bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of soil heterogeneity on load redistribution and settlement of a hyperstatic three-support frame
Authors: Houy L. , Breysse D. , Denis A.
Published: October 2009

Spatial and geometrical variability of mechanical soil properties can induce differential settlements and load redistribution in hyperstatic structures. Therefore damage prevention requires specific attention to be paid to the global mechanisms of soil–structure interaction. A reduced-scale model of a hyperstatic three-support frame (scale 1:100) is installed on the CEA-CESTA centrifuge, up to 100g. Various configurations are studied, with different loadings, different structural stiffnesses, and different geometries of the soil layer. Strain gauges are fixed at various points so as to enable the retro-analysis of all components of forces at free ends. Displacements are recorded at several points on the structure and on the free surface. A numerical model of the frame (based on beam theory with elastic supports) is calibrated, first to determine an equivalent support stiffness, and second to quantify the effect of variations of the structural stiffness/soil modulus ratio on the structural response. A probabilistic approach based on Monte Carlo simulation is thus developed. It mixes the soil description, based on random field theory and enabling the description of spatial correlation of properties and the frame model identified above. The influence of (a) scattering in soil properties and (b) spatial correlation of soil properties—through correlation length or scale of fluctuation—is quantified in terms of displacements and bending moments in the frame. The approach reveals the important weight/influence of soil variability on differential settlement and load redistribution, particularly when the scale of fluctuation of soil and length of span have the same magnitude. The analysis makes it possible to evaluate the risk that the bending moment in any critical section may be larger than predicted by the usual engineer's model. Some conclusions are drawn to better estimate ‘characteristic bending moments’ in the frame, accounting for both the soil variability and the soil–frame interaction.
Problems in identifying the effects of structure and critical state in a soil with a transitional behaviour
Authors: Ferreira P. M. V. , Bica A. V. D.
Published: October 2009

This work shows that some soils with an intermediate behaviour between clays and sands do not have a unique compression line, as has also been pointed out by Martins et al. It has been shown here that a unique critical state line could not be determined for the remoulded soil. Although the results shown here are for a reconstituted residual soil, similar behaviour in compressibility has been found in silts and mixtures of sand and kaolin. However, it has been found that the critical state framework can be applied using a family of parallel critical state lines depending on the initial specific volume. One of the questions raised by this work is how the effects of structure can be quantified if the intrinsic properties of the remoulded material are not unique. The compression and critical state lines of the remoulded material are not only non-unique but also of a distinctly different gradient from the natural material.
Exploring the macro- and micro-scale response of an idealised granular material in the direct shear apparatus
Authors: Cui L. , O'Sullivan C.
Published: October 2009

The development of the distinct element method (DEM) has presented researchers with a tool to obtain detailed information about the particle-scale interactions during the standard element tests routinely used by both practising engineers and researchers. The current study considers the response of a granular material in the direct shear apparatus by coupling physical tests with equiva DEM simulations. An idealised granular material, comprising uniform steel spheres, was considered in this study so that the specimen geometry and surface friction characteristics could be accurately replicated in the DEM simulations. The macro-scale response of the physical test specimens is compared with the macro-scale response observed in the DEM simulations for the purposes of validation of the numerical model. Using the DEM model the sensitivity of the macro-scale response to factors including the surface friction (both interparticle friction and particle-boundary friction) and the specimen generation approach is explored. The study also considers the stress inhomogeneities that develop within the specimen during testing. Considering a representative numerical specimen, an in-depth analysis of the micro-scale responses of the specimen is presented, including the distribution of the contact forces, the particle displacements and the particle rotations. The variation in volumetric and shear strains within the specimen is also considered. The response of this ideal granular material is shown to be sensitive to small variations in fabric.
A rheological model for the description of boulder impacts on granular strata
Authors: di Prisco C. , Vecchiotti M.
Published: October 2009

This paper considers the mechanics of rock boulders impacting on granular strata. The study is aimed at improving the numerical methods devoted both to describing boulder trajectories along slopes and designing preventive structures in mountain regions. The problem is analysed by using a simplified approach inspired by the lumped mass method. This is based on (a) the macro-element concept, (b) the definition of generalised stresses and displacements, and (c) delayed plasticity theory. Both vertical and inclined impacts on horizontal strata and vertical impacts on inclined slopes are discussed. The numerical results are obtained by using a finite difference numerical discretisation to integrate, over time, a coupled system of two-dimensional differential equations. Most of the input data requested by the model are basic and geotechnically meaningful, and comparison of the numerical results with the experimental data seems to be quite promising.
Inverse long-term stability analysis of a constrained landslide
Authors: Puzrin A. M. , Sterba I.
Published: October 2009

This paper deals with long-term stability analysis of a constrained landslide. The landslide has ‘nowhere’ to go and its downhill movement is slowing in time, which intuitively implies its long-term stability. However, exactly because the landslide is slowing, the shear strength on the sliding surface may decrease, leading to increase in compressive stresses at the landslide foot and, ultimately, to a failure. The proposed long-term stability analysis of such a landslide is based on an inverse analysis, which allows for the safety factor to be determined solely by curve-fitting the observed displacement data. For a safety factor lower than 1, the time of failure can be predicted using additional earth pressure measurements in the sliding layer. The proposed procedure is illustrated using the observation data from the Brattas–St Moritz landslide.
The provision of tension and compression reinforcement to resist in-plane forces
Authors: Clark L. A.
Published: October 2009

Synopsis

This paper presents equations for proportioning skew or orthogonal tension and/or compression reinforcement to resist a triad of in-plane forces. The problem obtaining a ductile failure is discussed, and limits applicability of mild and high-strength steel as pression reinforcement are suggested. It is also indicated how the design equations might be used to proportion reinforcement to resist combinations of moments in-plane forces.
Relationships between the British Standard tests for workability and the two-point test
Authors: Tattersall G. H.
Published: October 2009

Synopsis

Experimental results obtained by Scullion are found to be consistent with the suggestion that the slump test is a measure of the yield value of fresh concrete, and that the compacting factor test and the Vebe test each measure the apparent viscosity at an arbitrary effective rate of shear characteristic of the particular test. This leads to an equation relating results from the three British Standard tests. The equation is tested on extensive data published by other workers, and quite good agreement is found.
The workability of steel-fibre-reinforced concrete
Authors: Hughes B. P. , Fattuhi N. I.
Published: October 2009

Synopsis

Predicting the workability of fibre-reinforced composites is difficult because of the large number of parameters involved. However, by standardizing on the unreinforced concrete or mortar mixes, it has been possible to determine the effect of type, aspect ratio and volume fraction of various steel fibres upon the slump and Vebe times of these particular concretes and mortars. These relationships should be useful when designing fibrous mixes for any of the types of fibre used: plain round, Duoform, crimped and hooked steel fibres.
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.
Natural vegetable fibres as reinforcement in cement sheets
Authors: Lewis Gladius , Premalal Mirihagalia
Published: October 2009

Synopsis

Some relevant physical and mechanical properties of the fibres from water reed, elephant grass, plantain and musamba are discussed. The effect of elephant grass fibres upon the strength of reinforced cement sheets and the consistence of the mortar is shown to be beneficial.
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.
Response of the Bond in Reinforced Concrete to High Temperatures
Authors: Morley P. D. , Royles R.
Published: October 2009

Synopsis

The effect of high temperutures upon the bond between the steel und concrete in reinforced concrete was examined over a temperature range of 20–750°C. The concrete mix was constant throughout und 16 mm deformed reinforcing bar (Tor bar) was used in most tests. Various parameters were examined including different test conditions and depths of cover. The four test conditions used were: (l) stressed during heating (a steady-state bond stress of 3·70 N/mm2 was applied) and loaded to failure when hot, (2) stressed during heating and loaded to failure when cooled, (3) no applied stress during heating and loaded to failure when hot, and (4) no stress during heating and loaded to failure when cooled. Four different depths of concrete cover (25, 32, 46 und 55 mm) were l for the stressed/residual test condition, but only tht 55 mm cover was used with the other three test conditions. The effect of heat upon the compressive und tensile strength of the concrete was also considered, together with its effect upon the bond performance. Some 16 mm plain bar specimens were used in the tensile strength studies.

Introduction

When a reinforced concrete structure has been involved in a fire. it is often possible for it to remain standing, because of the good fire-resisting properties of the concrete. This means that. in dealing with such a situation. a choice can be made between reconstruction and reinstatement. Often reinstatement can be the quicker and cheaper alternative. However, before a decision can be made, it is necessar/10 establish whether or not the damaged structure is suitable for such treatment. To do this, its residual capacity for structural performance must be assessed, which requires knowledge of the properties of steel and concrete, and of the bond between them at temperatures experienced in fires.
Mechanisms of ‘shear’ failure
Authors: Kotsovos Michael D.
Published: October 2009

Synopsis

It is postulated that the various modes of diagonal failure exhibited byreinforced concrete beams under increasing load are associated with the multiaxial stress conditions that exist in the region of the path along which the compressive force is transmitted from support to support. This concept leads to a comprehensive description of the causes and mechanisms of diagonal failure which, in contrast with currently accepted concepts, is compatible with published experimental information. It is shown that, although current ‘shear’ design procedures may guard against diagonal failure within the shear span, they may lead to a ‘brittle’ type of failure outside this span which does not give adequate warning of impending structural collapse.
Durability of cement sheets reinforced with fibrillated polypropylene networks
Authors: Hannant D. J.
Published: October 2009

Synopsis

The durability of cement sheets reinforced with fibrillated polypropylene networks is examined in terms of the effects upon the tensile stress–strain curve of three years of natural weathering or of a similar period of indoor storage. It is shown that three years of exposure has little effect upon the strengths of the networks, but that increases in the strength and elastic modulus of the matrix in the naturally weathered specimens alter some features of the stress–strain curve in comparison with similar material stored indoors.
Properties of ultra-high-strength concrete containing a superplasticizer
Authors: Brooks J. J. , Wainwright P. J.
Published: October 2009

Synopsis

Tests have been undertaken over a period of one year to compare the time-dependent properties of high-cement-content (500–730 kg/m3) concretes with and without a superplasticizing admixture. For mixes containing the superplasticizer. there was an improvement in strength and modulus of elasticity and a decrease in shrinkage, but there were increases in creep and swelling. The process of microcracking is postulated to be a contributing factor in shrinkage and in creep under drying conditions.
Apparatus for measuring the transient thermal strain behaviour of unsealed concrete under constant load for temperatures up to 700°C
Authors: Sullivan Patrick J. E. , Khoury Gabriel A. , Grainger Brian N.
Published: October 2009

Synopsis

Apparatus was designed for the strain measurement of unsealed cylindrical concrete specimens under transient thermal states. This subject has received in sufficient attention to date arld is of interest io prestressed concrete nuclear reactor pressure vessel and fire applications. To simplify analysis of results, the imposed conditions includean arrangement for applying constant uniaxial compressive load and an automatic temperature control system which ensures as linear a rate of heating as possible and minimizes axial temperature differentials along the specimen. A strain measuring device was designed which produced accurate results under transient thermal states.
Torsion in plain and prestressed concrete beams containing polypropylene fibres
Authors: Narayanan R. , Kareem-Palanjian A. S.
Published: October 2009

Synopsis

Torsion tests on 23 plain and prestressed concrete beams containing polypropylene fibres are presented and discussed. The addition of these fibres to concrete is shown to improve the post-peak ductility, though there is no change in the ultimatc torsional capacity of the beams tested. A simple method of predicting the ultimate torsional capacity of these beams from a knowledge of the cube strength and the applied prestress is proposed; by comparison with the experimentally observed strengths, the method is shown to yield satisfactory predictions.
Comparisons between closed-loop and straight metal fibres inconcrete
Authors: Taylor Michael A.
Published: October 2009

Synopsis

Concretes containing closed-loop fibres and conventional straight fibresare compared for workability, bond strength, compressive strength, tensile strength, flexural strength and toughness. The concept of spacing is treated briefly. Tests indicate that all fibres have little effect until after significant cracking occurs. After cracking, closed loops offer much better integrity than straight fibres. Closed-loop fibres reduce the variability ofboth compressive and tensile strengths.
Shear transfer across cracks in reinforced concrete due to aggregate interlock and to dowel action
Authors: Millard S. G. , Johnson R. P.
Published: October 2009

Synopsis

Tensile cracking of reinforced concrete plate elements results in a significant reduction in the in-plane shear stiffness and strength. Shear can be transmitted across the cracks either by interlocking of the aggregate particles protruding from each face or by shearing of the reinforcement crossing the cracks. Tests of a new type are devised to study these mechanisms independently and the results are compared with several theoretical models. It is concluded that the aggregate mechanism results from a combination of crushing and overriding of the crack faces and can be predicted if the normal stiffness that restrains crack widening is known. The initial shear stiffness and ultimate shear strength due to dowel action are successfully predicted from theoretical models and an exponential curve is used to describe the intermediate behaviour.
Some preliminary test data on cement–pfa–anhydrite mixes
Authors: Hyde A. F. L.
Published: October 2009

Synopsis

Cement-stabilized pfa is commonly used as a load-bearing fill for civil engineering purposes. Anhydrite is often used for similar purposes in the mining industry. A series of compressive strength tests were carried out on combinations of these three materials to determine their potential as moderate to high-strength fills. The tests were carried out on 38mm dia. by 75mm long specimens prepared by static compaction techniques. Attempts to stabilize pfa using anhydrite showed little potential for increasing the load-bearing capacity of pfa. However, a study of the combination of cement and anhydrite in the stabilization of pfa showed these two materials to be complementary in increasing the compressive strength of compacted stabilized pfa compared with using just cement or just anhydrite as the stabilizing agent. The 14, 28 and 56 day strengths of cement-bound pfa were more than doubled by the replacement of 1·4% cement by weight with 10% anhydrite by weight. The addition of higher proportions of anhydrite could decrease this enhanced strength or give only a marginal increase. Long-term tests after a curing period of one year showed no apparent deterioration in strength.
A modification of the Tattersall two-point test apparatus for measuring concrete workability
Authors: Cabrera J. G. , Hopkins C. J.
Published: October 2009

Synopsis

This paper describes a mod2Jication of the Tattersall two-point test apparatus for measuring concrete workability. The modified apparatus is easier to operate, giving a full and permanent record of what happens during the test and eliminating operator bias, which exists in the present oil-pressure measuring system.
Improvements to the Figg method for determining the air permeability of concrete
Authors: Cather R. , Figg J. W. , Marsden A. F. , O'Brien T. P.
Published: October 2009

Synopsis

Modifications to the Figg method for in situ determination of the air permeability of concrete are recommended. These are the use of a hole size of 10mm diameter × 40 mm deep with a silicone rubber plug 20 mm from the surface and a digital solid-state manometer. The time, in seconds, taken for a pressure change from 55 to 50 kN/m2below atmospheric is taken as a measure of the air permeability. A table of protective quality of cementitious materials is tentatively proposed.
The turning-tube viscometer: an instrument to measure the flow behaviour of cement–pfa pastes
Authors: Hopkins C. J. , Cabrera J. G.
Published: October 2009

Synopsis

The instrument described in this paper uses falling ball viscometry to measure differences in the flow behaviour of cement-pfa pastes. This apparatus overcomes the problems of opacity and sedimentation normally associated with studies into cement paste rheology.
Shear strength of smooth unreinforced construction joints
Authors: Clark L. A. , Gill B. S.
Published: October 2009

Synopsis

The results of 60 tests on smooth unreinforced construction joints in concrete prisms are presented. Each specimen was subjected to loading which induced combined direct and shear stresses at the joint. It was found that shear was transmitted by a combination of ‘cohesion’ and ‘friction’. A slight dependence of the shear strength upon the age ofthe first pour of concrete at the time of the second pour was found. A relation for the shear strength of a smooth unreinforced construction joint is proposed as a function of concrete compressive strength and the associated direct stress at the joint.
Applications of diffusion theory to permeability tests on concrete Part I: Depth of water penetration into concrete and coefficient of permeability
Authors: Vuorinen Jukka
Published: October 2009

Synopsis

The paper describes an application of diffusion theory to the penetration of water under pressure into concrete. The resulting second-order differential equation is non-linear, because the water-storage capacity of the open pores in concrete depends upon the counterpressure arising. Numerical computer analysis of the permeability equation leads to a formula for calculating the coefficient of permeability when the values of the test parameters and the depth of water penetration are known. The application of the final formula to a series of laboratory test results shows that there is a fairly good correlation between the values of the coefficient of permeability so calculated and those based on direct measurement of water flow through a concrete specimen.
Applications of diffusion theory to permeability tests on concrete Part II: Pressure-saturation test on concrete and coefficient of permeability
Authors: Vuorinen Jukka
Published: October 2009

Synopsis

In addition to the conventional permeability tests, the coefficient of permeability of concrete can be found through interpretation of observations made during the pressure-saturation test. An opportunity for this offers itself in the application of diffusion theory to the mathematical model of this test. After explaining this procedure, the paper compares the results with those obtained by a method in which the depth of water penetration into concrete is measured. Although the correlation can be considered satisfactory from the practical point of view, it seems that the mathematical model used does not in all respects represent the complicated phenomenon of water outflow from a saturated concrete specimen.
A study of toughness indices
Authors: Barr B. I. G. , Hasso E. B. D.
Published: October 2009

Synopsis

The paper reviews various methods of evaluating the toughness of fibre-reinforced concrete materials by means of toughness indices and discusses in detail the use of various multiples of jirst-crack defection to define toughness indices. A new toughness index is proposed, based on the load–deflection curves obtained up to twice the defection at first cracking. The index is given by the ratio of two areas under the load–deflection curve and is expressed as a percentage which varies from zero for plain concrete, through 67% for an elastic-plastic material, to a theoretical maximum value of 100% for an extremely tough material. Both modulus-of-rupture and notched-beam test specimens were used in the study. Although only one geometry is reported and only Duoform steel fibre was used in the study, the method described is potentially applicable to all geometries and types of fibre. The proposed toughness index is shown to be independent of the notch depths used in the geometry reported and has well defined maximum and minimum values. It also has a large range, which should make it suitable to distinguish between various types and amounts of fibre.
Pore structure and permeability of hardened cement paste
Authors: Hughes D. C.
Published: October 2009

Synopsis

A review of the literature on flow through porous media suggests that the permeabilityof hardened cement paste should be related to pore size distribution, pore conductance, tortuosity and isotropy. It is likely that these factors do not exhibit a unique value. Tests were made on OPC and OPC/pfa pastes cured for I, 4 and 12 weeks in Ca(OH)2, solution. The permeability of both types was similar for those pastes cured for 4 and 12 weeks at 35°C, whilst after one week's curing the OPC/pfa paste was sign$cantly the more permeable. Pore size distribution was determined by using a two-stage mercuryintrusion technique. A simple model, based upon Poiseuille's formula, was developed and shown to yield a reasonable correlation with the experimental determination of permeability for the OPC pastes and on SRPCpaste cured for 4 weeks. The correlation was not so goodfor the OPC/pfa pastes, probably as a consequence of structural damage during mercury intrusion in such pastes.