Nonlinear Finite Element Analysis of Concrete Structures

- 117 -
that in all other structures where concrete in compression also
contributes to the failure load a horizontal force-displacement
curve at failure will be predicted as a result of the considered
softening behaviour of the concrete in the post-failure region.
The calculated failure loads of the panels are determined with
the above-mentioned in mind and a comparison with experimental
failure loads is given in the following table.
Table 5.1-1: Calculated and experimental failure loads.
F
exp.
a
F..
theo.
[kN]
[kN]
F /F
theo. exp.
0 10° 20° 30° 40°
392 433 425 381 400
394 386 384 384 384
1.01 0.89 0.90 1.01 0.96
Mean value of F.,
theo. 7 /F
exp.
=0.95
It appears that the predicted failure loads are in very close
agreement with the experimental ones in particular when recalling
that panels with a = 10° and 20° include vertical reinforcement
not considered in the analysis. On the average, the
analysis underestimates the failure loads by 5%.
The present section has in particular dealt with different aspects
when modelling reinforcement bars that are crossed by
cracks. Modelling of the lateral bar stiffness has received
special attention and it has been demonstrated that simulation
of this stiffness through a suitable shear modulus of the bar
material seems not to be a very advantageous method. This conclusion
is further supported in section 5.3 where beams failing
in shear are treated and it can therefore be concluded that
lateral bar stiffness should be treated through its bending
stiffness. Except for the purpose of sensitivity studies the
value K - 0 corresponding to no lateral bar stiffness will
therefore be utilized in the program. Using this value, the
analysis of different panels has demonstrated that the predic-