a strong force for winding.

A method for the estimation of collapse loads of corner girders and struts

Abstract: The equivalent thickness of deflected panels under compression and bending moment are estimated by the energy method. The effective flexural rigidity of columns with rather small slenderness ratio are estimated by using Johnson's and Euler's formula. Using these equivalent thickness and effective flexural rigidity, the collapse load of corner girders and struts are calculated by elastic finite element method. The collapse load and collapse mechanism are compared with experimental results. This method will be usefull at the initial design stage for the simplicity.