Fig. 18a displays the moment-deflection-curves in the center of
the slab determined by the FEM-program and compared to the
experimentally measured values. Looking at the two lines of one
slab, e.g. the three-layer strengthened slab, it is obvious that the
two moment-deflection-courses are similar. Furthermore, it is
apparent that a cracked concrete cross-section needs to be assumed
from a moment of approx. 40–50 kNm on. The stiffness loss
accompanying this expresses itself in a lower rise of the moment–
deflection-curve. At a deflection of approx. 60–80 mm, a further
decrease of the moment–deflection-rise due to stiffness losses becomes
evident. This is caused by the onset of the steel reinforcement
yielding which leads to a higher stress redistribution from
the steel to the textile reinforcement. That will subsequently be
decisive in the further load increase. Meanwhile, the steel can
hardly absorb more tensile forces due to its plastification [6].
Fig. 18a shows the good correlation of calculated and measured
failure moments. The maximum failure moment difference is approx.
8 kNm (values see Tables 4 and 2). The deflections show proportionally
larger tolerances. For example, when the FE analysis is
applied, the slabs strengthened with two and four layers show up
to 24 and 42 mm higher deflections than actually observed
experimentally.
An improved calculative approximation of the measured moment-
deflection-course can be achieved by increasing the textile