Solved: Brackets, such as the one shown, are used in

Chapter 9, Problem 9-52

(choose chapter or problem)

Brackets, such as the one shown, are used in mooring small watercraft. Failure of such brackets is usually caused by bearing pressure of the mooring clip against the side of the hole. Our purpose here is to get an idea of the static and dynamic margins of safety involved. We use a bracket 1/4 in thick made of hot-rolled 1018 steel, welded with an E6010 electrode. We then assume wave action on the boat will create force F no greater than 1200 lbf.

(a) Determine the moment M of the force F about the centroid of the weld G. This moment produces a shear stress on the throat resisting bending action with a “tension” at A and “compression” at C.

(b) Find the force component \(F_y\) that produces a shear stress at the throat resisting a “tension” throughout the weld.

(c) Find the force component \(F_x\) that produces an in-line shear throughout the weld.

(d) Using Table 9–2, determine A, \(I_u\), and I for the bracket.

(e) Find the shear stress \(\tau_1\) at A due to \(F_y\) and M, the shear stress \(\tau_2\) due to \(F_x\), and combine to find \(\tau\).

(f) Find the factor of safety guarding against shear yielding in the weldment. Since the weld material is comprised of a mix of the electrode material and the base material, take the conservative approach of utilizing the strength of the weaker material.

(g) Find the factor of safety guarding against a static failure in the parent metal at the weld.

(h) Assuming the force F alternates between zero and 1200 lbf, find the factor of safety guarding against a fatigue failure in the weld metal using a Gerber failure criterion.