sampling the concrete in the right places during the slab molding process (Fig. 3).
Multi-keys joint with rectangular concrete keys, preferably with
0.25
kk
lh=
is
considered. If necessary, key reinforcement is performed.
Figure 3. The arrangement of the keys in the longitudinal edges
of the no formwork slabs
The proposed methodology for joints calculating [12] takes into account the
nature of their destruction and the main determining factors: strength characteristics
concrete f
cd
and f
ctd
, the ratio of the depth l
k
and the height h
k
of the keys, the shape of
their cross section, the shape of the profile, reinforcement, the number of keys.
In one of the authors complex experimental researches [12], the effect of f
cd
and
f
ctd
values was studied, as well as reinforcement on the keys strength which are
destroyed by shearing. Samples had height
200
k
h
мм
=
and thickness
150
k
b
мм
=
.
Loading devices of width
50
()
k
ммl
were used, which corresponded to the ratio of
the keys dimensions
0.25
kk
lh=
. The keys were reinforced with transverse bars of
class A240C in the shear plane (two types of cage were used: with the reinforcement
in one level in the middle of the key height and in two levels). The reinforcement
percentage varied within
0.341.03%
w
=−
. The reinforcement was securely anchored
in the lateral side of the specimens. Heavy and ceramsite concrete with prism strength
f
c,prizm
= 10 ‒ 56.9 MPa was used.
The surface of destruction was outlined in a curve close to the vertical, and
consisted of compressed and tensile sections. An increase in reinforcement led to an
increase in the size of the compressed zones, in which the localization of plastic
deformation was recorded. Strains of concrete in the compressed zones reached the
level of
с
=
(100 – 300) ×10
-5
. However, large strains values occurred in the samples
with the location of the working reinforcement in two levels in height. Reinforcement
spacing has led to a significant increase in plastic deformations of concrete, which is a
main point for the joints of elements during construction in seismically dangerous
areas.
The stresses in the reinforcement intersecting the shear plane at the stage of
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