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Title: Bonded Laminates for Retrofitting of Reinforced Concrete Beams
Authors: Bansal, Prem Pal
Supervisor: Kumar, Maneek
Kaushik, S. K.
Keywords: Retrofitting, Laminates,Ferrocement, Beams, Concrete
Issue Date: 9-Sep-2008
Abstract: The RCC structures constructed these days suffer damage due to a large number of factors like improper design, faulty construction, overloading, change in codal provisions, non-engineered construction, explosions, wear and tear, earthquake, fire etc. A major part of the funds used in the construction industry is being spent on repair, retrofitting and rehabilitation of such structures. Retrofitting is different from repair or rehabilitation. It is basically a process of strengthening and enhancement of the performance of deficient structural elements in a structure or of the structure as whole. The extent of damage to a structure can be assessed with the help of modern non-destructive testing techniques and methods. Once it is established that a structural member is unable to resist the design loads, the structure has to be repaired/strengthened to make it functional. The repairing or strengthening of existing structures poses higher challenge to a civil engineer in comparison to design and construction of new structures. Specific technology has to be designed and developed to rehabilitate the damaged structures, and to improve the performance for new functions, of old undamaged structures. Thus, the technique to be used should be simple in execution; offer better performance when handled by less experienced workers, and must use materials that are readily available, durable, strong and economical. Retrofitting of deficient buildings can be done by increasing the strength, stiffness and/or ductility of its specific constituent elements or of the whole building. For any building, depending upon the requirement, a combination of the above may also be selected. Retrofitting of individual members or elements is referred to as local retrofitting. This retrofitting technique is normally adopted when, after the evaluation, only a few of the building’s elements are found to be deficient. For local repair and retrofitting a large number of techniques are being used. These include injection techniques, shotcreting, removal and replacement technique, external pre-stressing, plate bonding etc. Of all the above techniques plate bonding has been found to be the most effective and a very convenient method. In the plate bonding technique too, use of Fibre Reinforced Polymer (FRP) laminates has gained lot of popularity in the last decade or so. But FRP lamination requires a lot of skill and its initial cost is very high. As a substitute various authors have suggested the use of ferrocement jacketing as a more attractive option in place of FRP plate bonding due to its easy application, improved tensile strength, lesser weight, economical use, higher impermeability, and long life of the treatment. In the present study, an effort has been made to study the effect of ferrocement jacketing on the strength of retrofitted beams. The studies have been carried out for various combination’s of parameters like type of bonding agents, orientation and type of wire mesh, number of layers of wire mesh in the ferrocement jacket, initial stress level, and type of beam sections (under reinforced or balanced section). The effect of these parameters on the strength of reinforced concrete beams initially stressed in flexure to pre-determined levels, and subsequently retrofitted with jackets was investigated. A design methodology for the retrofitting of stressed beams, using a mathematical model developed based on the limit state design procedure, is provided and verified with the data generated from testing. A similar set of beams was also retrofitted using the GFRP jackets with orientation of fibres at 00 and 450 to the longitudinal axis of the beam, to study the behaviour of such beams. Some of the major conclusions drawn based upon the study are as follows: 1. GFRP jackets used for retrofitting of the under reinforced beams perform better with fibres at forty-five degree to the longitudinal axis of the beam. 2. The strength of the section decreased with increase in initial stress level. The maximum load carrying capacity of the retrofitted beams decreased due to decrease in stiffness of section with increase in initial stress level. 3. GFRP jacketing leads to improvement in energy absorption capacity of all the type of beams irrespective of the type of section (under reinforced or balanced) and orientation of fibres in the jackets. 4. Cement slurry is the most efficient plate bonding agent due to its low cost to strength ratio. 5. Welded wire mesh with forty-five degree orientation to the longitudinal axis significantly improves the load carrying capacity of the retrofitted reinforced concrete beams. 6. Woven wire mesh used for ferrocement jacketing of beams should be preferred over welded wire mesh due to larger improvement in load carrying capacity, ductility ratio and energy absorption. 7. Ferrocement jacketing leads to an improvement in the energy absorption capacity of all type of beams irrespective of the type of section (under reinforced or balanced) and reinforcement in the jackets. 8. The percentage increase in the load carrying capacity of beams retrofitted using ferrocement jackets, increase with an increase in percentage reinforcement in the jackets. 9. The percentage increase in the load carrying capacity of beams retrofitted using ferrocement jackets, decreases with an increase in the initial stress level and with increase in tension reinforcement in the unretrofitted beam. 10. The mathematical procedure proposed in the study can be efficiently used to predict the maximum and safe load carrying capacities of the initially stressed retrofitted beams.
Description: Ph. D.
Appears in Collections:Doctoral Theses@CED

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