Patent ID: 7442001

Claim:
A boom assembly which is bent at a longitudinal center portion thereof to present an upwardly convex shape, the assembly comprising: a front boom body including: a main body consisting essentially of a pair of right and left lateral plates and a top plate interconnecting upper edges of the respective lateral plates, the main body being formed with an upper face and a lower edge thereof being bent in a longitudinal direction thereof into an arc face having a predetermined radius of curvature, and a bottom plate disposed downwardly of the top plate and between the right and left lateral plates; a rear boom body including: a main body consisting essentially of a pair of right and left lateral plates and a top plate interconnecting upper edges of the respective lateral plates, the main body being formed with an upper face and a lower edge thereof being bent in a longitudinal direction thereof into an arc face having a predetermined radius of curvature, and a bottom plate disposed downwardly of the top plate and between the right and left lateral plates; wherein each main body is formed by bending a plate member into a reverse U-shaped cross section; each bottom plate is comprised of a plate member provided separately from said plate member forming the main body; and wherein a vertical distance between each bottom plate and a lower edge of each of its lateral plates form a pipe accommodating space at the longitudinal center portion of the boom assembly, downwardly of the bottom plate and between each of the left and right lateral plates, wherein the vertical distance is smallest at a longitudinal intermediate portion between each longitudinal end of the boom assembly and said longitudinal center portion, and the vertical distance progressively increases from each longitudinal intermediate portion toward the longitudinal center portion to form the pipe accommodating at said longitudinal center portion.