Extreme strength criterion and design of RC elements
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.
Concrete structure ownership and management: part 2
S. L. Matthews, Building Research Establishment, UK J. Jacobs, Technial Approvals and Standardisation Division, BBRI, Belgium I. Stipanovic Oslakovic, Civil Engineering Institute of Croatia, Zagreb, Croatia D. J. Cleland, Queen's University, Belfast, UK
With 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)
Design equation for predicting fire resistance of reinforced concrete columns
V.K.R. Kodur, Michigan State University, East Lansing, MI, USA N. K. Raut, Michigan State University, East Lansing, MI, USA
An 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.
Concrete structure ownership and management: part 1
S. L. Matthews, Building Research Establishment, UK J. Jacobs, Technial Approvals and Standardisation Division, BBRI, Belgium I. Stipanovic Oslakovic, Civil Engineering Institute of Croatia, Zagreb, Croatia D. J. Cleland, Queen's University, Belfast, UK
With 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.
Information-based formulation for Bayesian updating of the Eurocode 2 creep model
W. Raphael, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, Lebanon R. Faddoul, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, Lebanon D. El-Asmar Selouan, École Supérieure d'Ingénieurs de Beyrouth, St. Joseph Univeristy, Riad El Solh Beirut, Lebanon A. Chateauneuf, LGC-UBP Polytech Clermont Ferrand, Aubière, France
The 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.
Peeling failure in beams strengthened by plate bonding. A design proposal
E. Oller Ibars, Civil Engineering School, Technical University of Catalonia, Barcelona, Spain D. Cobo del Arco, Tec-Cuatro, SA, Barcelona, Spain A. R. Marí Bernat, School of Civil Engineering, Technical University of Catalonia, Barcelona, Spain
Existing 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.
