bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics of akwara as a reinforcing fibre
Authors: Uzomaka Osondu J. 
Published: October 2009

Synopsis Some relevant physical characteristics of akwara and akwara-reinforced concrete (akwaracrete) are discussed. Akwara is a natural vegetable stem fibre, dark brown in colour when mature, and has a hard smooth sheath enclosing a cellular core. Akwara is brittle and lighter than water. It is dimensionally stable in water, durable in a cement matrix environment, and has a low modulus of elasticity. Mixes containing akwara have lower mobility and compactibility than their plain counterpart. The fibre improves the impact resistance of concrete, but appears to have no effect upon uniaxial compressive strength or modulus of rupture.
Inelastic behaviour of reinforced concrete frames
Authors: Noor F. A. 
Published: October 2009

Synopsis The paper presents the results of tests on eight two-bay closed rectangular frames tested to destruction under different sequences of loading. In most cases, plastic hinges formed leading to the formation of collapse mechanisms. Under sway loads, the shear forces were higher and in some cases unexpected shear failures occurred. It is shown that the sequence of live loading is a major influence upon inelastic rotational capacity of a plastic hinge in a frame. Various methods of analysis and design are considered and design recommendations are given.
Flexural strength of concrete with randomly oriented glass fibres
Authors: Frondistou-Yannas S. 
Published: October 2009

Synopsis This paper discusses the problem of using basic fibre-matrix properties to calculate the flexural strength of concrete reinforced with randomly dispersed glass fibres. It reports an experimental test of the accuracy with which a theoretical model developed by Pakotiprapha et al. for steel-fibre-reinforced concrete can predict an extensive body of already published flexural strength data for concrete reinforced with glass fibres. The critical length and fracture stress (measured by pull-out tests) of alkali-resistant glass fibres embedded in a concrete matrix were determined by using matrix composition and preparation methods identical with those of the concrete composites for which the published flexural data had been obtained. Values of these experimentally determined properties were then introduced into the analytical model and calculations were made of the flexural strength of concrete composites covering a range of glass-fibre lengths and fibre volume fractions. Comparison of theory with experiment showed agreement well within 15%.
Local bond-stress–slip relationships under repeated loading
Authors: Edwards A. D. , Yannopoulos P. J. 
Published: October 2009

Synopsis Pull-out specimens in which the reinforcing bar was embedded for 38 mm were tested under nine slow load cycles of constant amplitude in order to determine the effect of repeated loading upon the local bondstress–slip relationships for deformed bars. The local bond-stress–slip curves obtained under repeated loading form hysteresis loops and have residual slip at zero load. The results show that bond effectiveness is particularly sensitive to the magnitude of the peak stress reached in preceding cycles. Load cycling of constant amplitude produces only a gradual deterioration of bond. The curves can be used for modelling bond at the steel–concrete interface in finite-element analyses of reinforced concrete members.
Structural idealization for deep beams with web openings: further evidence
Authors: Kong F. K. , Sharp G. R. , Appleton S. C. , Beaumont C. J. , Kubik L. A. 
Published: October 2009

Synopsis Further experimental evidence is produced to support a simple structural idealization for predicting the shear strength of reinforced concrete deep beams with web openings. The further tests were carried out on 17 normal-weight concrete beams, including a large beam of 3040 kN ultimate load. The exact analysis of deep beams with web openings presents formidable problems. However, the experiments have confirmed that the strength and serviceability of such beams are governed mainly by a small number of identifiable variables, and that for design purposes the proposed structural idealization could prove a useful new tool. A worked example is given in Appendix 1.
The response of reinforced concrete cross-sections to short-term and sustained loads
Authors: Constantinescu Dan R. , Illston John. M. 
Published: October 2009

SYNOPSIS The paper reports a computer analysis of the characteristic surface for a symmetrical reinforced concrete section in terms of axial load, moment and curvature. The consideration starts from a statement of the surface under short-term load, and is extended in detail to include the effects of cracking, creep and stress redistribution under sustained load. The modes of failure are discussed for both short-term and sustained load, and the influence of the relevant parameters (mechanical proportion of steel ω, relative cover a/h, and ultimate creep coefficient φ∞) are analysed. A simplified form of surface is demonstrated for short-term load, and modifications of the surface when the load is sustained are derived and assessed.
Shear strength of prestressed concrete beams without web reinforcement*
Authors: Nielsen M. P. , Bræstrup M. W. 
Published: October 2009

SYNOPSIS Using the theory of plasticity, coincident upper and lower bounds for the ultimate shear load are determined. The materials are assumed to be rigid, perfectly plastic, the tensile strength of the concrete being neglected. The unrealistic assumption of unlimited concrete ductility is amended by introducing an empirical effectiveness factor on the compressive strength. The solution, which gives the shear strength as a function of the shear-span ratio and the longitudinal reinforcement strength, is compared with the results of a test series, and excellent agreement is found. The dependence of the effectiveness ratio upon various factors, principally the concrete strength, is discussed by comparing it with a number of shear tests reported in the literature.
Fatigue strength of cold-worked non-prestressed reinforcement in prestressed concrete beams
Authors: Bennett E. W. , Joynes H. W. 
Published: October 2009

Synopsis Fourteen identical beams with limited prestress were tested to fatigue failure under different ranges of cyclic loading and the results used to derive the modified Goodman diagram for a 10 mm cold-worked deformed bar acting as non-prestressed reinforcement. The diagram was checked against the results of tests of two beams with different amounts of reinforcement and prestress. Two further beams which were tested under service loading conditions had not failed nor developed excessive deflection or width of cracks after 2 million cycles of load. The implications of the results for the design of ‘Class 3’ prestressed concrete members are discussed.
Measuring the crack width on concrete surfaces by light-dependent resistor
Authors: El Din A. S. Salah , Lovegrove J. M. 
Published: October 2009

Synopsis The theory is presented and the equipment is described for a technique which may be used when measurements of crack width have to be made on the surfaces of concrete structures. The technique is of most value when other, more standard methods for measuring crack width by microscope or mechanical and electrical gauges would be unsuitable. Measurements may be easily and accurately made by using the apparatus described and an application to crack width measurement during repeated loading is given. The equipment, which may be remotely controlled, may also be encapsulated and sealed against moisture for use in field conditions either underwater or underground.
Pore pressure in heated concrete walls: theoretical prediction
Authors: Bažant Zdeněk P. , Thonguthai Werapol 
Published: October 2009

Synopsis Pore-water pressures in concrete can be calculated by a previously developed theory which is based on thermodynamic properties of water and takes into account the huge changes in permeability and sorption isotherm with temperature, as well as the changes of pore space due to temperature and pressure. After reviewing the theory, finite-element solutions are com-pared with weight-loss tests of Chapman and England, and theoretical predictions are made for rapid heating of thick walls, either sealed or unsealed. A two-dimensional axisymmetric finite-element solution is developed to analyse theffect of a hot spot on the wall. The pore-pressure peaks are found to be much higher than for slow heating (25 atm versus 8 atm), and still about 50% higher when the heating is confined to a hot spot. The moisture movement in regions where the pressure gradient is opposite to the temperature gradient is found to be rather irregular and to exhibit oscillations. The theory predicts the phenomenon of ‘moisture clog’ suggested by Harmathy on the basis of tests.
Determining concrete strength by using small-diameter cores
Authors: Bungey J. H. 
Published: October 2009

Synopsis Estimates of concrete strength are often made from compression tests on cores which have a diameter considerably less than the recommended 100 mm. The paper examines the results of a laboratory investigation in which 44 mm diameter cores were cut and tested. The influence of both specimen and aggregate size upon height/diameter ratio and orientation effects is examined, and observed relationships between core strengths and measured control cube strengths are compared with those normally used for larger cores. It is shown that core strength is affected by both specimen size and aggregate size, and it is proposed that conversion to corresponding cube strengths should take this into account. The variability of results is also assessed in relation to the above factors, and an estimate made of the accuracy of predicted actual cube strength that is likely to be achieved from testing cores of this size.
Bimoment equilibrium of finite segments of Hillerborg plate
Authors: Gurley Colin R. 
Published: October 2009

Synopsis The term ‘Hillerborg plate’ is used in this paper to distinguish ‘no-torsion or’ ‘torsion-free’ plates, slabs or grillages subject to two-way bending. A wide range ofstructures (‘space deck’ roofs, bridge decks, concrete slabs) can be treated as Hillerborg plates. The paper examines the conditions for static equilibrium of a large plate segment of finite size, and concludes that there are four (NOT three) independent over-all equilibrium conditions. These conditions can be expressed naturally by introducing a new stressresultant - the ‘bimoment’. The role of bimoments in Hillerborg plate analysis is similar to the role of moments in beam analysis.
The application of the BS 4550 test for pozzolanic cements to cements containing pulverized-fuel ashes
Authors: Smith Micheal A. , Halliwell Freda 
Published: October 2009

Synopsis A large number of pulverized-fuel ashes were tested, in proportions of 20 to 40%, with Portland cement, in accordance with the chemical test for pozzolanic cements incorporated in BS 4550: Part 2:1970. The ashes had a range of particle-size distributions and losses-on-ignition. The results of the test were unrelated to the loss-on-ignition of the ashes, but strongly related to the particle-size distribution measured in terms of the residue on a 45 pm sieve, although other unidentified characteristics of the ashes also infiuenced the results. A positive result is unlikely to be obtained for an 80:20 0PC:pfa mix unless the pfa has a 45 pm sieve residue of less than 20%. Most pulverized-fuel ashes will only give a positive result if present in a proportion exceeding about 25%.
Torsional stiffness of reinforced concrete rectangular members
Authors: Sandegren D. Stephen , Yu C. W. 
Published: October 2009

Synopsis The paper deals with the determination of the torsional stiffness of rectangular reinforced concrete members under pure torsion and torsion combined with bending and shear. The energy principle is applied to a four-plate shear wall model representing the member to obtain the stiffness under pure torsion. The range of validity and the modification needed for the expression for stiffness thus obtained when the member is subjected to bending moment and shear force are investigated with reference to the results of tests on reinforced concrete space frames.
Influence of specific surface and concentration of solids upon the flow behaviour of cement pastes
Authors: vom Berg W. 
Published: October 2009

Synopsis A purpose-built coaxial-cylinders viscometer was used to obtain pow curves up to shear rates of 1800s–1. An equation in which the shear rate γ is expressed as a hyperbolic function of τ–τf, where τ is the shear stress and τf is the yield stress was found to fit the lower part of the pow curve and, by using this equation, the values of τf and ηo, the plastic viscosity at zero shear rate, were found. Relationships were then established between these two rheological parameters and the specific surface and concentration of solids.
Particle size of aggregate and its influence upon the expansion caused by the alkali–silica reaction
Authors: Hobbs D. W. , Gutteridge W. A. 
Published: October 2009

Synopsis Measurements of the expansion behaviour of mortar bars containing various proportions of a reactive porous op aline rock are described. It is shown that the age at which cracking occurred is essentially independent of particle size, and that the alkali-silica reaction rate is primarily a function of particle volume.
Factors affecting the relationship between rate of loading and measured compressive strength of concrete
Authors: Kaplan Seyit Ali 
Published: October 2009

Synopsis The effect of the free water, age and curing conditions upon the strengthlloading-rate relationship of concrete, mortar and neat cement paste was studied. It was found that the moisture content at the time of testing was one of the most important factors influencing this relationship, but any variables such as age or curing regime which affect the internal structure of the solid phase also have an influence. The data obtained under the different loading methods indicated that, when a specimen made from cement paste is loaded at slower rates up to approximately one-third of its ultimate strength value, the resulting ultimate strength is increased. However, ifa slower rate of loading is continued throughout the test, the ultimate strength is decreased significantly. This result is used to find the analytical form of the relationship between the stress-strain curve and strain rate of concrete and equations are proposed which closely agree with the existing data.
The effect of stress, frequency, curing, mix and age upon the damping of concrete
Authors: Jordan R. W. 
Published: October 2009

Synopsis The results of an investigation to study the effect of stress, frequency, curing, mix and age upon the damping of concrete are presented. The chosen factors were considered to be of greatest importance in determining the level of dumping in multi-flue chimneys and cooling towers under wind excitation. Each factor was considered at only two values or levels, to cover the range of interest, but each factor was studied at both levels of the other factors to form a factorial experiment. The data were then analysed statistically to identify the significant factors and interactions between factors. An attempt has been made to explain the observed changes in damping in term of three components; a coulomb damping component associated with microcracking, a hysteretic or solid dumping component associated with sliding friction within the solid gel structure and a viscous damping component associated with moisture movement. For the range of values of the factors studied, the component associated with micro-cracking was the most dominant, especially in dry concrete.
The air and water-vapour permeance of glass-fibre-reinforced cement
Authors: Langley A. A. 
Published: October 2009

Synopsis Experimental details and results are presented of an investigation of the air and water-vapour permeance of glass-fibre-reinforced cement sheet. Water-vapour permeance decreased with storage in moist conditions, falling to less than half its initial values after 2 years. The air permeance of material stored in dry conditions increased over this period, but low values resulted from exposure to moist environments. Material saturated with water was virtually impermeable to air. After extended periods, the rate of liquid water absorption fell to 2 × 10−3 ml m−2 S−1 (200 mm head) or less. This was compatible with the ‘impermeable’ result of the ISO Impermeability Test.
The development of waterproof insulating materials based on lightweight concrete
Authors: McClune C. R. , Moorhouse J. 
Published: October 2009

Synopsis This paper describes the results of tests developed to study the rate of water uptake and the equilibrium water content of light weight concrete specimens treated with a variety of waterproofing techniques. The k value and compressive strength of the treated specimens were also determined. The Waterproofing techniques used were: surface sealants; integral sealants, both reactive and non-reactive; waterproofing aggregates; combinations of these last two; cured concrete specimens saturated with a silicone water-repellent solution; replacing cement by resin binders. Some of these techniques were much more successful than others. The least successful was the use of reactive integral sealants, which had no effect upon water uptake. Easily the most successful method was the substitution of resin binders for cement; with these, the equilibrium moisture content was reduced to about l% by volume or less compared with about 20–25% by volume for untreated materials. A substantial increase in compressive strength was also observed. This work indicates that an insulating material with low k value, an adequate compressive strength for use in an engineering environment and a low water equilibrium value will be resin-based rather than cement-based.
The influence of pore pressure upon concrete
Authors: Butler J. E. 
Published: October 2009

Synopsis The effects of pore pressures within porous material have caused debate, especially in relation to internal uplift in gravity dams and the areas over which water pressures act. The background to these divergent views is reviewed in the paper. By using a direct-tension test method and experimental principles already reported, equipment was built capable of testing three specimens, subjecting them to uplift pressures, neutral pore pressures and external tensile stresses; strains were continuously monitored for periods of a few minutes to several days. Tests have been carried out in which uplift developed and caused failure or was progressively replaced by external load, or concrete was subjected to neutral pore pressures in conjunction with external load. The results established that Terzaghi's effective stress equation was applicable to concrete in any stress condition, and that the effective porosity of concrete was initially of the order of 0·5 to 0·65 and increased with crack propagation to unity.
A viscometric study of cement pastes containing superplasticizers with a note on experimental techniques
Authors: Banfill P. F. G. 
Published: October 2009

Synopsis Viscometric data on the influence of concentration of two superplasticizing admixtures upon the yield value and plastic viscosity of pastes made with four cements are reported. Yield value decreases exponentially with concentration, whilst plastic viscosity decreases linearly. These results are discussed in relation to the effect of superplasticizers upon the rheology of fresh concrete. Detailed differences in results obtained in viscometers of different geometries are reported and discussed.
The dimensional stability of glass-fibre-reinforced cement
Authors: Langley A. A. 
Published: October 2009

Synopsis The dimensional changes of glass-fibre-reinforced cement specimens, containingabout 5% by weight of glass fibre in a neat cement paste matrix, have been monitored during controlled cycles of drying and wetting following storage for up to two years in a range of environments. In situ monitoring of large panels of similar material undergoing continuous natural weathering has also been carried out. For specimens stored in moist conditions, initial drying shrinkage increased with storage time and was greater than that following storage in dry air. Reversible shrinkage of about 0·35% was observed for material stored in water for two years. Annual variations of around 0·08% were observed in situ during natural weathering of the large panels, together with short-term thermally induced changes.
Influence of pulverized–fuel ash and granulated blastfurnace slag upon expansion caused by the alkali–silica reaction
Authors: Hobbs D. W. 
Published: October 2009

Synopsis The effectiveness of seven pulverized-fuel ashes(pfa) and a ground granulated blastfurnace slag (gbfs) in reducing the expansion and cracking induced in mortar bars by the alkali–silica reaction is described. The proportion of reactive aggregate in the mortar bars was such that the water-soluble alkali to reactive silica ratio lay close to its critical value. It is shown that the partial replacement of a high-alkali cement by either pfa or gbfs reduces the expansion induced by the alkali-silica reaction and that with high-cement-content mixes it is necessary to replace more than 40% of the cement by pfa or gbfs to prevent damage from occurring due to the alkali-silica reaction. It is concluded that both materials act effectively asalkali diluters, gbfs being more effective in reducing damage due to the alkali-silica reaction than pfa.
The influence of water gain upon the tensile strength of concrete
Authors: Fenwick R. C. , Sue C. F. C. 
Published: October 2009

Synopsis The paper describes the results of an investigation into the effect of direction of load application relative to the direction ofcasting upon the tensile strength ofconcrete. A series of different concrete mixes were made in which the type of aggregate, the sand content and the water/cement ratio were varied. The test results show that water gain introduces directional properties into the concrete. The direct tensile strength for stresses acting parallel to the direction of casting was consistently less than that obtained when the stress was applied normal to this direction.
An apparatus for testing the response of small specimens to controlled environmental changes
Authors: Day Robert L. 
Published: October 2009

Synopsis A modular apparatus is described with which small specimens can be subjected to controlled changes of compressive load, temperature and humidity while concurrent measurements of immediate and time-dependent deformations are made. The versatility of the apparatus is demonstrated by noting how (a) the type of material, (b) the geometry of the specimen, and (c) the timing and size of changes in any of the three environmental parameters can be selected for specific examinations. Pilot tests and typical results from tests on hardened cement paste are used to demonstrate the sensitivity, accuracy and reliability of the apparatus.
The advanced strip method – a simple design tool
Authors: Hillerborg Arne 
Published: October 2009

Synopsis The advanced strip method is a method for the design of slabs which are partly supported on columns, re-entrant corners or other point supports. On the basis of this general method, it is possible to formulate simple and straightforward rules for the design of most slabs met with in practice. The calculation of the design, moments is then reduced to a simple application of ordinary beam theory, supplemented by taking into account a few rules regarding moment distribution and curtailment of reinforcement. The procedure is illustrated by examples, covering supports on interior columns, exterior columns, corner columns, a wall extending under part of the slab and a re-entrant corner. The method is simpler and safer than design based on yield-line analysis, and just as economical as regards reinforcement.