Influence of prestress level on NSM CFRP laminates for the flexural strengthening of RC beams

Abstract

This study presents an experimental program to evaluate the influence of the prestressing technique on the flexural behavior of reinforced-concrete (RC) beams strengthened with near-surface-mounted (NSM) carbonfiber-reinforced-polymer (CFRP) laminates. The experimental program was organized to highlight the benefits of this technique for flexural strengthening of RC beams with low reinforcement ratio, susceptible of not respecting serviceability-limit-state (SLS) conditions, namely the deflection limit. For this purpose, five RC beams were fabricated to be tested under monotonic four-point loading. One beam was kept unstrengthened as a control beam, and another one was strengthened with a non-prestressed NSM CFRP laminate. The remaining beams were reinforced with a NSM CFRP laminate prestressed at 20%, 30% and 40% of its nominal tensile strength. Based on the results, applying the prestress force provided an increase of load carrying capacity corresponding to the concrete cracking and steel yielding initiations compared to the non-prestressed strengthened beam. Moreover, the influence of prestress level on the prevailing failure mode of the tested beams was assessed, and the relevant results are presented and discussed. An advanced numerical strategy was also developed to simulate the tested beams, which was demonstrated capable of being used for the design of this type of structures.

Analytical approach for the flexural analysis of RC beams strengthened with prestressed CFRP

“…In fact, applying an appropriate prestress level on the CFRP reinforcement can significantly increase the load carrying capacity corresponding to concrete cracking and steel yielding initiations, as well as an increase of the load at serviceability limit state (SLS) conditions [11][12][13]. Prestressed CFRPs can also decrease the deflection and crack width when compared to the corresponding results obtained with non-prestressed CFRPs [14,15].…”

Load-bearing capacity of flexural reinforced concrete members strengthened with fiber-reinforced polymer in fracture stage

“…8,[34][35][36][37][38][39][40] For the practical applications in the field, it is easier to prestress FRP sheets/ plates by bonding them to concrete surface (EBR) 27,[35][36][37][38][39][40] in comparison to prestressing FRP rods/strips installed into the grooves on the concrete surface (NSM). 19,22,24 Moreover, it is necessary to access the ends of the beams in order to use the prestressing devices when strengthening by NSM method. In many cases, such access is limited or not possible at all.…”

“…The experimental results are collected from different scientific publications. 19,20,[22][23][24][25][26][27] A focus is made on the assessment of crack depth of critical normal section and evaluation of FRP strainstress relationship. The stiffness of strengthened flexural RC members is reduced because of the slippage between concrete and FRP.…”

“…Generally, we can classify FRP systems into two categories: externally bonded reinforcement (EBR), when FRP sheets, plates, or strips are bonded to the surface of the concrete; and near-surfacemounted (NSM), when circular or rectangular FRP bars or strips are installed and bonded in the grooves of the concrete surface. [19][20][21][22][23][24][25][26][27][28][29][30] Seven typical failure modes could be distinguished for RC structures strengthened with FRP: 18 (1) flexural failure caused by FRP rupture, (2) flexural failure caused by crushing of compressive concrete, (3) shear failure, (4) separation of concrete cover of tensile reinforcement, (5) interfacial debonding in FRP plate end, (6) interfacial debonding caused by flexural crack in midspan of the beam, and (7) interfacial debonding caused by intermediate flexural shear crack. Failure mode caused by FRP rupture (mode 1) is appreciated, because, in such case, the full strength of FRP would be used.…”

Concrete-Filled-Large Deformable FRP Tubular Columns under Axial Compressive Loading

“…The finite element results of these studies agreed with the experimental results with reasonable accuracy. For unconfined concrete material, the dilation angle is usually taken between 36° to 40° with an average value of 38° [21][22][23].…”