General Notation

 

The same NDS Supplement values are used in ASD and LRFD.

Adjustment factors remind designer not to overlook something.

Default-to-unity is common.

Factors that reduce strength/capacity must be considered.  Factors that increase strength may be considered.

 

 

ASD notation

units:  psi

actual stresses:  f_t = P / A

reference design values:  F_t

all values, except E, have already been reduced for safety
E values are averages

adjusted design values:  F'_t

f_t  ≤  F'_t  =  F_t  x  (adjustment factors)

design value	reference design value	adjusted design value
bending stress	Fb	F'b
tension stress parallel to grain	Ft	F't
shear stress parallel to grain	Fv	F'v
compression stress perpendicular to grain	Fc⊥	F'c⊥
compression stress parallel to grain	Fc	F'c
modulus of elasticity (or MOE)	E	E'
modulus of elasticity for stability calculations	Emin	E'min

adjustment factors:  C

CD	load duration factor  (ASD only)
CM	wet service factor
CF	size factor
Cfu	flat use factor
Ci	incising factor
Ct	temperature factor
Cr	repetitive member factor
CP	column stability factor
CL	beam stability factor

 

 

LRFD notation

units:  ksi

actual forces:  T_u  (factored loads)

reference design values:  F_t

all values, except E, have already been reduced for safety
E values are averages

nominal design values:  F_tn

F_tn  =  F_t  x  K_F
K_F  =  format conversion factor

nominal/adjusted design values:  F'_tn

F'_tn  =  F_tn  x  (adjustment factors)

nominal member resistance/capacity

T_n  =  F_tn  x  A  =  (F_t  x  K_F)  x  A

adjusted resistance

T'_n  =  F'_tn  x  A

T_u  ≤  Φ T'_n

Φ:  resistance factors (NDS Appendix N table N2)

design value	reference design value	nominal design value	adjusted design value	adjusted resistance
bending moment	Fb	Fbn	F'bn	M'n
tension parallel to grain	Ft	Ftn	F'tn	T'n
shear parallel to grain	Fv	Fvn	F'vn	V'n
compression perpendicular to grain	Fc⊥	Fc⊥n	F'c⊥n	P'⊥n
compression parallel to grain	Fc	Fcn	F'cn	P'n
modulus of elasticity (or MOE)	E	E	E'	--
modulus of elasticity for stability calculations	Emin	Emin-n	E'min-n	--

adjustment factors:  C

λ	time effect factor  (LRFD only)
CM	wet service factor
CF	size factor
Cfu	flat use factor
Ci	incising factor
Ct	temperature factor
Cr	repetitive member factor
CP	column stability factor
CL	beam stability factor