Thin Web Research Articles

The stress distribution near a loading point in a uniform flanged beam

The elementary theory of bending, which is the method by which the stresses in a uniform flanged beam subjected to transverse loading are usually determined, leads to certain incompatibilities of displacement and stress distribution near a section of the beam at which load is applied. The present paper endeavours to remedy these deficiencies. Two main cases are considered: that in which the beam is loaded through the web and that in which it is loaded through the flanges. In both of these the analyses lead to stress concentrations in the outer fibres of the flanges, and it is found that the maximum stress concentrations, which occur at the loading section, may be expressed with an accuracy sufficient for most engineering purposes by means of simple formulae. For both cases, maximum concentration factors occur in short beams having large flanges and thin webs. Results of strain-gauge tests carried out on mild steel beam specimens are presented which show very good agreement between the predicted and experimental stress distributions in the flanges, and a further part of the paper compares the present analyses with other recent work on the subject.

Bending Rigidity and Column Strength of Thin Sections

Abstract It has been found that elementary structural theory cannot be applied with accuracy to problems concerning beams and columns having thin deep webs and thin wide flanges, because of nonuniform stress distribution which exists in the flanges. In this paper the problems of nonuniform axial flange stress are treated by means of efficiency factors which apply to the flange material. These basic factors are evaluated from theoretical considerations. Then, given a particular section and the manner of loading, it is necessary only to apply the proper flange efficiency factor to calculate reduced or effective section properties, which can be used in place of the geometrical properties in the elementary formulas for lateral bending or lateral column buckling. The results are substantiated by empirical data. Practical usage is illustrated with examples. The tangentmodulus column curve is shown to apply to stiffened-skin panels when based on a “true slenderness ratio” which allows for shear lag effects. Conclusions are drawn indicating design for best efficiency.

Strain Energy Analysis of Incomplete Tension Field Web- Stiffener Combinations

The paper presents a minimum potential energy analysis of thin web beams subjected to shear loads above critical. The wave form of the buckled surface is approximated by a function that contains the wave length, wave angle, and wave depth as parameters. Four more parameters—namely, the stiffener compressive strain, the cap compressive strain, the cap bending deflection, and the panel shearing strain—are introduced, and the distribution of the mid-plane tensile, compressive, and shear stresses is worked out. The energy of the entire panel-load system is then computed and the resulting expression differentiated with respect to the strain parameters. The seven resulting equations define the equilibrium configuration of the panel. Expressions are obtained for the critical condition, principal midplane stresses, maximum web bending stresses, stiffener and cap compressive stresses, web wave length, wave angle, and wave depth. In particular, a formula is given for the bending loads on the stiffeners produced by the wrinkling of the web. The equations are shown to reduce to those of Wagner for an infinitely thin web. A comparison is presented which shows good agreement between theoretic and experimental values of the following: principal web stresses, stiffener compressive stresses, wave depth, and wave length.

Strength of Cotton Fiber Bundles

There appeared in the December 1942 issue of TEXTILE RESEARCH an article entitled "Plastic Bonded Cotton Fiber" by M.A. Goldman and Gerner A. Olsen, that has attracted some attention. In this article the authors de scribe a new process for laying a thin web of cotton fibers in parallel arrangement and bonding them to form un woven sheets. Early experiments have indicated that this method may utilize the inherent high tensile strength of the cotton fiber, which strength is, to a great extent, lost when the fibers are twisted to form a yarn. It is well known that the tensile strength developed by cotton yarn is only from 10 to 20 per cent of the combined strengths of the fibers in a given cross section of the yarn. A statement in the article that a part of the loss in strength is due to the fact that the full strength of a tensile member is only attained when it is perfectly straight, with the applied load acting along its longi tudinal axis, is confirmed by data given in the following letter received by Mr. Goldman from R. W. Webb:*

A NEW SPECIES OF DICTYA (SCIOMYZIDAE, DIPTERA)

Male. Wings with two brown spots in apical portion of subcostal cell. A row of about six short stout bristles on the distal half of the posteroventral surface of mid femora. Prosternum with a few hairs anteriorly and posteriorly, and a few hairs also present on the middle of the propleura in front of the spiracle. Genitalia similar to D. pictipes Loew, except the anterior claspers (see figure), which are bent forward hookwise, narrowly laterally expanded at the apex, and with a thin transparent web in the sinus of the hook.

Tapered Beams

PART III.—Taper Beams with uniform thin webs and concentrated booms of constant cross‐sectional area. This type of girder is shown in Fig. 1.

Working Stresses for Columns and Thin-Walled Structures

Abstract In metallic structures such as airplanes, airships, ships, bridges, etc. slender bars, thin webs, and thin-walled tubular members are very often used. In choosing working stresses for such structural elements, not only the mechanical properties of the material but also the elastic stability of these elements should be considered. The method of choosing working stresses for such structures is illustrated in this paper by several examples.

OENECTRA FLAVIBASANA, FERN

On the 20th of June, 1895, Mr. Balkwill brought to me some Tortricid moths which he found at rest upon honeysuckle in his garden. They were new to me. He asked if I wanted any more? I said I would take all he liked to bring of that kind; so by the 27th I had got about three dozen of them. Being desirous of learning something about them, I applied to Prof. C. H. Fernald for information, and sent some of the moths. He replied: “They are Oenectra flavibasana; Fern. That he had two specimens in his collection; the types: one from Texas and one from Illinois. That nothing is known of their early stages or food plants, and would be glad to have published all that was known on these points.” Up to the present time I can give nothing with certainty upon these points. Presumably, the larvæ had fed upon the honeysuckle, as chrysalids were found in the connate leaves with a thin silken web spun over them, one of which I raised to the moth. There is plenty of evidence of feeding having been done upon the plant, but nothing positive as to what did it. A lookout is being kept upon the plants for the next brood.

MICRO-LEPIDOPTERA

The following species, which have been described by Drs. Packard and Fitch, I have not met with. But for the convenience of those who may not have access to the writings of these gentleman, I condense the fol1owing account:–1. L. Argentifimbriella Clem. has been already mentioned at p. 57. It mines the under surface of leaves of the Chestnut oak and must resemble L. caryae-albella or L. lucidicostella. At p. 57, ante, it is suggested that L. querci-albella fitch may be the same insect. Dr. Fitch states that it mines the leaves of the White and chestnut Oaks indifferently. But Dr. Clemens says that Argentifimbriella makes a tent mine on the under side, has a cylindrical larva, and pupales suspended in a thin web in the mine like L. lucidicostella.