Civil Engineering Reference
In-Depth Information
Figure 6.33
2-D elements under cyclic shear
45
◦
) are severely 'pinched' near the origin, while the hysteretic loops of panel CE3
(
α
1
=
0
◦
) are fully rounded and robust. The 'pinched' hysteretic loops of panel CA3 reduce
its shear ductility and energy dissipation capacity by an order of magnitude as compared to
the 'fully rounded' hysteretic loops of panel CE3.
The behavioral comparison of panels CA3 and CE3 in Figure 6.32 clearly shows that the
magnitude of shear ductility and energy dissipation capacity are strongly effected by the
orientation of steel bars with respect to the directions of principal stresses (1-2 coordinate).
When the steel bars are oriented in the principal 1-2 coordinate, the hysteretic loops are fully
rounded and the behavior is ductile. When the steel bars are oriented at 45
◦
to the principal
1-2 coordinate, the hysteretic loops are severely pinched and the behavior is much less ductile.
The behavior of panels CA3 and CE3 clearly explains the observations of previous researchers
that the shear walls with vertical and horizontal steel bars (Figure 6.31a), are not ductile, while
the shear walls with diagonal steel bars (Figure 6.31b), are ductile.
Figure 6.32 also confirmed the validity of CSMM. This analytical model is capable of
predicting the pinched shape of the hysteretic loops of panels CA3 as well as the fully rounded
hysteretic loops of panel CE3. In Section 6.3.7, CSMM is also used to explain the presence
and absence of the pinching mechanism in RC 2-D elements under cyclic shear loading, as
well as the failure mechanisms of such elements (Mansour
et al.,
2001a; Hsu and Mansour,
2002; Mansour and Hsu, 2005b).
(
α
1
=
6.3.6.3 Deformation Characteristics
Figure 6.34(a) and (b) plots the horizontal strain
ε
H
versus vertical strain
ε
V
under cyclic shear
0
◦
), respectively. The predicted and experimental
curves are given side by side, the experimental solid curves to the right and the predicted
dotted curves to the left. Figure 6.33(a) and (b) shows that under positive shear stress, the
horizontal strain
45
◦
) and CE3 (
for panels CA3 (
α
1
=
α
1
=
ε
H
increases, while the vertical strains
ε
V
decreases. Under negative shear
stress, however, the horizontal strain
ε
H
decreases, while the vertical strain
ε
V
increases.
