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Fig. 7.17 Shear safety margins assuming regions cracked in bending (Series II)
On the other hand, shear strength values were more balanced when a/d ratio was
higher (3.4). Only HCS II-50-3.4b shows a shear SM lower than 1; it may be
justi
exural failure was observed
(II-0-8.6, II-50-8.6, II-70-8.6), failure loads did not reach the theoretical shear
strength (see rectangular boxes in Fig.
7.17
).
In Fig.
7.18
, only HCS with web shear tension failures have been represented,
plotting together the SM values calculated with both hypotheses: regions cracked in
bending (as were plotted in Fig.
7.17
) and regions uncracked in bending
(Table
7.6
), which means pure shear tension failures. As it can be seen in Fig.
7.18
,
for all HCS, except the II-50-3.4b (because of bad surface nishing), less SM were
obtained assuming uncracked region.
Precracking HCS before shear testing implied an increase in bearing load that
was equal to 24.92, 31.62 and 21.60 % for HCS made with 0, 50 and 70 kg/m
3
of
ed by a bad surface
nishing. Evidently when
fl
bers, respectively (Fig.
7.19
). It is evident that
fl
exural precracking makes diag-
onal tension crack propagation dif
cult and improves HCS behavior, observing that
precracked HCS reached higher ultimate loads than their analogous non precracked
(Table
7.8
). This behavior occurs since, in regions previously precracked, the
previous cracks intercept the stress
elds and generate new cracks that do not
correspond with the most unfavorable. From this Series, it can be observed that
Codes are more conservative for the HCS without
bers, this is when brittle failures
are expected; on the other hand, for ductile members, Codes give less SM [
10
],
[
11
]. This fact, which the present work detects, agrees with the observations made
by Peaston et al. [
2
]. In Fig.
7.20
is represented the capacity achieved in
fl
exure at
the time of failure (in Fig.
7.20
called SM in
fl
exure) versus a/d ratio. It can be
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