Civil Engineering Reference
In-Depth Information
Figure 6.35
Presence and absence of pinching mechanism.
At point C the vertical cracks close, while the horizontal cracks remain wide open. This
condition results in the formation of a series of horizontal concrete struts to resist the horizontal
compressive stress
σ
V
is resisted by the two
45
◦
steel bars. Conceptually, a truss is formed to resist the applied negative shear stress in
the 45
◦
direction and the shear stiffness increases dramatically. The two segments of BC and
CD in Figure 6.35(a) create the pinched shape in the hysteretic loops of the shear stress-shear
strain curves.
σ
H
. At the same time, the vertical tensile stress
0
◦
).
The absence of pinching mechanism in panel CE3 can be visualized by considering a cracked
element with horizontal and vertical steel bars, as shown in Figure 6.36(b). The drawing
on the left shows a 2-D element subjected to a negative shear stress, which is equivalent to
applying a horizontal compressive stress
Panel CE3 (
α
1
=
σ
V
of equal magnitude.
This 2-D element also has vertical and horizontal cracks induced by previous cycles of
shear stresses.
σ
H
and vertical tensile stress
