Written on 19 août 2011.
A.H. Alwathaf, Sana'a University, Yemen The characteristic behaviour and failure mechanism of a deep beam is investigated using non-linear finite-element analysis in this study. An accurate stress-strain relation is incorporated to describe the stress-strain behaviour of the concrete under compression for uniaxial and also for biaxial stress states. Material non-linearity in the compressive stress field is considered for the concrete in the orthogonal directions and the effect of microcracking confinement and softening on the stress-strain relationship under biaxial stresses are included, employing the equivalent uniaxial strain concept. A computer code FEARCB (finite-element analysis of reinforced concrete beams) is developed to analyse deep beams until failure. The applicability of the proposed finite-element model is investigated by demonstrating the non-linear structural response and failure mechanism of different deep beams and comparing with the available experimental work. Good agreement is achieved between the developed finite-element model and the experimental test results.
Written on 19 août 2011.
J. Naess, Aker Solutions AS, NorwayS.I. Giske, Aker Solutions AS, Norway L. Bjerkeli, Skanska Norge AS, Norway A concrete gravity-based structure, used as an offshore liquid natural gas (LNG) receiving and regasification terminal, has been built and installed in the Adriatic Sea. The design, construction and interfaces of the concrete structure posed many challenges which drew on expertise learnt elsewhere in the world of offshore marine concrete structures. The integration of the LNG tanks and the regasification topsides into a compact concrete structure tested the ability to produce a consistent and easily constructed solution. The resulting structure was simple, efficient, robust, durable and the first of its kind.
Written on 19 août 2011.
A.M. Ruiz-Teran, University of East London, UKUnder-deck and combined cable-stayed bridges are two relatively new bridge types that have been developed over the last 30 years. Most of these bridges have been constructed in Germany, Japan, France and Spain, and have been designed by outstanding structural engineers such as Leonhardt, Schlaich, Manterola, Virlogeux and Cremer. The main advantages of these bridge types are: their great structural efficiency; the small amount of materials that they require (allowing economic and sustainable proposals); their great construction possibilities, allowing an increase in the span range of certain construction methods; and their strong aesthetic characteristics owing to the different layouts that can be defined with the stay cables. This paper revises the structural behaviour and design criteria of under-deck and combined cable-stayed bridges, and summarises the main research contributions of the PhD thesis submitted by the author Dr Ana M. Ruiz-Teran, to whom the fib Diploma 2009 for Research (Young Engineers Award) has been recently presented for this work.
Written on 19 août 2011.
P.G. Debernardi, Politecnico di Torino, ItalyM. Taliano, Politecnico di Torino, Italy This paper reports the main results of a parametric analysis which was performed to define appropriate limits for the span-to-height ratio of prestressed concrete beams or slabs that are in compliance with the deflection control required by international standards (Eurocode 2, Model Code 1990) for concrete buildings structures. Two deflections were considered: the total deflection and the active deflection that occurs after construction, in both cases under the quasi-permanent load combination. The active deflection has to be considered when fragile elements such as partitions or glazing are present on the structure. Four structural systems were considered: simply supported fully or partially prestressed beams with an I-section and simply supported or fixed-end slabs with a rectangular cross-section. The load history first included the application of the prestress and the dead load and then the application of the remaining quasi-permanent load. Taking into account the effects of imposed deformations the structure was designed to obtain the geometrical properties strictly necessary for the ultimate limit state (ULS) and for stress limitation in service under quasi-permanent and characteristic load combinations. The results allow the influence of some of the variables that most affect the deflection to be evaluated, such as the span and the height of the beams, the concrete strength, the permanent load and the variable-to-permanent load ratio.
Written on 19 août 2011.
S. Leivestad, Standards NorwayJ. Mehus, Standards NorwayStandards are a system of tools that should be recognised by all the stakeholders in the construction industry and be used as the instrument that can provide structures that meet all societal expectations: safety, cost-effectiveness and sustainability.
Written on 19 août 2011.
S.B. Marinkovic, University of Belgrade, SerbiaV.M. Kokovic, University of Belgrade, SerbiaI.S. Ignjatovic, University of Belgrade, SerbiaV.H. Alendar, DN Engineering Consultants, Belgrade SerbiaThe structure of Delta City shopping mall in Belgrade consists of two separate structures: the structure of the mall and the structure of the multi-storey open garage. The overall dimensions of the irregular layout of the structure are 210 m x 120 m, with four main levels in the mall and five parking levels in the garage. Because of the different exposure conditions, the structure of the garage is separated from the mall's structure with an expansion joint at all of the levels, except the level of the foundation slab. The mall's framed structure is designed without any expansion joints, except for temporary joints during the construction stage. It consists mainly of reinforced concrete columns cast in place, at typical spans of 8.2 m x 8.2 m, precast reinforced concrete simple beams and precast prestressed hollow core slabs. The moment resistant reinforced concrete frames cast in place are designed mostly at the facade, to provide additional seismic resistance and to control lateral deflections. The main structure of the open multi-storey garage consists of reinforced concrete frames cast in place and precast hollow core slabs, and it is designed for exposure class XD3, with special attention paid to durability requirements. Owing to the mainly precast structure, especially the hollow core slabs as a floor solution, the complete concrete structure of approximately 80 000 m2 was constructed in less then 12 months.
Written on 19 août 2011.
S. Helland, Skanska Norge AS, NorwayR. Aarstein, Rakon AS, NorwayM. Maage, Skanska Norge AS, NorwaySince 1973 a total of 34 platforms for the oil and gas industry, representing 2 650 000 m3 high-strength concrete/high-performance concrete, have been installed in the North Sea. The structures have been closely monitored by the operating companies with regard to their in-field performance. This paper analyses chloride profiles from some 180 cores taken from ten structures after 2-26 years service. The profiles are applied to assess the remaining service life by modelling. Based on this, the remaining service life as a function of reliability for not passing a critical chloride content at the reinforcement, is directly quantified. The findings are compared with the requirements given in the present Norwegian standards for concrete works exposed to a harsh marine environment.
Written on 19 août 2011.
A. Semchenkov, Research and Development Institute for Concrete (NIIZhB), Moscow, Russia V. Meshkov, Research and Development Institute for Concrete (NIIZhB), Moscow, RussiaA. Kvasnikov, Research and Development Institute for Concrete (NIIZhB), Moscow, RussiaAt present in Russia hot-rolled reinforcing bars are mainly manufactured using two deformation (rib) patterns, either with ring-like ribs of constant height or with two-row crescent-shaped ribs of 'European' style. Steel of both grades A400C and A500C can be produced with one or other of these rib patterns. Often it is difficult to identify on site an actual grade of rebars. To improve the situation a new specific deformation pattern for A500C grade steel was developed. The rebar-to-concrete interaction for the three patterns mentioned above is evaluated by means of the analysis of failure of concrete keys formed between transverse ribs of a steel bar. For this purpose the authors employed some principles of analysis that previously had been used for key joints of concrete floor panels. The bond behaviour is subsequently classified as 'rigid' or 'soft', the latter being considered as more favourable. The structural advantages of commercial production in Russia of A500CP grade reinforcing steel using the newly developed deformation pattern are described.
Written on 19 août 2011.
H. Thun, Luleå University of Technology, Luleå, Sweden U. Ohlsson, Luleå University of Technology, Luleå, SwedenL. Elfgren, Luleå University of Technology, Luleå, SwedenA pullout test using post-installed inserts has been examined as an alternative to drilled cores to determine the in-place concrete compressive strength. Tests have been carried out on eight railway bridges from 1965 to 1980 and on a one year old concrete slab. An empirical strength relationship is proposed between the compressive strength of a drilled core with the diameter and height of 100 mm and the pullout force from the pullout test. It is a power function and the relationship is valid for concrete compressive strengths up to 105 MPa; it gives higher concrete strengths than earlier proposed functions.
Written on 19 août 2011.
R. Kumar, Indian Institute of Technology Roorkee, India B. Singh, Indian Institute of Technology Roorkee, India P. Bhargava, Indian Institute of Technology Roorkee, India In many structural applications it is desirable to use a high percentage of steel reinforcement in beams to minimise structural depth while still providing adequate stiffness. This investigation demonstrates that by confining the compression zone of an over-reinforced beam with a steel helix, considerable strength, stiffness and ductility can be achieved, even with a tension steel content as high as 4⋅79%. This is possible because the helically confined compression concrete becomes triaxially stressed during loading, leading to a high uniaxial strain capacity at an enhanced stress level. Self-compacting concrete has been used to ensure effective concreting of the over-reinforced beams. The proposed analytical approach based on the moment-curvature characteristics of the over-reinforced section gives a reasonably accurate prediction of the load-displacement behaviour of the over-reinforced beams. The serviceability limit states of cracking and deflection have been examined and the quality of the hardened self-compacting concrete in the beams has been found to be satisfactory from ultrasonic pulse velocity measurements.
Written on 19 août 2011.
O. Larsson, Lund University, SwedenEffects of surrounding climate impose temperature variations in both time and space for concrete structures. The associated thermal strains may give rise to stresses and cracking due to external or internal restraint. This will affect the performance of the structure. It is therefore important to analyse the temperature variations and the extreme situations that can occur. To predict the dynamic thermal conditions in concrete structures a finite-element model has been developed. The ability of the model to describe correctly the various boundary conditions such as solar radiation, outgoing long-wave radiation and convection is investigated in this paper. Field temperature measurements in a concrete slab placed outdoors are used for the validation. The necessary climatic input data for the model were obtained from measurements in the vicinity of the slab. The results show that the model can describe with good accuracy the effects of different climatic factors in extreme situations and is well suited to use in further studies.
Written on 19 août 2011.
A. K. Parande, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India R. H. Chitradevi, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, IndiaK. Thangavel, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, India M. S. Karthikeyan, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, IndiaB. Ganesh, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, IndiaN. Palaniswamy, Central Electrochemical Research Institute, Karaikudi, Tamilnadu, IndiaThe utilisation of calcined clay in the form of metakaolin as a pozzolan for concrete has received considerable interest in recent years. The use of metakaolin as a mineral admixture for concrete is a well-documented practice. Metakaolin is a quality enhancing pozzolan for concrete. In this review paper the work done by various researchers on the effect of the addition of metakaolin to modify the properties of concrete are documented; source and manufacture, fresh concrete properties, hardened concrete and durability. From the survey it is concluded that metakaolin enhances early strength in concrete through a filler effect. Metakaolin also enhances long-term strength and durability of concrete and corrosion resistance. Less work has been carried out in corrosion studies and some of these works are highlighted in this review paper.
