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This paper presents a theoretical model for structural concrete in pure torsion which is comparable in rationality and generality to the well known theory for flexure. As in flexure the theory is formulated by considering the equilibrium conditions, the geometry of deformation, and the stress-strain characteristics of the steel and the concrete. The model is capable of predicting the complete post- cracking torsional behavior of symmetrically reinforced structural concrete members. In the paper the theory is applied to the following cases: the torsional response of reinforced and prestressed concrete members; the torsional capacity of under-reinforced, partially over-reinforced and completely over-reinforced members; and the prediction of balanced reinforcement ratios. [ABSTRACT FROM AUTHOR]

This paper presents the results of tests on 24, rectangular, reinforced concrete panels which were simply supported along all edges and subjected to uniaxial compression. The panels were constructed of normal weight concrete with design strengths of 2500 and 3000 psi (17.2 MN/m- and 20.7 MN/m²) and were reinforced with two-way, steel wire mesh placed in one and two layers. The panels were all loaded to failure. Failure was preceded in each case by plate buckling (biaxial curvature). In all cases the panels failed in a collapse mechanism sim-ilar to that for simply-supported plates which are subjected to uniform, transverse loads. The final load-carrying capacities of the panels were greater than their initial buckling capacities by from I to 24 percent. Formulas for the prediction of the loads at which buckling in such plates will occur are pre-sented and comparisons made with the experi-mental results. The formulas are in closed form and are suitable for design applications. [ABSTRACT FROM AUTHOR]

A simple method is described for visualising regions of bone that have yielded in tension. The appearance of such regions is quite different from that of regions that have yielded in compression. The significance of these findings is discussed. [ABSTRACT FROM AUTHOR]

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An experimental study was carried out on structural lightweight concrete under short-term biaxial compression. Strength, deformational behavior and fracture under various compressive stress combinations were studied. Stress-strain relationships are reported for uniaxial and biaxial compression. Failure stress envelopes were compared with results for normal concrete, obtained by various authors, and with results for lightweight concrete obtained by one other author. The modes of failure of specimens indicated that tensile deformation is dominant in the failure mechanism of structural lightweight concrete loaded in both uniaxial and biaxial compression. The application of transverse compression on the specimens caused a strength increase (24 to 28 percent) compared to uniaxial compressive strength. This strength increase is dependent on the stress combination (maximum at approximately σ2/σ1 = 0.4 to 0.5), but not very much on composition of the concrete. [ABSTRACT FROM AUTHOR]

A mathematical model based on time-shift prin-ciple is used for predicting creep of concrete at constant and variable temperatures. Previously published experimental creep data for concrete specimens loaded in compression at constant or variable temperatures were used to compare the predicted creep strains with the experimental re-sults. In both cases good agreement was observed. [ABSTRACT FROM AUTHOR]

This paper presents the development of a theory for bonded prestressed concrete rectangular beams subjected to combined torsion, bending and shear. The analysis Is similar to the one proposed by Collins et al for reinforced concrete beams. Strength equations are derived for Mode 1, 2 and 3 failures. An empirical equation is developed for the case of shear-compression mode of failure. The predictions of the theory are compared with over one hundred test results available in the literature. In general the agreement is good. The strength was not over-estimated for any of the test beams. [ABSTRACT FROM AUTHOR]

Research on the properties of concrete is taking place in many universities, in specialist research institutions, at ready-mixed concrete and precast concrete plants, and within construction companies throughout the world. The need for more work is questioned and discussed in relation to research on the behavior of concrete under load, and subjected to different environmental histories, with particular reference to the current strength and deformation studies at the Cement and Concrete Association. [ABSTRACT FROM AUTHOR]

Comparative tests on four types of beams, (three beams of each type) all having the same initial pre-stressing force (being cast in the same prestressing bed), were carried out by the authors at the Uni-versity, Southampton, 1970-71. All four types were of about the same ultimate resistance, but had dif-ferent amounts of nontensioned steel in the ratios I : 2.68 : 4.0 : 5.22. Intensified and accelerated cur-ing of the 12 beams was carried out during 86 days, at an average temperature of 38 C (I OOF) and a humidity of 32 percent. Different kinds of strain measurements were made and showed very good agreement with the formulas suggested by CEB-FIP, according to which shrinkage and creep values can be calculated for varying conditions. The effec-tive prestress with maximum amount of nonten-sioned steel was only 60 percent of that with mini-mum amount of nontensioned steel. Based on the good agreement between measurements and CEB-FIP formulas, the losses were evaluated for humidi-ties between 50 percent and 100 percent for the four types of beams of different percentages of nontensioned steel which indicates that the pre-stressing losses at infinity increase substantially with reduced humidity and enlarged percentage of non-tensioned reinforcement. [ABSTRACT FROM AUTHOR]

Presents a number of revisions to the ACI Building Code. The revisions deal with minimum lap length of reinforcement, tension splice requirements, tension and axial loads, notation in shear and torsion, shear-friction, development lengths of rein-forcement, anchorage of web reinforcement, precast concrete details and erection requirements, and intentional roughness of composite flexural members. The proposed changes are explained. [ABSTRACT FROM AUTHOR]

Using 2 in. cubical specimens, biaxial compres-sion-compression strength envelopes were obtained for three strengths of ⅜ in. (10 mm) MSA all-light-weight aggregate concrete: 2 ksi, 3.5 ksi, and 5 ksi (140, 245, and 350 kgf/cm²). The desired stress state and the elimination of friction were achieved by loading the specimens through wire bristle compression platens in a spe-cially designed two-channel, closed-loop, electro-hydraulic testing facility. In contrast to a previous investigation, the shape of the failure envelope was found to differ from that for regular weight concrete. Furthermore, an investigation of the influence of loading path showed that two-step sequential load-ings resulted in strengths significantly lower than those obtained by proportional loadings. [ABSTRACT FROM AUTHOR]

Previous tests indicate that a reasonable, although not exact, assumption in the prediction of creep strains resulting from multiaxial stresses is that the Poisson's ratio for creep is constant and equal to the static elastic value. To predict creep under multiaxial loading this assumption was combined with the rate of flow method, developed essentially for the prediction of axial creep strains under uniaxial loading. Creep predictions, on the basis of independently obtained control data, are compared with the experimental strains obtained from multiaxially loaded concrete specimens. Only moderate stress levels were considered and all specimens were sealed. The results of the comparison indicate satisfactory agreement between the proposed method and the test results. Second-order effects not taken into account in the analysis are discussed. A numerical example is included in the Appendix to show the application of the proposed method. [ABSTRACT FROM AUTHOR]

A series of 26 prestressed concrete beams was tested to investigate the upper limit of the shear strength, associated with inclined compressive failure of the web. The cross section, web reinforce-ment, prestress, and shear span were varied. The results showed that the behavior at failure could be represented by a truss formed by the stirrups and concrete struts in the web further strengthened by the flanges. Design formulas are suggested. [ABSTRACT FROM AUTHOR]

It is suggested that creep is due to oriented internal moisture diffusion caused by a free energy gradient and to slow deformation of the elastic skeleton of the gel induced by viscous deformation of adsorbed water. Shrinkage actually realized is affected by the relief of stress in the elastic skeleton by creep. The nature of moisture diffusion suggests that creep strains may not be superposable under multiaxial stress. Creep recovery is shown to depend both on creep at tne time of unloading and on magnitude of elastic strain recovery. A rheological model is proposed. Some supporting experimental data are presented. [ABSTRACT FROM AUTHOR]

Results are given for the creep of concrete under various three dimensional compressive stress systems at two temperatures for a loading period of 2 years. The existence of a creep Poisson's ratio of a similar magnitude to the elastic Poisson's ratio has been confirmed and a simple formula is given for the prediction of creep under multiaxial stress systems from the more easily obtained uniaxial creep curves. Creep recovery after the removal of three-di-mensional stress systems is shown to bear no direct relation to either measured elastic strain recovery or measured creep magnitude. [ABSTRACT FROM AUTHOR]

Tests are reported on the creep and recovery of concrete under uniaxial compression and tension, applied at advanced ages of over a year. The characteristics of the creep components ( irrecoverable or flow, recoverable or delayed elastic) for young and mature concrete are compared, and found to be in reasonable agreement. The rate of flow method (based on the two components) for calculating strain under variable stress is discussed. In particular, it is compared favorably with superposition. [ABSTRACT FROM AUTHOR]

The compressional resilience of Acrilan, Terylene, and Tricel fibers at pressures ranging from 0.001 to 1.0 psi is reported, and the effects on the resilience of various fiber properties are determined experimentally. The behavior of a mass of fibers in compression can be adequately described by an equation of the form: T = aP-b, where T is thickness of the fibrous mass, P is the pressure, and a and b are constants which depend on fiber properties and also on the experimental conditions. Fiber properties investigated were staple length, fineness, crimp and interfiber friction. Crimp has the highest influence on resilience, whereas fiber friction and fineness indicate comparatively less effect. Fiber length shows no correlation with resilience. There is little difference between Acrilan, Terylene, and Tricel as suitable materials for fiberfill. [ABSTRACT FROM PUBLISHER]

A method was developed for preparing small specimens of oriented nylon 6-10 bristle suitable for the measurement of the behavior in compression parallel to the direction of orientation. The stress-strain curve in compression differed markedly from the tensile curve, being sharply bent toward the elongation axis. At room temperature, the stress reached a maximum of 0.45 g/den at about 10% strain, and at 100°C this maximum was reduced to 0.18 g/den at 6% strain. Con trary to the indications of the stress-strain curves, the elastic recoveries from up to 20% strain in compression and tension were quite similar. At 100°C, however, the elastic recovery in compression was greatly reduced, strains above about 5% being unrecoverable. The rate of stress relaxation in tension and compression were compared. Both the tensile and compression relationships must be known to predict bending behavior. An example analyzed indicates that, in a bend of radius of curvature 10 times that of the fiber, the maximum strain in compression on the inside of the bend is 50% greater than that in tension on the outside. [ABSTRACT FROM PUBLISHER]

Certain aspects of the handle of fabric laminates are related to properties of the component fabrics. Particular attention is paid to a theoretical prediction of the bending stiffness of a laminate from the bending and tensile properties of its components. This theoretical stiffness is a minimum value; if, in practice, the observed stiffness is much greater than this, it may generally be assumed that excess of adhesive or of melted foam is the cause. The paper also reports work on other features of the bending behaviour, such as the degree of recovery from bending, and on the shearing behaviour. The work is concluded by a brief study of some faulty laminates. [ABSTRACT FROM AUTHOR]

The problems involved in making a mechanical analysis of bending deformations in textile fabrics are discussed. It is suggested that progress can be made by making simplifying assumptions concerning the geometry of fabric structure and deformation and using energy considerations to calculate forces and moments. Certain simple examples are given of the usefulness of this approach. A foundation is laid for the construction of a computer model that will, it is hoped, simulate the viscoelastic bending and creasing behaviour of textile fabrics from a knowledge of the bending and torsional viscoelastic properties of the constituent fibre(s) and their relative geometrical arrangement. [ABSTRACT FROM AUTHOR]

The mechanism investigated is one of a type used on a 400-in. R.S. felt loom. A test rig was used for the experimental work and a dynamic model of the mechanism was constructed. The displacement and velocity of the shuttle at the start of the pick and the effect of various loom parameters on the maximum shuttle velocity were investigated. [ABSTRACT FROM AUTHOR]

A study of the recovery of single fibres from bending is reported for nylon, polypropylene fibre, Courtelle, and some carpet fibres. Most of the recovery takes place during the first hour, with further small increases for up to seven days. The effects of heat treatments both before and during bending are examined. Poor correlation between bending and tensile recoveries leads to a consideration of tensile and axial compressive effects. Further work is desirable on the latter aspect. [ABSTRACT FROM AUTHOR]

An investigation of the effect of moisture and temperature on the crease-recovery of 100% cotton and 67% polyester-fibre-33 % cotton fabrics, untreated and cross-linked with dimethylol dihydroxy ethylene urea, is described. Cross-linking improves the level of crease-recovery at any temperature and partly offsets the reduction in crease-recovery caused by an increase in temperature. The polyester-fibre-cotton fabrics show a gradual decline in the values of crease-recovery as temperature increases, whereas the treated cotton fabrics show minimum values at 67 °C, and an explanation for this is offered. [ABSTRACT FROM AUTHOR]

An account is given of an investigation of the crease-recovery behaviour of 100% cotton fabrics, untreated and cross-linked with dimethylol dihydroxy ethylene urea, over a range of moisture content, and an explanation for the behaviour is suggested, a recent hypothesis involving actual and potential recovery being applied. The existence of a maximal crease-recovery value at moisture contents equal to that observed during cross-linking is shown, and an explanation for this is offered. [ABSTRACT FROM AUTHOR]

The three-dimensional nature of the knitted structure is considered by studying the thickness and compression behaviour of a wide range of plain-knitted fabrics. Compression-recovery curves were obtained for several plain-knitted fabrics in both their dry-relaxed and their completely relaxed states. The compression of the various fabrics is interpreted in terms of several different mechanisms. The effect of fabric tightness on the compression-recovery curves was investigated. The parameters t/l and p were determined for all the fabrics tested, where l is the fabric loop length, t the 'geometrical' thickness of the fabric, and ρ the fabric bulk density. A proportional relation between the parameter t/l and the fabric tightness was found to exist, and this is interpreted in terms of the basic plain knitted-fabric geometry. In addition, a linear relation between fabric bulk density, ρ, and the parameter g K/1·3 was observed, where K is the fabric-tightness factor and g the fibre specific gravity (g = 1·3 g/cm³ for wool). Specific examples cf this general relation agree with experimental observations made by other workers. The variation with fabric tightness of the felting-shrinkage rate for plain-knitted wool fabrics can be explained in terms of the relation between fabric bulk density and tightness factor. [ABSTRACT FROM AUTHOR]

Equations are given that relate the structure of spirally wrapped elastomeric-fibre core yams to their stretch properties. The model employed improves upon previous ones by considering the effect of covering-yarn diameter. Graphs are given that facilitate the use of the theory for manufacturing purposes. A comparison with available experimental data indicates an improved agreement between actual and predicted values of retraction in the most important case, where the input and output yam lengths are measured. It is expected that the improved theory given here will show to much greater advantage with the present commercial fine-core wrapped structures. In the special case where the wrapping or covering yarns have very low twist, the basic theory is inadequate. Modifications to account for compression of the cover yam are accordingly included to enable an approximate relationship between yam structure and stretch to be obtained in this case. [ABSTRACT FROM AUTHOR]