Allowable Bearing at bolt holes

[Jatfuentes]

Hi guys,
Please , somebody coluld explain me why AISC-ASD Eq.( J3-1)
allows a bearing strength Fp= 1.2*Fu?
I understand that the maximum strenght the steel can reach is Fu, the rupture strength, then how I can allow 1.2 Fu?.
Thanks in advance

jatfuentes

 

[Taro]

Fu is the maximum TENSILE strength. Higher strength is applicable to bearing.

 

[UcfSE]

Higher strengths for bearing are based on bolt hole deformation and limiting such deformation. Depending on whether you want to limit deformation at the hole or not you may use J3-1 or J3-4 for ASD, or J3-2a, 2b or 2c for LRFD. These limits keep the hole from elongating too much (>0.25") and also keep the hole from splitting parallel to load due to the bearing prior to a transverse fracture on the net section.

Check out the commentary for J3 in the 3rd LRFD ed. or the 9th ASD ed.

 

[Jatfuentes]

Thanks for the reply,
Really, Fu is the rupture in a tension test, and the bearing strength is not the case.