Written on 19 août 2011.
A. S. Alnauimi, Sultan Qaboos University, Sultanate of OmanP. Bhatt, University of Glasgow, UKThis paper, Part I, presents a general 'direct design procedure' for the design of reinforced concrete hollow beams subjected to a combined load of bending, shear and torsion. Elastic stress field in conjunction with Nielsen's twodimensional yield criterion for reinforced concrete subjected to in-plane forces were used in the design of reinforcement. This procedure is based on and satisfies the lower bound theorem of the classical theory of plasticity. The main features of this procedure are the precluding of the use of empirical equations as is the case with existing codes of practice and in addition to satisfying the requirements of the theory of plasticity it reduces the ductility demand assumed by this theory. Comparison between the direct design procedure and the truss analogy showed that the direct design procedure leads to steel requirements close to those of the truss analogy when the angle of inclination of the struts is 458. The direct design procedure produced much less reinforcement than the American Concrete Institute and the British Standards Institute codes.
Written on 19 août 2011.
A. El-Nabawy Atta, Tanta University, EgyptS. El-Din Fahmy Taher, Tanta University, EgyptA.-H. A. Khalil, Tanta University, EgyptS. E. El-Metwally, Tanta University, EgyptDesign provisions of many international codes for beam-column joints are limited to ordinary-strength concrete. The experimental work presented in Part I of the paper (Structural Concrete, 2003, 4, No. 4, 175-183) has indicated a significant difference in behaviour of normal concrete joints from those made of hybrid or monolithic high-strength concrete joints. To conduct an extensive parametric study, a non-linear, three-dimensional finiteelement analysis was carried out for external reinforced concrete type-1 joints under quasi-static monotonic loading. The computational model has been verified and validated against several experimental tests. The numerical work was aimed at providing more insight about the behaviour and determining the fundamental mechanisms of load transfer within the joint. The basic parameters included the effects of geometrical aspects as well as the amounts of reinforcement and detailing in column, girder and joint. Furthermore, the strength parameters, existence of axial column load, presence of vertical haunches and the restraining effects by transverse elements have been considered in the analysis. The present study indicated that the modes of failure and shear behaviour of high-strength concrete connections behaved differently from normal-strength concrete connections at various axial loading levels.
Written on 19 août 2011.
T. Pregartner, Engineering Office Eligehausen & Asmus, Stuttgart, GermanyJ. Cairns, School of the Built Environment, Heriot-Watt University, Edinburgh, UKJ. Ozbolt, Institute for Construction Materials, University of Stuttgart, GermanyIn the present paper a simple approach to model the effects of corrosion on bond between plain bar reinforcement and concrete with the finite element method (FE method) is shown. With the combination of a non-linear FE-solver and a discrete bond model it is sufficient to simulate corrosion by radial expansion of a concrete cylinder. The bond model used accounts for the effects of confinement and stresses in the vicinity of the reinforcement bar. Hence the effects of corrosion could be investigated with this simple approach. The model is calibrated on pull-out tests with RILEM specimen. Calculations conducted on beam end specimen containing plain surface bars show a plausible agreement with test results and with results known from literature.
Written on 19 août 2011.
R. Vedalakshmi, Corrosion Science and Engineering Division, Central Electrochemical Research Institute, KaraikudiS. Srinivasan, Corrosion Science and Engineering Division, Central Electrochemical Research Institute, KaraikudiK. Ganesh Babu, Department of Ocean Engineering, Indian Institute of Technology, Madras, IndiaIn the present investigation the strength and permeability characteristics of blended cements such as Portland pozzolana cement and Portland slag cement were evaluated in 20, 30 and 40 MPa concretes. The cements were produced by intergrinding mineral admixtures such as fly ash and slag with clinker and gypsum in the plant. The compressive strength over a period of 1 year and water permeability at the end of 7, 28 and 90 days were evaluated and the results were compared with ordinary Portland cement. Thermo-gravimetric analysis was also carried out to assess the pozzolanic reaction of blended cements. The results show that blended cement concretes have lower strength than Portland cement concrete at all ages in all of the grades of concrete studied. Porosity in terms of water absorption of blended cement concretes is less than Portland cement concretes in 20 MPa concrete but was not significantly different in 30 and 40 MPa concretes. Thermo-gravimetric and differential thermal analysis reveals that there is a reduction in Ca(OH)2 content in blended concretes indicating the consumption of hydroxide in pozzolanic reaction.
Written on 19 août 2011.
A.W. Beeby, The University of Leeds, UKMany formulae for the prediction and control of crack widths in reinforced concrete members assume that the transfer length over which force is transferred by bond from the reinforcement to the concrete on either side of a crack is proportional to the parameter φ/ρeff, where φ is the bar diameter and ρeff is an effective reinforcement ratio. This paper aims to examine the validity of this assumption by comparing the predictions of the theory which leads to the derivation of the parameter φ/ρeff to data from experimental programmes where crack widths were measured. These comparisons strongly suggest that φ/ρeff has minimal influence on crack widths.
Written on 19 août 2011.
Written on 19 août 2011.
P. J. Nixon, Centre for Concrete Construction, Building Research EstablishmentK. Quillin, Centre for Concrete Construction, Building Research EstablishmentG. Somerville, Associate, Building Research EstablishmentAs the premier construction material across the world, concrete has a major determining role on the effects, good or bad, of construction on the environment. Working towards a more sustainable form of concrete construction, within an overall strategy for more sustainable construction, can, therefore, have major environmental benefits. 'Sustainable concrete construction' is, however, a multi-faceted objective and demands many diverse approaches. This paper examines how the objectives and themes of sustainable concrete construction can be met by using the concepts of service life design.
Written on 19 août 2011.
Y. Gholipour, Department of Civil Engineering, University of Tehran, IranStructures are often subjected to various types of dynamic loads and the need to accurately predict the structural response and reserve capacity under such loading has led to an interest in the properties of composite materials. Fibre reinforcement improves the dynamic behaviour of reinforced concrete and ferro cement under impact loading. This paper reports an experimental investigation of the dynamic behaviour of composite slab panels under impact loads. Impact tests were carried out on various types of fibre-reinforced cement concrete slabs and fibre-reinforced ferro-cement slabs to study the influence of fibres on the energy absorption. The response of all the above specimens were examined and compared. Analytical solutions were obtained from a finite element analysis and the results are also compared.
Written on 19 août 2011.
E. Caetano, Faculty of Engineering of the University of Porto, PortugalA. Cunha, Faculty of Engineering of the University of Porto, PortugalThis paper describes the experimental and numerical study of the dynamic behaviour of a stress-ribbon footbridge constructed at the campus of the Faculty of Engineering of the University of Porto, Portugal. This bridge has not displayed any vibration problem, as yet, but significant levels of vertical oscillation have been observed under pedestrian use. Therefore, a site observation programme was developed in order to assess the main dynamic characteristics and levels of vibration of the bridge, to compare them with limit values recommended by structural codes, and to validate a numerical model to be used in predicting the bridge response under extreme loadings.
Written on 19 août 2011.
N. Shafiq, Department of Civil Engineering, University Technology Petronas, Tronoh, Perak, MalaysiaThis study investigated the effects of fly ash on chloride migration in concrete and calculation of cover depth in order to protect the embedded steel reinforcement against the occurrence of severe corrosion. A rapid chloride migration test was conducted for determination of the coefficient of chloride diffusion. The resulting coefficient of chloride diffusion was used for calculation of minimum cover depth required for a specified service life of concrete structure. Concrete made of 40 and 50% fly ash as partial replacement of cement resulted in a lower coefficient of chloride diffusion and hence a cover depth of 75 mm or less was calculated for a specified service life of 120 years. On the other hand a higher value of the coefficient of chloride diffusion was determined for 100% ordinary Portland cement (OPC) concrete, therefore a thick concrete cover such as 150 mm was calculated for a similar life span.
Written on 19 août 2011.
A. A. Di Maio, CONICET-LEMIT, ArgentinaL. J. Lima, University of La Plata, ArgentinaL. P. Traversa, CIC-LEMIT, ArgentinaSteel corrosion is one of the main causes of damage in reinforced concrete structures. Recent studies carried out in Argentina indicate that the percentage of damage in concrete structures induced by corrosion of reinforcement is 16%. In structures located in marine environments the corrosion is due fundamentally to the action of chlorides. Chlorides penetrate concrete by different processes; in structures exposed to atmosphere, the ingress process is by diffusion. Ingress depends on the characteristics of concrete and of its distance to the sea (marine environment). In this paper, assessment of durability of concrete structures exposed to marine (Atlantic Ocean coast) environments is reported. The ages of the evaluated structures, bridges and buildings, vary between five and 67 years. Surface chlorides concentration (environmental loads) and the effective diffusion coefficient, calculated using Fick's second law, are included. Furthermore, the quality of the cover concrete is characterised by means of the specific gravity and porosity accessible to water methods.
Written on 19 août 2011.
Vijay Chandra, Parsons Brinckerhoff Quade and Douglas, Inc.Anthony L. Ricci, Massachusetts Turnpike AuthorityPaul J. Towell, Parsons Brinckerhoff Quade and Douglas, Inc.Keith Donington, Parsons Brinckerhoff Quade and Douglas, Inc.Boston, in the forefront of the American Revolution over two centuries ago, is now in the forefront of another revolution - in the field of cable-stayed bridge technology. A highly complicated structure, unique in the world, is complete. New technologies and innovations have become hallmarks of the Leonard P. Zakim Bunker Hill Bridge. This crossing of the Charles River at the north end of Boston was a challenging assignment from the start. It brought the community, engineers, and architects together to create a 'signature bridge' and a 'gateway' to the city. Located at a pre-eminent point where Paul Revere crossed in 1775, warning colonists that the British were coming, the bridge took on special meaning from a historical perspective. Numerous alternatives were studied for the crossing and the interchange configurations on both sides of the river. Eventually, the option known as the 'non-river tunnel' alternative was chosen, which required a ten-lane crossing of the Charles River. The ten lanes include four lanes each for Interstate 93 (I-93) northbound and southbound, as well as a two-lane ramp on the east side. Some impediments the bridge had to contend with included the Orange Line subway adjacent to and below the bridge; the close proximity of the Charles River lock and dam, and the need to maintain navigation; a major water main in the area of the south tower footing; a cantilevered two-lane ramp on only one side of the structure; the existing Storrow Drive ramps at the south end, dictating the arrangement of the stay cables in the back spans; and a new tunnel at the south end of the structure.
