A uniaxial cyclic model for confined and unconfined concrete is developed. Starting from an existing model, the cyclic rules to define inelastic strain and degradation of strength and stiffness are first reviewed and then modified to produce a new concrete model with enhanced performance. Comparisons at the stress-strain level between the new and existing concrete models reveal the adequacy of the new model in terms of numerical stability and increasing degradation of strength and stiffness under increasing cyclic strain. The proposed model is validated by comparing analytical predictions with experimental results of reinforced concrete members under cyclic and dynamic loading. Good agreement is observed between analysis and experiments, confirming the ability of the model to predict the cyclic and dynamic behavior of reinforced concrete members with mixed axial-flexural response characteristics.

Confined concrete model under cyclic load

Seismic Design, Assessment and Retrofitting of Concrete Buildings

Fiber-reinforced polymer composites in strengthening reinforced concrete structures: A critical review

Fiber-reinforced polymer (FRP) composites are extensively used in advanced concrete technology given their superiority over traditional steel reinforcements. These materials possess high strength capacity and corrosion resistance and can be employed as the main reinforcements in combination with adhesives and anchorages to strengthen reinforced concrete (RC) beam members. RC beams are designed to provide resistance against flexure , shear, torsion, fatigue, impact, and blast loading. The strength and ductility of RC beams can be improved via FRP strengthening techniques with a combination of fibers. The overall strength of FRP composites in RC beams is controlled by fiber type , configuration, and materials and strengthening technique. This review focuses on the characteristics and behaviors of FRP-strengthened RC beams under various loading conditions. It also presents the typical FRP composites with the properties, features, and applications. This review demonstrates that FRP composites can be used to recover the strength of damaged and corroded beams and exhibit good durability and insulation performance. It also provides a straightforward perspective of strengthening and retrofitting techniques for RC beams using FRP composites.

Strengthening of reinforced concrete beams by using fiber-reinforced polymer composites: A review

The use of a new type of reinforced concrete (RC) jacket for RC exterior beam-column connections damaged by seismic excitations is addressed and experimentally investigated. The proposed jacket has very small thickness and includes small diameter steel reinforcement. This jacketing applies at the joint region and at a small part of the columns and the beam. The main advantage of the proposed thin and locally applied jacket compared with the commonly used concrete jacket is the fact that its application is not restrained by space limitations, and since it slightly changes the initial size of the elements, the building's dynamics and seismic behaviour remain practically unaffected. For the needs of this study, 10 exterior beam-column joint subassemblages were constructed and subjected to increasing cyclic loading. Later, the damaged specimens were locally retrofitted using the proposed thin RC jackets and they were retested with the same load sequence. Three different specimen configurations with various amounts of shear reinforcement in the joint area were examined and two types of jackets (a) with light and (b) with dense reinforcement were applied. Test results indicated that the seismic performance of the retrofitted specimens was fully restored and in some cases substantially improved with respect to the performance of the same specimens in the initial loading, since they exhibited higher values of load capacity and hysteretic energy dissipation. Discussion for the conditions of the use of the examined jacketing techniaue either as a repair or as a strengthening method is also included.

Local retrofit of exterior RC beam–column joints using thin RC jackets—An experimental study

The scope of this study is to present results of an experimental investigation on the behaviour of critical external beam–column joints repaired or/and strengthened with a combination of epoxy resin injections and carbon-fibre-reinforced plastics (C-FRP) sheets and to extract useful and practical conclusions. The experimental program comprises 12 external beam–column joint connection subassemblages tested in cyclic loading. From the observed responses of the examined specimens it can be deduced that the technique of epoxy resin injections is appropriate for the total rehabilitation of the joints seismic capacity, since no damages have been observed at the joint area of the specimens after the repair. The combination of this technique with the use of C-FRP sheets leads to a significant improvement of the loading capacity, the energy absorption and the ductility and finally it leads to improved type of damages compared with the damage modes of the specimens during the initial loading. Shortcomings of the application of C-FRP sheets for practical use are also pointed out. Copyright © 2008 John Wiley & Sons, Ltd.

Strengthening and rehabilitation of RC beam–column joints using carbon-FRP jacketing and epoxy resin injection

The influence of masonry infills with openings on the seismic performance of reinforced concrete (R/C) frames that were designed in accordance with modern codes provisions is investigated. Two types of masonry infills were considered that had different compressive strength but almost identical shear strength. Infills were designed so that the lateral cracking load of the solid infill is less than the available column shear resistance. Seven 1/3 – scale, single–story, single–bay frame specimens were tested under cyclic horizontal loading up to a drift level of 40%. The parameters investigated are the opening shape and the infill compressive strength. The assessment of the behavior of the frames is presented in terms of failure modes, strength, stiffness, ductility, energy dissipation capacity, and degradation from cycling. The experimental results indicate that infills with openings can significantly improve the performance of RC frames. Further, as expected, specimens with strong infills exhibited better ...

Influence of masonry strenght and openings on infilled r/c frames under cycling loading

The influence of the structural pounding on the ductility requirements and the seismic behaviour of reinforced concrete structures designed to EC2 and EC8 with non-equal heights is investigated. Special purpose elements of distributed plasticity are employed for the study of the columns. Two distinct types of the problem are identified: Type A, where collisions may occur only between storey masses; and Type B, where the slabs of the first structure hit the columns of the other (72 Type A and 36 Type B pounding cases are examined). Type A cases yielded critical ductility requirements for the columns in the pounding area mainly for the cases where the structures were in contact from the beginning of the excitation. In both pounding types the ductility requirements of the columns of the taller building are substantially increased for the floors above the highest contact storey level probably due to a whiplash behaviour. The most important issue in the pounding type B is the local response of the column of the tall structure that suffers the hit of the upper floor slab of the adjacent shorter structure. In all the examined cases this column was in a critical condition due to shear action and in the cases where the structures were in contact from the beginning of the excitation, this column was also critical due to high ductility demands. It can be summarized that in situations of potential pounding, neglecting its possible effects leads to non-conservative building design or evaluation that may become critical in some cases. Copyright © 2004 John Wiley & Sons, Ltd.

Earthquake‐induced interaction between adjacent reinforced concrete structures with non‐equal heights

The behaviour under torsion of reinforced concrete beams with steel fibres as mass reinforcement is experimentally investigated. Short hooked-ended steel fibres with aspect ratio lf/df = 37.5 are used. Test results of 35 beams with rectangular, L-shaped and T-shaped cross-sections tested in pure torsion are presented and discussed. Various configurations of conventional and fibre steel reinforcement are examined. The experimental program includes (i) plain concrete beams (control specimens), (ii) specimens with longitudinal reinforcing bars and (iii) specimens with bars and stirrups. All cases are examined with 0%, 1% and 3% steel fibre volume fractions. The use of steel fibres as the only shear torsional reinforcement is also reported herein, in an attempt to examine the effectiveness of fibres as a potential replacement of stirrups. Test results indicated that fibrous concrete beams exhibited improved overall torsional performance with respect to the corresponding non-fibrous control beams. The addition of steel fibres was essential to the tested beams without or with inadequate conventional steel reinforcement. Fibres prevented the sudden brittle failure of both rectangular and non-rectangular beams and proved to be under some circumstances adequate to provide for enhanced torsional moment capacities, even in the case of full replacement of stirrups with steel fibres.

Chris G. Karayannis

Papers

Local retrofit of exterior RC beam–column joints using thin RC jackets—An experimental study

Strengthening and rehabilitation of RC beam–column joints using carbon-FRP jacketing and epoxy resin injection

Influence of masonry strenght and openings on infilled r/c frames under cycling loading

Earthquake‐induced interaction between adjacent reinforced concrete structures with non‐equal heights

Effectiveness of the use of steel fibres on the torsional behaviour of flanged concrete beams