# Structural Behavior of Large-Scale I-Beams with Combined Textile and CFRP Reinforcement
## 2 Experimental Investigation: Materials and Methods  
### Reinforcement  
For the experimental part in this study, various non-metallic reinforcement types were combined to make use of their individual strengths. The main reinforcement in the tension flange of the I-shaped beams was a non-prestressed CFRP rebar (Figure 1c, and Table 2) with milled helix ribs. As shear reinforcement, an epoxy-impregnated biaxial carbon grid was utilized. This type of reinforcement is pre-impregnated and pre-hardened by the manufacturer. Figure 1a shows the open structure of the symmetrical reinforcement with a 38 mm axial spacing of the yarns in both directions. Pre-formed textile grids made of CFRP (Figure 1b) or alkali-resistant (AR-) glass (GFRP) served as reinforcement of the flanges. Both had the same mesh geometry as the planar shear reinforcement. As the yarns were fully impregnated, a homogeneous stress distribution over the cross-section with full activation of all filaments can be assumed, while non-impregnated \"dry\" yarns would exhibit different behavior, with telescopic failure and inhomogeneous stress distribution [33]. Thus, in the present case, material characteristics (strength, modulus of elasticity) can be tested on individual yarns extracted from the grid without surrounding concrete [34]. Key properties are listed in Table 1. The ultimate stress and modulus of elasticity were analyzed in uniaxial tension tests on individual yarns according to the setup described in [35]. It should be highlighted that, due to the well-known statistical effects for a bundle of linear-elastic yarns with brittle failure, the strength of an individual yarn underestimates the strength of the fabric [36; 37]. For the textile reinforcement in this study, [PERSON] proposes a reduction factor of 0.85 [34; 38] for \(n\) -> \(\infty\) yarns. The bond properties of the textile reinforcement were analyzed in a previous study [39; 40]. The complete epoxy impregnation enables form closure with splitting of the concrete as primary bond mechanism. This is different from non- or incompletely impregnated textiles with failure mechanisms such as pull-out and jamming of the yarns [41]. The bond strength is highly dependent on local yarn geometry. Resulting from the production process of the pre-formed grids, individual filaments are less straight than in planar grids. This results in a higher waviness, as can be seen in Figure 1a,b. As a consequence, higher form closure and higher tendency for splitting [42; 43; 44] occur. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Characteristic**} & \multicolumn{1}{c}{**Unit**} & \multicolumn{1}{c}{**Carbon**\({}^{*}\)} & \multicolumn{2}{c}{**AR-Glass**\({}^{*}\)} \\ \hline  & & **(\(\boldsymbol{0^{\circ}}\))** & **(\(\boldsymbol{0^{\circ}}\))** & **(\(\boldsymbol{0^{\circ}}\))** \\ \hline Modulus of elasticity & [MPa] & 244,835 & 243,828 & 70,843 & 74,618 \\ Mean ultimate stress & [MPa] & 3221 & 3334 & 1590 & 1599 \\ \((n=200)\)\({}^{*}\) & \((n=218)\)\({}^{*}\) & \((n=448)\)\({}^{*}\) & \((n=477)\)\({}^{*}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Reinforcement characteristics for impregnated planar carbon and alkali resistant (AR)-glass grid (properties of one individual yarn, from [34] with test setup according to [35]). Figure 1: Reinforcement types: (**a**) Planar biaxial carbon fiber reinforced polymer (CFRP) grid; (**b**) pre-formed CFRP grid; (**c**) CFRP rebar with milled ribs. In preparation of the large-scale tests, uniaxial tensile tests on the main CFRP rebar were conducted to verify the manufacturer's specifications. While test procedures for FRP elements exist (e.g., [45; 46]), they were typically developed for glass-fiber reinforced polymer bars. With higher fiber strength, anchorage failure might occur despite longer sleeve length prior to failure in the free length. ASTM D7205 recommends 460 mm sleeve length for a 9.5 mm CFRP bar. More sophisticated clamping devices use inversely segmented cones [47; 48] or a pressure gradient.