bluuebunny/crossref_metadata_2025 huggingface dataset:
Isolation of floor machines by lever-type inertial vibration corrector
Authors: Ivovich V. A. , Savovich M. K.
Published: November 2009

This paper proposes and examines a lever-type vibration isolation system that is used to reduce transmitted oscillations from machines onto their floor support. This is a system with a lever mechanism for motion transformation and an auxiliary mass corrector. The substance of this mechanism is that the corrector significantly reduces oscillations from low frequency harmonic excitation by virtue of its additional inertial force. It may be used in conjunction with the classical passive isolation system when greater performance is required and when a conventional technique cannot perform adequately. With the addition of a corrector, the low frequency performance is improved overall. Some analytical results for two-degree-of-freedom (2DOF) machine-floor systems have been presented. Thereafter, the numerical analysis of the dynamic response of this system is carried out using a state space formulation approach. Extensive parametric studies have shown the effects of various levels of base flexibility, viscous damping and mass ratio on the efficiency of this isolation. The results obtained are useful for the design of lever-type isolators. In fact, the highlight of this paper is the design aspect of this novel isolator. Numerical examples of the steady-state response and the time response of two isolation systems (with and without the presence of the lever mechanism) for floor-supported industrial fans are presented. These examples illustrate the application of the formulation and the theory. Finally, the proposed isolator has been validated by dynamic testing and good agreement between theoretical and experimental results has been obtained.
Performance and management of post-tensioned structures
Authors: Tilly G. P.
Published: November 2009

Post-tensioned structures have performed well for some 60 years and justified their early promise. There have, however, been instances of brittle fractures of cold-quenched steel experienced in Germany, cracking and deflection of cantilever bridges, defective grouting, and corrosion of the post-tensioning steel in most countries. These problems have been responsible for isolated failures of various structures including buildings, walkways and bridges. The embargo on new construction of post-tensioned bridges in the UK, placed by the Highways Agency in 1992, had a salutary effect on the industry and led to a determined effort to improve standards. The resulting research and development showed that one of the main shortfalls has been caused by the use of unstable grouts coupled with standard performance tests that have been inadequate. The instability has led to bleeding and formation of voids which expose the steel strands to potential corrosion. The work has led to the development of improved formulations of grout and more discriminating performance tests. Also, it has been shown that the quality assurance of the grouting operations can be improved by use of equipment such as flowmeters to measure the rate and quantity of grout injected into each duct, and pressure sensors to identify blockages and leaks. With these improved procedures there should be no reason for defective grouting in the future. For the management of existing structures, there are suites of methods to enable post-tensioning to be inspected, monitored, refurbished, repaired and strengthened.
Design of steel I-beams curved in plan to BS 5950
Authors: Bradford M. A. , Pi Y.-L.
Published: November 2009

This paper is concerned with the strength design of class 1 and class 2 steel I-beams that are curved in plan under vertical (or transverse) loading. It proposes and exemplifies straightforward lower bound interaction equations for designing steel I-beams curved in plan against combined bending and torsion actions, which are both easy to use and consistent with the corresponding methods of BS 5950 for designing steel members subjected to bending. The interaction equations incorporate the significant effects of the included angle and the secondary minor axis bending and torsion actions, and allow for different configurations of lateral bracing. The use of the proposed interaction equations will facilitate the strength design of steel I-beams curved in plan, and lead to safe and more economical structures.
Testing of coupling beams with equal end rotations maintained and local joint deformation allowed
Authors: Kwan A. K. H. , Zhao Z. Z.
Published: November 2009

The strength and ductility of the coupling beams in coupled shear walls can significantly affect the nonlinear behaviour and earthquake resistance of the whole building structure. However, although extensive testing of coupling beams has been performed, the boundary conditions—that the rotations at the two ends of a coupling beam are equal and that local deformation occurs at the beam–wall joints, which could have substantial influence on the test results—have not been correctly simulated. Herein, a new method of testing reinforced concrete coupling beams that ensures equal rotations at the ends of the beam specimen and takes into account local deformation at the beam–wall joints is developed. The method has been successfully applied to test typical reinforced concrete coupling beams with relatively small span/depth ratios and proven to be suitable for studying the post-peak behaviour and failure characteristics of short coupling beams. Test results obtained so far indicate that reinforced concrete coupling beams with small span/depth ratios behave quite differently from ordinary beams in frame structures and that the local deformation at beam–wall joints is quite substantial. Complete load–deflection curves have been acquired and the strength and ductility of the coupling beams evaluated.
Methodology for modal testing of the Millennium Bridge, London
Authors: Pavic A. , Armitage T. , Reynolds P. , Wright J.
Published: November 2009

Measurement of Frequency Response Functions (FRFs) on the Millennium Bridge in London was a key part in the validation of the retrofit solution for excessive sway vibration caused by walking pedestrians during the bridge opening in June 2000. The measured FRFs were employed to verify the analytical response analysis and to estimate and confirm analytical predictions of natural frequencies, modal damping ratios, mode shapes and modal masses corresponding to various configurations of prototype viscous and tuned mass dampers. These results were used to experimentally assess the effectiveness of the proposed retrofit solution. Although FRF measurement technology is fairly standard in many engineering disciplines, its application on the Millennium Bridge was quite problematic and required some unique solutions which are described in this paper. Modal testing of the Millennium Bridge clearly demonstrated that it was possible to measure good quality FRFs around a frequency as low as 0·5 Hz, which was the natural frequency of the first lateral mode of vibration. This was achieved by designing, constructing and installing a bespoke hydraulic shaker featuring a translatory moving mass of 1000 kg. As the shaker was not able to produce perfectly sinusoidal excitation for stepped-sine testing, FRFs were successfully estimated using the so-called Resolver method in conjunction with an Hc estimator. The standard H1 FRF estimator, which is used in the vast majority of modern digital spectrum analysers nowadays, was demonstrably unable to produce meaningful FRF estimates when using the Resolver approach. The FRF estimation and curve-fitting performed in situ proved to be crucial for the success of the modal testing of the Millennium Bridge. By evaluating the estimates of the experimental FRFs and the corresponding modal properties during the testing programme on site, a number of test errors were spotted. This, in turn, enabled immediate repetition of measurements and/or evaluation of the structural behaviour which would have been impossible if the FRF data analysis had been performed after the testing had been completed.
Seismic behaviour of knee braced frames
Authors: Williams M. S. , Blakeborough A. , Clément D. , Bourahla N.
Published: November 2009

This paper describes the development of the concept of knee bracing for improving the seismic performance of steel frames. In a knee braced frame the main diagonal braces are connected to short knee elements which span diagonally across the beam–column joints. The knee elements act sacrificially, reducing the demands on the main structure during a small or medium earthquake, and can be replaced after the event. Results from a series of parametric analyses are presented, which demonstrate the potential benefits of the approach. However, careful design of the knee elements is required to ensure that they are able to absorb energy through repeated large plastic deformations without suffering collapse or instability. To optimise the design, an extensive programme of finite element modelling and experimental testing has been undertaken. It is shown that excellent performance can be achieved using standard hot-rolled sections, modified by the addition of web stiffeners to prevent localised buckling failure. Weakening of the knee elements so that they yield very early in an earthquake has potential benefits, but is shown to be unsafe as it promotes premature failure of the element.
Earthquake resistance of flush end-plate steel joints for moment frames
Authors: Thomson A. W. , Broderick B. M.
Published: November 2009

The rotational stiffness of flush end-plate connections ensures that moment-resisting frames in which they are employed will possess some lateral resistance even in the absence of bracing members – a property which is widely exploited in the wind-moment method of design. This paper describes an investigation of whether this approach can be extended to include earthquake resistant design. The results from an experimental study of the cyclic response of flush end-plate joints is presented. The responses of eight different beam-to-column sub-assemblages subjected to monotonic or cyclic loading are compared in terms of rotational stiffness, failure mode, ultimate moment resistance and rotation ductility capacity. A response prediction model has been developed, and the experimental and predicted results are compared. Moment–rotation curves obtained from this model are employed in design case studies in which the earthquake resistance of steel moment frames is evaluated. These concentrate on identifying the maximum ground acceleration that can be resisted by individual frames that have already been designed for a given level of wind loading.
A tiered approach to the fatigue assessment of composite steel and concrete bridge beams
Authors: Oehlers D. J. , Seracino R.
Published: November 2009

The behaviour of composite steel and concrete beams subjected to fatigue loads is complex due to the slip between the steel and concrete components that is required to load the mechanical shear connectors and which is found to change continually with time. Most new designs are based on a generally conservative assumption of full interaction; however, in the assessment of existing structures, and in order to reduce costs, it is often necessary to use the bridge to its full potential, which requires advanced analysis techniques that allow for interface friction and partial interaction. A tiered approach to assessment of simply supported beams is described that starts with a simple but conservative assessment and gradually increases in complexity and accuracy. For example, if the first simple assessment finds the structure inadequate then the complexity of the analyses can be gradually increased to extract more of the potential strength and endurance. Should the full potential of the structure still be found to be inadequate, then this tiered approach can also be used in the assessment of the effect of remedial measures.
A new technique for retrofitting damaged concrete structures
Authors: Karihaloo B. L. , Alaee F. J. , Benson S. D. P.
Published: November 2009

A new retrofitting technique based on a material compatible with concrete is currently under development at Cardiff University. It overcomes some of the problems associated with the current techniques based on externally bonded steel plates and FRP (fibre-reinforced polymer) laminates which are due to the mismatch of their tensile strength and stiffness with that of the concrete structure being retrofitted. This paper will describe the technology necessary for preparing high performance fibre reinforced mixes, designated CARDIFRCs. They are characterised by high tensile/ flexural strength and high energy-absorption capacity (i.e. ductility). The special characteristics of CARDIFRC™s make them particularly suitable for repairing and upgrading (i.e. retrofitting) existing concrete structures, as well as for other remedial activities. The promising results of several studies using CARDIFRC™s for retrofitting damaged concrete structural members will be presented. It will be shown that damaged reinforced concrete beams can be successfully strengthened and rehabilitated in a variety of different retrofit configurations using pre-cast CARDIFRC™ strips adhesively bonded to the prepared surfaces of the damaged beams.
Flexural strength and ductility of reinforced concrete beams
Authors: Kwan A. K. H. , Ho J. C. M. , Pam H. J.
Published: November 2009

In the design of reinforced concrete beams, especially those made of high-strength concrete and those in earthquake-resistant structures, both the flexural strength and ductility need to be considered. From the numerical results obtained in a previous study on the post-peak behaviour and flexural ductility of reinforced concrete beams, the interrelation between the flexural strength and the flexural ductility that could be simultaneously achieved was evaluated and plotted in the form of charts. Using these charts, a new method of beam design called ‘concurrent flexural strength and ductility design’ that would allow engineers to consider both the strength and ductility requirements at the same time before deciding on whether to use high-strength concrete or add compression reinforcement has been developed. For application to cases in which the concrete grade is prescribed, a simpler method of first determining the limits of steel ratios that would satisfy the ductility requirement and then designing the reinforcement details according to the strength requirement has also been proposed. Examples are presented to illustrate the application of these methods.
Human loading on staircases
Authors: Bougard A.
Published: November 2009

A study of human loads on staircases has been undertaken to provide data to support the assessment and rationalisation of British design codes. The purpose of this paper is to explain the experimental method and to compare the measured loads with the characteristic loads specified in current British design codes. The experimental method was developed for measuring loads due to individuals, small controlled groups and crowds on staircases. The dynamic loads have been expressed as a factor of the static weight of the individual or crowd applying the load. The majority of the measured loads have been found to be less than the characteristic loads. However, in some cases the characteristic loads have been exceeded although no signs of damage or distress to the staircases have been observed. It is concluded that the safety factors used by staircase designers appear to be sufficient to ensure that staircases in the UK are unlikely to be damaged by dynamic load imposed by humans.
High-strength steel–concrete composite columns for buildings
Authors: Uy B.
Published: November 2009

High-strength quenched and tempered structural steel has seen an increased usage in the application to heavily loaded columns in multi-storey building construction. This has been particularly true in nations where such steels are abundantly produced, particularly Australia and Japan. Many current international codes do not cater for the use of high-strength steel and thus research is required to give structural engineers the confidence to use this new and innovative material in a safe and efficient manner in construction. Previous research on the use of high-strength structural steel for columns is outlined herein and a summary of previous applications in multi-storey buildings is provided. The paper provides a very comprehensive summary of experimental results on the uses of high-strength structural steel in composite columns specifically for multi-storey building construction. Calibration of these experiments with theoretical models and the Eurocode 4 approach has highlighted some of the differences that need to be implemented in order to design building structures safely with this material. Suggested design recommendations as well as further research is therefore summarised.
Strengthening concrete structures with fibre composites
Authors: Clarke J. L.
Published: November 2009

The use of fibre composites, formed from high modulus carbon, glass or aramid fibres combined with suitable resins and adhesives, for strengthening concrete structures is growing rapidly. This paper summarises The Concrete Society Technical Report 55, Design Guidance for Strengthening Concrete Structures Using Fibre Composite Materials, which is the first document to give design guidance in accordance with British codes. The report also describes some of the systems that are available and summarises the properties of the various materials. Typical applications are described along with the requirements for quality control both of the materials and the site operations.
Behaviour and strength of FRP-strengthened RC structures: a state-of-the-art review
Authors: Teng J. G. , Chen J. F. , Smith S. T. , Lam L.
Published: November 2009

Extensive research has been carried out in recent years on the use of fibre-reinforced polymer (FRP) composites in the strengthening of reinforced concrete (RC) structures. This paper provides a concise review of existing research on the behaviour and strength of FRP-strengthened RC structures, with a strong focus on those studies which contribute directly to the development of strength models. Topics covered include flexural and shear strengthening of beams, flexural strengthening of slabs, and strengthening of columns subject to both static and seismic loads. For each of the topics covered, the methods of strengthening are first explained, followed by a description of the common failure modes. Available strength models are then summarised and discussed.
Influence of furnace bottom ash on properties of concrete
Authors: Bai Y. , Basheer P. A. M.
Published: November 2009

Furnace bottom ash (FBA) is a by-product from thermal power plants. Unlike its companion, pulverised fuel ash (PFA), FBA has coarse particle size, higher water absorption and usually no pozzolanic effect. Therefore, it is dumped in landfill sites. Past recycle attempts of FBA have been mainly focused on using it in blocks, highway embankments, subgrades, sub-bases and structural fills. However, this may still be a source of environmental contamination by way of leached trace elements. A previous investigation carried out by the authors has indicated that FBA would be a potential fine aggregate in concrete. The effects of FBA on workability, compressive strength, permeability, depth of carbonation and chloride transport of concrete were further investigated and the results are reported in this paper. The natural sand was replaced with FBA by 0, 30, 50, 70 and 100% by mass, at fixed free water–cement ratios of 0·45 and 0·55 and a cement content of 382 kg/m3. The results indicated that the workability of the concrete increased with an increase in replacement level of natural sand with the FBA. Most of the FBA concrete was lower in compressive strength than the control that was manufactured with the natural sand up to an age of 28 days for both the water–cement ratios, but most of the FBA concretes were comparable with that of the control concrete at 365 days. The air permeability, water absorption and the carbonation rate at the age of 365 days were higher than those of the control concrete. However, the chloride transport coefficient decreased with the increase of the replacement level of natural sand with FBA up to 50% and it increased beyond this replacement level for both the water–cement ratios. Further investigation is required to assess whether properties of concrete could be improved by taking account of the decrease in water demand of the FBA concrete while determining the water–cement ratio of the mix.
Strengthening of London's Lambeth Bridge
Authors: Kumar A.
Published: November 2009

This paper summarises the findings of the principal inspection and load assessment of Lambeth Bridge, which had identified a structural deficiency in the original construction of the arched steel ribs of the bridge. The design for the strengthening of the bridge involved rectification of this deficiency as well as consideration of other repairs and repainting of the bridge. The paper briefly describes the various site operations involved in the works contracts resulting in the strengthening of this landmark bridge in London.
Bridges: when is single mode seismic analysis adequate?
Authors: Isaković T. , Fischinger M. , Kante P.
Published: November 2009

Single-degree-of-freedom (SDOF) models are frequently used in the seismic analysis of bridges, in particular in recent years when inelastic, SDOF-based push-over analysis has become increasingly popular. However, the scope of applicability of these models has not yet been clearly defined (e.g., in the Eurocode 8/2). Using SDOF models, displacements and forces could be significantly underestimated, especially in ‘irregular structures’. The authors have therefore proposed a more adequate criterion for the applicability of SDOF models, and a clearer definition of regularity. The seismic response of some typical European viaducts has been studied. Several different seismic analysis methods, both elastic and inelastic, were used, incorporating different levels of structural model simplification. Differences in the response obtained by using SDOF and multi-degree-of-freedom (MDOF) models were analysed. If these differences were significant, the response was considered to be irregular and the SDOF model unsuitable. For the quantitative estimation of the regularity and applicability of SDOF models a ‘regularity index’ has been introduced. The index is based on a comparison between the different displacement shapes obtained within two iterations of the single mode static analysis. Using this index the main parameters influencing the irregular response of the viaducts were identified and analysed.
Hybrid concrete: improved processes and performance
Authors: Barrett P. S.
Published: November 2009

This paper presents the results of a study of three very successful Hybrid * concrete projects. Supply chain analyses are described and, in the event, the situations found are typified as networks. Problem areas are identified together with various illustrations of good practice, with a particular stress on the necessity for intensive and effective informal communications. The particular problems attendant on the design side of the process, rooted in role confusion and a lack of design fixity are highlighted. This links to the suggestion that as the knowledge of Hybrid systems becomes better understood and is more fully communicated through codification then many of these problems should evaporate. That is, Hybrid can move from being a disruptive technology and become a sustaining technology for the industry and its clients.
Blast-induced vibrations in urban residential buildings
Authors: Carvalho E. M. L. , Battista R. C.
Published: November 2009

The effects of the vibration waves induced by underground explosions on the reinforced concrete framed structure of a residential building and consequent damage caused to the building non-structural components, together with other effects on user comfort, are outlined in this paper. Some conclusions are drawn based on the theoretical and experimental results obtained for frequencies and amplitudes of the vibration modes of the structure. These results are, in their turn, analysed in the light of the recommendations of international codes.
Oblique bending in U-shaped steel sheet piles
Authors: Byfield M. P. , Crawford R. J.
Published: November 2009

U-shaped Larssen steel sheet piles are normally driven in pairs. The common interlock may be crimped or welded to prevent inter-pile movement, creating an asymmetric section which may exhibit a reduced bending strength due to oblique (biaxial) bending. The recently introduced Eurocode 3: part 5 takes this into account and applies a reduction factor on bending strength. This paper provides information on the selection of values for the reduction factor and will be of interest to designers of U-section steel sheet pile retaining walls. Experimental tests carried out on one-sixth scale U-piles are reported, together with a theoretical analysis of oblique bending. The research shows that freedom of lateral movement is important to the development of oblique bending. Furthermore, pile walls restrained against lateral movement by soil–structure interaction, among other things, will not exhibit significant oblique bending.
Reliability of nailed timber connections with gusset plates
Authors: Drummond I. , Kermani A.
Published: November 2009

First order second moment (FOSM) analysis techniques, recently employed in the development of limit states design codes allow the engineer/designer to take into account the variations and random nature of the material properties and load effects present in the design of structural timber. A generated non-linear equation is used in conjunction with basic design mechanics to model the moment–rotation behaviour of dowel type (nailed) timber connections. The connections examined incorporated a series of nailed gusset beam to column joints with varying number of nails, subjected to a series of permanent and variable loading conditions. Joint reliability is evaluated by imposing an end rotation and calculating the reliability index under imposed deformation levels. The parameters of the equation considered as random variables were nail diameter, timber density, connection geometry and the applied loading condition. The statistics of the random variables considered are modelled using the normal, lognormal and extreme value type-1 (Gumbel) distributions. Results show that irrespective of the magnitude of variation of the other parameters, nail diameter significantly influences the moment-capacity of the connection, especially for smaller diameters. Use of probabilistic analysis techniques in design is intended to provide improved insight into system behaviour, the influence of different random variables on system performance and the interaction between different system components. This paper demonstrates how the incorporation of FOSM analysis with a non-linear moment–rotation model provides a more rational description of connection behaviour without the need to resort to more traditional Monte Carlo simulation, which can be both costly and time consuming.
Measurement of floor vibrations using a heel drop test
Authors: Blakeborough A. , Williams M. S.
Published: November 2009

As floor vibration problems increase, there is a need for simple and reliable methods of determining a floor's dynamic properties. This paper presents a technique called the instrumented heel drop test, in which the floor is excited by a series of heel drops performed on top of a slim load cell placed on the floor. The test is shown to give excellent resolution of natural frequencies in the range 2 – 15 Hz, which corresponds well with the frequency range of interest in floor vibration problems. The method appears to offer some advantages over the well-established technique of instrumented hammer testing, in terms of the quality of frequency resolution and the speed of the test.
Ductility and deformability of fibre-reinforced polymer-strengthened reinforced concrete beams
Authors: Tann D. B. , Delpak R. , Davies P.
Published: November 2009

This paper discusses the definition of, and the distinction between, deformability and ductility of reinforced concrete (RC) beams that are strengthened by advanced composites. The study examines the suitability of a new, design-based method for the determination of deformability, as well as an energy-based process, which is found to be suitable for quantifying the ductility levels of fibre-reinforced polymer (FRP)-strengthened RC members. Ten FRP-strengthened RC beams and four slabs have been load-tested to ultimate failure in the current study. The test results, together with the load–deflection data of an additional 26 beams from literature, form the basis of analyses and discussions. The paper concludes that high deformability does not necessarily lead to good ductility, as very brittle failure modes of such beams have been observed in the experimental studies and reported in literature. It was found that a ductility index of between 2·0 and 2·5 reflects 25–33% of elastic energy stored in the strengthened system. This level of elastic energy is considered to be the maximum acceptable in FRP-strengthened concrete flexural elements for ductile behaviour. It was also found that for ductile failure modes the deformability and ductility indices tend to converge, whereas for brittle behaviour the deformability index could be up to 33% higher. The results presented in this paper provide a rationale for the ductility considerations to be incorporated into the development of design equations for FRP strengthening.
Interfacial stresses in soffit-plated reinforced concrete beams
Authors: Yang J. , Teng J. G. , Chen J. F.
Published: November 2009

A popular new method for retrofitting reinforced concrete (RC) beams is to bond a fibre-reinforced polymer (FRP) plate to their soffit to increase their flexural strength. An important failure mode of such strengthened members is the debonding of the FRP plate from the concrete due to high interfacial stresses near the plate ends. This paper presents an explicit solution for interfacial stresses in a simply supported beam bonded with a thin plate and subjected to arbitrary loads. A set of arbitrary loads is decomposed into a symmetric component and an antisymmetric component. Closed-form solutions are derived for both the symmetric and antisymmetric load cases. The solution for arbitrary loading is obtained by superimposing the results for both load cases. The solution considers the non-uniform stress distributions in the adhesive, and satisfies the stress-free boundary condition at the ends of the adhesive layer and FRP.
Strength of steel fibre reinforced concrete ground slabs
Authors: Chen S.
Published: November 2009

Tests are reported on four full-scale concrete ground slabs. Two types of steel fibre have been used to reinforce the concrete, with fibre contents of 20 and 30 kg/m3, which is lower than the minimum recommended in the Chinese construction practice. It is found that flexural toughness has an effect on the load-carrying capacity of steel fibre reinforced concrete (SFRC) ground slabs. The ultimate load capacity of the ground slabs is assessed and compared with the test results from different sources. The load-carrying capacity of the SFRC ground floors with flexural toughness effect is assessed. The horizontal thrust induced by the friction between the slab and the subgrade is also analysed.
Modelling dynamic behaviour of a cantilever grandstand
Authors: Mandal P. , Ji T.
Published: November 2009

This paper investigates the dynamic behaviour of a cantilever grandstand using two-dimensional (2D) frame, three-dimensional (3D) open-ended and 3D enclosed finite-element models. The effects of bracing systems, stiffness of seating decks and eccentricity of connections are examined. This comparative study also considers the relative advantages of the typical 2D and 3D models used in the study of dynamic behaviour and the response of grandstands to human loads. It is concluded that a 2D frame model is accurate enough for examining the dynamic behaviour of the grandstand in the vertical and front-to-back (also termed transverse) directions, and appropriate bracing systems can effectively increase structural stiffness of grandstands in the side-to-side (or longitudinal) and front-to-back directions. (The terms side-to-side and front-to-back have been used from the spectator's point of view.) While designing a grandstand for dynamic loads, it is customary to include the first few modes in a mode superposition based analysis. However, from the present study it has been observed that some vibration modes of interest could be at a much higher order than normally anticipated.
Review of tests on bolted joints between pultruded GRP profiles
Authors: Turvey G. J. , Cooper C.
Published: November 2009

Fifty-nine moment–rotation tests on bolted beam-to-column joints between pultruded glass-reinforced plastic (GRP) profiles form the basis of the review. Joint test methods are discussed. The joints are sub-divided into five groups. The joints in each group are described and their test data appraised. Sketches of the joints and summaries of the test data are presented in tables. Three broadly similar categories of joint (web cleat, web and flange cleat and high stiffness and strength joints) are identified. For each category, the joint test data—initial rotational stiffness, ultimate moment and ultimate rotation—are compared. The variations in the test data highlight the need for further testing of a variety of nominally identically in order to improve both understanding of joint behaviour and joint design. A round robin exercise, in consultation with pultruders, fabricators and designers, is suggested as a means of achieving this goal.
Response of cantilever grandstands to crowd loads. Part 1: serviceability evaluation
Authors: Ellis B. R. , Littler J. D.
Published: November 2009

This paper considers the problem of human acceptance of vibration in grandstands. It adopts the BS frequency weighting methodology and uses the vibration dose value (VDV) as an indication of when adverse comments may be expected. Measurements were taken on a number of cantilever grandstands during concerts and football matches. These were analysed to determine peak accelerations and VDVs and some empirical relationships were derived. As human reaction at these events relates more to vibration tolerance than perception, it has been necessary to consider a logical extrapolation based on current BS guidance to suggest VDVs that are appropriate for grandstand vibration. The reactions and VDVs recorded on the grandstands appear to support this suggestion. The calculation of VDVs is also considered, but this depends to a great extent on the calculation of peak accelerations, which is considered in another paper. Finally a number of key points arising from this work are discussed.
Testing a composite box-girder bridge with precast decks
Authors: Ryu H.-K. , Shim C.-S. , Chang S.-P.
Published: November 2009

In order to design continuous composite bridges with full-depth precast decks, several factors should be considered, and confirmed through experiments: details of connections, serviceability of cracking and inelastic behaviour. After reviewing previous experiments, an experiment was executed with a steel box-girder bridge model having two spans of 10 m each. Because there is no reinforcement at the transverse joints except prestressing tendons, a design criterion for the prevention of cracking at the joints is not to allow tension at the joints under service loadings. In this paper, a major interest is in the behaviour of a composite section in a negative moment region. Therefore the elastic and inelastic behaviour of the model was carefully observed to provide proper design bases. In particular, cracking load, crack width and moment curvature of composite sections were investigated. The validity of the stiffness of the concrete slab in the negative moment region is discussed in terms of serviceability and ultimate limit states. After cracking at the joints, the flexural behaviour of a beam was observed carefully to estimate tension stiffening effects of the tendon and moment redistribution. Test results showed that uncracked section analysis for the concrete slab in a negative moment region could be used for serviceability, and a cracked section for ultimate limit states.
Response of profiled barriers subject to hydrocarbon explosions
Authors: Louca L. A. , Boh J. W. , Choo Y. S.
Published: November 2009

This paper presents a numerical methodology to investigate the response of stainless steel profiled barriers when subjected to blast loading generated from a hydrocarbon explosion. Results from three large-scale explosion tests are used to validate the Abaqus/Explicit finite-element code adopted in the analyses. A simple failure algorithm based on equivalent plastic strain has been implemented in the numerical code to model the ductile weld tearing behaviour. The effects of strain rates, sensitivity of mesh densities and load idealisation will be discussed. A brief review of deep trough corrugated blastwalls that exhibit very different response behaviour will also be presented. The paper concludes with some parametric studies on load characteristics to determine the capacity of the deep trough corrugated blastwall.
Shear strength of tapered steel plate girders
Authors: Zárate A. V. , Mirambell E.
Published: November 2009

Hot rolled beams can show insufficient strength or inertia and result in the inclusion of steel plate girders in the design (portal frames, steel and composite bridges). More efficient structural elements can often be achieved by designing these plate girders with a tapered girder profile. One of the main distinctive features of tapered steel plate girders is the significant slenderness of the web. In this paper, an analytical model to evaluate the shear capacity of tapered plate girders is presented. The model is based on diagonal tension field theory. The analytical formulation presented, obtained on the basis of numerical studies of plate instability and shear capacity, takes into account the real geometry of the tapered plate girder and the actual boundary conditions of the web panel. The shear model considers the bending stresses on the web panel, which appear as a result of the variation of the structural depth of the steel girder. Finally, analytical results of shear strength of tapered steel plate girders obtained using the proposed model are compared with those derived from the numerical model, which is based on the finite element method.
Dynamic characteristics of single-layer cylindrical lattice shells
Authors: Chen Y. B. , Li Q. S. , Chen J. M.
Published: November 2009

This investigation is concerned with the free vibration and seismic response of single-layer cylindrical lattice shells. The effects of basic structural parameters such as the ratio of rise to span, mass, damping, the ratio of length to span and the rigidity of supports, on the dynamic behaviour of single-layer cylindrical lattice shells are investigated in detail. In this paper the finite-element method is used, in which three-dimensional beam elements are employed. Both the natural frequencies and their associated modes of vibration are obtained with a subspace iteration technique, and the direct dynamic analysis method is adopted to analyse the dynamic responses of single-layer lattice shells under vertical and horizontal earthquake excitations. The objective of this study is to achieve a better understanding of the dynamic characteristics and seismic behaviour of single-layer lattice shells. The results are valuable for the earthquake-resistant design of such structures.
Shear deformation debonding of adhesively bonded plates
Authors: Oehlers D. J. , Liu I. S. T. , Seracino R.
Published: November 2009

Adhesive bonding of fibre reinforced polymer (FRP) and steel plates to the surfaces of reinforced concrete structures is an efficient form of retrofitting, as the plated structure is mechanically efficient, the plate is unobtrusive, and—for FRP plates—the plate is durable and the application is inexpensive owing to the lightness and flexibility of the pultruded or wet lay-up plate. In this paper it is shown: from a comparison of the main FRP plating guidelines, that there is now a general agreement on the major plate debonding mechanisms; that current rules in national standards for the shear capacity of prestressed beams can be used to quantify a major plate debonding mechanism due to beam shear deformations, that is critical diagonal crack (CDC) debonding; and that these developments allow a simple design approach to be used for FRP and steel plated beams and slabs with longitudinal plates.
Strengthening of critically designed girders with dapped ends
Authors: Taher S. E.-D. M. F.
Published: November 2009

Reinforced concrete (RC) beams with dapped ends are frequently found in bridge girders and precast concrete construction. A reduction in depth near the supports tends to produce a stress concentration and hence requires special analysis and detailing of any reinforcement used. Improper dimensioning and distribution of reinforcing steel can lead to undesirable cracking and failure mechanisms that need to be predicted in order that a proper strengthening system be applied. The experimental programme described in this paper incorporated 52 specimens with dapped ends; three main defects were intentionally introduced at the recess zone and 12 different strengthening techniques were applied. The defects included an inadequate development length of bottom longitudinal reinforcement at the dapped ends, and elimination of either horizontal or vertical shear reinforcement at the ends. External bonding of the steel angle at the reentrant corner, unbonded bolt anchoring, external steel plate jacketing, exterior carbon fibre wrapping and/or stripping were applied in order to determine the best strengthening technique. A strut-and-tie model was used in the analysis of such discontinuity regions and a strength enhancement index procedure was introduced. A comparative study was undertaken in order to evaluate the various strengthening techniques applied.
Experimental assessment of bonded FRP-to-steel interfaces
Authors: Harries K. A. , Webb P.
Published: November 2009

The use of bonded fibre-reinforced polymer (FRP) materials for the repair of civil infrastructure is becoming well established. The majority of applications are ‘bond critical'; that is, the dominate limit state is affected by the FRP debonding from the substrate. Considerable research has been conducted on the behaviour of FRP bonded to a concrete substrate; however, there is a growing interest in using FRP bonded to a steel substrate. In the former case, bond behaviour is dominated by cohesive failure in the concrete substrate; in the latter, bond is dominated by adhesive behaviour. As a result of not needing to consider substrate failure in the case of FRP-to-steel applications, the FRP may be utilised much more efficiently, provided bond can be maintained. This paper briefly reviews factors affecting bond of FRP-to-steel and presents a relatively simple laboratory test method for assessing bond performance. The method is well suited to comparing performance of different applications, surface preparations, environmental exposures and so on, but also yields quantitative data in the form of the steady-state energy release rate useful for modelling and designing FRP-to-steel bonded interfaces.
Strain localisations in FRP-confined concrete: new insights
Authors: Bisby L. A. , Take W. A.
Published: November 2009

Circumferential confinement of reinforced concrete columns with externally bonded fibre-reinforced polymer (FRP) wraps is now widely implemented as a method to strengthen and/or enhance the deformability of deficient or damaged reinforced concrete columns. A fundamentally important parameter in the design of these members is the so-called strain efficiency of the FRP wraps – the ratio of the tensile hoop strain in the FRP at failure to the average failure strain observed in direct uniaxial tensile coupon tests. Available experimental hoop strain data obtained using localised strain gauges provide little insight into the variation of hoop strain over the surface of FRP wraps, the factors influencing strain efficiency and the resulting strain efficiency that should be assumed in design, and these remain essentially unknown. In this paper, a novel digital image correlation technique is used to provide a detailed experimental quantification of the axial and hoop strain variation over the surface of FRP confined concrete cylinders. Potential implications for the analysis and design of FRP confined concrete are discussed.
Strengthening RC beam–column connections with FRP strips
Authors: Shrestha R. , Smith S. T. , Samali B.
Published: November 2009

Reinforced concrete connections, designed prior to the implementation of earthquake design standards, may be vulnerable to shear failure during a seismic attack. Addition of externally bonded fibre-reinforced polymer (FRP) composites can enhance not just the shear capacity but the deformation and energy absorption capacity of the connection. The majority of research studies to date have opted for complete or near-complete coverage of the joint region with FRP and have subjected the test specimens to cyclic (push–pull) loading. Such strengthening schemes and method of loading make it quite difficult to accurately monitor and hence understand the behaviour of the FRP and the concrete beneath. This paper presents results of a series of tests on the strengthening of shear deficient connections with FRP strips subjected to either cyclic or monotonic loading with the primary motivation being accurate description of the behaviour of the FRP. The tests also enable the failure modes to be more accurately reported and classified especially due to the use of monotonic loading. An analytical model is finally presented which accurately describes the mechanics of the FRP strengthening with the model predictions correlating reasonably well with the test data.
Mechanics of debonding in FRP-plated RC beams
Authors: Teng J. G. , Chen J. F.
Published: November 2009

Both the flexural and shear strengths of reinforced concrete (RC) beams can be substantially increased using externally bonded fibre-reinforced polymer (FRP) reinforcement in the forms of sheets/strips/plates (all referred to as plates for brevity). Failures of such FRP-plated RC beams often occur by debonding of the FRP plate from the RC beam in a number of distinct modes. This paper provides a summary of the current understanding of the mechanics of debonding failures in FRP-plated RC beams largely based on the research of the authors and their co-workers. A systematic classification of possible debonding failure modes is presented following a brief outline of the common strengthening methods. The interfacial stresses and bond behaviour between FRP and concrete are then discussed before the mechanisms and processes of debonding failures are examined. Furthermore, advanced strength models for the key debonding failure modes are presented. The paper concludes with a brief discussion of future research needs.
Cost-effective management of scour-prone bridges
Authors: Whitbread J. E. , Benn J. R. , Hailes J. M.
Published: November 2009

This paper discusses the nature of scour at bridge structures and reviews the available methods of assessing scour potential and the risk of failure. A management system based on the authors’ practical experience of bridge scour assessments is also proposed as a means of identifying this risk and minimizing it in an efficient and economic manner.