Showing papers in "Magazine of Concrete Research in 1970"
TL;DR: In this paper, the ductility of concrete can be increased by confinement in steel binders but, for a proper analysis of the ultimate strength of structures utilizing this gain, an undertsanding of the st...
Abstract: Synopsis The ductility of concrete can be increased by confinement in steel binders but, for a proper analysis of the ultimate strength of structures utilizing this gain, an undertsanding of the st...
78 citations
TL;DR: In this article, the mechanism of regain of strength as observed in work on the glazing of concrete was investigated on fired and unfired industrially made masonry units by methods including DTA, pore size distribution, and determination of the degree of carbonation.
Abstract: Synopsis The mechanism of regain of strength as observed in work on the glazing of concrete was investigated on fired and unfired industrially made masonry units by methods including DTA, pore size distribution, and determination of the degree of carbonation. Immediate loss of strength after firing is attributed to the dehydration of cement paste gel, and the main factor in the regain of mechanical strength in a fired block is a carbonation process facilitated by a new capillary system created in firing.
64 citations
TL;DR: In this article, the effects of moisture content, condition of the cement gel, time of loading and time of unloading upon the creep and creep recovery of sealed and unsealed concrete specimens are described.
Abstract: Synopsis Experiments designed to investigate the effects of moisture content, condition of the cement gel, time of loading and time of unloading upon the creep and creep recovery of sealed and unsealed concrete specimens are described. Comparisons are made between the creep and creep recovery responses of specimens sealed immediately after curing and of unsealed specimens. The results of the experiments carried out on the drying (unsealed) specimens were easily predictable by existing theory. However, the experiments performed on the sealed specimens produced data not so easily explained. For example, under certain conditions, the creep of unsealed specimens was less than that of sealed specimens, and a period of time during which the creep potential of sealed specimens increased with age at time of loading was observed. These results are discussed in terms of the major variables affecting the creep of concrete: the degree of hydration at the time of loading, the amount of water present and not chemically...
23 citations
TL;DR: In this article, the shrinkage and creep of concrete made with Portland cement of three different grades of fineness, but of similar composition except for gypsum content, was reported.
Abstract: Synopsis Tests are reported on the shrinkage and creep of concrete made with Portland cement of three different grades of fineness, but of similar composition except for gypsum content. The programme comprised tests of unrestrained shrinkage, restrained shrinkage and cracking by a ring test, and creep over periods up to four-and-a-half years. The results indicate that there is an increase of unrestrained shrinkage and creep with finer cement but that, owing to the higher strength, there is no tendency for undesirably rapid shrinkage cracking to occur.
23 citations
TL;DR: In this paper, the influence of mix parameters on the strength and deformation of plain concrete subjected to uniaxial tensile or compressive stress was examined and the results obtained from 94 mixes were used to develop charts which permit reasonably accurate prediction of any of the four properties listed above for a wide range of mixes.
Abstract: Synopsis The paper examines the influence of mix parameters upon the strength and deformation of plain concrete subjected to uniaxial tensile or compressive stress. Parameters considered are the effective water/cement ratio, aggregate/cement ratio, aggregate maximum size and grading defined in terms of mean particle size, and the strength, elastic modulus and crushing value (B.S. 812) of the coarse aggregate. Tensile and compressive strength, tensile strain at failure and compressive strain at 50 % compressive strength are related to each parameter in turn, often by expressing the values in relative terms. The results obtained from 94 mixes are used to develop charts which permit reasonably accurate prediction of any of the four properties listed above for a wide range of mixes.
20 citations
TL;DR: In this paper, the authors reported results for tests to failure on 39 concrete blocks loaded through rigid plates extending across the full width of the block, and expressions were developed for the ultimate bearing.
Abstract: Synopsis Results are reported for tests to failure on 39 concrete blocks loaded through rigid plates extending across the full width of the block. Expressions are developed for the ultimate bearing...
19 citations
TL;DR: In this article, the Anchorage zone stresses in post-tensioned members of uniform cross-section are determined by using a finite element procedure for the elastic analysis of three-dimensional solids.
Abstract: Synopsis Anchorage zone stresses in post-tensioned members of uniform cross-section are determined by using a finite element procedure for the elastic analysis of three-dimensional solids. Stress d...
18 citations
TL;DR: In this article, the usual geometrical, statical and physical conditions for the anisotropic, perfectly plastic plate are given and it is demonstrated that the normal moment criterion usually employed in mode
Abstract: Synopsis The usual geometrical, statical and physical conditions for the anisotropic, perfectly plastic plate are given It is demonstrated that the normal moment criterion usually employed in mode
16 citations
TL;DR: In this article, the effect of shape and size of a cylindrical sample on the unconfined compressive strength of coarse sand, coarse sand and fine crushed rock was investigated.
Abstract: Synopsis An investigation has been carried out into the effect of the shape and size of the specimen upon the unconfined compressive strength of cement-stabilized gravelsand-clay, well graded sand and fine crushed rock. A range of cement contents was used with each material to give a range of strengths up to about 14 N/mm2 after 7 days' curing. To enable valid comparisons of strength to be made, the specimens were compacted to produce similar dry densities. Relationships were obtained between the strength of cylindrical specimens of different height to diameter ratios and between the strengths of cubes and cylindrical specimens. The average ratios of the strength of cylindrical specimens with a height:diameter ratio of 2:1 to the strength of specimens with a height: diameter ratio of 1:1 were 0·89, 0·74 and 0·65 for 150, 100 and 50 mm diameter specimens respectively. The differences in strength between specimens with height:diameter ratios of 1:1 and 2:1 is thought to be associated with the effect of the ...
14 citations
TL;DR: In this paper, the variation of the tensile strength of concrete with age and the relationship between the compressive and tensile strengths during the period of hardening was investigated. But the results were limited to the case of concrete.
Abstract: Synopsis The variation of the tensile strength of concrete with age, and the relationship between the compressive and the tensile strength during the period of hardening, are investigated. Some fac...
12 citations
TL;DR: In this paper, some experimental creep data are analyzed with reference to recent ideas that creep can be separated into recoverable and irrecoverable basic creep and recoverable, irrecoverably drying creep.
Abstract: Synopsis Some experimental creep data are analysed with reference to recent ideas that creep can be separated into recoverable and irrecoverable basic creep and recoverable and irrecoverable drying creep. Data on lateral strain behaviour are also presented. It is shown that this division of creep on the basis of axial strain measurements is not satisfactory. The implications of the results for future work on creep under uniaxial and multiaxial loading are indicated.
TL;DR: In this article, destructive tests on prototype reinforced concrete slabs designed by Johansen's yield-line method and Hillerborg's strip method are described, and the yield and failure characteristics of these slabs are then compared with those obtained from slabs constructed by an optimum lower-bound approach.
Abstract: Synopsis Destructive tests on prototype reinforced concrete slabs designed by Johansen's yield-line method and Hillerborg's strip method are described. All the slabs were square, simply supported and uniformly loaded. The yield and failure characteristics of these slabs are then compared with those obtained from slabs designed by an optimum lower-bound approach. The optimum slabs contained 37 % and 16 % less reinforcing steel than the slabs designed by Johansen's and Hillerborg's methods respectively.
TL;DR: In this article, lead compounds may occur in rocks used as aggregates in concrete and those soluble in lime water will affect the rate of hardening of the concrete, but subsequent strength will be as good as or better than for concretes with an equivalent aggregate without the lime-soluble lead.
Abstract: Synopsis Lead compounds may occur in rocks used as aggregates in concrete and those soluble in lime water will affect the rate of hardening of the concrete. The set will be delayed for 7 days by 0·8 % lead soluble in limewater, for 1 day by 0·15 %. Smaller amounts will delay the set and lower the early strength, but subsequent strengths will be as good as or better than for concretes with an equivalent aggregate without the lime-soluble lead.
TL;DR: In this paper, an analytical approach to shear cracking at vertical web-flange junctions is outlined and its predictions are compared with the results of a limited group of tests by the authors.
Abstract: Synopsis The four major modes of shear failure—diagonal tension, shearing, shear-compression and web crushing—are discussed briefly and equations are given for predicting resistances to them. The larger part of the paper is devoted to two other design criteria. An analytical approach to shear cracking at vertical web-flange junctions is outlined and its predictions are compared with the results of a limited group of tests by the authors. A semi-empirical equation is derived for the calculation of limit state of local damage resistance as determined by widths of shear cracks, and is compared with more extensive test data for various types of beam tested by the authors and others.
TL;DR: In this article, the authors carried out tests on 24 beams pre-tensioned with Dyform strand and 6 beams pretended with standard strand to determine and compare transmission length, flexural strength and behaviour.
Abstract: Synopsis Tests were carried out on 24 beams pre-tensioned with Dyform strand and 6 beams pre-tensioned with standard strand, to determine and compare transmission length, flexural strength and behaviour. It was found that the transmission length was greater for specimens incorporating Dyform strand than for those with standard strand, both at transfer and after a period of some months. Ultimate load tests indicated that the flexural behaviour of the two types of specimen was similar.
TL;DR: In this article, measurements have been made of the strains which occur in cement paste specimens in the two minutes immediately after they have been loaded, and it is suggested that the same processes govern this short-term time-dependent behaviour as govern longer-term creep.
Abstract: Synopsis Measurements have been made of the strains which occur in cement paste specimens in the two minutes immediately after they have been loaded. At a given time after loading, the time-dependent component of the total strain has been found to be directly proportional to the applied stress, to increase with increasing temperature and to be substantially unaffected by the previous loading history. At a given time after loading andfor a given stress, both the elastic and the time-dependent strains are smaller, the older the specimen. The time-dependent component is largely recoverable on unloading, but less so for young specimens. It is suggested that the same processes govern this short-term time-dependent behaviour as govern longer-term creep. The elastic and time-dependent strains are thought to be caused by different processes.
TL;DR: In this article, the authors provide some direct evidence on the amount of web reinforcement required for the attainment of flexural capacity, eleven beams with varying spans and web reinforcement were tested and compared with theoretical predictions and with British and American Codes of Practice.
Abstract: Synopsis The shear reinforcement of beams su~iected to uniformly distributed loading, constituting a most important design case, is specified in Codes of Practice and has been treated theoretically on the basis of evidence derived from point load tests. In order to provide some direct evidence on the amount of web reinforcement required for the attainment of flexural capacity, eleven beams with varying spans and web reinforcement were tested. The results are compared with theoretical predictions and with British and American Codes of Practice.
TL;DR: In this article, a method for finding the optimum arrangement of reinforcement in a concrete slab element subjected to general combinations of moments and membrane forces is presented, based on the study of strain distributions which satisfy certain conditions at the positions where reinforcement is to be provided.
Abstract: Synopsis The paper presents a method for finding the optimum arrangement ofreinforcement in a concrete slab element subjected to general combinations of moments and membrane forces. The method is based on the study of strain distributions which satisfy certain conditions at the positions where reinforcement is to be provided. For some combinations of stress-resultants, explicit equations can be derived for the required areas of steel: in the special cases of membrane forces only, or of moments only, these equations reduce to previously published results. Some numerical examples are given.
TL;DR: In this paper, a computer technique is proposed as a means of solving the problem of finding the yield-line pattern which minimizes the collapse load on a slab, where a collapse load is calculated as a function of several pattern parameters and a previously constructed sub-routine is used to minimize this function and thus find the most critical mechanism.
Abstract: Synopsis A computer technique is proposed as a means of solving the problem of finding the yield-line pattern which minimizes the collapse load on a slab. A mechanism is assumed and the collapse load calculated as a function of several pattern parameters. A previously constructed sub-routine is then used to minimize this function and thus find the most critical mechanism. Two examples are given; the computation time required is extremely small.
TL;DR: A concrete tensile test was proposed by the Department of Energy, Mines and Resources, Ottawa, Canada as mentioned in this paper, and some preliminary trials using this method have been carried out at the University of Nottingham which concern their conclusions, and it is suggested that their apparatus may dispose of many of the objections to existing tests.
Abstract: Synopsis This note draws attention to a new concrete tensile test proposed by the Department of Energy, Mines and Resources, Ottawa, Canada. Some preliminary trials using this method have been carried out at the University of Nottingham which concern their conclusions, and it is suggested that their apparatus may dispose of many of the objections to existing tests.