Written on 19 août 2011.
G. Bertagnoli, Politecnico di Torino, Italy G. Mancini, Politecnico di Torino, Italy Many experimental campaigns on hollow core slabs put into evidence critical shear behaviour of such structures. Widespread perplexities on the actual shear resistance of such members took place in the scientific community when the results of these experimental campaigns were published. As a first result the model proposed in the Model Code 90 and in the Eurocode to evaluate the uncracked shear capacity of prestressed elements was supposed to overestimate the real ultimate strength of the members. A more careful interpretation of the shear design of such structures is presented in this paper and shows that there is no safety risk if these slabs are designed with care. The ultimate behaviour of hollow core slabs mainly subjected to shear actions is related to many different phenomena such as prestressing dispersion, anchorage of prestressing strands, cracking bending moment and, of course, shear resistance. The mutual interaction of such phenomena asks for a multi-criteria design approach which is presented in the following and which gives very good results when compared to experimental campaigns output.
Written on 19 août 2011.
V. P. Mitrofanov, Poltava National Technical University, Ukraine This paper presents an improved design of reinforced concrete elements (RCE) subjected to flexure and eccentric compression or tension. The disadvantages of the traditional deformational strength criterion of concrete as confirmed by experimental data are noted. Emphasis is put on the difficulties in determining ultimate concrete strain experimentally, as well as in accounting for the influence of many conditions and factors. To remove these disadvantages, the extreme strength criterion (ESC) is proposed and used. The ESC expresses the determination of the maximum load parameter as a function of the extreme fibre compression compressive strain ecu in a RCE section at failure. On the basis of the ESC, a new general design method is developed for RCEs under bending and eccentric compression/tension. In addition to the constitutive relations for concrete and steel, the plane sections hypothesis and the balance equations, the proposed method includes the ESC, which replaces the traditionally used concrete strength criterion. The advantages of the proposed method are demonstrated to be generality, completeness, exactness, reliability and systematic accounting of a large number of factors. The proposed method does not require the experimental determination of the ultimate concrete strain, because the ecu is found during solution of the RCE strength problem as one of the unknowns of the equation system.
Written on 19 août 2011.
L. da Conceição Domingues Shehata, Universidade Federal Fluminense, Niteroi, BrazilA. Lopes de Paula, Engevix, Rio de Janeiro, BrazilI. Abd El Malik Shehata, COPPE - Universidade Federal do Rio de Janeiro, Rio de Janeiro, BrazilThe use of high-strength concrete (HSC) is more advantageous in structural elements under compression and the compressive stress-strain relationship is a relevant characteristic of the concrete required for behaviour analysis and design of those elements. For cross-section design, the codes of practice usually allow curved-rectangular and/or simplified rectangular idealised concrete stress blocks. Comparisons between idealised concrete stress blocks of different codes are presented and examples of their influence on the cross-section theoretical axial load-bending moment interaction diagram are given in this paper. The theoretical strengths obtained considering those compressive stress diagrams for the concrete are compared with experimental strengths of 403 elements subjected to pure axial load or to combined axial load and bending moment. Besides the cross-section type (square or rectangular), the elements had the variables of dimensions, steel and concrete strengths, load eccentricity and reinforcement ratios and configuration. The analysis of the comparisons between experimental and theoretical strengths considering different stress diagrams for the concrete under compression provides an insight to the level of safety related to the different design procedures, which is highly relevant for those who want to design HSC structures.
Written on 19 août 2011.
S. L. Matthews, Building Research Establishment, UKJ. Jacobs, Technial Approvals and Standardisation Division, BBRI, BelgiumI. Stipanovic Oslakovic, Civil Engineering Institute of Croatia, Zagreb, CroatiaD. J. Cleland, Queen's University, Belfast, UKWith correct design, specification and construction, concrete structures provide high-performance durable assets with long service lives. Owners can maximise the benefits to be gained from concrete structures, while minimising through-life cost and sustainability impacts, by taking a through-life perspective on the design, specification and management of their structures; rather than simply focusing on first cost. This second part of a two-part paper provides an overview of the advice given in the fib guide to good practice entitled Concrete Structure Management - Guide to Ownership and Good Practice (fib Bulletin 44)
Written on 19 août 2011.
V.K.R. Kodur, Michigan State University, East Lansing, MI, USAN. K. Raut, Michigan State University, East Lansing, MI, USAAn empirical equation for evaluating the fire resistance of reinforced concrete (RC) columns is presented. Data from a large set of experimental studies are analysed to study the influence of various parameters on the fire resistance of RC columns. The fire test data are utilised to develop a simplified equation for expressing the fire resistance of RC columns as a function of influencing parameters. The validity of the equation is established by comparing the predictions from the empirical equation with data obtained from fire resistance experiments and analytical studies. Predictions from the proposed equation are in good agreement with the test results and computer models, and provide better estimates of fire resistance than those predicted from current codes of practice. The proposed equation also incorporates parameters such as load eccentricity, which is not included in the current equations available in the literature. Furthermore, the proposed equation expresses the fire resistance in terms of conventional structural and material design parameters, and thus facilitates easy calculation of fire resistance.
Written on 19 août 2011.
S. L. Matthews, Building Research Establishment, UKJ. Jacobs, Technial Approvals and Standardisation Division, BBRI, BelgiumI. Stipanovic Oslakovic, Civil Engineering Institute of Croatia, Zagreb, CroatiaD. J. Cleland, Queen's University, Belfast, UKWith correct design, specification and construction, concrete structures provide high-performance durable assets with long service lives. Owners can maximise the benefits to be gained from concrete structures, while minimising through-life cost and sustainability impacts, by taking a through-life perspective on the design, specification and management of their structures; rather than simply focusing on first cost. This first part of a two-part paper provides an overview of the advice given in the fib guide to good practice entitled Concrete Structure Management - Guide to Ownership and Good Practice (fib Bulletin 44): the paper deals with general issues associated with concrete structure ownership, giving owners an insight into their responsibilities and obligations, what they should do and seek to achieve in the context of concrete structure management, and information regarding potential deterioration mechanisms and the merits of adopting proactive as opposed to reactive structure management.
Written on 19 août 2011.
W. Raphael, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, LebanonR. Faddoul, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, LebanonD. El-Asmar Selouan, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, LebanonA. Chateauneuf, LGC-UBP Polytech Clermont Ferrand, Aubière, FranceThe disparity between theoretical and experimental results reveals that the creep of concrete is often underestimated by most, if not all, codes of design; this is particularly true in the case of Eurocode 2. Thus it is necessary to calibrate the present code models. Bayesian-type inferences turn out to be an especially suitable tool for the work needed in revising and updating design codes. This is by virtue of their capability to incorporate additional information resulting from current practice and research so as to improve existing models. In this paper, corrective coefficients are proposed for the Eurocode model, allowing better estimation of the long-term creep of concrete. To achieve this aim, the authors rely on a large database of experimental results compiled by collecting data from several research institutions in Europe. Two descriptive statistical methods are applied in order to compare the experimental results from the above-mentioned database with results calculated using the Eurocode 2 model for the same input parameters. A Bayesian-type statistical inference is then performed to evaluate the corrective coefficient for different categories of concrete strengths using various prior distributions. The approach presented here has proven to be an effective and systematic framework for the consideration of all possible types of uncertainties in model calibration. The results obtained are very interesting for engineers involved in design and supervision of structures. The adoption of such a design approach would improve long-term serviceability of structures subjected to creep.
Written on 19 août 2011.
E. Oller Ibars, Civil Engineering School, Technical University of Catalonia, Barcelona, SpainD. Cobo del Arco, Tec-Cuatro, SA, Barcelona, SpainA. R. Marí Bernat, School of Civil Engineering, Technical University of Catalonia, Barcelona, SpainExisting experimental research has shown that the application of externally bonded laminates to strengthen reinforced concrete (RC) structures can lead to brittle failures involving debonding of the laminate before the design load is reached and a classical failure mode occurs. In an externally bonded RC beam, this peeling failure can initiate either near mid-span owing to the effects of flexural or shear cracks, or at the laminate end as a result of stress concentration at the laminate cut-off point. The design procedure to obtain the laminate area to strengthen a RC element should avoid these premature peeling failures. Therefore, there is a need to understand the mechanics of the laminate debonding process in order to prevent it. The evolution of the debonding process can be analysed by using non-linear fracture mechanics assuming a bilinear constitutive law for the interface. The crack propagation process is described through the evolution of different stages, in which the interfacial shear stresses can be obtained. As the transfer of stresses from laminate to concrete through the interface is a critical parameter in the correct performance of externally bonded structures, the transferred force should be limited to a maximum value in order to prevent peeling failure. A shear-bending interaction diagram based on this maximum transferred force associated with peeling failure is the main point of the design proposal presented in this paper.
Written on 19 août 2011.
Written on 19 août 2011.
H. Y. Leung, Hong Kong College of Technology, Hong KongA. Nadeem, Hong Kong College of Technology, Hong KongG. K. W. Tse, Hong Kong College of Technology, Hong KongThis paper examines the water permeability and chloride penetrability of self-compacting concrete with fly ash and silica fume as admixtures. The influence of 28-day concrete strength on concrete permeability is also investigated. It was found that addition of fly ash and silica fume was effective in reducing the concrete permeability. Most self-compacting concrete specimens showed low to very low water permeability and chloride penetrability. Test results also indicated that the 28-day concrete strength should not be used as an indicator for concrete permeability.
Written on 19 août 2011.
S. Hetland, Aker Solutions, Lysaker, NorwaySakhalin II is an integrated oil and gas development in the Russian Far East. It involves the installation of a large offshore platform at the Piltun sector of the Piltun-Astoskhskoye field (PA-B) and a single large platform at the Lunskoye gas field (LUN-A). These platforms, together with the existing Molikpaq drilling and production platform, are equipped to export their output by pipeline to Sakhalin. From here it is transported by way of an onshore link of 800 km to Prigorodnoye, Aniva Bay at the south of the island, which is the location for a major liquefied natural gas (LNG) storage facility and terminal, and oil handling terminal. The two fields contain an estimated 1.2 billion barrels (190 000 000 m3) of crude oil and 500 billion m3 of natural gas. Output is scheduled at up to 9.6 million of LNG per year and about 180 000 barrels per day (29 000 m3/day) of oil. The project partners are Gazprom (50% plus one share), Shell (27.5%), Mitsui (12.5%) and Mitsubishi (10%). The GBS contracts were issued on 1 July 2003 and both platforms were installed during the summer of 2005.
Written on 19 août 2011.
