Civil Engineering Reference
In-Depth Information
a
2
C
2
C
1
a
1
C
3
a
3
Figure 13.7
Hydrostatic element.
C
1
T
C
2
Figure 13.8
Nodal zone formed by the extension of the members.
the different faces of the node. At these nodes the following conditions need
to be satisfied:
1. The resultants of the three forces coincide
2. The stresses are within the limits
3. The stress is constant on any face
Nodal zones fail by concrete crushing. Again, the anchorage of tension ties
must be provided. Within a node, if a tension tie is anchored, incompatibil-
ity of tensile strain in the rebars and the compression strain in the concrete
take place, which weaken the compressive strength of the concrete.
According to Appendix A of ACI-318-2012, the limiting compressive
strength on a face of a node is given by
′
F
=
0 85
.
β
f A
(13.9) (ACI [eqs. A-7 and A-8])
nn
n c
n
where for
CCC node b
n
= 1.0
(ACI [sect. A-5.2.1])
CCT node b
n
= 0.8
(ACI [sects. A-5.2.2 and A-5.2.3])
CTT node b
n
= 0.6
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