Nonlinear Finite Element Analysis of Concrete Structures

- 113 -
600 ^
500 t-
CT uit = 518 MPa
400 -
'o
| 300 ~
200 l
100 -
0 *
o
Peter (1964) "
approximation
..... a... I
4 5
Fig. 5.1-2: Experimental and approximated stressstrain
curve for bar material.
perimental values and for the predicted values using different
K-values. It should be recalled that for a = 10° and 20°the experimental
panels include vertical reinforcement not considered
in the analysis. It is also important to note that the loading
causes cracks so large that aggregate interlock can hardly be
present, i.e., all forces along the crack planes must be attributed
to the reinforcement bars. As an illustration, the largest
horizontal displacement occurs experimentally for a = 30°. Experimentally
the mean crack width was determined to be 0.44 mm
and assuming that all horizontal displacements occurred along
the crack planes the maximum mean horizontal displacement along
a crack plane was determined to be 0.11 mm which is quite small
compared to the crack width.
From the horizontal displacements shown in fig. 3 it appears
that an optimal value of K seems to be located in the range
K = 0.10-0.25. However, fig. 4 indicates that the predicted vertical
displacements are strongly dependent also on the K-value.
This constitutes in fact a major objection against the method
used here for considering the lateral stiffness of a reinforcement
bar, as in reality the axial and lateral stiffnesses of a
bar are quite independent. Obviously, the axial bar stiffness is
the matter of major importance and even small K-values between