Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

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Properties of Form Material 51
Bearing
Length 0.5-in. 1.0-in. 1.5-in. 2.0-in. 3.0-in. 4.0-in. 5.0-in. ê 6.0-in.
Value
of C b
1.75 1.38 1.25 1.19 1.13 1.10 1.075 1.0
TABLE 4-8 Adjustment Factors C b
for Bearing Area
Adjustment Factor C L
for Beam Stability
The beam stability factor C L
in the NDS is a multiplier to reduce the
reference design value of bending stress based on the depth-to-thickness
ratio (d/b) of the beam. When the conditions in Table 4-6 are satisfied,
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the beam stability factor C L
= 1.0; therefore, no adjustment is required
in the reference design value in order to determine the allowable
bending stress. The (d/b) ratios in Table 4-6 are based on nominal
dimensions. For conditions where the support requirements in Table
4-6 are not met, the designer should follow the requirements of the
NDS to reduce the reference design value by the adjustment factor C L
in order to determine the allowable stress in bending.
It is often possible to design members to satisfy the conditions in
Table 4-6 to allow the designer to utilize the full allowable bending
stress. One example of providing lateral support for bending members
is by placing decking on the top of beams. Although the beam is
used to support the decking, the decking can be fastened along the
compression edge of the beam throughout the length of the beam to
provide lateral stability. There are other methods that can be used by
the designer to satisfy the requirements of providing adequate lateral
bracing of bending members.
Adjustment Factor C P
for Column Stability
The column stability factor C P
in the NDS is a multiplier to reduce the
reference design value of compression stress parallel to grain based
on the slenderness ratio (l e
/d) of the beam. Shores are column members
with axial loads that induce compression stresses that act parallel
to the grain. Reference design values are presented in Tables 4-2
and 4-3 for compression stresses parallel to grain. However, these
compression stresses do not consider the length of a member, which
may affect its stability and strength. A column must be properly
braced to prevent lateral buckling because its strength is highly
dependent on its effective length.
The slenderness ratio for a column is the ratio of its effective
length divided by the least cross-sectional dimension of the column,
l e
/d. It is used to determine the allowable load that can be placed on
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