18-04-2012, 10:37 AM
RETROFITTING OF REINFORCED CONCRETE STRUCTURES USING WRAPPING TECHNIQUE
RETROFITTING OF REINFORCED CONCRETE.pdf (Size: 629.42 KB / Downloads: 265)
INTRODUCTION TO SEISMIC STRENGTHENING
Seismic evaluation and assessment have been addressed in a comprehensive way in a number of
publications (ATC-40, 1996; Bulletin 24, 2003; FEMA-310, 1978; FEMA-356, 2000; SERC-IITDST
Manual, 2005). Improved detailing procedures have been formulated for reinforced concrete
structures under seismic motion (IS:13920, 1993). Repair and retrofitting of concrete structures have
been attracting the attention of researchers over the last two decades. The various repair/retrofit
options available today include crack injection, shortcreting, steel jacketing, steel plate bonding,
CFRP/GFRP jacketing, RC jacketing, addition of new structural elements (braces, walls, etc.),
incorporation of passive energy dissipating devices, and provision of base isolation. Retrofitting can
be at the system level or at the local level. Introduction of additional shear wall, braces, base isolation
etc., to enhance the performance of a structure belong to the former category, while repair of a beam
or column element using various jacketing techniques, such as jacketing using micro-concrete, steel,
carbon fibre reinforced plastics (CFRP) and glass fibre reinforced plastics (GFRP) essentially fall
under the category of local retrofitting. Repair and retrofit techniques can be used for enhancing the
stiffness, the strength, and/or ductility.
Conventional Detailing
A number of beam-column joints have been tested using CFRP and GFRP wrappings. Schematic
diagram of loading on beam-column joint is shown in Fig. 4, and the reinforcement details are given
in Fig. 5. The load-deflection diagrams of various beam-column joints tested are shown in Figs. 6
and 7. Fig. 8 gives the failure of a typical beam-column joint strengthened with CFRP wrap. The
details of the beam-column joints tested are given in Table 3.
CONCLUSION
The need for evaluating the various repair strategies for use in improvement of seismic performance
of reinforced concrete structures has been highlighted. The behaviour of repaired beams and beam
column joints has been discussed. It is observed that inherent deficiencies in detailing in beamcolumn
joints get reflected even after repair, though the performance factors indicate significant
improvement. There is a need to evolve suitable performance factors when the system shows a
negative stiffness. Two of the logical extensions show the repair would not be as effective in these
cases.