Civil Engineering Reference
In-Depth Information
Figure 6.7
Crack width development for top-loaded walls.
The values of maximum crack width for bottom-loaded (L2) walls are
summarised in
Figure 6.8.
This figure exhibits values of mid-span crack
width up to 1.2 mm. In specimen W4, the first crack appeared at a load of
130 kN and measured 3.5 mm. This large instantaneous crack width was
predictable because of the absence of vertical reinforcement in W4.
Under combined top and bottom loads, the maximum crack width was
also recorded on horizontal cracks at mid-span.
Figure 6.9
shows these
values for crack widths up to 1.2 mm for the specimens loaded under equal
top and bottom loading (L3). It is clearly shown in Figure 6.8 and 6.9 that
when load was applied at the soffit, the crack width in the wall-beams was
directly dependent upon the amount of vertical reinforcement.
6.7
Design approaches
6.7.1.
American Concrete Institute
The ACI Building Code 318M-83 presents a series of rules applicable to
flexural members with a clear span to effective depth ratio (
L
o
/
d
) less than 5
and loaded at the top face.
For members subject to shear and flexure the nominal shear strength
V
n
is
found from the contributions of steel and concrete, i.e.
V
n
=
V
c
+
Vs
.
If
(6.1a)
