Civil Engineering Reference
In-Depth Information
If the calculated bearing stress exceeds the allowable stress, it is necessary to spread
the load out, as by using larger members or by using a bearing plate or a hardwood cap on
top of the shore.
4
Another bearing stress situation is presented in Example 20.4, where the bearing
stress caused in the wales of a wall form by the form ties is considered.
EXAMPLE 20.4
Form ties are subjected to an estimated force of 5000 lb from the fresh concrete in a wall form. The
load is transferred to double 2-
4-in. wales through brackets or washers, as shown in Fig-
ure 20.7. Are the calculated bearing stresses within the permissible values if the wales are Douglas
fir, coastal construction and if the bearing locations are at interior points in the wales?
3
2
-in.
Bearing Area
(
)(3.50)
2
4
SOLUTION
(0.625)(3.50)
7.43 in.
2
Bearing stress
5000
7.43
673 psi
8
Allowable compression ⊥ to grain
(490)
3.50
0.375
3.50
(490)
543 psi
673 psi
No good
Use larger washers or smaller spacing of ties because allowable bearing is not satisfactory.
2 × 4 wales
3
2
"
washer (or bearing plate)
1.50"
0.625" = separation distance
between wales
bearing area
is hatched
1.50"
Figure 20.7
4
Hurd,
Formwork for Concrete
, pp. 88-93.
