Flexural ductility of high-strength concrete beams
L. F. A. Bernardo, Lecturer, University of Beira Interior, Covilhã, Portugal S. M. R. Lopes, Assistant Professor, FCTUC, University of Coimbra, Portugal
This paper describes an experimental study on the flexural ductility of high-strength concrete beams. Nineteen isostatic beams, simply supported, were tested in the course of this work. Two symmetrical concentrated loads were applied to the beams at intervals of approximately one-third of the span. Ductility was studied by defining certain parameters, which have been termed ductility indexes. The main variables in this study are the compressive strength of the concrete and the longitudinal tensile reinforcement ratio. The results of the tests are examined and discussed, and some conclusions are drawn. The test results were compared with recommendations suggested by codes of practice and again conclusions are drawn.
Ultimate strength of damaged post-tensioning tendons
Eva M. Eichinger, Vienna University of Technology, Institute for Structural Concrete, Vienna, Austria Thomas Petraschek, Vienna University of Technology, Institute for Structural Concrete, Vienna, Austria Johann Kollegger, Vienna University of Technology, Institute for Structural Concrete, Vienna, Austria
In order to assess the influence of the bond action between wires, injection grout and the surrounding concrete on the ultimate load of damaged post-tensioning tendons more accurately, a series of tensile tests on tendons, which were built using old wires from a demolished bridge, was carried out. Wire breakage was included in the tendons at specified patterns. The results of the test series show that tendons with damaged or broken wires are able to carry a very high percentage of the ultimate load of an undamaged tendon. Even in situations where no confinement of stirrups in the surrounding concrete is present, the load-carrying capacity of tendons with broken wires is excellent. If the distance between the wire breakages is about half the anchorage length, the decrease in strength is about 20%. The results of these tests will be used to assess the tendon strength in comparable bridge structures where damage to the tendon is likely to be present.
The vibration resistance of young and early-age concrete
Anders Ansell, Postdoctoral fellow, Department of Civil and Architectural Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden Johan Silfwerbrand, Director, Swedish Cement and Concrete Research Institute (CBI), Stockholm, Sweden
During early age, concrete is vulnerable to disturbance from vibrations of large magnitudes. Today, conservative vibration limits are used as standards, and guidelines provide little information. The literature cited in this study contains experiences and results from the construction and civil engineering field, in-situ testing, laboratory testing and computer modelling. On the basis of the reviewed literature, recommended maximum vibration levels for young and early-age concrete are given.
Investigation of temperature and strain distribution in reinforced-concrete wall of a rapeseed storage silo
K. Diamoutene, Wroclaw University of Technology, Poland M. Kaminski, Wroclaw University of Technology, Poland
The results of experimental research carried out on reinforced-concrete storage silos and of a numerical analysis of the temperature distribution in the silo wall are presented. Temperature fields in the structure were determined and the finite element method was applied to analyse the forces and moments generated by the thermal fields.
Theoretical model for the determination of plastic rotation capacity in reinforced concrete beams
R. N. F. do Carmo, Department of Civil Engineering, ISEC-Polytechnic Institute of Coimbra Portugal S. M. R. Lopes, Department of Civil Engineering, FCTUC-Polo II-University of Coimbra Portugal L. F A. Bernardo, Department of Civil Engineering, University of Beira Interior Portugal
Evaluating the ducility of reinforced concrete beams is essential in order to avoid a fragile collapse of the structure by ensuring an adequate deformation at ultimate load. This paper presents a theoretical model for the calculation of plastic rotation. Results obtained are compared with those obtained from an experimental programme in which a set of beams were tested to failure. From the comparison, a good agreement between theoretical and experimental results was achieved. The proposed theoretical model considers the influence of certain factors: steel properties, concrete strength, section depth, and the tension stiffening effect. Concrete strength, particularly, is an interesting parameter since for high-strength concrete, the ultimate concrete strain, εcu, decreases as the concrete strength increases.
This paper provides a brief overview of Session 8 'Durability of Concrete Structures' of the fib 2002 congress on Concrete Structures in the 21st Century, which was held in Osaka on 13-19 October 2002. The keynote speaker of the session, Dr Odd E. Gjørv, Professor and Head of the Department of Building Materials at the Norwegian University of Science and Technology at Trondheim, has conducted concrete research for more than 40 years. His research has focused on a broad range of topics related to the durability of reinforced and prestressed concrete structures in severe environments. His paper addressed durability and service-life issues of concrete structures. In addition to the keynote address, more than 50 papers were considered for this session, covering topics in the following areas: general issues related to concrete serviceability and durability, corrosion of reinforcement, and grouting of post-tensioned systems, as well as several case studies. The highlights of some of the papers are described here.
