# Shear Capacity of Textile-Reinforced Concrete Slabs without Shear Reinforcement
## 4 Discussion
### Effect of Shear Span Length  
The question of an influence by the shear slenderness on shear capacity is of high interest for both researchers and for design in practice. Researchers need to design future experiments with an appropriate load-to-support distance to avoid overestimation of the shear capacity. On the other hand, engineers in practice exploit the direct stress transfer of concentrated loads near supports by reduction of the design shear force according current design provisions.  
Figure 7a shows the ultimate shear force from all experiments in relation to shear slenderness. The shear force caused by self-weight of the specimens is neglected, because it differs along the shear span and along the critical shear crack. All results are displayed regardless of their failure mechanisms (a usual procedure, see for example in [75]). As discussed before, the specimens with \(d=4\) cm failed in bending. These results are therefore to be considered and compared with caution.  
The highest shear forces in this test series occurred for an \(a/d\)-ratio of 4. It is noteworthy that there, the scatter for the three identical beams with the largest effective depth is highest. With increasing \(a/d\), the shear resistance diminishes. This general observation is not surprising and well-known from steel-reinforced concrete [75] and concrete with FRP-reinforcement [76; 77]. However, it should be highlighted that usually, an influence of a direct compression field is assumed up to \(a/d=2.5\)-3. Here, the significant difference of shear resistance between \(a/d=4\) and 5 (while all other experimental parameters are kept the same) indicates a direct load transfer between load introduction and support, at least up to the shear slenderness of 4. There is no significant difference between \(a/d=5\) and 6, as indicated by the red and green dashed trend lines. The red dashed linear trend line for an effective depth of 4 cm is significantly influenced by the three values at \(a/d=7\), where earlier bending failure due to the higher moment governed. One possible explanation for the phenomenon of increased direct load transfer might be the influence of longitudinal cracking in the layer of reinforcement. The crack  
Figure 7: Results of experimental test program: (**a**) Influence of the ratio of shear span to effective depth on shear force; (**b**) Influence of effective depth on shear stress (size effect).  
patterns in Figures 5 and 6 clearly show longitudinal cracks (resulting from high local bond stress introduced by the reinforcement) at the level of one layer of reinforcement, which connect individual bending cracks. Those longitudinal cracks lead to a reduction or even a total loss of local bond between reinforcement and matrix. Yet, the end-anchorage was sufficient, as the longitudinal cracks did not propagate to or beyond the supports. In consequence, the tension stress in the reinforcement is constant in the center part along the beam length, resulting in a more efficient tied arch action. The analysis of the crack pattern of the beams with the highest loads (C3-2-12-1, 27.3 kN and C3-2-12-2, 35.2 kN) underlines this hypothesis. There, longitudinal cracks are present almost all the way to the support, whereas for C3-2-12-2 with its 71% lower resistance (20.6 kN), fewer longitudinal cracks were visible. The first two specimens' shear resistance seems to be significantly influenced by tied arch action rather than beam action.