# Shear Capacity of Textile-Reinforced Concrete Slabs without Shear Reinforcement
## 3 Results  
### Failure Mechanisms  
In the experimental program, two main different failure mechanisms were observed, bending and shear failure. The smallest specimens with a cross-sectional height of about \(\sim\)60 mm and an effective depth of \(\sim\)40 mm failed in bending by rupture of one or several yarns. Figure 3a shows three representative examples for the three different load-support-distances (span lengths). For some specimens, a diagonal crack originating from the layer of reinforcement occurred prior to failure. However, this crack was not the ultimate reason for failure. Three specimens (C3-1-4-1, C3-3-4-1, and C3-3-4-3) showed significant crack formation along the layer of reinforcement prior and subsequent to rupture of one yarn. Their failure mechanism is therefore described as bending failure with subsequent shear failure. All specimens with an effective depth of 80 and 120 mm failed in shear. Because their compression zone was further constricted by the critical shear crack prior to failure, the term shear compression  
Figure 3: Failure mechanisms observed in experimental study (**a**) bending failure; (**b**) shear-compression failure. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Substance** & **Density** & **Content** \\ \hline  & **kg/m\({}^{3}\)** & **kg/m\({}^{3}\)** \\ \hline Cemertitious binder compound CEM II/[PERSON] & 2962 & 707 \\ Fine quartz sand F38 S & 2650 & 294 \\ Quartz sand 0.1–0.5 mm & 2630 & 243.2 \\ Quartz sand 0.5–1.0 mm & 2630 & 201.4 \\ Quartz sand 1.0–2.0 mm & 2630 & 148.9 \\ Quartz sand 2.0–4.0 mm & 2630 & 593.5 \\ Superplasticizer (polycarboxylatter-basis) MC-VP-16-0205-02 & 1070 & 15 \\ Water & 1000 & 165 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mix design of cementitious matrix for HF-2-165-4 (mix design adapted from [70]). failure is utilized. Figure 3b illustrates a typical failure phenomenon which occurred for several specimens. The sudden propagation of the shear crack into the compression zone led to the brittle failure. The sudden release of stored energy resulted in a mutual sliding and a vertical shift of one half of the specimen. Note that the reinforcement in the tension zone was sheared at the crack in all layers without adding significant resistance and ductility to the failure mechanism. This is typical for the anisotropic fiber-reinforcement material, but even more pronounced for textile reinforcement due to the relatively low transversal stiffness of the individual yarns. For all specimens, one can observe that the residual compression zone in mid-span is only few millimeters deep. This can be explained by the high compressive resistance of the concrete and the good compaction of the concrete resulting in a dense and tough uppermost cementitious layer. The shear cracks passed through the aggregate grains. At failure, the constricted compression zone often buckled in the vertical direction. The high utilization of the concrete in this zone is shown in Figure 4 exemplary for three specimens, all having an effective depth of 80 mm but with different \(a/d\)-ratios. All specimen showed a linear-elastic branch in their load-deflection curve up to a high first-cracking load. This high load and the severe drop after first cracking are not surprising for the high-strength concrete with its corresponding stiffness. Subsequent bending cracks are clearly visible in the diagram. The end of the test was marked by a sudden drop of the load without residual capacity. At this point, the compressive strain directly below the load introduction at mid-span reached or even exceeded the ultimate strain of the concrete taken from uniaxial compression tests on cylinders. Next to the observations of the crack pattern after failure, this additionally confirms the hypothesis of shear compression failure. The highest compressive strains were reached for the smallest shear slenderness (\(a/d\) = 4.1 for C3-3-8-2 in Figure 4b). One explanation for this observation is the superposition of compressive stress from beam action and from direct stress fields.