Deformations at flexural yielding of members with continuous or lap-spliced bars
Dionysis Biskinis, University of Patras, Greece Michael N. Fardis, University of Patras, Greece
Models are developed and calibrated for the moment, the chord rotation and the secant stiffness at flexural yielding of reinforced concrete beams, rectangular columns or walls and members of T-, H-, U- or hollow rectangular section, on the basis of a databank of tests on members with continuous bars. Criteria are developed for the identification of adverse shear effects on the yield moment. The models apply only to members whose yield moment is not reduced by shear effects. They employ simple, explicit expressions suitable for practical application without moment-curvature analysis. They are extended to members with bars lap-spliced starting at the end section. The effect of biaxial loading on member yielding is examined. Most of the models have been adopted in Eurocode 8, Part 3.
Experimental investigations of partially-damaged RC beams and columns
Andrew Pullen, Imperial College London, UK Ali Abbas, Imperial College London, UK
This paper summarises experimental investigations of undamaged and partially damaged reinforced-concrete beams and columns. The aim of the work was to establish and carry out experimental methods for determining the load-deformation behaviour and strength of these simple structural elements under varying levels of localised pre-damage (such as weakening or partial loss of concrete material). In particular, the effect of such partial/local damage on the overall behaviour and, crucially, its contribution to structural collapse, were also studied. There is little experimental evidence to validate predictions obtained from analysis or numerical modelling of partially damaged concrete members. Often, the ultimate capacity is the primary output of interest and it is usually determined using specimens that have no prior local damage. The present study produced data that led to a comparative study between the structural behaviour of both damaged and undamaged structural elements in order to help understand the effect of local damage and its contribution to structural collapse. The experimental results can also be used for future modelling and validation purposes.
Deformation of continuous reinforced concrete beams during patch repair
John Cairns, Heriot Watt University, UK Eoin Coakley, Conventry University, UK
This paper describes an experimental and numerical investigation examining the effect of reinforcement exposure during the patch repair process on the behaviour of continuous beams. Particular attention is paid to moment transfer and change in strain patterns during concrete breakout. The test programme embraced a range of parameters including the length and position of breakout and a variety of reinforcement arrangements. Moment transfer during concrete breakout was monitored to assess whether breakout at one location would cause overstressing in other parts of the structure. Results from tests and numerical analysis show increases in section deformations away from the breakout were small when compared to those within the breakout length. It is surmised that there is little danger of overstraining in locations away from the breakout zone while breakout does not extend past a point of contraflexure.
Concrete in high-rise buildings: practical experiences in Madrid
H. Corres Peiretti, FHECOR Ingenieros Consultores, Spain M. Gómez Navarro, MC-2, Estudio de Ingeniería, Spain
The use of concrete in high-rise buildings has increased significantly in the last 20 years mainly owing to improvement in all of the technologies associated with this material: admixtures, pumping, transportation and elevation methods, etc. These enhanced possibilities are illustrated by means of four high-rise buildings that were built recently in Madrid, each about 250 m high. The main structural elements of these buildings are presented focusing on the advantages offered by concrete compared to other materials that are commonly used in high-rise construction. The types of concrete considered are high-resistance concrete up to C80, self-compacting concrete, precast and in situ concrete, reinforced or prestressed concrete, as well as normal weight or lightweight concrete. These examples clearly show that, even in structures where the role of self weight is determinant, concrete can be the best solution if all of the different factors involved in the success of a construction site are considered: geometry, ease of construction, means of elevation, prefabrication at factory, repetitiveness, material costs, control requirements, and so on.
Flexure-controlled ultimate deformations of members with continuous or lap-spliced bars
D. Biskinis, University of Patras, Greece M.N. Fardis, University of Patras, Greece
A databank of cyclic or monotonic tests to flexure-controlled failure is used to develop/calibrate models for the curvature and the chord rotation of reinforced concrete members at flexure-controlled ultimate conditions - at a 20% post-ultimate strength drop in lateral force resistance - under monotonic or cyclic loading. Models are developed for beams, rectangular columns or walls and members of T-, H-, U- or hollow rectangular section, with or without detailing for earthquake resistance and with continuous longitudinal bars. The models employ simple, explicit expressions for practical application without moment-curvature analysis and are on the safe side for biaxial loading. They are extended to members with longitudinal bars lap-spliced in the plastic hinge region.
Anchorage of composite laminates in RC flexural beams
Francesco Micelli, University of Salento-Lecce, Italy Andrea Rizzo, University of Salento-Lecce, Italy Donatella Galati, University of Salento-Lecce, Italy
This paper focuses primarily on flexural strengthening with pre-cured fibre-reinforced polymer laminates applied on reinforced-concrete beams with different anchoring devices, both chemically and mechanically applied. The results showed that the ultimate load of the strengthened beams was 35-80% higher than the control beam, depending on the type of strengthening system applied. The lower value corresponds to the beam strengthened using carbon-fibre-reinforced polymer without anchor spikes, the use of which increased the ultimate load by about 14%. The best performance of the strengthening was obtained for the beams strengthened with the hybrid laminates: steel anchors reduced the load drop after the peak, while in the case of the hybrid system and mechanically fastened carbon-fibre-reinforced polymer, the use of the mechanically fastened system resulted in a pseudo-ductile mode of failure. The experimental results were compared with analytical results obtained from the application of recently developed guidelines, published by the Italian Research Council (CNR).
