Page 230 - Civil Engineering Formulas

164 CHAPTER SIX

F

b
φ/2
M 1
φ
A B
φ/2
f 1
C
f 2 M 2

FIGURE 6.1 Timber joint.

ADJUSTMENT FACTORS FOR DESIGN VALUES

Design values obtained by the methods described earlier should be multiplied by
adjustment factors based on conditions of use, geometry, and stability. The
adjustments are cumulative, unless specifically indicated in the following.
The adjusted design value F b for extreme-fiber bending is given by
F b F C C C C C C C C C C f (6.19)
M
D
b
t
fu
V
c
r
L
F
where F design value for extreme-fiber bending
b
C load-duration factor
D
C M wet-service factor
C temperature factor
t
C beam stability factor
L
C size factor—applicable only to visually graded, sawn lumber and
F
round timber flexural members
C volume factor—applicable only to glued-laminated beams
v
C flat-use factor—applicable only to dimension-lumber beams 2 to
fu
4 in (50.8 to 101.6 mm) thick and glued-laminated beams
C repetitive-member factor—applicable only to dimension-lumber
r
beams 2 to 4 in (50.8 to 101.6 mm) thick
C curvature factor—applicable only to curved portions of glued-
c
laminated beams
C form factor
f
For glued-laminated beams, use either C or C (whichever is smaller), not both.
L
v
The adjusted design value for tension F t is given by
(6.20)
F t F t C D C M C t C F
where F is the design value for tension.
t