Ametal bar with a rectangular cross section of height, h, and width, w, is fastened to a rigid wall with three pins. the pins will fail in shear at a stress level of τ fail. assuming that there is a gap, s, between the edge of the pin holes and the edge of the pins and that the pins are fixed to the wall, determine the change in temperature required to bring the end pins to the point of failure (assume direct shear failure). s = 2.5 mm h = 60 mm w = 45 mm diam_pin = 20 mm τ fail = 110 mpa l = 1.4 m α_bar = 17x10^-6/deg c e_bar = 200 gpa