Problem $4$

The bracket below is held onto a column by $3M121\mathrm{.}75$ steel bolts $(11$ mm diameter, $380$ MPa proof strength$).$ Find the safety factor for the most demanded bolt under the following conditions:

a$)$ No preload.

b$)$ The bolts are $75\%$ preloaded and the friction coefficient between the column and the bracket is $0\mathrm{.}1.$

Note: all dimensions in mm $.$

Answers:

A$)$ FOS$=0\mathrm{.}52$ for top bolt $($normal stress is zero, total shear stress is $421\mathrm{.}26$MPa$)$

B$)$ FOS$=0\mathrm{.}57$ for top bolt $(7$kN is neutralized by friction, not other one. Normal stress is $285$MPa, shear stress is $346\mathrm{.}6$MPa$)$