Problem $4$

A rigid beam ABC carries a load $P$ and is

supported by a pinned connection at C and a tie$-$rod

BD at B such that the allowable normal stress in

the tie is $145$ MPa $.($a$)$ Find the maximum load $P$

that can be supported if the tie BD has a cross$-$

section of $25$ mmx $25$ mm $.($b$)$ Find the diameter of

the tie rodBD if the $P=85kN.$