bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction and interpretation of pore pressure dissipation for a tapered piezoprobe
Authors: Whittle A. J. , Sutabutr T. , Germaine J. T. , Varney A.
Published: October 2009

This paper describes a combined theoretical and experimental study of a tapered piezoprobe device that has been designed to measure the in-situ pore pressures in offshore geotechnical site investigations. Predictions of pore pressure dissipation are obtained using a non-linear coupled consolidation analysis, with effective stress–strain properties of the soil characterised by the MIT-E3 model, and initial conditions computed by a strain path model of undrained probe penetration. Although the initial dissipation times of the probe are much shorter than for a conventional piezocone, the response is retarded by the arrival of a pore pressure front from above the taper section. The analyses suggest that more reliable predictions of in-situ pore pressures can be achieved in a shorter timeframe by introducing a second porous filter on the shaft above the tapered section and correlating the pore pressure dissipation at the two sensors. Entire dissipation responses of the tapered piezoprobe and piezocone devices have been measured concurrently at a well-documented site near Boston. The results show excellent agreement between the predicted and measured dissipation curves at depths of 20–35 m. However, backfigured values of hydraulic conductivity are consistently less than laboratory measurements at the same elevation by a factor of 2. In-situ pore pressures can be estimated accurately within 1 h at this site by correlating the dissipated pore pressures measured at the tip of the tapered piezoprobe and the response at the base of the piezocone.
Quantitative characterisation of the geometry of discret particles
Authors: Sukumaran B. , Ashmawy A. K.
Published: October 2009

A new technique is described to quantify particle shape and angularity using an image analyser. The method relies on discretising the two-dimensional projection of the particle and comparing the projected outline with that of a standard geometric shape, namely a circle. Two new parameters for particle shape and angularity were formulated and their values were determined for various materials. The relationship between the new parameters and large-strain (steady-state) internal friction angle as well as pluviated void ratio was examined. Overall, the results indicate that as shape and angularity parameters increase, the drained friction angle and pluviated void ratio increase. In addition, shape and angularity were found to influence the measured maximum void ratio and, to a lesser extent, the minimum void ratio.
The strength of unsaturated bentonite-enhanced sand
Authors: Stewart D. I. , Tay Y. Y. , Cousens T. W.
Published: October 2009

A modification to Rowe's stress-dilatancy equation is presented that extends its range of application to include unsaturated soil behaviour. The results of a programme of constant water content triaxial tests on unsaturated bentonite-enhanced sand (BES) are reported, together with those of a programme of saturated drained triaxial tests on the sand. It is shown that the variation in the rate of dilation at failure with the sand relative density is similar for the two materials. It is proposed that the packing and friction angle of the sand particles and the degree of saturation control the shear strength of unsaturated BES containing modest amounts of bentonite, and that the shear strength of the bentonite component can be ignored.
Failure modes of drilling fluid filter cake
Authors: Cerasi P. , Soga K.
Published: October 2009

Filter cakes formed on well bore walls during the drilling process need to be ruptured to start oil production. In this study, the failure of external filter cakes from water-based drilling fluids was investigated when the damage incurred by the formation is due almost entirely to brine and polymer invasion during filtration. It is proposed that in such cases the two-phase flow behind the filter cake, in the rock, combined with the cake's mechanical properties determines the mode in which it will fail. The two different failures, ‘pinholing’ of the cake and ‘lift-off’, are both observed in the experiments, with the mode of failure depending on the pressure drop across the cell. At a low pressure drop the cake deforms locally, separating from its substrate. Pinholes subsequently appear above these detached zones. For a large pressure drop the original deformed zones grow in size and ultimately merge. This leads to a large portion of the cake separating from the rock. A simple model of filter cake failure, based on a classical elastic cavity expansion analysis, is proposed. The model predicts pinholing or lift-off behaviour, depending on the cake's stress state and the degree of fingering in the two-phase formation.
Three-dimensional site characterisation: neural network approach
Authors: Juang C. H. , Jiang T. , Christopher R. A.
Published: October 2009

Site characterisation is an important task in geotechnical engineering practice. The ultimate goal in site characterisation is to be able to estimate in situ soil properties at any half-space point at a site based on limited tests. This estimate may be a point estimate or expressed in terms of some statistical parameters. Geostatistical and random field methods have been applied with limited success. This paper presents a new approach, based on artificial neural networks, for site characterisation. Emphasis is placed on the application of generalised regression neural networks for site characterisation. The results show that the neural network approach has the potential to be a practical tool for site characterisation.
Evaluation of continuous hyperplastic critical state (CHCS) model
Authors: Einav I. , Puzrin A. M.
Published: October 2009

A continuous hyperplastic critical state (CHCS) model was developed in a companion paper by Einav and Puzrin, within a unified hyperplastic/continuous-hyper-plastic framework. This framework ensures that the laws of thermodynamics are always obeyed, and allows a possible modelling of continuous and abrupt yielding in the same package. The current paper briefly describes the CHCS model and presents its evaluation against triaxial test data for different stress paths, stress histories and loading conditions. Evaluation of the CHCS model against experimental data from two geotechnical boundary value problems is performed using the finite difference technique. The model is shown to provide reasonable simulations of the experimental data from both the lab tests and field measurements.
Tensiometer saturation and the reliable measurement of soil suction
Authors: Take W. A. , Bolton M. D.
Published: October 2009

Recent advances in the technology for measuring matric suction have permitted the direct measurement of gauge pore water pressures lower than −100 kPa—that is, absolute tensions. This significant accomplishment has opened up a realm of research possibilities into the nature and behaviour of unsaturated soils. However, the widespread exploitation of this technology has been limited by the lack of a commercially available tensiometer capable of measuring high suctions, and by the complex and highly experience-driven nature of the filter saturation process. Much of the research on the direct measurement of matric suction has focused on achieving the maximum attainable suction value with high-pressure-range devices and large saturation pressures. However, there are many applications in physical modelling and laboratory testing where smaller suction ranges are of interest (< 400 kPa), illustrating the need for more sensitive, lower-pressure-range devices. As a consequence of the lower pressure range of these devices, the devices cannot be subjected to the high saturation pressures described in the literature. As a result, additional investigations into the processes involved in filter saturation are required. This paper investigates the importance of high initial saturation, and presents conditions for quality-assured suction measurements.
Total suction measurement of unsaturated soils with a device using the chilled-mirror dew-point technique
Authors: Leong E.-C. , Tripathy S. , Rahardjo H.
Published: October 2009

The total suction of a soil consists of two components: matric suction and osmotic suction. There are different techniques for measuring the total, matric and osmotic suction. The total suction of the soil is related to the water vapour pressure in the air space of the soil, and can be measured by devices capable of measuring relative humidity. A range of devices is available to measure relative humidity. In this paper, a device using the chilled-mirror dew-point technique with a selectable temperature environment was used to measure the relative humidity of a soil sample. Two residual soils of Singapore were used in the evaluation of the device for total suction measurement. The residual soils were compacted at various water contents and with three compaction efforts to provide soil samples of various suction values. The total suction of the compacted soil was measured and compared with its matric and osmotic suctions as independently measured using the null-type axis-translation apparatus and the pore fluid squeezer respectively. The time to equilibrium to obtain the total suction of the soil samples varied between a couple of minutes to about 18 min. The test results show that total suctions obtained using the device are always greater than the sum of the matric and osmotic suctions measured independently. The discrepancy increases as suction increases and is attributed to the limitations of the device for measuring the relative humidity of the soil samples accurately. However, by accounting for the discrepancy, the device can be used as a rapid means of determining the total suction of unsaturated soils.
Patterns and mechanisms of migration of light non-aqueous phase liquid in an unsaturated sand
Authors: Sharma R. S. , Mohamed M. H. A.
Published: October 2009

The paper presents patterns and mechanisms of light non-aqueous phase liquid (LNAPL) migration in an unsaturated/saturated sand, based on a detailed experimental investigation using a fully instrumented two-dimensional model with dimensions of 120 × 120 × 10 cm. Suction head and degree of saturation were monitored simultaneously using tensiometers and time domain reflectometry (TDR) transducers respectively. LNAPL spills into the unsaturated zone were simulated to investigate the influence of new variables of practical importance, including the spill area, volume of spill and fluctuations of groundwater table, on the patterns of LNAPL migration. The patterns are explained in terms of the relationship between matric suction and degree of saturation. Fluctuations of water level are found to have a major influence on the distribution of LNAPLs in the unsaturated/saturated sand for large volumes of LNAPL spill. Measurements of degree of saturation of water at different levels are used to explain the LNAPL migration. It was found that water suction head was not affected by migrating LNAPL if the degree of saturation of water was above the residual saturation. Results of LNAPL suction head were found to be consistent with the migration patterns. Additionally, the average suction head difference between different levels indicated accurately the direction of LNAPL migration, which was in good agreement with the patterns observed using electronic imaging.
Soil matrix suction: some examples of its measurement and application in geotechnical engineering
Authors: Ridley A. M. , Dineen K. , Burland J. B. , Vaughan P. R.
Published: October 2009

Soil matrix suction is assuming an increasing importance in geotechnical engineering. It is now recognised that soil suction is not confined to arid or semi-arid regions of the world. It is frequently encountered in a great many geotechnical problems in temperate climates. For example, all fills and compacted soils have an inherent suction when they are formed; many slopes, both natural and man-made, have in-situ suctions; and all samples that are removed from the ground during a site investigation possess a soil suction in their unconfined state. Measurements of soil matrix suction can be used to: (a) identify disturbance and/or desiccation in samples removed from the ground; (b) estimate the average in-situ effective stress once the effect of disturbance and/or desiccation has been quantified; (c) apply more rigorous controls to the compaction of fill materials where swelling is likely to cause problems; and (d) assess the stability in natural and engineered slopes. This paper describes and compares three methods of matrix suction measurement: the filter paper method, the Imperial College suction probe, and a new in-situ tensiometer that is well suited to long-term observations of in-situ suctions up to about 90 kPa. The principles of their operation, the procedures by which they can be routinely used, and advice on how the results can be interpreted, are presented.
Observations on the behaviour of clay fill containing occluded air bubbles
Authors: Vaughan P. R.
Published: October 2009

Clayey soils can be saturated, and they can exist with continuous pore air and water phases. An intermediate stage occurs when air is present but only as occluded bubbles. In both the continuous air and the occluded air state there are two pore pressures, water and air: the latter is higher by capillarity. Three aspects of the occluded air state are considered. First, the difference between the air and water pressures decreases as the degree of saturation increases. It is shown that this can be due to the way in which the pore structure of the soil constrains the bubbles. Second, a fill in the field may start with continuous air and change to the occluded air state as it is loaded. While air remains, continuous air drainage is likely. Once it becomes occluded, air drainage ceases. Laboratory tests are usually undrained throughout. Tests on samples of a clay compacted in the field show that initial air drainage has a measurable effect on subsequent behaviour but not a dominant one. Third, occluded air may develop as a result of flooding a compacted fill that initially has continuous air. Tests on specimens compacted in the field show that the pore pressure parameter Bw = Δuw/Δσ then becomes very close to 1, even though the fill is not saturated. The fill will then behave as though it is saturated in, say, drawdown of a clay embankment slope, even though it is not. Measurement of Bw = Δuw/Δσ = 1 is not a proof of saturation.
Small-strain stiffness and damping ratio of Pisa clay from surface wave tests
Authors: Foti S.
Published: October 2009

Small-strain stiffness and damping ratio are important parameters for modelling the dynamic behaviour of soils. In particular, the experimental evaluation of the damping ratio is problematic, especially for hard-to-sample soils. Surface wave tests have proven to be a reliable tool for the in-situ determination of soil stiffness at very small strains. Recently, the simultaneous determination of stiffness and damping ratio has been developed. The technique is based on the measurement and inversion of dispersion and attenuation curves of Rayleigh waves. In this paper a novel transfer function procedure is presented. The application to data collected at the Leaning Tower of Pisa testing site, where many results from previous in-situ and laboratory test are available for comparison, is reported.
An alternative mechanism of pile failure in liquefiable deposits during earthquakes
Authors: Bhattacharya S. , Madabhushi S. P. G. , Bolton M. D.
Published: October 2009

This paper proposes an alternative mechanism of pile failure in liquefiable deposits during earthquakes. This failure mechanism, based on pile buckling, is formulated by back-analysing 14 case histories of pile foundation performance during earthquakes and verified using dynamic centrifuge tests. A new parameter, the slenderness ratio of a pile, is introduced to classify pile performance in liquefiable soils. This parameter fits very well both the reported case histories and the centrifuge test results.
A review of Beliche Dam
Authors: Alonso E. E. , Olivella S. , Pinyol N. M.
Published: October 2009

Beliche Dam, a zoned earthdam with rockﬁll shoulders and a central clay core, experienced large collapse settlements due to reservoir impounding and direct action of rainfall. Long-term field records of vertical and horizontal displacements are available as well as a set of large-scale laboratory tests on rockfill specimens. It has been the subject of several numerical analyses that failed to capture the relevant effect of weather conditions on the behaviour of the dam. Recent developments in the constitutive modelling of rockfill allow a substantial improvement of modelling capabilities, and this is illustrated in the paper. Laboratory test results under dry and flooded conditions were interpreted, and material parameters were identified. The complete history of dam construction, impoundment and rainfall was then simulated by means of a coupled flow–deformation model. Deformations during construction and impoundment have been reproduced. Long-term deformations have consistently been related to rainfall records. In general, long-term deformations are controlled by the varying wetting history of the dam shoulders and by an intrinsic deformation component. The wetting action comes to an end when the relative humidity of the rockfill reaches 100% for the first time. The paper also discusses scale effects and the role of rockfill permeability in the development of deformations.
Coupling of hydraulic and mechanical behaviour in unsaturated compacted clay
Authors: Tarantino A. , Tombolato S.
Published: October 2009

An experimental study was carried out to investigate the shear strength of a compacted non-active clay (Speswhite kaolin). A total of 33 statically compacted specimens were prepared, at vertical stresses of 300, 600 and 1200 kPa and water contents ranging from 0·24 to 0·34. This made it possible to explore a broad range of initial compaction-induced conditions and hence to examine whether differences in water retention characteristics and shear strength are due to differences in initial compaction-induced state or are to be attributed to fundamentally different microfabrics. A shearbox was modified to allow the direct measurement of negative pore water pressure using Trento high-suction tensiometers. Tests were carried out at constant water content by monitoring suction changes. In these tests, it was possible to investigate the transition from unsaturated to saturated states. In the first stage of the test, the specimen was compressed at constant water content. The specimen was therefore wetted, in the sense that its degree of saturation increased. Compression data were then used to investigate the influence of void ratio on the main wetting curve. Shear data were used to put forward a critical state framework for unsaturated compacted clay. This is described by three equations linking shear stress, normal total stress, suction, void ratio and water ratio.
Post-liquefaction undrained monotonic behaviour of sands: experiments and DEM simulations
Authors: SITHARAM T.G. , VINOD J.S. , RAVISHANKAR B.V.
Published: October 2009

This paper presents the results of a series of servo-controlled cyclic triaxial tests and numerical simulations using the three-dimensional discrete element method (DEM) on post-liquefaction undrained monotonic strength of granular materials. In a first test series, undrained monotonic tests were carried out after dissipating the excess pore water pressure developed during liquefaction. The influence of different parameters such as amplitude of axial strain, relative density and confining pressure prior to liquefaction on the post-liquefaction undrained response have been investigated. The results obtained highlight an insignificant influence of amplitude of axial strain, confining pressure and a significant influence of relative density on the post-liquefaction undrained monotonic stress–strain response. In the second series, undrained monotonic tests were carried out on similar triaxial samples without dissipating the excess pore water pressure developed during liquefaction. The results highlight that the amplitude of axial strain prior to liquefaction has a significant influence on the post-liquefaction undrained monotonic response. In addition, DEM simulations have been carried out on an assembly of spheres to simulate post-liquefaction behaviour. The simulations were very similar to the experiments with an objective to understand the behaviour of monotonic strength of liquefied samples from the grain scale. The numerical simulations using DEM have captured qualitatively all the features of the post-liquefaction undrained monotonic response in a manner similar to that of the experiments. In addition, a detailed study on the evolution of micromechanical parameters such as the average coordination number and induced anisotropic coefficients has been reported during the post-liquefaction undrained monotonic loading.
A water retention model for deformable soils
Authors: TARANTINO A.
Published: October 2009

The paper presents an experimental study on water retention behaviour of two reconstituted soils, a silty clay (Speswhite kaolin) and a sandy clayey silt (Barcelona silt) and two compacted soils, a silty clay (Speswhite kaolin) and a silty sandy gravel (Adige river embankment). These soils were used with the aim of encompassing a wide range of soil types and soil fabrics. Specimens were subjected to drying and wetting ‘hydraulic' paths by removing or adding water under zero total stress and to ‘mechanical' wetting paths by compressing specimens at constant water content. To investigate a broad range of void ratios, the reconstituted sandy clayey silt was initially reconstituted from slurry by applying different consolidation vertical stresses, whereas the compacted Speswhite kaolin and Adige river embankment were compacted to a broad range of water contents and compaction energy. On the basis of the experimental data, a modification to the van Genuchten's model is proposed to account for the effect of void ratio on ‘main drying' and ‘main wetting' behaviour. The model is based on parameters having clear physical meaning and can properly describe water retention at medium and low degrees of saturation. It is formulated in such a way that effect of void ratio on ‘scanning' behaviour can potentially be accounted for. The model applies to both the compacted and reconstituted soils investigated in this programme and describes water retention behaviour regardless of whether the degree of saturation is changed in a mechanical or hydraulic fashion.
Macro-void structure and permeability of Auckland residual clay
Authors: PENDER M.J. , KIKKAWA N. , LIU P.
Published: October 2009

The properties of the residual clays derived from in situ weathering of the Waitemata group sandstones and siltstones, found around Auckland, are known to be surprisingly variable. In addition, it is known that the permeability of the material decreases rapidly as the effective consolidation pressure is increased. A possible contribution to both the variability and the rapid decrease in permeability might be the void structure of the soil. The advent of micro-CT (computed tomography) scanning equipment provides an opportunity to examine how the shapes and sizes of the voids change with increasing consolidation pressure. This note presents a discussion on some preliminary results on small specimens of Auckland residual clay. These indicate that at low effective confining pressures there are some quite large macrovoids. These are found to be greatly diminished in size when the effective confining pressure reaches about 200 kPa. From very low effective consolidation pressures up to about 200 kPa the permeability decreases markedly.
Deflection control by span/depth ratio
Authors: Neville A. M. , Houghton-Evans W. , Clarke C. V.
Published: October 2009

Synopsis

Control of deflection by span/depth ratios in the structural codes of various countries is considered, and comparisons are made with designs according to CP110:1972. A modified design procedure based on the West German approach is suggested. A sample calculation is included as an appendix.
Some properties of flint particles and their behaviour in concrete
Authors: Roeder A. R.
Published: October 2009

Synopsis

This paper describes and discusses the formation and types of flint as well as some of the physical and chemical properties relevant to their use in concrete. The results of practical examinations of flints of different colours separated from gravel from one source indicate some differences in properties and the influence they have upon the strength and freezing-and-thawing resistance of concrete. Results of tests on concrete made with the different coloured flints are also reported.
An equilibrium—compatibility approach to the determination of the strength of reinforced concrete rectangular beams under combined bending and torsion
Authors: Sandegren D. Stephen , Yu C. W.
Published: October 2009

Synopsis

The strength of reinforced concrete members under combined bending and torsion is evaluated in this paper by a method that uses both the equilibrium of forces and moments and the compatibility of strains in longitudinal and stirrup reinforcement and in concrete. This method also takes account of the initial T/M ratio while determining the failure surface and of the ultimate T/M ratio while calculating the strength. The assumptions made in the method are first listed, and the step-by-step procedure to find the failure moments is explained by means of a numerical example. Experimental evidence is also presented in this paper and the results obtained by a few current theories are compared.
A machine for cold-rolling deformed reinforcing bars for model tests
Authors: Evans D. J. , Clark L. A.
Published: October 2009

Synopsis

This paper describes a machine which has been developed for cold-rolling a 1:6·76 scale model of a 12·7 mm prototype deformed reinforcing bar. It is shown that the model reinforcement scales in all respects except for the rib width and the stress—strain characteristics in the vicinity of the yield point. Further development of the machine awaits the results of bond tests which are currently being carried out.
A gauge for measuring long-term cyclic strains on concrete surfaces
Authors: el Din A. S. Salah , Lovegrove J. M.
Published: October 2009

Synopsis

The theory and construction of a gauge for measuring long-term cyclic strains on concrete surfaces is presented. The gauge transforms axial concrete strains to smaller bending strains by means of a formed metal strip. Four e.r.s. foil gauges are used to sense the central bending strain in the strip. Calibration of the gauge shows that it is capable of reducing the concrete strains by a factor of about 25 and that the gauge factor is about 2·5 microstrain per microvolt. The gauge performs in a stable manner and an application to long-term strain measurement on a number of concrete beams repeatedly loaded at 1Hz during a period of about two years is described.
Oil permeability of hardened cement pastes and concrete
Authors: Watson A. J. , Oyeka C. C.
Published: October 2009

Synopsis

The paper describes an investigation into the permeability of cement paste and concrete to crude oil. The permeability was studied by using a specially constructed permeameter. Ordinary and sulphate-resisting Portland cements were used. The concrete mixes covered a wide range of workabilities (slumps), four aggregate grading zones and a wide range of cement contents –between 225 and 625 kg/m3. The measured co-eficients of permeability were related to various mix design parameters, concrete porosity, compressive strength and applied-fluid pressure. The best prediction of permeability came from the calculated total porosity.
An upper-bound rigid–plastic solution for the shear failure of concrete beams without shear reinforcement
Authors: Kemp K. O. , Al-Safi M. T.
Published: October 2009

Synopsis

In recent years research workers at the Technical University of Denmark and elsewhere have shown that simple rigid–plastic methods of analysis can be used to predict closely the experimental shear failure loads of reinforced and prestressed concrete beams. The method has proved sufficiently attractive in Europe to be considered as a basis for new code of practice formulations for shear failure, but has so far been rather neglected in the United Kingdom. In this paper, rigid–plastic analysis is applied to the shear failure of reinforced or prestressed concrete beams without shear reinforcement. A new upper-bound solution for this problem is derived and compared with the previous ‘exact’ solution derived by Nielsen and Braestrup. The new upper-bound solution is shown to produce lower failure values of shear stress for certain ratios of compression to tension steel.
Effect of boundary conditions upon the behaviour of concrete under concentrations of load
Authors: Kotsovos Michael D. , Newman John B.
Published: October 2009

Synopsis

A non-linear finite-element technique incorporating a constitutive model of concrete behaviour has been used to analyse plain concrete structural forms under concentrations of load induced by a wide range of boundary conditions. The influence of boundary conditions upon strength, deformation and fracture processes has been investigated and the most critical boundary conditions are identified. The predicted behaviour is found to be in close agreement with experimental values when the boundary conditions assumed for the analysis simulate closely those imposed by the testing techniques.
The splitting strength of concrete prisms subjected to surface strip or patch loads
Authors: Oehlers D. J. , Johnson R. P.
Published: October 2009

Synopsis

Analyses of computer studies and of over 200 tests lead to a method of predicting the load at which a concrete prism splits or bursts when subjected to a concentrated surface strip or patch load, and the range over which this splitting determines the ultimate strength. The effects upon the splitting strength of eccentricity of loading, the length of the prism, external lateral restraint and internal reinforcement are also determined.
Constitutive relationships and a failure criterion for concrete based on fundamental material properties
Authors: Montague P. , Kormi K.
Published: October 2009

Synopsis

The functional stress-strain relationships obtained by Kotsovos from his application of regression analysis to empirical data are used as the basis for a derivation of multiaxial constitutive relationships, for concrete subjected to compressive stresses, which distinguish between loading and unloading. A model is proposed in which internal cracking is accompanied by an internal transfer of energy from the deviatoric stress system to the spherical stress system, resulting in modified values of the effective internal spherical and shear stresses and of the shear strain. This transfer of energy is regarded as an irreversible process which can only take place during loading and internal crack propagation. The proposed failure criterion is that failure of the material takes place when, under any system of applied compressive stresses, the internal shear stress reaches a unique value equal to that which exists at failure in a uniaxially compressed solid cylindrical specimen of 100 mm diameter and250 mm length. For any other general compressive stress state which generates a modified octahedral shear stressless than this unique value, the concrete will retain its load-bearing capacity.
Forces in the vicinity of edge columns in flat-slab floors
Authors: Hall A. S. , Rangan B. V.
Published: October 2009

Synopsis

Tests were carried out on four half-size models of flat-slab floors. Each model represented two panels at the edge of a building. They were tested under simulated uniformly distributed load with the object of investigating the distribution of moments and shears on the three faces of an edge column. The three force components at the pin support at the foot of the test column were measured; strain gauges were also attached to the reinforcement. From these measurements, expressions are developed which predict what proportions of the total panel moment and shear enter the column directly as bending and shear at the column face. The remainder enters via the spandrel beam or spandrel-strip. Statics then enables the torsion, shear and bending in the spandrel to be calculated,
Compression testing and cracking of plain concrete
Authors: Shrive N. G.
Published: October 2009

Synopsis

Flaws such as pores and voids are present in cement paste, and thereforein concrete. These flaws act as stress-raisers and cause the initiation of cracks in compressive stress fields. By analysing the stress state in compressive test specimens – recognizing that testing machines apply displacement conditions – and examining the stresses which may then exist around a spherical void, it is possible to explain the typical cracking patterns observed in such specimens. It is also possible to explain the cracking patterns and apparent changes in strength observed under externally applied biaxial stress conditions. This analytical work is restricted to elastic isotropic media and spherical voids, so the potential effect of aggregate particles is examined. Aggregate is shown to cause stress variation on a local basis, which may aid crack formation close to aggregate particles, andthe extension of cracks around aggregatelcement paste interfaces. It is concluded that cracks are initiated at flaws such as pores or voids. It is suggested that, since fracture mechanics deals with the fracture of heterogeneous non-brittle materials, it may be worth while considering the application of appropriate fracture mechanics methods to the fracture of concrete.
Factors affecting concrete permeability to cryogenic fluids
Authors: Hanaor Ariel , Sullivan Patrick J. E.
Published: October 2009

Synopsis

Substantial cost saving and enhanced safety could achieved in the construction of storage tanks for liquefied natural gas (LNG). if it could be demonstrated that prestressed concrete can be reliably used in the construction of the primary, as well as the secondary container. Available information on the mechanical properties of concrete at very low temperature is adequate in establishing its suitability as a cryogenic construction material. Very little work, however, has been done on the factors and mechanisms governing the flow of cryogenic fluids through the essentially porous material. The work presented here outlines design and analysis of an experiment aimed at establishing the effects of eight factors upon the permeability of concrete specimens to liquid nitrogen. The results suggest that the mechanisms governing the permeability of concrete at ambient and at cryogenic temperatures differ fundamentally. In particular, the aggregate plays a major role in the cryogenic permeability of concrete. A model is proposed, whereby incompatibilities between the physical and thermal properties of the aggregate and the cement paste give rise to microcracking below a certain temperature. Such a model is capable of accounting for the observed results, as well as for phenomena previously reported.
A temperature-matched curing system controlled by microcomputer
Authors: Wainwright P. J. , Tolloczko J. J. A.
Published: October 2009

Synopsis

The paper describes the design and development of a curing system for concrete using a microcomputer to control the apparatus and store the data. The adiabatic temperature rise of a concrete can be recorded and reproduced within the curing tanks in which test specimens can be stored. It is also possible to reproduce any predetermined temperature cycle, provided it lies within certain limits. The equipment is extremely versatile and precise and avoids the use of multichannel chart recorders or digital data-logging systems to measure and record the data.
Two simple techniques for testing the performance of repair materials for concrete cracks
Authors: Fattuhi N. I.
Published: October 2009

Synopsis

The paper describes two simple testing techniques for evaluating the effectiveness of a repair material in sealing cracks and in transmitting tensile stresses across cracks. The techniques also enable comparisons to be made between different repair materials used under varying conditions of temperature and moisture. For the first testing technique, grooves in concrete beams were formed during casting for crack simulation purposes, and were filled with different repair materials such as epoxy resins and mortars. Then the beams were subjected to different temperatures before testing in flexure. For the second testing technique, halved concrete cylinders were joined by repair materials and the cylinders were subjected to different temperatures before testing in splitting tension. The results indicated that the effectiveness of the repair materials in transmitting the tensile stresses varied and was reduced considerably at higher temperatures. The beam and cylinder results under the same testing conditions were generally consistent for the same material.
A photoelastic investigation of anchorage bearing stresses
Authors: Rasheeduzzafar  , Allison I. M. , Al-Saadoun Saadoun Saad
Published: October 2009

Synopsis

This investigation focuses on a number of features which have hitherto been less researched but which have been found to be critical in the behaviour and failure mechanism of anchorage zones. These include the mode of load transfer, the proximity of the anchorage unit to the surface plane and the critical role of the high sub-surface shear in the immediate vicinity of the anchorage unit. The results show the significant advantages of the embedded anchorage over the corresponding external unit and the critical dependence of the surface stresses upon the proximity of the anchorage unit. In a typical multi-anchorage end-block. the behaviour of adjacent units is found to be sensibly independent.
The shear design of in situ reinforced concrete beam–column joints subjected to monotonic loading
Authors: Sarsam K. F. , Phipps M. E.
Published: October 2009

Synopsis

Research into in situ reinforced concrete joints has been almost exclusively restricted to the study of their behaviour under seismic loading. Different research workers in different parts of the world have used widely differing cyclic loading patterns and this has led to inconsistencies in the proposals put forward for the design of a joint for shear. Even for single-cycle (static or monotonic) loading, there is widespread disagreement on how a joint should be designed. In this paper. a method is proposed for ultimate shear strength design for joints subjected to monotonic loading which gives reliable predictions for an extensive range of test results. A proposal for predicting the serviceability limit state, or the diagonal cracking strength of a joint, which may be necessary for some designs is also given.
Shear transfer in cracked reinforced concrete
Authors: Millard S. G. , Johnson R. P.
Published: October 2009

Synopsis

Tests of a new type are described in which reinforced concrete plate specimens are cracked in direct tension. The tensile force is maintained while in-plane shear forces are applied across the crack. Measurements are taken of the shear stiffness and subsequent crack widening, together with the tensile forces in the reinforcement, using strain gauges embedded within the bars. A technique of resin injection is used to study the variation in the width of a crack beneath the surface of the concrete. Contrary to the results of previous studies, no significant variation was observed. The shear stiffness of cracked reinforced concrete specimens was compared with results from previous aggregate interlock and dowel action tests. It can be predicted from available theoretical models, provided that the anchorage stiffness of the reinforcement is known.
Additional strains in unbonded tendons during loading
Authors: Iványi G. , Buschmeyer W. , Müller R.-A.
Published: October 2009

Synopsis

Additional strains occurring in unbonded tendons during the loading of prestressed beams or slabs cannot be calculated by simple methods. Therefore in the national codes some simplified design formulae are proposed. However, the validity of such approaches is very limited. Analogously to the simple kinematic model of limit state design, in the present paper a single-crack element with real physical properties is developed. To calculate the additional strains in unbonded tendons of prestressed beams or slabs from the rotations of these elements, the single-crack elements have to be related to a compatible kinematic model. As shown in the paper, the calculated strains based upon this model agree well with the measured ones observed in bending tests on unbonded prestressed concrete slabs.
Influence of lightweight aggregates on thermal strain capacity on concrete
Authors: Brooks J. J. , Bennett E. W. , Owens P. L.
Published: October 2009

Synopsis

The tensile strain capacities of concretes with densities between 1200 and 2300 kg/m3 are determined by means of a short-term stressing technique. The thermal strain capacity of lightweight aggregate concrete is up to 2½ times greater than that of flint gravel concrete of similar workability and strength. Lightweight aggregate concretes also have lower coeficients of thermal expansion and reach slightly higher maximum temperatures due to hydration. It is demonstrated that the main influencing parameter on tensile strain capacity is the strengthlelastic modulus ratio.
Concrete strength evaluation through the use of small diameter cores
Authors: Yip W. K. , Tam C. T.
Published: October 2009

Synopsis

When cores are tested to establish the in situ strength of hardened concrete, it is current practice to use 100 or 150 mm diameter cores. For various reasons. such as the small size of a member or congestion of reinforcement, drilling of smaller cores is preferred, but these are not yet fully recognized in standards and guidance documents.

The compressive strengths of 50mm diameter cores are compared with the strengths of 100mm diameter cores and control cubes. Other effects on the measured strengths of 50 and 100mm diameter cores are studied, including diameter, length/diameter ratio, direction of drilling, curing conditions, age of concrete and location of cored specimen. The results are compared with available published data.

Results obtained. involving over 1000 samples, support the viability of using 50mm diameter cores to estimate the in situ strength of hardened concrete.
Dynamic modulus of Portland cement paste and mortar as affected by ambient relative humidity
Authors: Al-Mudaiheem J. A.
Published: October 2009

Results are given of an investigation into the influence of drying and wetting on changes in weight and dynamic modulus of paste and mortar specimens dried at different relative humidities at room temperature. Drying causes a significant drop in the dynamic modulus probably due to moisture stress gradients and removal of interlayer water which is recovered from subsequent wetting of the specimens. This suggests that drying-induced microcracking is unlikely to occur. The percentage reduction in dynamic modulus of prisms (2·5 mm × 10 mm × 75 mm) increases with increasing aggregate concentration and decreases with increasing water/cement ratio.
Force transfer in compression lap joints in reinforced concrete
Authors: Judge R. C. B. , Scott R. H. , Gill P. A. T.
Published: October 2009

Five reinforced concrete compression specimens were tested, each reinforced with a pair of lapped rods. Shortterm longitudinal reinforcement strain distributions were measured using electrical resistance strain gauges installed within the reinforcement. Lap length and rod diameter were both varied. Embedment strain gauges were installed in one specimen to measure internal circumferential concrete strains. Typical reinforcement strain distributions are presented to show the behaviour of the specimens as a whole, and the development of end bearing at the lap ends in detail. The relative contributions of bond and end bearing to force transfer are discussed, and indications are given of the strains developed in the concrete.
An investigation on the effect of vibration on the workability of fresh concrete using a vertical pipe apparatus
Authors: Tattersall G. H. , Baker P. H.
Published: October 2009

Using an apparatus in which fresh concrete is allowed to flow out of a vertical pipe while being vibrated, it is confirmed that under vibration and at low shear rates the material behaves as a Newtonian liquid. Effectiveness of vibration is to be assessed in terms of maximum velocity but there is a threshold amplitude below which, and an upper limiting frequency above which, vibration has no effect. It is shown that fluidity determined by this method correlates with fluidity determined earlier by an entirely different method.
Variation of concrete crack widths through the concrete cover to reinforcement
Authors: Yannopoulos P. J.
Published: October 2009

The determination of the relationship between the width of main cracks at the steel surface to that at the external concrete surface is reported. A series of tests was carried out for this purpose on specimens that simulate the part between two adjacent cracks on a long reinforced concrete tension member. Measurements were taken of the concrete surface strains, the extension of steel embedded in concrete and the relative slip between steel and concrete under increasing load.
Fictitious crack model of concrete fracture
Authors: Brincker R. , Dahl H.
Published: October 2009

The substructure method introduced by Petersson is reformulated for the three-point bending specimen in order to obtain complete load-displacement relations without signficant truncation. The problem of instability caused by the linearization of the softening in the fracture zone is discussed, and an alternative energy formulation is given so that it is possible to distinguish between stable and unstable situations. The reformulated substructure method is implemented on computer to give a multilinear stress crack opening displacement relation for the material in the fracture zone, and some qualitative results are given.
PFA fineness and its use in concrete
Authors: Hughes B. P. , AL-Ani M. N. A.
Published: October 2009

The object of the investigation was to determine a satisfactory method of assessing the Jineness of pulverized fly-ash (PFA) which provided a reasonable correlation with the workability of concretes with similar compositions except for the type of fly-ash used. Neither the standard air permeability tests nor the residue on a 45 μm sieve were found to provide a good indication of the complete size distribution of a fly-ash. The air permeability provides a value which does not necessarily vary with the specific surface, and the 45 μm sieve merely considers the division at one size only. However, if an accurate assessment of the size distribution is expressed in terms of a simple parameter such as the grading modulus, the latter then shows very good correlation with the workability of the resultant PFA concretes, as indicated by the VB time. A useful indication of the potential strength of the PFA concrete could also be given by the grading modulus.
An assessment of concrete curing efficiency using gas permeability
Authors: Cabrera J. G. , Gowripalan N. , Wainwright P. J.
Published: October 2009

The current practice of assessing the efectiveness of a concrete curing compound is based on evaporation measurements from cement mortar slabs. The lack of precision of individual moisture loss measurements has prompted further investigation to measure other parameters to assess curing eficiency. This Paper reports preliminary results of a method based on oxygen permeability to assess curing eficiency. A comparison is made with results obtained using the method recommended in a British Standard draft.3 The oxygen permeability method can also be applied to traditional methods of curing such as those utilizing wet hessian or burlap.