Nonlinear Finite Element Analysis of Concrete Structures

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no stiffness of the concrete in question should be retained when
secondary cracking has occured. This assumption is also utilized
here, cf. section 4.2.2.
The sensitivity study of the parameters has focussed on their
influence on the failure load. However, some other aspects of
beam behaviour are also affected. For instance, use of the .-alue
< = 0.25 instead of K = 0 results in increased secondary cracking
along the main reinforcement and it decreases the midspan deflection
around 8%. Use of the value n = 0.10 instead of n =
0.01 also decreases the midspan deflection around 8%.
The previous analysis using the program in its standard form has
demonstrated a close agreement with experimental data. However,
one significant disagreement exists. This is shown in fig. 13,
where the relative vertical displacements across the beams are
depicted. The experimental values indicate that in contrast
to the OA-2 beam a considerable thickening occurs for the A-2
beam with stirrups. T^is phenomenon is not reflected in the calculated
values which grossly overestimate the thickening of the
beams. This picture is influenced only insignificantly when
using the different assumptions given in table 2. One exception
is case no. 3 where the shear retention factor is increased,
decreasing the thickening values by a factor of approximately
2. Even so, a considerable overestimation results. It is of
importance to note that even giving consideration to dowel action
through the shear deformation of the reinforcement, cf. case
no. 1 with no. 2 and case no. 6 with no. 7, has no significant
influence on the results. However, as the reason for the much
smaller experimental values in fact is believed to be dowel
action of the reinforcement, this is to say that consideration
to dowel action must be treated through the bending of the bars
and not through their shear deformation. This important conclusion
supports the use of the value K - 0 in the standard
version of the program. However, another important consequence
may also be derived from fig. 13. The figure shows that the
predicted strains in the stirrups are far too large. Therefore,
the predicted influence of stirrups is underestimated and this
explains why the existence of stirrups resulted experimentally