PERFORMANCE OF WEAK-BEAM, STRONG-COLUMN RC FRAMES STRENGTHENED AT THE JOINTS BY FRP

Despite  the  large  volume  of  work  reported  on  the  behaviour  of  reinforced  concrete joints, only a few studies have been carried out to investigate the influence of retrofitting joints by FRP  composites  on  the  overall  behaviour  of  an  RC  frame. To  study  the  seismic  performance  of Moment  Resisting  RC  frames  retrofitted  at  joints  by  FRP,  experimental  and  numerical investigations  are  carried  out  on  a  scaled-down  frame  of weak-beam,  strong-column  type, retrofitted  by  applying  the  FRP  laminates  at  the  web  of  the  joints.  Representing  constitutive models are used to introduce the behaviour of concrete, steel and fibre-reinforced polymers in the numerical  investigation.  Full  post-peak  behaviour  of  the  joints  is  captured  considering  strain softening of concrete. Finite element results show good agreement with the experimental findings. It  is  found  that  the  maximum  load  carrying  and  displacement  capacities  of  the  joint  after strengthening  are  increased  and  that  the  first  steel  yielding  and  development  of  crack  occur  at higher loads, further away from the joint, into the beam. The effects of different values of fracture energies  on  the  behaviour  of  the  reinforced  concrete  joint  are  also  investigated.  Nonlinear pushover  analyses  are also  carried  out to  predict  the  seismic  performance  of  an  eight-storey  and two additional low-rise frames retrofitted by steel braces and FRP. It is shown that by using FRP laminates at the web of the joints, the stiffness, the behaviour factor, R, performance level and the lateral load-carrying capacity of the damaged/plain frame are markedly increased.