Transfer zone of prestressed CFRP reinforcement applied according to NSM technique for strengthening of RC structures

Abstract

This study presents an experimental program to assess the tensile strain distribution along prestressed carbon fiber reinforced polymer (CFRP) reinforcement flexurally applied on the tensile surface of RC beams according to near surface mounted (NSM) technique. Moreover, the current study aims to propose an analytical formulation, with a design framework, for the prediction of distribution of CFRP tensile strain and bond shear stress and, additionally, the prestress transfer length. After demonstration the good predictive performance of the proposed analytical approach, parametric studies were carried out to analytically evaluate the influence of the main material properties, and CFRP and groove cross section on the distribution of the CFRP tensile strain and bond shear stress, and on the prestress transfer length. The proposed analytical approach can also predict the evolution of the prestress transfer length during the curing time of the adhesive by considering the variation of its elasticity modulus during this period.

Comparison of Prestressing Methods with CFRP and SMA Materials in Flexurally Strengthened RC Members

“…The state-of-the-art strengthening with prestressed FRP materials was published in [ 9 , 34 , 51 , 52 , 53 ]. Three main CFRP prestressing techniques were published in [ 9 ]: Externally applied reinforcement (EAR) which include both externally bonded reinforcement (EBR) and unbonded reinforcement (without adhesive between composite and concrete); the unbonded reinforcement system is much less popular, but the applications can be found in [ 47 , 54 ]; Near-surface mounted reinforcement (NSMR) [ 55 , 56 , 57 , 58 , 59 , 60 , 61 ]; Externally post-tensioned (EPT). …”

“…The flexural strengthening of RC members strengthened with pretensioned NSM FRP stirps or bars confirms the much higher efficiency of this technique compared to the passive strengthening. The main effect of pretensioning is based on the higher utilization of the tensile strength of the FRP materials, which contributes to the higher load-bearing capacity under service and ultimate load [ 55 , 56 , 57 ]. The effectiveness of the NSM method significantly depends on several factors including pretensioning level, cross-section and stiffness of FRP materials, and internal steel reinforcement ratio.…”

Flexural strengthening of pre-cracked RC slabs with prestressed NSM CFRP laminates and evaluation of strain loss

“…Furthermore, limited studies have taken into account the strain loss in prestressed NSM CFRP laminates for designing strengthening interventions (Badawi et al, 2011;Rezazadeh and Barros, 2015). For obtaining an accurate estimation of prestress level in CFRP laminates, parameters of strain loss and transfer length were investigated in the present study by executing an experimental program consisted of five series of tests including damaged and non-damaged RC slabs flexurally strengthened with prestressed NSM CFRP laminates.…”

Flexural Strength of RC Beam Strengthened by Partially De-bonded Near Surface-Mounted FRP Strip

“…In case of the strengthening of a long member, an excessive vertical deflection of FRP material may occur during the construction and it can give a negative effect in inserting the FRP into the groove and fixing it. Considering this merit, several researchers (Ali et al 2008;Seracino et al 2007a, b;Seo et al 2013;Rezazadeh and Barros 2015;Yost et al 2007;Seo 2012) have performed various experimental and analytical works about the NSM FRP retrofit to find both the bond capacity and a proper design process.…”

“…As a recent research, Rezazadeh and Barros (2015) performed an experimental work for the beams retrofitted by pre-stressed CFRP whose shape is very thin. In the manner of construction labor, the groove for vertical embedment of a thin FRP strip is little bit narrower and deeper than that for square or round one.…”