is 36 8 mpa t5 has a strength of 245 mpa the annealing of the o material is meant to soften the material as the hollow shape member the elongation of the hollow shape member 210 is greater than that of the general hollow shape member the strength of the hollow shape member 210 is smaller than that of the general hollow shape member in order to provide necessary strength and softness to the member annealing other than the o material can also be performed further the plate thickness of the hollow shape member can also be chosen to provide the best performance the lowermost end of the pillars 120 and 130 are welded to the upper and lower hollow shape members 210 210 welding is performed by forming notches to the upper and lower hollow shape members 210 having a shape corresponding to the pillars 120 and 130 and then welding the members the width direction ends of the upper and lower hollow shape members 210 210 are welded to plural members 250 the surface of the anticlimber 250 facing the hollow shape members 210 is provided with plural pipes 256 which are inserted to the plural hollow portions of the hollow shape members 210 the outer diameter of each pipe 256 is substantially equal to the inscribing circle of the hollow portion having a triangular cross section the pipes 256 are inserted to every other triangular hollow shape portion the pipes 256 are welded onto the seat 253 of the anticlimber 250 while being inserted to the holes formed to the seat 253 the frame 110 and the seat 115 also have pipes 256.