Bearing at Supports

 

Bearing Stress ⊥ to Grain

ASD:  f_c⊥ = P/A ≤ F'_c⊥
LRFD:  P_u ≤ P'_c⊥n ≤ F'_c⊥nA

l_b = bearing length measured grain

 

Bearing Area Factor, C_b

NDS table 3.10.4

conservative to always use 1

C_b increases l_b by 3/8" for wood fibers close to contact edge  (see textbook Fig. 6.16b)

 

Adjusted Design Values

F'_c⊥ = F_c⊥(C_D)(C_M)(C_t)(C_L)(C_F or C_V)(C_fu)(C_c)(C_i)(C_r)(C_b)
F'_c⊥n = F_c⊥n(Φ_c)(λ)(C_M)(C_t)(C_L)(C_F or C_V)(C_fu)(C_c)(C_i)(C_r)(C_b)

C_D is not used because F_c⊥ is based on a 0.04" deformation limit in ASTM D143

F_c⊥0.02 = 0.73F_c⊥ for 0.02" deformation limit  (deformation critical designs)

 

Bearing Stress // to Grain

ASD:  f_c = P/A ≤ F^*_c
LRFD:  P_u ≤ P^*_cn ≤ F^*_cnA

NDS section 3.10.1

use steel bearing plate when f_c > 0.75F^*_c

 

Bearing on Angled Surfaces  (rafters)

NDS section 3.10.3, NDS appendix J

Hankinson formula

see textbook Example 6.17