bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of compressive stress on the dynamic modulus of concrete
Authors: Elvery R. H. , Furst M. 
Published: July 2012

Summary Tests have been carried out to determine the effect of compressive stress on the dynamic modulus of concrete. These have indicated that a small reduction of modulus occurs when concrete is loaded but that no subsequent reductions occur while the load is maintained for periods up to six months. A similar reduction also occurs on releasing the load and with subsequent loading cycles. This effect, which is independent of the age of the concrete after fourteen days, is approximately proportional to the applied stress and becomes successively smaller for subsequent loading cycles. The reduction in dynamic modulus is always small, being about 5% or less.
The influence of shear span and concrete strength upon the shear resistance of a pre-tensioned prestressed concrete beam
Authors: Hicks A. B. 
Published: July 2012

Summary The research was planned to establish the various types of failure of a typical pre-tensioned prestressed concrete I beam, to establish the limits of the shear span to depth ratio within which each type of failure occurred, and, generally, to investigate the effect of the shear span and concrete strength upon the shear resistance of a concrete beam of this type. Four types offailure were observed; a fifth (bond failure) was carefully avoided. The limits of the shear span to depth ratio within which each type of failure occurred were as follows: shear distortion 0-1½ diagonal compression 1½-4½ to 5 diagonal tension 4½ to 5-9 flexural 9-∞ The first two types are discussed and the results are compared with the Draft Code of Practice for Prestressed Concrete.
The strength of reinforced concrete beams in shear
Authors: Sunderland A. 
Published: July 2012

Summary: The determination of the magnitude and distribution of the shearing stresses in reinforced concrete beams is one of the most difficult problems that faces designers at the present time. A research programme has been pursued for some two years in the Civil Engineering Laboratories of Leeds University and this paper deals with the results of tests on 39 beams designed to fail in shear or diagonal tension. Many factors influence the resistance of reinforced concrete in shear and the factors investigated so far are the effects of variations in (a) spacing of vertical stirrups and percentage web reinforcement, (b) ratio of depth of beam to the span. It is seen that vertical stirrups, even with spacings a little greater than the moment arm, always increase the ultimate shearing loads, the effectiveness of the stirrups falling gradually when the spacing exceeds about one-half the moment arm. The widths of inclined cracks in beams with mild steel vertical stirrups were less than 0·005 in. at a stress of 18,000 lb. per sq. in. and with square twisted steel stirrups about 0·006 in. at 25,000 lb. per sq. in. Vertical stirrups usually attain their ultimate strengths and, in shallow beams, a load factor of 2·5 is satisfactory. The capacity of doubly-reinforced beams to resist shear, in virtue of an action analagous to that of an open-frame girder, is considerable. A comparison is made of the observed shearing failing loads with the loads derived from British and American Codes of Practice from which it is seen that the present British Code of Practice is too conservative.
An investigation into the cause of cracking in a reinforced concrete silo containing cement
Authors: Rowe R. E. 
Published: July 2012

Summary The paper describes a series of tests carried out to determine the cause of cracking in a reinforced concrete silo used for storing cement. The tests covered the location of the steel reinforcement and the measurement of the laps in the horizontal steel, the pressures exerted on the walls, and the temperature differential through the walls. The cause of cracking was a combination of the effects of pressure in excess of that designed for, large temperature differentials through the walls of the silo, and a deficiency in reinforcing steel. From the results obtained it is clear that Janssen's theory for the pressure exerted by granular materials on the walls of a container is inapplicable to cement. An alternative method of determining the pressures, based upon the experimental results, is put forward. The temperature differential through the walls was about 33°C during the tests and indicates that this factor must be considered in the design of a cement silo. Finally the need is stressed for further tests on actual cement silos so that a more realistic method of design can be evolved.
Creep of lightweight concrete
Authors: Best C. H. , Polivka M. 
Published: July 2012

Summary Creep data covering periods of up to 18 months for concretes made with expanded-shale aggregates and having compressive strengths of 3,000 and 5,000 lb/in2 at 28 days are reported. These are compared with data for sand-gravel concretes of comparable strength. It was found that, contrary to current opinion, creep in lightweight concrete was essentially equal to or less than that in normal-weight concrete of comparable strength. The aggregates used in this investigation are typical of expanded-shale aggregates and natural sand-gravel aggregates available on the west coast of the United States, and the results may, therefore, not be directly applicable to materials available in other countries or in other parts of the United States. However, since the three expanded-shale aggregates used are typical of products that can be obtained by sintering clays and shales to incipient fusion, the results reported should be generally applicable to concretes containing such aggregates. A brief description of the hydraulic loading equipment used in the creep tests is included. The equipment, performed satisfactorily throughout this investigation with very little maintenance; it may be expected to perform similarly at any stress level normally encountered in creep studies. Some brief comments relative to the merit of current techniques for studying creep in concrete are made, and a new approach to the problem is suggested.
The shrinkage and creep of concrete
Authors: Lyse Inge 
Published: July 2012

Summary This paper describes an investigation made at the Laboratoires du Bâtiment et des Travaux Publics at Paris into the principal factors influencing the creep and shrinkage of concrete. The main conclusions drawn are that both creep and shrinkage are directly proportional to the amount of cement paste in the concrete, that creep is directly proportional to the sustained stress, and that both creep and shrinkage are greatly affected by the relative humidity of the atmosphere. Three equations are given from which shrinkage, creep, and total shortening can be calculated.
The workability of concrete
Authors: Murdock L. J. 
Published: July 2012

Summary An analysis is made of a large number of tests for workability as measured by the compacting factor, in order to determine how workability is related to the grading and shape of aggregate, the mix proportions and the water/cement ratio. An index is developed which takes account of the influence of particle size on workability, and largely overcomes the limitations of the fineness modulus and surface area coefficients. Similarly, an angularity index is introduced which is based on a test on the aggregate and is shown to take account of its shape. The relation between workability and mix proportions is assessed. It is established that a proportion of the water, equivalent to a water/cement ratio of about 0·25, is required to wet the cement, and that any additional water may be regarded as available to make the mix workable. An approximate relation is given for the calculation of compacting factors, and a worked example illustrates the use of this relation for mix design.
The lateral buckling of slender reinforced concrete beams
Authors: Siev A. 
Published: July 2012

Summary The paper gives a brief summary of the theory of buckling for homogeneous materials, with special reference to reinforced concrete, account being taken of variations in shape and in loading. The method involves the determination of the flexural and torsional rigidities in the uncracked, cracked elastic, and cracked plastic states. Tests were made on two series of beams: six of rectangular section (1 ½ × 16 in.), andfour inverted L beams. It is concluded that the spanlwidth ratio is not the only factor affecting buckling; the widthlheight ratio and the percentage of reinforcement and its distribution are of equal importance.
A new machine for the fatigue testing of reinforced concrete beams, and some preliminary results
Authors: Larnach W. J. 
Published: July 2012

Summary The paper describes the construction and operation of an hydraulically operated fatigue machine of 5 tons capacity for tests in bending or compression. The machine proved capable of long periods of service with the minimum of attention. A series of fatigue tests in bending on normally reinforced concrete beams indicated that high proportions of the static failing load could be applied as many as 300,000 times without significantly altering the ultimate strength of the beams.
Reinforced concrete joints between prestressed concrete members
Authors: Reeves J. S. , Morice P. B. 
Published: July 2012

Summary The practice has developed in recent years of constructing statically indeterminate prestressed concrete structures by applying connecting restraints to two or more statically determinate prestressed concrete members. The present paper discusses a joint that may be used to convert two or more simply supported prestressed concrete beams into a continuous beam by joining them together over the supports. This joint utilizes unprestressed continuity steel contained within the crosssection of the continuous beam. Alternative designs for such a joint are proposed and examined for suitability in fulfilling the necessary functions. Some remarks are added on the design of composite continuous beams. Tests are reported on five two-span composite beams each made from two post-tensioned, grouted beams. The ratio of the ultimate moments of resistance of the critical sections was varied. The tests demonstrated the essentially satisfactory nature of the proposed joint.
Tests on a one-tenth scale model of a hyperbolic paraboloid shell roof
Authors: Jones L. L. 
Published: July 2012

Summary Tests which have been carried out on a one-tenth scale model of a hyperbolic paraboloid shell roof have given data from which the tie-bar force, corner reactions, deflexion and stress distribution of the actual structure have been calculated. In the interior of the shell, the stresses calculated are in good agreement with those calculated by the membrane theory. Near the edge beams both the forces and the moments increase rapidly; since, however, the edges of the shell were thickened, the maximum stresses in the structure under a working load of 60 lb/ft2 were only 250 lb/in2 compression and 100 lb/in2 tension. At this load the maximum deflexion would be 0·5 in. The tie-bar force measured was only two-thirds of that predicted by the membrane theory, and equilibrium conditions revealed that the lower corners were carrying approximately 0·4 and the higher corners 0·1 of the total load. The model shell had a load factor of at least 5.
Some tests on the durability of concrete mixes of similar compressive strength
Authors: Keene P. W. 
Published: July 2012

Summary The practice of specifying that concrete should have a certain minimum strength has recently become more general, and this, together with the increased use of vibration as a method of compacting concrete on site, has often led to the use of leaner mixes of lower workability. However, although their compressive strength may be similar, little is known about the durability of these mixes compared with that of richer, more workable mixes suitable for hand-compaction. A series of tests has therefore been carried out on mixes made with different cements, of varying degrees of workability, having aggregate/cement ratios ranging from 4·0 to 7·5 by weight, all with an average compressive strength of about 4,500 lb/in2 at 28 days. The durability of the concrete was assessed by measuring the change in weight and in compressive strength of cubes immersed in sulphate solution and the change in weight of, and in ultrasonic pulse velocity through, cubes subjected to repeated cycles of freezing and thawing. In addition, tests were carried out for absorption, drying shrinkage, and moisture movement. It was found that the leaner mixes of lower workability tended to have a slightly greater resistance to alternate freezing and thawing, lower absorption, and less drying shrinkage and moisture movement. No difference was observed between the leaner and richer mixes in resistance to sulphate attack. It is concluded that the durability of fully compacted medium-strength concrete of low workability is not affected adversely by the use of aggregate/cement ratios of up to 7·5 by weight.
The effect of air-entrainment on the shrinkage of concrete stored in laboratory air
Authors: Keene P. W. 
Published: July 2012

Summary Tests are described comparing the shrinkage of air-entrained concrete with that of concrete of similar workability and strength but without entrained air. Changes in length of 3 × 3 × 10 in. prisms were measured by means of a micrometer screw gauge. Some specimens were cured in moist air for the first 7 days before being transferred to the air of the laboratory; the others were stored throughout in the air of the laboratory. Some time after the specimens had reached maximum shrinkage they were measured for moisture movement. The conclusions drawn from the results of the tests are that the shrinkage of concrete of medium strength and workability is not significantly affected by air-entrainment, but with or without entrained air the shrinkage is greater for concrete cured in moist air for the first 7 days than for concrete allowed to dry immediately.
Studies of pore size distribution in mortars
Authors: Kroone B. , Crook D. N. 
Published: July 2012

Summary Pore size distributions of mortars cured by hydration, carbonation, and under atmospheric conditions were measured down to pore sizes of 0·01μ diameter by the method of mercury penetration. It was found that hydration decreased the volume of the larger pores and that carbonation decreased the volume of the intermediate size pores but increased the volume of pores exceeding 5μ in diameter. The main effect of curing in carbon dioxide was evident after 1 day, but equilibrium during hydration was reached in about 12 days. The pore size distribution was not greatly affected by curing under atmospheric conditions. The larger pore sizes (>5μ) appeared to be affected by the extent to which the samples were compacted in moulding. The volume of pores between ∞ and 0·01μ as determined by mercury penetration is, for mortars with low cement/water ratios, considerably less than the total porosity determined by saturation with water. This points to the existence of capillaries of diameters of 0·01μ and less, or of cavities with entrances of these diameters in set cement, as deduced by Powers, Copeland and Mann from permeability data.
The behaviour and ultimate strength of prestressed concrete hollow beams under combined bending and torsion
Authors: Swamy Narayan 
Published: July 2012

Summary This paper summarizes the results of an investigation into the behaviour and ultimate strength of post-tensioned prestressed concrete hollow beams under combined bending and torsion. Twenty-four full-size beams were tested with ratios of bending moment to twisting moment varying from pure bending to pure torsion. The size and shape of the hollow, and the shear reinforcement were varied. The deflexions and strains due to bending and torsion were measured at selected points. With low ratios of bending moment to twisting moment, a primary torsion failure occurred and with high ratios a primary bending failure resulted. Between these two types of failure, there is a transition from cleavage to crushing failure. The presence of small amounts of torsion decreased the bending strength, whereas the addition of small quantities of bending increased, within certain limits, the torsional strength. The experimental results show that the customary failure theories do not give satisfactory results for all stress combinations, and that they cannot adequately explain the failure conditions. It is suggested that any failure criteria must be based on the tensile and compressive strength of concrete and that more test data are necessary before a simplified design approach can be proposed.
Dynamic loading of prestressed concrete beams
Authors: Oladapo I. O. 
Published: July 2012

Summary The paper describes experiments to compare the behaviour of prestressed, post-tensioned concrete beams under dynamic loading with that under static loading. The total loading time was reduced from 10 min for the static loading to 0·05 s for the dynamic. This change in the rate of loading produced significant increases in the cracking strength of the concrete and in the ultimate moment of the beam. It was found that under dynamic loading prestressed concrete considerably increased its capacity for sustaining elastic deformation and for absorbing energy by inelastic deformation.
The deformation of a rectangular slab with free edges under transverse loads
Authors: Severn R. T. 
Published: July 2012

Summary The Rayleigh-Ritz energy method is used to obtain an approximation to the deflected shape of a flat slab which is loaded transversely and which is supported either on columns (Part 1), or on an elastic foundation (Part 2) for which the upthrust at any point is directly proportional to the displacement at that point. Computer programmes (Ferranti Pegasus) are briefly described by use of which solutions can be obtained in about four minutes.
Redistribution of moments in two-span prestressed concrete beams
Authors: Mallick S. K. 
Published: July 2012

Summary The results of experimental and analytical studies on the redistribution of moments in 21 beams tested to destruction under certain arrangements of concentrated loads are presented. For most of the beams, the results differed from those computed by Guyon's method. An extension of this method has been proposed by taking into consideration the concentration of curvature at the plastic hinges. Close agreement was found between the experimental and the calculated results based on the modified procedure.
The influence of transverse prestress on the strength of prestressed concrete bridge slabs
Authors: Cusens A. R. , Abbasi A. F. 
Published: July 2012

Summary The paper describes the results of tests on eight square prestressed concrete slabs having unbonded wires. The ratio of transverse prestress to longitudinal prestress (γi,) was varied hetween 0 and 100%. A system of wheel loads based on AASHO specifications was used and it was found that, for the upper range of values of γi ultimate loads were considerably in excess of those predicted by the use of yield-line theory. It is suggested that at least part of this increased load capacity could be utilized if a suitable design criterion were adopted.
The effect of the type of aggregate on the diagonal cracking of reinforced concrete beams
Authors: Taylor R. , Brewer R. S. 
Published: July 2012

Summary Comparative rests are reported on reinforced concrete beams without shear reinforcement made with different types of aggregate: two types of lightweight aggregate and one gravel aggregate were used. Other variables were the concrete strength and the type of reinforcement. The principal results of the tests were as follows. (1) For concretes of similar cube strength, the average diagonal cracking loads of the beams made with lightlveight aggregate were lower than those of the beams made with gravel aggregate. (2) The average diagonal cracking loads of beams reinforced with ordinary mild-steel were higher than those of the corresponding beams reinforced wirh an equivalent area of cold-worked deformed hars. (3) The diagonal cracking load increased with increasing concrete strength, the rate of increase heing similar for all three types of concrete.
The suitability of a lightweight aggregate (Aglite) for structural concrete
Authors: Evans R. H. , Dongre A. V. 
Published: July 2012

Summary This paper gives the results of tests on Aglite concrete to establish its tensile and compressive strengths, its absorption and permeability characteristics, and the behaviour and ultimate strength of reinforced beams in shear and flexure. Throughout the work, the values obtained were compared with those for a gravel concrete having the same 28-day compressive strength.
The ultimate flexural strength of reinforced concrete rafts
Authors: Ranganathanm B. V. , Hendry A. W. 
Published: July 2012

Summary A description is given of an experimental and analytical investigation into the flexural strength of reinforced concrete rafts. In conformity wuh the concepts of soil mechanics, the contact pressure is generalized by paraboloids. The structural analysis is based on the yield-line theory. Some solutions based on lower bound technique are shown to give identical values for the collapse load. The magnitude of the collapse load for a rectangular raft in terms of the yield moment has been computed for a wide range of values of the three different parameters, characterizing the contact pressure distribution, the ratio of sides, and the coefficient of orthotropy. Tests carried out on reinforced plaster mortar slabs supported on springs confirm reasonably well the soundness of the structural analysis.
Some fatigue tests on reinforced concrete beams
Authors: Taylor R. 
Published: July 2012

Summary In a previous paper(1), a new method was proposed for proportioning stirrups in a reinforced concrete beam. This paper is a report of some fatigue tests on beams designed in accordance with these proposals. The results indicate that, although the shear reinforcement provided was sufficient to prevent shear failure of the beams, the inclined cracking due to shear affected the fatigue resistance of some of the beams.
Tensile membrane behaviour of uniformly loaded rectangular reinforced concrete slabs with fully restrained edges
Authors: Park R. 
Published: July 2012

Summary A theory is developed for the load carried at large deflexions by the tensile membrane action of uniformly loaded rectangular slabs with edges restrained against all translation. It is assumed that the reinforcement acts as a plastic membrane. On comparison with test results the theory is shown to be conservative. The load carried by tensile membrane action is found to be considerable and for heavily reinforced slabs it can exceed the ultimate flexural strength.
Cracking and failure in plain concrete beams
Authors: Oladapo I. O. 
Published: July 2012

Summary This paper describes experiments to determine the loads and the strains at which cracks occur in different concrete mixes; an attempt was also made to investigate whether there is any correlation between these and the measured values of load and strain at failure. Measurements of strain distribution on the tensile surfaces of beams were used to detect the presence of cracks. It was found that the formation of cracks is a gradual process. The early stages are probably due to bond cracks between the aggregates and mortar; a critical stage develops when cracks in the mortar itself link up the existing bond cracks to form a continuous pattern. In each mix, the stress at the critical load shows good agreement with that obtained from tensile splitting tests on cylinders. The strain at the critical load is not constant but varies with the strength of the mix. The load and the strain at failure are influenced by both the strain and the load at the critical stage.