4.2 - VSL
4.2 - VSL
4.2 - VSL
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from tendons passing near the column<br />
should be investigated with the help of a<br />
space frame model. The distance between<br />
the outermost tendons to be taken into<br />
account for direct load transfer and the edge<br />
of the column should not exceed d s on either<br />
side of the column.<br />
The favourable effect of the prestress can<br />
be taken account of as follows:<br />
1 The transverse component Vp∞ resulting<br />
from the effectively present prestressing<br />
force and exerted directly in the region of<br />
the critical shear periphery can be<br />
subtracted from the column load resulting<br />
from the applied loads. In the tendons, the<br />
prestressing force after deduction of all<br />
losses and without the stress increase<br />
should be assumed. The transverse<br />
component Vp is calculated from Fig. 30<br />
as<br />
Vp=Σ Pi . ai = P. a (3.21.)<br />
Here, all the tendons situated within the<br />
critical shear periphery should be<br />
considered, and the angle of deviation<br />
within this shear periphery should be<br />
used for the individual tendons.<br />
2 The bending reinforcement is sometimes<br />
taken into account when establishing the<br />
permissible shear stress [37], [38], [39].<br />
The prestress can be taken into account<br />
by an equivalent portion [15], [16].<br />
However, as the presence of concentric<br />
compression due to prestress in the<br />
column area is not always guaranteed<br />
(rigid walls etc.) it is recommended that<br />
this portion should be ignored.<br />
3.2.3. Carrying out the calculation<br />
A possible design procedure is shown in [14];<br />
this proof, which is to be demonstrated in the<br />
ultimate limit state, is as follows:<br />
Rd ≥ 1.4 . V g+q - Vp (3.22.)<br />
1.3 1.3<br />
The design value for ultimate strength for<br />
concentric punching of columns through<br />
slabs of constant thickness without<br />
punching shear reinforcement should be<br />
assumed as follows:<br />
R d = u c . ds . 1.5 . Tud (3.23.)<br />
U c is limited to 16 . d s , at maximum and the<br />
ratio of the sides of the rectangle surrounding<br />
the column must not exceed 2:1.<br />
T ud can be taken from Table I.<br />
10<br />
If punching shear reinforcement must be<br />
incorporated, it should be designed by<br />
means of a space frame model with a<br />
concrete compressive zone in the failure<br />
state inclined at 45° to the plane of the slab,<br />
for the column force 1.8 V g+q-Vp . Here, the<br />
following condition must be complied with.<br />
2 . R d ≥1.8 . V g+q -V p<br />
(3.24.)<br />
For punching shear reinforcement, vertical<br />
stirrups are recommended; these must pass<br />
around the top and bottom slab<br />
reinforcement. The stirrups nearest to the<br />
edge of the column must be at a distance<br />
from this column not exceeding 0.5 • d s. Also,<br />
the spacing between stirrups in the radial<br />
direction must not exceed 0.5 • d s (Fig.31).<br />
Slab connections to edge columns and<br />
corner columns should be designed<br />
according to the considerations of the beam<br />
theory. In particular, both ordinary<br />
reinforcement and post-tensioned tendons<br />
should be continued over the column and<br />
properly anchored at the free edge (Fig. 32).<br />
Figure 32: Arrangement of reinforcement at corner and edge columns<br />
Figure 31: Punching shear reinforcement