PSI - Issue 44

Guadagnuolo M et al. / Procedia Structural Integrity 44 (2023) 942–949 Guadagnuolo et al. / Structural Integrity Procedia 00 (2022) 000–000

943

2

Nomenclature d b

outside diameter of bar effective embedment length

L eff

S b

lateral hole surface

concrete compressive strength

f c

bond strength bar strength

f bd

N bar N Rs N exp

theoretical pull-out force experimental pull-out force

τ

stress due to theoretical pull-out force stress due to experimental pull-out force

τ *

A simple and widespread method for designing strengthening with bars and evaluating its effectiveness is the pull-out test. These tests can be carried out according to different methods, and conditions (Barros 2011; Deng et al. 2022), even if, each one shows advantages or limitations(Sadeghi and Sharma 2019). Commercially available FRP bars consist of glass (GFRP), carbon fibres (CFRP), aramid (AFRP), or basalt (BFRP) fibres, immersed in (mostly) thermosetting polymer matrices. They have different cross-sections (rectangular, round, solid, or hollow) and are made mainly by pultrusion processes, which may be followed by stages of braiding or weaving of transverse filaments of fibres around the cross-section to produce systems that provide better bar-cement conglomerate adhesion (Ascione et al. 2020). The possibility of using many types of bars explains why there is still no comprehensive and exhaustive standard regulation for the design and testing of FRP anchorages in concrete. Moreover, it is also mandatory to determine the behavior of non-standardized commercial bars (Baena et al. 2009). EOTA (2010) meets many requirements for construction and design practices for it, while EN 1504-6 (2007) seems to be inadequate (Fuchs and Hofmann 2021). A complex three-dimensional stress field characterizes their bonding behavior (Barbieri et al. 2016; Greco et al. 2015), and 2D numerical analyses are not adequate to explain the experimental evidence. In addition, the groove geometry significantly affects the bond line strength and the associated failure mode (Mosallam et al. 2022), as well as the relative width of FRP and concrete and the scaling effect (Hariyadi et al. 2017) strongly influence the strength of the system. Further experimental and numerical investigations therefore still seem necessary. 2. Highlights of available research 2.1. Support 2.1.1. Concrete Many authors (Benmokrane et al. 1996; Kanakubo et al. 1993; Larralde and Silva-Rodriguez 1993) investigated the bond stress transfer between FRP bars and concrete using a pull-out test, but too many parameters influence this mechanism (Achillides and Pilakoutas 2004; Li and Xian 2020; Kang et al. 2022; Kim 2021; Malvar 1994). An example is the existing condition of the concrete element (Fuchs & Hofmann 2021). Several authors (Baena et al. 2009; Brown et al. 2021; Mazhorova et al. 2021) have shown that the influence of the rebar surface treatment depends not only on the concrete strength but also on the width, thickness, spiral spacing, bar diameter (Hammerl et al. 2021), degradation due to exposure to various chemical environments (Tomasz et al. 2022), and time scale (Boumakis et al. 2022). The presence of stirrups (the confined effect) is instead related to pullout failure with greater ductility and higher bond strength and corresponding slip (Gao et al. 2019). Fiber properties have a major influence on the effectiveness of anchorages (Clarke et al. 2021; Lengsfeld et al. 2020), and are highly dependent on the manufacturing method. For example, the impregnation rate and the temperature affect the mechanical properties of epoxy-based carbon fiber pultruded bars (CFRPs) (Kang et al. 2022; Li and Xian 2020). A specifically closed winding (GFRP-CW) eliminates defects and allows for full utilization of