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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 1
Reliability of buildings in service limit state for maximum horizontal displacements
crete retains a tension corresponding to 20% of peak tension indefinitely.
For the tensioned concrete, the constitutive model of FIGUEI-
RAS [8] is adopted, following Figure 2 (centre). For the reinforcing
steel, an elasto-plastic model with hardening is considered (Fig-
ure 2, right). Details of the adopted constitutive models and of the
strategies used to solve the non-linear problem are presented in
CORELHANO [3].
2.3 Simplified material non-linear analysis
Brazilian code ABNT NBR6118:2003 [1] proposes two alternatives
for the simplified material non-linear analysis of reinforced con-
crete structures. These models penalize stiffness of the cross-sec-
tion, in order to take into account, in a simplified way, the effects of
concrete cracking. In the first model, bending stiffness of columns
(6)
f
c
'
= f
ck
+ 3.5MPa
where:
'
c
f
: maximum compressive strength of concrete;
0
ε
: specific deformation of concrete corresponding to maximum
tension;
c
ε
: specific deformation of concrete ;
σ
: tension in concrete.
Segment BC is a line defined by the point of maximum compressive
strength and by the point corresponding to 50% of the maximum com-
pressive strength. In segment CD it is admitted that the compressed con-
Figure 2 – Constitutive model for compressed (left), tensioned (centre) concretes and for steel (right)
Figure 3 – Geometry of the studied frames: 4 floors (left), 8 floors (centre),
and 12 floors (right), all measures in cm