## 4 Results and Discussion
### Push-Off Shear Tests  
There is no universal test for obtaining shear strength in concrete. Structural concrete standards [8; 12] consider the contribution to shear of fiber-reinforced concrete based on residual strength \(f_{R3}\), obtained in standard bending tests [23; 24]. That is why it is necessary to assess directly shear strength. There are three experimental methods for this [34], although none of them lack bending side effects. Among these three methods, the simplest and most straightforward method is push-off as it is not affected by possible side effects caused by the disposition of the test. For this reason, the push-off method has been chosen to analyze shear behavior of fiber-reinforced concrete, starting from the residual halves of bend tested specimens. Push-off shear tests were carried out with four specimens for VCLP6, three for VCCP10 and two for SCCS70 respectively. All the specimens were monitored on their front and rear face to obtain the cracking patterns in the shear ligament and to assess strain (in bulk sound material) and opening and sliding of the shear cracks. The first analysis of push-off shear tests results was performed to compare the shear behavior of various concrete types. The nominal resistant area of the ligament was 150 mm wide by 90 mm height. After testing, the real area of the ligament was assessed. Figure 11 shows the shear stress (average of experimental results of tested specimens) vs. shear sliding in the fracture ligament. The shape of the curves is quite different from the one obtained in the tensile and bending tests. As in the previous tests, a first straight line of stress increases up to the limit of proportionality, \(f_{LOP}\), when the matrix of concrete cracks. The \(f_{LOP}\) is associated with the strength concrete matrix. After that, two different behaviors can be observed. For VCCP10 and SCCS70 the curve shows a steep drop in the residual shear stress, while for the VCLP6 there is no such abrupt drop. In all cases analyzed, the descending branch did not show a subsequent increase in residual shear stresses, except in the case of SCCS70, with a high amount of steel fibers, in which a slight recovery occurs. The concrete with the highest ratio of reinforcement shows the highest loss of residual stresses. It is worth noting that for a sliding of 2 mm, the residual stress supported by the concrete with 70 kg/m\({}^{3}\) steel fiber is very similar to the one with of 10 kg/m\({}^{3}\) of polyolefin fibers. Another analysis to be carried out is the comparison of the CM-2010 and the EHE-08 [8; 12] Standards prescriptions with and the experimental results. As noted above, the shear resistance values calculated according to the Standards are based on the bending residual stress value for 2.5 mm CMOD (\(f_{R3}\)). Both Standards consider the contribution of fiber reinforcement to the resistance of concrete in an additive way to the shear reinforcement. However, both Standards do not consider this contribution in the same way, as it can be seen in Equations (3) [8] and (4) [12]. According to CM-2010, the contribution of fibers (\(f_{Fluk}\)) takes the value of \(f_{R3}/3\), affected by the compression resistance of concrete (\(f_{ck}\)). EHE-08  
Figure 11: Shear stress (average of experimental results of tested specimens) vs. crack sliding displacement (CSD) in the ligament for the push-off tests. includes the contribution of the fibers in a term independent of concrete (\(\tau_{fd}\)). This value is considered equal to 0.166\(f_{R3}\). For a more detailed analysis of the formulation, see [8; 12; 35]. \[V_{Rd,F}=\Bigg{\{}\frac{0.18}{\gamma_{c}}k\bigg{[}100\rho_{1}\bigg{(}1+7.5\frac{f _{Fthk}}{f_{ckt}}\bigg{)}f_{ck}\bigg{]}^{\frac{1}{3}}+0.15\sigma_{cp}\Bigg{\}}b _{w}d \tag{3}\]  
\[V_{rd}=V_{cu}+V_{fu}=\Bigg{[}\frac{0.18}{\gamma_{c}}\varepsilon(100\rho_{1}f_{cv })^{1/3}+0.15\sigma^{\prime}_{cd}\bigg{]}b_{0}d+0.7\varepsilon\tau_{fd}b_{0}d \tag{4}\]  
Table 4 shows the comparison of experimental results and analytical values obtained by Equations (3) and (4).