bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-frequency soundproof concrete
Authors: Li Z. , Sheng P. , Siu W.-L.
Published: October 2009

A low-frequency soundproofing concrete has been developed. In this type of concrete, lead spheres coated with silicone rubber are used as aggregates, the lead ball being heavy and rigid, and the silicone rubber light and soft. The coated lead spheres are uniformly embedded into a short fibre reinforced cement-based matrix. When a sound wave approaches such a concrete panel, localised excitation in the coated lead balls will be induced at certain frequencies. Resonant excitation can consume a considerable amount of energy and thus the sound transmission through the panel at these frequencies can be greatly reduced. Experimental results show that concrete with the embedded coated lead spheres produces resonance at about 150 Hz and also improves the sound insulation at the low frequency range.
Using the split Hopkinson pressure bar to investigate the dynamic behaviour of SFRC
Authors: Lok T. S. , Zhao P. J. , Lu G.
Published: October 2009

The dynamic characteristics of steel fibre reinforced concrete (SFRC) have been obtained through 75 mm diameter split Hopkinson pressure bar (SHPB) tests. In order to understand the intrinsic dynamic behaviour of the material, this paper reviews the SHPB testing technique, and presents the principles and limitations of the equipment. Using a linear-shaped striker bar, a half-sine incident loading waveform is generated which eliminates attendant problems such as non-uniform stress distribution and wave oscillation. Following the verification of the SHPB equipment, a number of dynamic uniaxial compression and tension splitting tests were conducted on SFRC specimens. The influence of strain rate on the response of SFRC specimens is presented. Results indicate that dynamic uniaxial compressive strength of SFRC increases moderately at relatively high strain rate, and the tensile splitting strength increases many times at moderate strain rate loading compared with its static value. Further, the stress–strain relationship of SFRC does not exhibit the ductility that is evident when the material is tested at static load condition.
Multipliers for deflections in reinforced concrete flat slabs
Authors: Vollum R. L.
Published: October 2009

Ideally, slab deflections should be calculated using non-linear cracked section analysis. In practice, slabs are often designed using elastic finite element analysis and deflections are estimated using a reduced elastic modulus for the concrete. This paper examines the problem of determining an equivalent elastic modulus that accounts for the increase in deflection due to cracking, shrinkage and creep. A method is proposed for estimating long-term deflections in flat slabs by increasing elastic deflections with multipliers derived from analysis of equivalent beam strips. Deflections in flat slabs are usually governed by cracking during construction in which case deflection multipliers are almost independent of the permanent design load under which EC2 requires deflections to be calculated. In this case, it is shown that cracking and shrinkage increase long-term deflection multipliers for flat slabs by a factor of approximately two.
Modelling the strain-softening behaviour of plain concrete using a double-exponential model
Authors: Barr B. , Lee M. K.
Published: October 2009

The paper reports on a proposed double-exponential (double-e) model to describe the strain-softening behaviour of plain concrete. The model describes the strain-softening behaviour via one continuous function and has the advantage of being mathematically efficient, lending itself readily to differentiation and integration. A parametric study was carried out to investigate the applicability and sensitivity of the model. The double-e model has been found to be capable of modelling the strain-softening behaviour typical of plain concrete and appears to have a wide scope of application ranging from brittle responses to elastic–plastic behaviour. In addition, a method has been developed whereby model parameters are determined objectively.
Estimates of the yield curvature for design of reinforced concrete columns
Authors: Hernández-Montes E. , Aschleim M.
Published: October 2009

A recent advance in displacement-based seismic design procedures relies on an estimated yield displacement as the basis for determining seismic design forces in order to satisfy seismic performance objectives. Simple expressions for the yield curvature of circular and rectangular reinforced concrete column cross sections are presented here, based on moment–curvature analyses. The estimated yield curvatures correspond to the flexural strengths determined using Eurocode 2, and thus are useful for the practice of earthquake-resistant structural engineering. Unlike earlier proposals, the expressions presented here account explicitly for the axial load ratio. These expressions are presented in terms of the depth of tension steel, which is shown to be preferable to the overall section depth, used in a previous recommendation. An example illustrates the preliminary design of a bridge pier using Yield Point Spectra and the recommended expressions for estimating the yield curvature.
Compressive behaviour of CFS strengthened concrete specimens with various cross-sectional shapes and laminations
Authors: Kim J.-H. J. , Yi S.-T. , Lee S.-H. , Park S.-K. , Kim J.-K.
Published: October 2009

The repairing technique of surface wrapping concrete structural members using fibre composite sheets has been widely used. Therefore, significant research efforts have concentrated on understanding the mechanism of concrete members wrapped with fibre composite sheets for lateral confinement. In order to apply the carbon fibre sheet (CFS) surface wrapping technique in retrofitting of aged concrete column structures, the effect of cross-sectional shape on concrete columns with CFS wrapping has been studied. In this research, compression tests have been performed on CFS reinforced concrete specimens with various cross-sectional shapes (i.e. square, octagonal, and circular) and lamination schemes (i.e. [0/0/0/0], [90/90/90/90], [0/45/−45/90], and [0/90/90/0]). The specimens were tested in order to understand the confinement effect of CFS from square to circular members. The test results showed that the strength and ductility of the specimens depend on the CFS fibre direction. Also, the specimens with octagonal cross-sectional shape behaved in a similar manner to the circular specimens, indicating that the retrofitting and strengthening of square columns can be effectively performed by converting them into octagonal columns. Based on the research results, a new repairing method of converting a square cross-sectional column to an octagonal one for CFS surface wrapping is currently being studied.
Qualitative analogy between performance loss and microstructural manifestation of different damaging effects on concrete
Authors: Soroushian P. , Elzafraney M.
Published: October 2009

The effects of different controlled damaging phenomena on the performance characteristics and microstructural attributes of concrete were investigated. The microcracking system of concrete following different damaging effects was investigated under microscopy; analogies were drawn between the extent/nature of microcrack growth in concrete and the corresponding loss of concrete engineering properties. Normal-strength, high-strength and fibre reinforced concrete materials were investigated. The damaging phenomena considered included compression loading, freeze–thaw cycles, restraint of shrinkage in different climates and exposure to elevated temperature. The engineering properties investigated included compressive, flexural and splitting tensile strength. The results provide insight into the damage and failure process of concrete.
Investigation into backprop forces and deflections at St George Wharf
Authors: Vollum R. L.
Published: October 2009

The first part of the paper shows that good estimates of backprop forces are obtainable from the Cardington building if the slab stiffness is reduced to allow for cracking. This is significant since it resolves an apparent inconsistency between the author's work on deflection and Beeby's work on forces in backprops. The second part of the paper investigates the forces in backprops and slab deflections at St George Wharf, London. The work was carried out to investigate the validity of design procedures based on research at Cardington that have been widely disseminated in Best Practice Guides and elsewhere. Measured and predicted backprop forces and deflections are shown to compare well at St George Wharf which increases confidence in the Cardington research. The paper also describes the backpropping arrangement used at St George Wharf for construction of the 600 mm thick transfer slab at the 15th floor. The backpropping arrangement was designed using the traditional assumption that loads are equally shared between floors since the frame contractor could not justify the design using the improved methods developed by Beeby from research at Cardington. Back analysis shows that the design can only be justified if preload is taken into account in the backprops.
Steel-reinforced concrete joints under reversal cyclic load
Authors: Swaddiwudhipong S. , Jiang D. , Cheng W.
Published: October 2009

The performance of structural joints comprising built-up steel-reinforced concrete (SRC) columns connecting to reinforced concrete (RC) beams under reversal cyclic loads is described in this paper. Eight composite joint specimens were tested to failure. Three modes of failure, namely, bending failure in beam, bending–shear failure in beam and shear failure in beam and joint were observed. Test results indicated that energy dissipation capacity of the SRC joint depends on the modes of failure and the levels of axial load imposed on the column. The higher the level of axial force imposed on the column, the lower the energy dissipation capability but the larger shear capacity of the joint. An analytical model for the evaluation of the shear capacity of SRC joint taking into account the effects of the presence of steel section, stirrups, axial force in column and ductility demand is proposed. Analytical and experimental results show good agreement.
Numerical method for analysis of concrete under multi-axial loads
Authors: Tho K. K. , Seow P. E. C. , Swaddiwudhipong S.
Published: October 2009

A constitutive model for plain concrete under monotonic increasing multi-axial loads is presented. An equation for determining the incremental tangent modulus is adopted and modified for implementation in finite element analysis. The parameters required in this model are the stresses and strains at failure, and the Poisson ratio. The equivalent uniaxial strain, adopted by some earlier researchers, is replaced by the strain indicator, εsi, proposed in the present study. A five-parameter failure surface is used to predict the stresses at failure, and a numerical method for obtaining a closed-form solution is developed. The constitutive model is then implemented in a well-established finite element software via a user subroutine and the analytical results are verified against established experimental values. The predicted ultimate stress of the concrete falls within a 20% deviation from the experimental value and the proposed model is able to approximate the stress–strain curve reasonably well.
Development of deflection equations using moment–curvature relationships for reinforced concrete beams strengthened with fibre-reinforced polymer (FRP) plates
Authors: Faruqi M. , Wu C. C. , Benson F.
Published: October 2009

This paper presents a rational and relatively simple method for calculating the deflections of reinforced concrete (RC) beams strengthened with fibre-reinforced polymers (FRP) plates. Basically, RC beams strengthened with externally bonded FRP plates to the tension face can display flexural strength several times greater than their original strength. An idealised load–deflection curve for a RC beam strengthened with externally bonded FRP plates can be separated into four different linear stages. Based on these stages, this project is developed from linear elastic theory and analyses of the moment–curvature relationships, which are assumed to be linear. An improved analytical procedure for calculating the deflection of the plates strengthened with FRP is developed. The analytical expressions are verified by comparisons with some experimental and American Concrete Institute (ACI) results in the literature. The analytical results correlated well with the experimental results.
Punching resistance of RC slabs with rectangular columns
Authors: Oliveira D. R. C. , Regan P. E. , Melo G. S. S. A.
Published: October 2009

Fifteen tests on high strength concrete slabs with rectangular supports and three different load patterns are reported. The results show that current code preovisions can overestimate punching resistance in some cases. An investigation, made using the finite element method, shows the influences of the shape of a support and the pattern of loading on the distribution of shear. Factors are proposed to allow for these effects while using the control perimeter and basic shear resistance of the CEB Model Code 90, and it is demonstrated that this approach provides strength estimates better than those of MC 90, BS 8110 and ACI 318. There remains a problem of the punching capacity of slabs almost failing in flexure and this is discussed.
Shear strength of RC beams with defective stirrup anchorages
Authors: Regan P. E. , Kennedy Reid I. L.
Published: October 2009

The effects of corrosion removing the end anchorages of stirrups were investigated by tests of beams in which up to 75% of the shear reinforcement lacked end anchorages. In some beams a further effect of corrosion was simulated by the lower main steel being half-exposed. A small number of bond tests were also performed on vertical bars of the same types as the stirrups. The beams' shear strengths agree well with simple truss model calculations made treating the effectiveness of web steel as being a function of its anchorages above and below shear cracks. A more complete model of actual behaviour is given by a modified truss system.
Deformability and ductility in over-reinforced concrete structures
Authors: Whitehead P. A. , Ibell T. J.
Published: October 2009

It is often useful to use a high percentage of steel reinforcement in a concrete flexural member in order to minimise structural depth and still provide adequate stiffness. This paper shows that, by placing a steel helix in the compression zone of a heavily over-reinforced concrete beam, considerable strength, stiffness and ductility may be achieved, even when the steel percentage is as high as 7%. This is because the concrete in compression becomes triaxially stressed and confined during loading, leading to a high uniaxial strain capacity in the concrete at an enhanced stress level. It is shown that, even though the serviceability limit states of deflection and cracking are critically important, they are just satisfied under normal conditions. The testing programme described here consisted of seven tests on rectangular steel-reinforced concrete beams. Each helically reinforced specimen contained a single helix with a 20 mm pitch. The helices were formed from either 3 mm or 4·8 mm diameter mild steel wire. To show the full benefit of the presence of a circular helix, control specimens (no helix) and specimens containing a similar volume by weight of rectangular links were tested for direct comparison purposes. This research is exciting, as it demonstrates that it is possible to heavily over-reinforce concrete structures and nonetheless expect a ductile response. This is potentially very useful to clients, consultants and contractors who wish to use shallower concrete members. Further, two analytical approaches are developed here for predictive assessment. A full load–displacement approach is presented, followed by a simpler design-oriented approach. Both methods predict behaviour reasonably accurately.
Development of a microwave frequency sensor for the long-term localised moisture monitoring of concrete
Authors: Malan F. S. , Ahmet K. , Dunster A. , Hearing R.
Published: October 2009

Monitoring the moisture levels in concrete over long periods of time is important, as moisture plays a pivotal role in the corrosion process of embedded reinforcement steel in concrete. It is also key in a number of other deterioration processes, and can be used as an indication of changes in the conditions, thus providing a useful early warning system for potential chemical attack. Maintenance needs are thus flagged up before damage is caused. Following an overview of these deterioration processes in concrete, this paper outlines the development of a microwave frequency sensor operating at around 1 GHz and utilising a transmission line either embedded into the concrete at the time of production or encapsulated in a porous medium and inserted into the concrete. It has been amply demonstrated that the method is capable of measuring the moisture content over a wide dynamic range, up to saturation. Trials showed that the encapsulating medium has necessarily to have a microstructure similar to the concrete to be monitored to ensure effective tracking of the concrete moisture content. The sensor appears to fulfil the various stringent conditions necessary for long-term condition monitoring of concrete structures.
Statistical evaluation for impact resistance of steel-fibre-reinforced concretes
Authors: Song P. S. , Hwang S. , Sheu B. C.
Published: October 2009

A statistical evaluation for the impact resistance of steel-fibre-reinforced concrete was performed using 0·5% and 1·5% fibre volumes, in comparison with non-fibrous concrete and in the presence of pronounced variability. The concretes were each drop-weight tested in a 36-disc batch. The resistance, including first-crack and failure strengths and residual impact withstanding capacity, improved with the increase in fibre volume and reached its peak at 1·5% volume; the control over the resistance trended towards upgrade at 1·5% but downgrade at 0·5%, compared with non-fibrous concrete. The distributions of the two strengths were approximately log-normal at 0·5% volume, normal at 1·5% volume, and again log-normal for the non-fibrous concrete; following Kolmogorov–Smirnov calculations. Using the measured first-crack strength, good simulation of failure strength development in the steel and non-fibrous concretes was achievable through three regression models.
Corner effects in CFRP-wrapped square columns
Authors: Karam G. , Tabbara M.
Published: October 2009

An experimental investigation of the corner sharpness effect in square columns with carbon fibre-reinforced polymer (CFRP) wraps is presented using traditional compressive testing of short square columns as well as an innovative set-up that allows testing directly for the CFRP strength when wrapped around the corner of a flat slab. Both types of test confirmed the observation that the confinement efficiency decreases as the corner sharpness increases, owing to stress concentrations that cause localised failure of the CFRP.
Hydration process of interfacial transition in potassium polysialate (K-PSDS) geopolymer concrete
Authors: Zhang Y. S. , Sun W. , Li J. Z.
Published: October 2009

Environmental scanning electron microscopy (ESEM) was used to study the hydration process of the interfacial transition zone (ITZ) between coarse aggregate and potassium polysialate (K-PSDS) geopolymer under an 80% relative humidity environment. An energy dispersion X-ray analysis (EDXA) was also used to distinguish the chemical composition of the hydration products. The ESEM micrographs and corresponding EDXA results show that the development of the microstructure of ITZ is quite different from that of matrix. At the beginning there were many large voids filled with water (about 50 μm) in the fresh ITZ, but these voids were not found in the bulk matrix. As hydration proceeded, gel products gradually precipitated on the edges of these voids and extended outward. Eventually these voids were completely filled with hydration product. At this stage, the difference in the micrograph between the ITZ and the matrix was hardly distinguishable. However EDXA results showed that the contents of K/Al and Si/Al in the ITZ were higher than those in the bulk matrix. This indicates that K and Si accumulate in the ITZ, which results in a difference in chemical composition between the ITZ and the matrix. In addition, well-developed crystals were not found in the ITZ at any stage and sponge-like amorphous gel was always observed instead.
The use of MRI to observe the structure of concrete
Authors: Marfisi E. , Burgoyne C. J. , Amin M. H. G. , Hall L. D.
Published: October 2009

A range of magnetic resonance imaging (MRI) measurements of water in concrete samples and their constituent materials is described and it is demonstrated that MRI can be used to (1) discriminate the spatial distribution of aggregates within a fresh sample, (2) measure changes in water content during the hardening process of cement, and (3) detect fractures and voids within a water-saturated sample. The requirements of the magnetic resonance technique that the sample be free of iron impurities necessitated an investigation of a range of materials for manufacturing suitable concrete samples. This led to a mix design which is representative of normal concretes yet MRI compatible. MRI can achieve image acquisition using a number of different protocols which are defined and optimised according to the equipment available, the properties of the sample and the particular type of image required. Suitable protocols for detecting the water in concrete are described. Magnetic resonance (MR) images of the internal structure of concrete are presented, which allow the aggregate, sand and matrix to be distinguished as well as any voids that are present. It is shown from our experiments that the measurable water present in wet concrete is in two forms, and the amount and proportions of these two components alters during hardening, which allows the progress of the associated chemical reaction to be studied. It is shown that fractures can be detected, but it is concluded that rather than attempting to determine both the structure and the fracture state from a single MRI image, it is far better to measure two separate images, one optimised to show the structure and the second for delineating the fractures.
The use of MRI to observe fractures in concrete
Authors: Marfisi E. , Burgoyne C. J. , Amin M. H. G. , Hall L. D.
Published: October 2009

This study extends previous work and demonstrates that magnetic resonance imaging (MRI) of water allows the internal crack pattern of hardened concrete to be observed along with the internal aggregate structure. The ability to reconstruct three-dimensional images is demonstrated and the importance of image registration is discussed. By using aramid fibre-reinforced plastics (AFRP), it is possible to make reinforced concrete specimens that can be measured by MRI. Plain concrete cylinders and others externally confined by AFRP spirals have been tested in compression and scanned after various amounts of load have been applied to show the progress of fracture development. Samples have also been made with straight AFRP rods cast into the concrete which, when pulled out, give bond failures and internal cracking. It is possible not only to observe the fractures, but also to relate them to the internal concrete structure determined by previous scans of the freshly prepared concrete samples.
Probability of fatigue failure of steel fibrous concrete
Authors: Singh S. P. , Singh B. , Kaushik S. K.
Published: October 2009

The paper presents a study on the fatigue strength of steel fibre reinforced concrete (SFRC) at various stress levels. To obtain the fatigue lives of SFRC at various stress levels beam specimens of size 500 mm × 100 mm × 100 mm were tested under four-point flexural fatigue loading. Static flexural tests were also carried out to determine the static flexural strength of SFRC prior to fatigue testing. The specimen incorporated three volume fractions, namely 0·5, 1·0 and 1·5% of corrugated steel fibres of size 0·6 mm × 2·0 mm × 30 mm. All the fatigue tests were conducted on a 100 kN closed-loop universal testing machine. Fatigue life data thus obtained were analysed in an attempt to determine the relationship for SFRC between stress level S, number of cycles to failure N and probability of failure Pf for SFRC. It was found that this relationship can be represented reasonably well graphically by a family of S–N–Pf curves for SFRC containing different volume fractions of fibres. The experimental coefficients of the equation were determined from the fatigue test data to represent the S–N–Pf relationships analytically.
Predicting the compressive strength of concrete: the effect of bleeding
Authors: Lecomte A. , de Larrard F. , Mechling J.-M.
Published: October 2009

Models for predicting concrete compressive strength, such as those of Bolomey and Abrams, base their validation on producing concrete mixtures of optimised packing density. More advanced models such as the Laboratoire Central des Ponts et Chaussées (LCPC) model predict an increase in concrete strength as a result of a high coarse aggregate content, which results in a simultaneous reduction in the volume of entrapped air and a decrease in the space between coarse aggregate particles. It is therefore important to find out if mixtures rich in coarse aggregate really perform better than mixtures containing the same volume of binding paste but with an optimised size distribution. Observations show that this is not the case and that the strength drops significantly, apparently due to bleeding which affects most mixtures and alters the bond between aggregates and the binding matrix. The bond parameter of the model is therefore correlated to a qualitative bleeding index so as to reflect the experimental strength. This index is also linked with the internal fine phase, which governs the phenomenon and therefore enhances the prediction of the compressive strength of mixtures based upon bleeding. This work may lead the LCPC model to incorporate the effect of bleeding in the mix design of concrete in general and of high-performance concrete in particular.
Non-linear model for reinforced concrete under cyclic loading
Authors: Said A. , Elmorsi M. , Nehdi M.
Published: October 2009

Most of the available shear models for reinforced concrete rely on empirical formulations. In this study, a rational shear stress function is used to define the shear stress–strain envelope for reinforced concrete. Cyclic rules are proposed to define the loading, unloading and reloading relationships for reinforced concrete under shear stress reversals. A normal stress function describing the cyclic relationship of concrete under axial stress is also introduced. The proposed functions are verified using experimental data of reinforced concrete panels tested under monotonic and cyclic loading. Subsequently, the normal and shear stress functions along with their cyclic rules are integrated in a non-linear finite element analysis code. The resulting model accounts for tension stiffening, crack opening and closing, compression hardening and softening, degradation of concrete strength and stiffness in the direction parallel to the crack, compression unloading and reloading, as well as non-linear steel behaviour (strain hardening and Bauschinger effect). The finite element model is then used to analyse two Portland Cement Association shear walls with different geometries tested under cyclic loading. The results show a good agreement between analytical and experimental data. The model showed an excellent capacity of predicting shear deformations of reinforced concrete elements under cyclic loading with minimal computational efforts.
Partial-interactive behaviour of steel–concrete members under static and fatigue loadings
Authors: Jeong Y. J. , Kim S. H. , Ahn J. H.
Published: October 2009

This paper deals with the static and fatigue behaviour according to the partial interaction of steel–concrete composite members. To examine these, a steel–concrete composite bridge deck, which was designed so that it could have higher structural performance and lower deck depth in comparison with the conventional cast-in-place concrete deck, was fabricated as static flexural test and fatigue test specimens having various degrees of interaction. The results of the static flexural tests were compared with those of structural partial-interaction analysis. Based on the results of these, the static and fatigue behaviour characteristics to the partial interaction were examined and several conclusions were drawn. The structural partial-interaction behaviour can be efficiently and effectively predicted by the partial-interaction analysis, and this may be attributed to the potential advantage of the proposed method over the conventional method. For the fatigue design, the assumption of the full interaction leads to the over-estimate for the fatigue life, and the partial-interaction approach is more practical for fatigue.
Strength impairment of concrete mixed in hot weather: analysis in relation to physical and chemical properties of hardened concrete
Authors: Mouret M. , Bascoul A. , Escadeillas G.
Published: October 2009

A previous paper reported that reductions in 28-day strengths were observed for manufacturing control specimens produced in summer conditions. It was shown that they were dependent on the porosity of the bulk paste of fresh concrete according to the initial temperature of the mix. Here, further investigations using physical and chemical approaches to seek explanations for these strength decreases in relation to the 28-day microstructure of concrete are presented. Scanning electron microscope observations revealed air bubbles and well-developed calcium hydroxide crystals which could explain in some cases the drops in strength. Porosity to water and absorption of water were increased whereas the degree of hydration was not affected. Secondary effects were highlighted when standard curing temperature (20°C) was not satisfied.
The plasticity of unreinforced concrete
Authors: Heyman J.
Published: October 2009

Mass concrete is a brittle material. If a structure is cast in unreinforced concrete—a dome, say, or a Roman cross vault—then that structure will inevitably crack in response to the movements imposed by the environment (settlements of foundations, spread of abutments). Such cracks are in themselves not signs of danger; they allow the structure as a whole to deform in a ductile way, and its behaviour may be interpreted by the use of plastic theory.
When plasticity?
Authors: Morley C. T.
Published: October 2009

The paper considers the broad question of when and to what extent the theory of plasticity is useful in the analysis and design of reinforced concrete structures at the ultimate limit state of collapse. It covers early lower- and upper-bound approaches to design, and discusses various objections to the application of plasticity theory to concrete, concentrating on the need for adequate ductility – nowadays perhaps provided by fibre rather than bar reinforcement – and the crucial matter of size effect. It concludes that plasticity theory can be useful for the design of ordinary concrete structures known to have ductile failure modes, but that great care and wariness are needed when attempting to extrapolate its use to unusual structures and particularly to structures of large size without adequate ductility.
Generalised collapse analysis of concrete bridges
Authors: Middleton C. R.
Published: October 2009

An automated yield-line analysis technique for reinforced concrete slab structures has been developed at the University of Cambridge and implemented in a computer program called COBRAS for use in assessing the ultimate flexural strength of concrete bridges. The program employs recent developments in solid modelling theory to create a three-dimensional model or ‘picture’ of a bridge and all its components within the computer. This model is built up from a number of separate layers of polygonal regions, each of which represents the plan location within the bridge of a particular structural feature. In combination, these polygons provide all the information necessary to describe the structural parameters of the material components and dimensions of the bridge, the external loading acting on the bridge and the geometric information required for the collapse mechanism analysis. This enables realistic bridge and load configurations to be analysed rigorously and very rapidly. An extensive theoretical and experimental validation programme was undertaken in collaboration with the Transport Research Laboratory and the program has been adopted widely by bridge engineers in the UK and also abroad, primarily for use in assessing the load capacity of short-span reinforced-concrete slab bridges.
Automated lower bound analysis of concrete slabs
Authors: Burgoyne C. J. , Smith A. L.
Published: October 2009

A method is developed that allows automated lower bound analyses of concrete slabs to be carried out, with the specific aim of producing a technique that can be applied to existing structures which are being assessed after many years in use and for which the original calculations, and hence the assumed methods of load distribution, have been lost. It is shown that any load distribution within the slab can be expressed in terms of an equilibrium state and a set of states of self-stress. Optimisation techniques are developed that allow the highest lower bound to be found. It is shown that an analysis based on the original Hillerborg two-strip model fails to find a reasonable lower bound when the slab is subjected to point loads and in the corners of slabs but a refinement using four sets of strips at 45° to each other can give very good agreement with both exact analytical solutions and upper bound methods.
Non-linear finite-element analysis of the shear response in prestressed concrete bridges
Authors: Broo H. , Plos M. , Lundgren K. , Engström B.
Published: October 2009

For the structural assessment of concrete bridges, the non-linear finite-element method has become an important and increasingly used tool. The method has shown a great potential to reveal higher load-carrying capacity compared with conventional assessment methods. However, the modelling method used for reinforced and prestressed concrete members subjected to shear and torsion has been questioned. The aim of this study is to present an analysis method for evaluation of the load-carrying capacity of prestressed concrete bridges, when failure resulting from shear and torsion is the main problem. The modelling method used was previously worked out and verified for shear-type cracking and shear failure. Here, shell elements with embedded reinforcement were used together with non-linear material models, taking into account the fracture energy of cracking plain concrete and the reduction of the concrete compression strength owing to lateral tensile strain. Analyses with the method proposed have shown to predict the shear response and the shear capacity on the safe side. In the work presented here, the load-carrying capacity of a box-girder bridge was evaluated as a case study. The whole bridge was modelled, but only the part that was most critical to shear and torsion was modelled according to the method previously worked out and was combined with beam elements for the rest of the bridge. The case study showed a substantially higher load-carrying capacity for the bridge compared with the assessment with conventional methods. In the evaluation, several possible safety formats were used in combination with the non-linear finite-element method. It was shown that the format using partial safety factors gave unrealistic conservative results; it is more correct to use the semi-probabilistic formats for non-linear finite-element analysis.
Combinations of NSM and EB CFRP strips for flexural strengthening of concrete structures
Authors: Lim D.H.
Published: October 2009

The purpose of this study is to investigate the flexural strengthening effectiveness of beams reinforced with near-surface mounted (NSM) carbon-fibre-reinforced polymer (CFRP) strips and externally bonded reinforcing (EBR) CFRP strips. To accomplish this objective, a total of nine concrete T beams were tested and two groups of experimental study were carried out, one for the beam series reinforced with NSM CFRP strips and the other for the beam series combined reinforced with NSM and EBR strips. From this study, it is found that the flexural stiffness and strength of the beams reinforced with NSM and EBR strips were significantly improved compared with the beams strengthened only with NSM CFRP strip. The maximum increase of flexural strength was 347% compared with the control beam. Failure of the beam reinforced with NSM and EBR strips is initiated by debonding EBR strips attached on the bottom face, and it is succeeded by a partial separation of NSM strips along the longitudinal direction and secondly failure of NSM strips. As the load increases, diagonal cracks are formed and eventually sudden explosive failure occurs with the separation of concrete cover in the shear region. The maximum tensile strains measured in the NSM and EBR CFRP strips of the beam reinforced with T-shape strips were noticed in the range 8200–11 600 με and 7000–8900 με respectively. This result shows that the NSM and EBR strips have good combination to resist applied load and the combined reinforcement of NSM and EBR strips can appropriately redistribute the total stress subjected to the concrete beam to the EBR and NSM strips.
Evaluation of the alkali–silica reactivity potential of sands
Authors: Lukschová š. , Přikryl R. , Pertold Z.
Published: October 2009

The alkali–silica reactivity potential of 20 different Quaternary natural aggregates (sands and gravels) from the Czech Republic has been evaluated by petrographic and dilatometric methods. Petrographic techniques, both qualitative (optical and scanning electron microscope (SEM)/energy dispersive spectrometer (EDS) microscopy of thin sections) and quantitative (petrographic image analysis of thin sections), have been applied for the disused specimens. The dilation of the mortar-bar test specimens (according to ASTM C1260) ranged nine samples to the non-reactive, nine samples to reactive and two samples to potentially reactive categories. These categories, based on the dilation values, do not however satisfactorily correlate to the volumes of individual groups of aggregates identified petrographically in mortar-bars. More detailed petrographic examination showed the subdivision according to the presence/absence of deformation sings inhibitors and/or grain size. These results show that the optical microscopy of mortar-bar specimens provides detailed identification of alkali reactive samples according to their spatial relationship with ASR products. The same approach also allows direct identification of gels and alkali–silica reactive fragments.
Estimating the discharge capacity of doubly sinuous compound channels
Authors: Lambert M. F. , Sellin R. H. J.
Published: October 2009

With the increased emphasis on more environmentally appropriate drainage and river channel design, new techniques must be developed to allow designers adequately to assess the discharge capacity of these systems. Unlike the more traditional channel designs that were typically straight and prismatic in cross-section, the modern view of an environmentally and aesthetically pleasing channel is one which is compound in cross-section and, typically, meandering. This paper describes a discharge estimation technique which may be used to calculate the discharge capacity where both the main channel and the flood plain are meandering. This type of channel has been previously termed a ‘doubly sinuous compound channel’ by the authors. A technique for determining the average cross-sectional properties and channel slope for a particular reach is described in this paper, which allows traditional uniform flow resistance equations like the Manning equation to be applied. An experimental programme was undertaken at HR Wallingford and provided valuable insights into this complex flow phenomenon. It was found that the commonly used vertical division of the compound channel at the edges of the main channel was much less satisfactory than a horizontal division across the top of the main channel. The reasons for this are outlined in the paper.
Wall pressure field downstream of deflectors. Part 1: without aeration
Authors: Narayanan R. , Kavianpour M. R.
Published: October 2009

Experiments have been carried out to determine the characteristics of the re-attaching flow downstream of deflectors placed in a duct with and without aeration. In Part 1 the presentation of experimental results pertaining to the mean velocities and wall pressure is restricted to flows without aeration. Fluctuations of pressures are presented in terms of their root-mean-square values and their probability distributions. The mean pressures presented will be of interest in the design of aerators. The mean velocities and wall pressures are analysed numerically by a discrete vortex model and the computed results are compared with the experimental results. It is hoped that information provided in this paper will also be useful in assessing the likelihood of cavitation in reattaching flows occurring within boundaries of similar geometry. How air injection affects the wall pressure field in the wake of deflectors will be reported separately in Part 2.
The Sarawak River barrage—hydrotechnical and geotechnical aspects
Authors: Sharp J. J. , Howe L. Y.
Published: October 2009

Studies conducted over the last ten years have resulted in the construction of a lock and barrage on the Sarawak River in the state of Sarawak, Malaysia. The barrage controls river and tidal flows and has eliminated most of the tidal variation in water level which was formerly experienced in Kuching, the state capital of Sarawak. This paper reviews the hydrotechnical and geotechnical studies of the river and outlines the current operation and effects of the barrage.
Development of a reach scale two-dimensional finite element model for floodplain sediment deposition
Authors: Hardy R. J. , Bates P. D. , Anderson M. G. , Moulin C. , Hervouet J.-M.
Published: October 2009

This paper discusses the development of a two-dimensional finite element coupled hydraulic–sediment transport scheme for application to lowland floodplain environments. Recent developments in numerical algorithms have led to the development of two- and three-dimensional hydraulic models which are capable of simulating open channel and floodplain hydraulics at river reach scales of 1–60 km. However, these hydraulics schemes have not been linked with suitable sediment dynamics schemes. This paper describes the numerical developments necessary to extend an existing two-dimensional finite element solution of coupled hydraulic and sediment transport to fluvial floodplains. These include correct choice of numerical solvers to prevent artificial build-up of tracer mass in dry areas, control of artificial diffusion and implementation of an equation base appropriate to moving-boundary problems. Four experiments of increasing complexity were undertaken in order to ascertain the predictive ability of the model to produce realistic simulations of floodplain sediment deposition. Results showed that a two-dimensional-depth averaged flow field representation captures much of the gross behaviour of suspended sediment transport for reach scale fluvial applications.
Modelling the impact of urban discharges on receiving waters
Authors: Mansell M. G.
Published: October 2009

The modelling of urban pollution has tended to concentrate on the hydraulic performance of the drainage systems and in particular of combined sewer overflows. This paper describes the modelling of various urban catchments together with the catchment of the receiving water in a holistic fashion and investigates the overall contribution of rainfall patterns and catchment characteristics to the impact which urban discharges have on receiving waters.
A review of accidents and failures of stepped spillways and weirs
Authors: Chanson H.
Published: October 2009

Recent advances in technology have permitted the construction of large reservoirs and chutes. These developments have necessitated the development of new design and construction techniques, particularly with the provision of adequate flood release facilities and safe energy dissipation. The latter may be achieved by the construction of steps on the chute. This paper discusses issues of the operation and safe design of stepped chutes. It describes the operation of several structures worldwide, focusing on accidents and failures. The causes of failures are analysed and discussed. Problems specific to stepped-chute design are discussed in the light of over 20 accidents, and common mistakes are described. The safe operation of several old stepped chutes and the experience gained from past failures must be used to gain further expertise and knowledge about the hydraulics of stepped chutes.
Long-term morphological variations of a sandbank system
Authors: Reeve D. E. , Li B. , Fleming C. A.
Published: October 2009

Long-term variations in nearshore coastal morphology can be an important influence in shaping the strategy for management of coastal regions. The design of sea defences, ports and harbours are reliant on adequate understanding of the long-term evolution of coastal morphology. Statistical techniques, known as eigenfunction or empirical orthogonal function (EOF) methods, have been applied to a series of historical bathymetric surveys of a nearshore sandbank system covering a period of almost 150 years. The sandbanks cover an area measuring approximately 30 × 10 km and lie several kilometres offshore from Great Yarmouth which is situated on the east coast of the United Kingdom. This paper presents the results of a statistical analysis of the data. The results provide quantitative support for the presence of quasi-periodic variations in the sandbank morphology of periods that are germane to coastal planning.
Ground-penetrating radar survey to detect sub-slab voids beneath the East Promenade at Rhyl
Authors: Nichol D. , Reynolds J. M.
Published: October 2009

At Rhyl, a tourist resort on the North Wales coast, the East Promenade is susceptible to damage by marine scouring processes. Concealed scour cavities were suspected following the sudden collapse of a segment of the promenade and the recognition of numerous depressions and zones of cracking elsewhere in the concrete pavement. The full threat posed to the integrity of the promenade and to the safety of pedestrians remained uncertain and costly reconstruction was anticipated. Ground-penetrating radar was used along a 260 m stretch of the promenade to determine the full extent of voiding beneath the surface.The geophysical survey delineated the known cavity and, contrary to expectations, demonstrated that the sub-slab voiding beneath the remainder of the promenade was relatively minor. The more subdued radar features encountered were interpreted as minor separation beneath slabs due to consolidation. The results provided a basis for design and construction of effective and inexpensive repairs to the promenade foundations that ensured the public safety.