Problem $2-$ expected time: $25$ minutes

A truss structure made of three steel bars $($with circular cross

section$)$ is subjected to the given loads.

a$.$ Determine the axial force in all the bars

b$.$ Determine the minimum diameter $d($to the nearest

mm $)$ for bar AB if the allowable stress is ${}_{\text{a}\text{l}\text{l}\text{o}\text{w}}=50$

MPa

Please show all the FBDs needed, and use the correct sign

convention for the internal forces. Provide results in $kN,m.$

Partial solutions: $N_{AC}=+125kN,N_{BC}=-90\mathrm{.}14kN,d=36$

mm