bluuebunny/crossref_metadata_2025 huggingface dataset:
Managers and Students as Newsvendors
Authors: Bolton Gary E. , Ockenfels Axel , Thonemann Ulrich W.
Published: July 2012

We compare how experienced procurement managers and students solve the newsvendor problem. We find that managers broadly exhibit the same kind of pull-to-center bias as students do. Also, managers use information and task training no better than students. The performance of managers is positively affected by the level of their education and their level in the organizational hierarchy. We discuss implications for theory and for how ordering might be improved in practice.

This paper was accepted by Teck Ho, decision analysis.
Knowledge Recombination Across Technological Boundaries: Scientists vs. Engineers
Authors: Gruber Marc , Harhoff Dietmar , Hoisl Karin
Published: July 2012

Building on the seminal work of Thomas J. Allen, we contribute to the emerging microlevel theory of knowledge recombination by examining how individual-level characteristics of inventors affect the breadth of their technological recombinations. Our data set combines information from 30,550 European patents with matched survey data obtained from 1,880 inventors. The analysis supports the view that inventors with a scientific education are more likely to generate patents that span technological boundaries (in our case, 30 broad, top-level technological domains) than inventors with an engineering degree. A doctoral degree is associated with increased recombination breadth for all groups of inventors. The breadth of an inventor's technological recombinations diminishes with increasing temporal distance to his education, but the differences between scientists and engineers persist over time. Our findings provide several new insights for research on inventors, the literature on organizational learning and innovation, and strategy research.

This paper was accepted by Lee Fleming, entrepreneurship and innovation.
Some investigations of the effects of core size and steel and concrete quality in short reinforced concrete columns
Authors: King J. W. H.
Published: July 2012

Summary:

The work described is a continuation of earlier work on short concrete columns, which had as its object the determination of the effect of lateral reinforcement on column strength. It was clear from this earlier work that relative core size would be likely to have a significant effect on strength, and the present investigations were initiated primarily to examine this.

On the assumption that the currently accepted formula for helically bound columns had some justification for taking as one of its terms “"core area by concrete strength,” it was believed that high quality concrete would demonstrate the effect of core size better than a more ordinary concrete and a series of tests (Group I) was carried out in this way. As the tests failed to indicate any marked effect, columns (Group II) were made with normal concrete and high quality steel. To round off the work a third group was made of normal quality steel and concrete.

In the main, binders were of a normal square type and of a materially constant strength, but a few were of modified shapes.

As a result of the tests it has been possible to formulate general conclusions concerning the effect of core size, cover thickness, concrete and main steel strength, and core shape, to confirm the general conclusions of earlier work that binder contribution to strength was proportional to 1/pitch2 and to indicate that there is material advantage in using high quality steel as main reinforcement.

Actual test loads are compared in the tables with loads calculated by a formula derived from the earlier tests, where core area was a constant proportion of the column area (51 per cent.), where concrete strength was sensibly constant, and where main steel consisted of various sizes of normal black bar. The significance of the various changes is thus revealed more clearly.
A plastic theory of design for ordinary reinforced and prestressed concrete including moment re-distribution in continuous members
Authors: Baker A. L. L.
Published: July 2012

Summary:

A general expression is derived for the ultimate strength in bending of ordinary reinforced concrete and two types of prestressed concrete beams, taking into account plasticity. A method of calculating elasto-plastic deformations is developed and applied to the problem of re-distributing bending moments in continuous members and frames.
The non-destructive testing of concrete
Authors: Jones R.
Published: July 2012

Summary:

A method is described which has been used to determine the velocity of longitudinal waves in concrete specimens by measuring the time taken for an ultrasonic pulse to travel through a known length of concrete. Results are given which illustrate the use of the method for studying the variations occurring among laboratory specimens.

The value of the longitudinal wave velocity as an index of concrete quality is discussed, with reference to tests made on a variety of specimens subsequently subjected to compressive and flexural strength tests and density analysis. Deterioration of concrete quality due to freezing and thawing can be detected before superficial damage occurs.

The Poisson's ratio of several types of concrete has been measured and values from 0·16 to 0·31 obtained depending mainly upon the type of aggregate.
Steam curing of concrete
Authors: Nurse R. W.
Published: July 2012

Summary:

The various methods of steam curing are briefly described and preliminary laboratory data on the effect of low pressure curing are given. An approximate method for assessing the effect of a stated cycle of operations is described.

The effects of time and temperature, type of aggregate, type of cement and size of specimen are discussed.
The distribution of concrete stress in reinforced and prestressed concrete beams when tested to destruction by a pure bending moment
Authors: Prentis J. M.
Published: July 2012

Summary:

A method is given for utilizing experimental data derived from bending tests on reinforced and prestressed concrete beams to determine the stress-strain relationship for concrete. No initial assumption is made as to the shape of this curve, and the result obtained is unique for the given test data, so that the factors which govern the validity of the final result are simply the basic assumptions of the method of analysis.
Principles underlying the steam curing of concrete at atmospheric pressure
Authors: Saul A. G. A.
Published: July 2012

Summary:

This paper summarizes the conclulions drawn from experimental work carried out at the Cement and Concrete Association Research Station and elsewhere concerning the principles underlying steam curing at atmospheric pressure.

It is shown that if the temperature gradient of the concrete after the time of mixing does not exceed a certain value, the concrete gains strength during and after treatment in relation to its “maturity” (reckoned in temperature-time) approximately in accordance with the same law as holds for normally cured concrete. Concrete which is raised in temperature more rapidly is shown not to obey this law, and to be adversely affected in strength at a later age.

The use of the too rapid early temperature rises often employed in practice introduces various opposing variables which suggest optimum temperatures, delayed treatments and other arrangements of the curing cycle; such expediencies are unnecessary, however, if a slow initial temperature gradient is used.

The paper contains tables of results supporting these conclusions, and an appendix in which a possible cause of the phenomena is suggested.
A theory of deflexion of reinforced concrete beams under short-term loads
Authors: Blakey F. A.
Published: July 2012

Summary

From elementary elastic theory a method for calculating the deflexion of simply reinforced concrete beams under short-term loads is developed. It is shown that the results obtained in this way are in better agreement than those obtained from any other method of calculation.
Progress in prestressed concrete research
Authors: Cooley E. H.
Published: July 2012

Summary

Prestrevsed concrete is now firmly established as a new method of building construction and in this report an attempt is made to review the present day progress in research and development. Much still remains to be done and suggestions are put forward for future work, the needfor co-ordination of effort between the various research organizations being emphasized.
Experimental blastfurnace cement incorporating high-magnesia slag
Authors: Stutterheim N. , Nurse R. W.
Published: July 2012

Summary:

Experimental granulations have been carried out on slags from blastfurnaces employing a dolomitic burden. The resulting slags, containing 15–18 per cent MgO, were made up as Portland blastfurnace cements and standard tests were carried out. Cements of good quality were obtained, although the substitution of MgO for CaO in the slag results in a fall in strength. In spite of the high MgO contents, no periclase was formed in the slags, and the cements showed no long-term unsoundness.
Tests on end-anchored unbonded prestressed concrete beams having parabolic steel eccentricity, subject to uniformly distributed loading
Authors: Gifford F. W.
Published: July 2012

Summary

Tests were carried out on a series of four rectangular beams in which the prestressed was induced by two 5 mm wires placed in parabolic grooves cast into the sides of the beams. The loading applied was approximately uniformly distributed, and while the widths of the beams were varied, the working stress in the concrete was maintained at approximately one-quarter of the cube strength, necessitating varying initial stresses in the steel.

The beams were tested to destruction, the main object being to establish the factors of safety against cracking and failure, and to obtain data in connexion with the theory of the ultimate strength of prestressed concrete beams.
The percentage voids in compacted gravel as a measure of its angularity
Authors: Shergold F. A.
Published: July 2012

Summary

The British Standard for concrete aggregates (B.S. 882:1944) distinguishes “rounded” from “angular” aggregates, but gives no method for defining or measuring different degrees of angularity. The present article describes the development of a test for this purpose. A study of the literature was followed by experimental work which showed thar the most suitable method for expressing the degree of angularity of gravels was the measurement of the proportion of voids in the single-sized aggregate when compacted in a prescribed way. This proportion was found to vary from about 33 per cent in a well-rounded beach gravel to about 45 per cent in a very angular crushed rock. The test result is expressed thus:—

“Angularity number” = percentage voids — 33. The angularity number of about 100 samples of aggregate ranged from 0 for very rounded gravel to 11 for an angular crushed material, and showed good agreement with personal opinions of the relative angularity of the samples and with the compacting factor of concrete made from some of the aggregates. Full details of the method of test are given in an appendix.
Test of a prestressed concrete building frame
Authors: Shepley E.
Published: July 2012

Summary

The behaviour of a multi-storey building frame under vertical loading has been simulated in a test to destruction of a full-size replica of a single storey. Reinforced concrete columns and prestressed beams were monolithically married at the joints by in situ concrete and mild steel bars and, during the test, measurements of joint moments and span de flexions were made. The frame was designed according to elastic theory and the sections were detailed in contemporary fashion as regards working stresses in the respective components, i.e. reinforced, prestressed and composite. The test confirmed that a satisfactory design with an adequate factor of safety against collapse can be made on the basis of an elastic analysis.
A method for determining the dynamic Young's modulus of concrete specimens developed for corrosion studies
Authors: Stutterheim N. , Lochner J. P. A. , Burger J. F.
Published: July 2012

Summary

The effect of aggressive environments on concrete can conveniently be studied by observing the resultant changes in the dynamic modulus of elasticity of test specimens. An apparatus for rapid and accurate measurement of the fundamental transverse and longitudinal frequencies of a 1 × 1 × 11 in. concrete specimen is described. Typical experimental results are presented.
The thermal properties of composite concrete floors
Authors: Moore A. E.
Published: July 2012

Summary

An investigation of the relative comfort of various types of concrete floors is reported. An apparatus is described which compares the heat loss from a body on different types of floor. Results of measurements on ten floors with various kinds of insulation are shown and discussed. In the light of these experiments, tentative recommendations are made for the construction of improved floors.
A variable-air-gap inductance strain gauge
Authors: Simmons J. C.
Published: July 2012

Summary

This note describes a sensitive inductance strain gauge designed for use on wet concrete test specimens. The gauge is of the variable-air-gap type and depends on the strain of the test specimen causing a change in length of a small air gap in a magnetic circuit. An a.c. bridge network and an amplifier enable the output signal to be measured by a d.c. milliameter. The sensitivity of the gauge can be varied over a wide range and, over the range of sensitivities tested, the calibration curve was sensibly linear. At maximum sensitivity strains of the order of 2 × 10−7 could be detected.
Poisson's ratio of concrete: a comparison of dynamic and static measurements
Authors: Simmons J. C.
Published: July 2012

Summary

This paper describes static and dynamic tests carried out on a series of concrete specimens to determine the values of Poisson's ratio. Three values of the ratio were determined, the static value and two values derived from the dynamic tests. Where possible the values are related to each other and to other properties of the concrete. Values of the elastic moduli determined from both types of tests are also compared. From the results of the dynamic tests an equation is derived by which the dynamic elastic modulus may be determined from measurements of the ultrasonic pulse velocity.
The effect of varying the pre-tension and area of reinforcement on the ultimate bending strength of concrete beams
Authors: Prentis J. M.
Published: July 2012

Summary

Tests on eighteen pre-tensioned concrete beams are reported. The beams were cast in groups of three, the members of anyone group differing only in the amount of pre-tension. The percentage of reinforcement varied between groups but was always sufficient to preclude failure by steel rupture.

Two series of tests were made. In the first, three groups of three beams were made and tested by the author who used an extreme range of pre-tension. The second series was made and tested independently by Mr F. C. H. Nisbet, who repeated the author's tests in respect of beam dimensions and percentage of reinforcement, but who used rather higher concrete strengths and a more practical range of pre-tension.(1)*

The beams were all 4 in. deep with an effective depth of 2½ in. Two widths were used: 1⅛ in. and It in. The length between supports was 45 in. and under four-point loading the central 15 in. was subjected to a uniform bending moment.

Both the area of steel and the degree of pre-tension were found to have an appreciable effect on the bending strength of the beams.
A portable ultrasonic concrete-testing apparatus
Authors: Elvery R. H. , Vale D. W.
Published: July 2012

Summary

The new apparatus described is basically similar to the Road Research Laboratory ultrasonic equipment but has been designed to be more convenient for field testing work. It has been built in two separate units for easy portability and the weight has been reduced to approximately half that of the original apparatus. It is still necessary to provide an a.c. mains supply for the equipment. A number of new features have been incorporated, providing greater convenience in use and servicing.
Maturity and the strength of concrete
Authors: Plowman J. M.
Published: July 2012

Summary

The relationship between concrete strength and its maturity is examined and the datum temperature for maturity calculations determined. Strength-maturity results from varying sources are examined and a law stated relating the strength at any maturity to that at a given maturity. This law is shown to be independent of water/cement ratio, aggregate/cement ratio and cement quality. Examples of the uses of this law are given.
The minimum transverse strength of slab bridges
Authors: Morice P. B.
Published: July 2012

Summary

A theoretical analysis of the modes of failure and ultimate strength of slab bridges shows that the normal method of elastic analysis leads to a design in which the transverse flexural strength is considerably greater than that required to give a factor of safety in the structure as a whole equal to that of longitudinal elements considered alone. It is suggested, therefore, that in the design of slab bridges advantage can be taken of this by permitting moderate tensile stresses when calculating the degree of transverse prestressing required, and that in reinforced slab bridges the amount of transverse reinforcement can be appreciably reduced.
The effect of temperature on the compressive strength of concrete
Authors: Malhotra H. L.
Published: July 2012

Summary

As part of an investigation on the effect of temperature on the crushing strength of concrete, tests have been carried out using 2 in. diameter by 4 in. long specimens made with ordinary Portland cement, river sand and gravel aggregate, having various mix proportions and water/cement ratios.

The crushing strength of concrete at temperatures up to 600°C was independent of the water/cement ratio used but was influenced by the aggregate/cement ratio. Concrete specimens loaded to produce normal design compressive stress during the period of heating showed less reduction in strength than specimens without imposed load. There was afurther loss in the compressive strength of the specimens when cooled after heating to a given temperature.
Site determination of friction in prestressing cables and interpretation of test data
Authors: Trimble E. G.
Published: July 2012

Summary

This paper describes tests carried out on site to determine friction loss in Freyssinet cables in lead-lined steel Kopex tube,* the results of which largely confirm some of the figures published previously by Cooley.† The tests were based on force measurements and it is shown that extension measurements may not always be reliable. It is shown also that the effect of friction may result in the cable tension at the centre-line being higher than that at the anchorages.
A compilation of X-ray powder diffraction data of cement minerals
Authors: Midgley H. G.
Published: July 2012

Summary

X-ray powder diffraction methods are being used increasingly for the identification of minerals in cement. Since the last compilation was made a considerable amount of work has been done and this new compilation includes the most recent data.
The relation between bond strength and maturity for ordinary Portland cement concrete
Authors: Plowman J. M.
Published: July 2012

Summary

This paper shows a relation between bond strength and maturity similar to that between crushing strength and maturity previously reported. A direct relation between the constants used in the two mathematical expressions is deduced. The results relate to a limited number of tests under constant temperature curing and maximum humidity.
An approximate solution to the problem of longitudinally continuous shells
Authors: Morice P. B.
Published: July 2012

Summary

An orthogonal series of functions, described by Inglis as “basic functions”, provides the basis of a method of analysing shells with end conditions other than the usual case of simple support. Owing to the differential relations of the basic functions, it is necessary to use the Schorer shell equation. It is shown that the membrane equations and the simple edge beam analyses yield solutions compatible with that of the edge disturbance problem so that a complete shell edge beam analysis is possible.
An appreciation of the Schmidt rebound hammer
Authors: Kolek J.
Published: July 2012

Summary

The Schmidt rebound hammer is described and some theoretical aspects underlying the functioning of the hammer are discussed and supported by some experimental results. The method of performing the test and its limitations under different conditions are described. Correlations with rate of wear of concrete and compressive strength on the basis of 500 cube results are derived. The Schmidt rebound hammer is recommended for use in two categories of application—on the building site and in precast works.
A sand drier for a concrete laboratory with an Appendix on thermal performance
Authors: Hopkins H. J. , Neville A. M.
Published: July 2012

Summary

This article describes a rotary sand drier made of stock items of equipment to serve the requirements of a laboratory at Canterbury University College, Christchurch, New Zealand, in which all concrete for experimental and demonstration purposes is made with dry aggregate conforming to pre-determined grading curves. From 15 to 20 tons of aggregate are used each year.
Measurement of the thickness of concrete pavements by dynamic methods: a survey of the difficulties
Authors: Jones R.
Published: July 2012

Summary:

This note reviews the practical difficulties and errors occurring in the methods employed in determining the thickness of concrete pavements by non-destructive methods based on the propagation of sound waves in the pavement.

Most of the methods give errors in the determination of the thickness of imperfectly compacted slabs when a variation of sound velocity occurs with depth in the slab, but calculations are given which show that the method based on the reflection of an ultrasonic pulse by the bottom of the slab could be made to yield accurate results should the present experimental difficulties be overcome.
The relation between the strains in the concrete and the steel in reinforced and prestressed concrete beams
Authors: Evans R. H. , Williams Alan
Published: July 2012

Summary

Information, obtained by X-ray photography, is presented on the strains in the steel and concrete and on the slip occurring in concrete beams reinforced or prestressed with various types of bar and wire.

An expression is derived relating strain in the steel, virtual strain in the concrete, and slip at the steel-concrete interface. A comparison is made between strains in the concrete at the interface and at the surface. It is found that, for reinforced concrete beams, the strain at the surface is lower than the strain in the interior.

The strain in the steel at the section of failure is compared with the average surface strain in the concrete at the level of the steel. The influence of several factors on this ratio is discussed. It is found that the ratio of the strain in the steel to the average strain in the concrete has a value greater than unity for reinforcement with good bond characteristics and that the ratio increases as loading increases and when the section of failure occurs at a peak in the bending moment diagram.
The use of gamma radiography to detect faults in grouting
Authors: Forrester J. A.
Published: July 2012

Summary

This paper describes the use of gamma radiography to detect defective grouting. The technique was used to examine a prestressed beam which had been badly grouted intentionally; faults were detected, and their presence was confirmed by breaking open the specimen.
The estimation of the strength of concrete made with lightweight aggregate
Authors: Shirayama Kazuhisa
Published: July 2012

Summary

In an earlier paper the author proposed an experimental formula for estimating the compressive strength of lightweight aggregate concrete by an extension of Abram's water/cement ratio theory. The present paper describes compressive strength tests performed on concrete made with expanded clay aggregate produced in Norway which show good agreement with the formula. The relations between cube strength and cylinder strength and modulus of elasticity are discussed, and a Table of mix proportions for this lightweight aggregate concrete is proposed.
Variations in concrete proportions due to side vacuum treatment
Authors: Buchan A. R. , Hawkes J. M.
Published: July 2012

Summary

A technique for the analysis of fresh concrete into its constituent parts was perfected. Tests using this technique were made on concrete which had been subjected to side vacuum treatment to determine the effect of: the duration of treatment; the application of vibration; variations in the initial water/cement and aggregate/cement ratios; redistribution of the water content after treatment. The results indicate that: treatment causes migration of the finer particles (sand and cement) towards the processed face (this is increased if the concrete is vibrated); as the initial water/cement ratio increases, the movement of sand and cement. increases, but raising the aggregate/cement ratio decreases the movement of sand; immediately after treatment the water content is non-uniform, with a minimum value at the vacuum face, but gradual redistribution occurs after treatment stops.
Test on a prestressed concrete hollow-box bridge deck
Authors: Gifford F. W.
Published: July 2012

Summary

Hollow-box pre-tensioned beams laid side by side and held together transversely by prestress or other means are advocated for bridge decks of spans from 30 up to about 90 ft. A detailed account is given of tests on a one-third scale model of a 30 ft span. Comparisons, both general and with reference to tests by the Cement and Concrete Association, are made with the type of deck comprising inverted T beams transversely reinforced and completed with in situ concrete above.
Further studies of pore size distribution in mortars
Authors: Kroone B. , Crook D. N.
Published: July 2012

Summary

The method of mercury penetration was used to study the influence of variations in the sandi cement and waterlcement ratios on the pore size distributions of mortars, down to pore sizes of 0·01μ; diameter. It was found that the total volume of the pores with diameters greater than 5μ; increased as the sandi cement ratio increased, but decreased as the waterlcement ratio increased, within the limits of the experiments.

It was also found that the cross-section of the pores became more irregular as the sand content increased. and that at low waterlcemem ratios an increase of the water/cement ratio tended to produce pores of more regular cross-section.
Strength tests on scaled-down concretes suitable for models, with a note on mix design
Authors: Johnson R. Paul
Published: July 2012

Summary

The paper describes procedures for testing the strength of “scaled-down” concrete mixes suitable for models of concrete structures. The effects of the scale of mix and the size of test specimen on the magnitude and scatter of the results are given in detail. It is concluded that tests on 1½ in. diameter cylinders 3 in. long give a satisfactory measure of the strength of concrete made with aggregate passing a 3/16 in. sieve. Mix design curves are given for a limited range of mixes of medium workability.
The rotation of reinforced concrete plastic hinges at ultimate load
Authors: Chan W. W. L.
Published: July 2012

Summary

On the basis of the simplified ultimate load theory which assumes elastic members spanning between plastic hinges, the procedure for checking required rotations caused by moment redistribution and rotation capacities of plastic hinges is outlined, and the influences of strength of concrete, compression and tension reinforcement, and form of loading on hinge rotations are discussed. In particular, it is shown that compression steel, which significantly affects flexural rigidity in structural members, as well as concentrated rotations at plastic hinges, provides a convenient means of adjusting deformations in ultimate load design.

From a study of test results from 54 beams and 13 struts, the paper shows that the methods and parameters that are recommended in the recently published report on “Ultimate load design of concrete structures” for the computing of plastic hinge rotations are safe and statistically acceptable.
The deformation of a rectangular slab stiffened by beams under transverse loads
Authors: Severn R. T.
Published: July 2012

Summary

A rectangular slab spans between simple supports and is stiffened by beams of uniform cross-section (Figure 1). Complete composite action is assumed to exist between the slab and the beams. Each panel of the slab can carry point loads, acting at any point of the panel, and a uniformly distributed transverse load, and the beams carry loads which are either uniformly distributed along their lengths or are concentrated so as to act as point loads. The magnitudes of the loads carried by each panel and by each beam will generally not be the same.

It is assumed that the transverse deflexion of the structure and the stress function that describes forces in the plane of the slab are governed by independent biharmonic equations. To these equations series solutions are taken and the coefficients which they contain are determined by satisfying the conditions of compatibility and continuity at the slab-beam junctions. The results of experiments with models are described and brief details are given of computer programmes which may be used to carry out the computations involved.
A lower bound solution to the collapse of an orthotropically reinforced slab on simple supports
Authors: Kemp K. O.
Published: July 2012

Summary

Although upper bounds to the collapse loads of simply supported, orthotropically reinforced concrete slabs can be readily calculated by application of the yield-line theory, corresponding lower bound solutions which must satisfy equilibrium and the yield criterion at all points in the slab are not yet available.

A lower bound solution to the collapse of a simply supported, rectangular slab, orthotropically reinforced and carrying a uniformly distributed load is developed. It is based on one originally proposed by Sawczuk(4) but the distribution of twisting moments has been modified to just produce positive yield moments at all points in the slab and negative yield moments at the corners.

The lower bound collapse loads calculated for a range of coefficients of orthotropy μ, and ratio of width to length of slab λ, agree extremely closely with the upper bound values derived from the yield-line theory. The yield lines, however, are quite different and are found to be an infinite set of curves in the lower bound solution.

Finally, the solution is used to determine the extent of negative reinforcement required in the corners of the slab and the loads transmitted to the supporting edges.
A stress-strain function for concrete subjected to short-term loading
Authors: Liebenberg A. C.
Published: July 2012

Summary

The author develops a function relating stress and strain for concrete subjected to short-term non-repetitive uniaxial loading. The function is based on well established empirical relations and its mathematical form corresponds with the suspected nature of the physical behaviour of concrete under stress.
Thermal stresses in reinforced concrete slabs
Authors: Hannant D. J. , Pell P. S.
Published: July 2012

Summary

A description is given of an experimental and theoretical investigation into the stresses induced in steel and concrete in reinforced concrete slabs subjected to high temperatures and thermal gradients.

It is shown that the observed stresses in the steel are dependent on time and previous temperature cycling of the slabs. Initially, the stresses in the steel were in close agreement with the values derived from the elastic analysis but as shrinkage and creep increased, with time and temperature, large losses of tensile stress were measured until, in several cases, the steel developed compression even while the thermal gradients were considerable. The main cause of the loss of tensile stress in the steel was attributed to the increased rate of concrete shrinkage at temperatures near or above 100°C, with secondary effects due to creep and reduction in the expansion coefficient.

Design recommendations are made which enable the final equilibrium stresses to be determined within fairly wide limits and it is shown that the final steel stresses are likely to bear little relation to the stresses calculated from an elastic analysis alone.
General relation between mix proportion and cement content of concrete
Authors: Popovics Sándor
Published: July 2012

Summary

Semi-empirical equations are presented for the relation between cement content and mix proportion of concrete. Other variables are the consistence, specific gravities of cement and mineral aggregates, grading of aggregate, and air content. The paper shows equations for the case in which only one material is used as mineral aggregate (equations 1–4), and for the more general case in which a blend of two materials is used (equations 5–8). The form of the equations is relatively simple considering the large number of variables involved.

The values calculated from the equations are compared with results of experiments performed by various research workers, and it is shown that there is good agreement between calculated and experimental values.
The flexural rigidity of reinforced concrete
Authors: Everard K. A.
Published: July 2012

Summary

By assuming that for short tests the stress at a-particular point in a reinforced concrete beam may be identified with a particular strain, a general non-linear theory of bending is proposed. The case of parabolic stress distribution in a rectangular beam is examined in detail and expressions describing the moment-curvature relations for various parameters are obtained. These expressions can be used to calculate the angles of discontinuity which may be developed in a reinforced concrete section at moments up to the ultimate.
The thermal conductivity of concrete
Authors: Campbell-Allen D. , Thorne C. P.
Published: July 2012

Summary

A simple theory is developed which gives the thermal conductivity of concrete in terms of the thermal conductivity of its constituents. The predictions of this theory concerning the variation of the thermal conductivity of concrete with moisture content have been tested by experiment and have been found correct; this experimental work covers the effect of moisture content on the thermal conductivity of concrete made with three different aggregates, namely, dolerite, haematite and barytes.
The materials testing laboratory of the Cement and Concrete Association
Authors: McIntosh J. D.
Published: July 2012

Summary

A new laboratory for research on the engineering properties of concrete and its constituent materials has been erected for the Cement and Concrete Association at its research station at Wexham Springs to re-house various departments which had been operating in temporary accommodation. The paper describes the measures taken to deal with problems applicable to all buildings of this type.

Air-conditioning of many of the rooms influenced the siting, planning and method of construction of the building. Particular problems included reducing nuisance from the dust and noise of many operations, preventing the spreading of shock and vibration to the rest of the structure, planning a convenient flow pattern for routine operations while allowing adequate versatility for other techniques, and filtering “live” cement from liquid waste. Although all the desirable refinements were not included at the time of erection, provision was made, where possible, for them to be incorporated later.
A note on the effect of frequency on the behaviour of fresh concrete during vibration
Authors: Green H. , Roberts A. B.
Published: July 2012

Summary

The behaviour offresh concrete during vibration varies with thefrequency of the vibration applied. For each mix there is a particular frequency at which a drastic change in the acceleration of the mould and the mix takes place during vibration with constant power input. The strongest concrete is produced at this frequency of vibration.
The effect of grout properties on the structural behaviour of post-tensioned concrete beams
Authors: Geddes J. D. , Soroka I.
Published: July 2012

Summary

The effect of grout properties on the structural behaviour of 18 post-tensioned prestressed concrete beams was investigated. The beams were 6 × 10 in. in cross-section and 10 ft long with an average concrete compressive strength of approximately 8,500 lb/in2. In each beam the prestressing cable consisted of eight 0·2 in. smooth high-tensile wires having a nominal eccentricity of 2 in. All the beams were identical but the properties of the grouts were varied over a wide range. The fluidity (immersion test) varied between 4 and 85 s, the bleeding (“tin-can” method) varied between 0 and 16·9%, the volume change (“tin-can” method) varied between 18 % sedimentation and 11·1 % expansion, and the cylinder compressive strength at 21 days varied between 2,100 and 4,300 lb/in2 Air-entraining agents, plasticizers and expanding agents were used in some of the grouts.

At 28 days the beams were tested to failure by two-point symmetrical loading and the following factors were determined: the ultimate strength; the ratio of steel stress at failure to its ultimate tensile strength (λ); the pattern of cracking (number, spacing and width of cracks).

Evaluation of the results clearly suggests that the structural behaviour of grouted post-tensioned prestressed concrete beams subjected to bending is not significantly affected by extreme variations in the properties of the injected grouts.
Resin-bonded glass-fibre tendons for prestressed concrete
Authors: Somes N. F.
Published: July 2012

Summary

The high strength and low modulus of elasticity of resin-bonded glass-fibre tendons have prompted consideration of their use in prestressed concrete. The paper describes development work carried out with this material and reports on the testing of eight prestressed beams. Failure loads show agreement with those calculated by the strain compatibility method. Considerable difficulty was encountered in developing a satisfactory anchorage. The use of the correct stress at tensioning and the avoidance of surface damage at casting are shown to be very important, and bond and transmission characteristics were found to be similar to those of steel wire of the same diameter. Bondedfibre tendons may successfully be employed in prestressed units if their initial anchoring stress does not exceed 0·45 of the short-term strength.
A new method of proportioning stirrups in reinforced concrete beams
Authors: Taylor R.
Published: July 2012

Summary

A possible basis from which to elaborate an empirical design method for proportioning stirrups in reinforced concrete beams is developed from a consideration of the actual behaviour of a beam under load and the designer's need for simplicity. Empirical values of the design factors involved are suggested. Reference is made to the results of tests on beams in which the shear reinforcement was designed in accordance with the proposals.
The effect of curing conditions on the physical properties of concrete
Authors: Elvery R. H. , Evans E. P.
Published: July 2012

Summary

An investigation has been carried out to study the effect of different curing conditions on certain physical properties of concrete. The conditions ranged from a temperature a little above freezing to that of high-pressure steam, and included normal and tropical temperatures. The properties measured included crushing strength, dynamic and static moduli, ultrasonic pulse velocity and modulus of rupture.
Determining the thickness of concrete pavements by mechanical waves: directed-beam method
Authors: Bradfield G. , Gatfield E. N.
Published: July 2012

Summary

The device described forms a compact and convenient means of determining the thickness of concrete roads and pavements (and of similar rock-like materials) to an accuracy of a few per cent; this can probably be improved upon by refinements discussed. An interesting outcome of the development is that it appears to be possible to measure accurately the velocity of irrotational waves propagating on or just below the surface of the specimen. The paper mentions possible applications to mining, the measurement of Poisson's ratio and crack detection.
Researches into the complete stress-strain curve for concrete
Authors: Barnard P. R.
Published: July 2012

Summary

This paper describes two series of tests on concrete specimens for the purpose of determining the complete stress-strain relation in uniaxial compression, including the falling branch. In the second series, lateral as well as longitudinal strains were measured which showed that initial tension cracking occurs locally within the gauge length and that portions of this length may be uncracked at maximum load on the specimen. The results included in the paper demonstrate the ability of concrete to undergo very large changes in length without ceasing to carry load.
The measurement of particle elongation and flakiness: a critical discussion of British Standard and other methods
Authors: Lees G.
Published: July 2012

Summary

The author has given reasons elsewhere for recommending a more careful study of particle shape in engineering aggregates. Measurements of flakiness and elongation have long been considered important, but methods of determining these qualities both by direct measurement and by means of gauges are in need of some revision. This paper points to some of the difficulties and fallacies concerned and suggests means to overcome them.
Yield criterion for initially isotropic reinforced slab
Authors: Kwiecinski M. W.
Published: July 2012

Summary

This paper deals with the problem of formulating a yield criterion for quasi-isotropic reinforced slabs. The possibility of the kinking of reinforcement bars on the open fracture line is taken into account and a detailed analysis of yield moment on the plastic hinge is made. Both the “square” yield criterion and the criterion for perfect kinking of reinforcement prove limiting cases of the proposed partial-kinking theory. Values of plastic moments obtained from this criterion are more optimistic than those obtained by Johansen's criterion. The proposed theory enables one to describe analytically the results of some former experimental investigations which have shown that the ultimate moment in an initially isotropic slab is not independent of the plastic hinge inclination.
The action of ammonium salts on concrete
Authors: Lea F. M.
Published: July 2012

Summary

Results are reported on the action of 5% solutions of ammonium salts on a Portland, a Portland-pozzolana, and a high alumina cement concrete. Ammonium chloride and nitrate solutions had a strong leaching action, acting as dilute acids owing to loss of ammonia by reaction with lime. Strengths of concrete cubes with all three cements fell by at least a half in four years without outward signs of deterioration. Analysis of the specimens showed large reductions in the lime content of the cements. In the action of ammonium sulphate on Portland cement, the expansion caused by formation of calcium sulpho-aluminate is dominant. High alumina cement was unaffected by ammonium sulphate.
Some tests on the yield criterion for a reinforced concrete slab
Authors: Kwiecinski M. W.
Published: July 2012

Summary

This paper describes experimental work to verify the yield criterion for an isotropically reinforced concrete slab based on the concept of kinking of reinforcement bars across a fracture line. Sixteen model slabs with various arrangements of reinforcement were tested in one-way bending and experimental results have been compared with theoretical predictions. It appears that the concept of kinking is well confirmed although more tests on the behaviour of a fracture line arbitrarily inclined to the direction of the bars seem desirable.
Developments in apparatus for recording load-strain curves of concrete beams loaded in flexure
Authors: Hanks B. J.
Published: July 2012

Summary

A technique has been developed at the Road Research Laboratory for automatically recording the load-strain curves in flexural tests of concrete beams at the standard rate of loading specified in B.S. 1881. The new technique almost completely eliminates the noise and electrical pick-up associated with the resistance strain gauges previously used, and overcomes the undesirable drying-out of the concrete beams resulting from the employment of epoxy resin adhesives to attach the resistance strain gauges. Strains were measured by an inductive transducer combined with an oscillator and ademodulator, the output of which drives the Yinput of an X- Y plotter. The load applied to the specimen is measured by the distortion of a large spring with a travel of 4 in. A linear potentiometer attached to the spring is fed with a direct supply of 500 m V. The output from this potentiometer drives the X input of the X- Y recorder. The apparatus takes only about five minutes to prepare and thus expedites the work of testing concrete beams.
Cube tests and the uniaxial compressive strength of concrete
Authors: Hughes B. P. , Bahramian B.
Published: July 2012

Summary

The cube is undoubtedly the most convenient specimen to use when large numbers of crushing tests are required for concrete control purposes. The cylinder, or prism, on the other hand can give a much better estimate of the uniaxial compressive strength of concrete. The recent tendency has been to favour the adoption of the cylinder as the standard specimen, despite its shortcomings regarding convenience. The paper shows that variable differences can occur between the cube crushing strength and the uniaxial compressive strength, and then indicates how these differences can be greatly minimized by a suitable modification of the testing technique. This simple modification to the cube test enables the uniaxial strength to be determined very readily. The extremely convenient cube specimen can therefore now be used for uniaxial compressive strength determinations as well as for normal control purposes. The continued use of the cube as the standard form of test specimen is therefore recommended.
A method of studying the effect of vibratory stress, including fatigue, on concrete in flexure
Authors: Gatfield E. N.
Published: July 2012

Summary

The method and apparatus enable vibratory flexural stresses of magnitudes comparable with those used in conventional quasi-static tests to be applied to concrete beams. The beam is mounted horizontally on rigid supports and is vibrated inflexure by a moving-coil vibrator coupled to the upper face of the beam at the centre. The frequency of resonance and the strain in the beam at the centre of the top face are measured and, in normal operation, the driving current is adjusted to maintain a constant value of strain whilst changes of frequency with time are observed. A decrease in frequency indicates a decrease in the dynamic Young's modulus of elasticity of the concrete, and is associated with a development of micro-cracks in the concrete. The cracks which form at sufficiently high levels of strain fatigue have been observed by a photo-elastic technique before the appearance of visible cracks. Strains between 60 and 120 × 10−6 ultimately led to fatigue of the concretes tested. Stress-strain relationships were derived from curves relating resonant frequency with magnitude of strain, and were found to be approximately linear for un-fatigued specimens and markedly non-linear for specimens which had become fatigued.