17 18 are subjected to higher compressive stresses than the upper side web sections 15 16 the present invention therefore in part advantageously employs a wider bottom plate 12 and reduced height inclined lower side plates to reduce the possibility of buckling of the bottom plate under compression thus producing the irregular octagon vertical cross section to the crane boom the angles between the side web sections and the adjacent plates 11 12 are correspondingly different fig4 shows an outer end of one boom section 10 wherein the end region is reinforced by peripheral straps 23 extending all the way around the section 10 and part straps 22 which only enclose the lower part of the boom the straps being joined by horizontal tie bars 27 in fig5 an alternative method of reinforcement is shown with vertical reinforcement plates 24 25 extending between the top and bottom plates 11 12 26 denotes a horizontal axle for carrying the pivot pin at the base of the boom in fig6 is shown a further alternative with vertical reinforcement plates 24a 24b seated on the inclined side web parts 15 17 16 18 respectively instead of the top and bottom plates the end of the boom has two circumscribing straps 23 between which on the top plate 11 are seated a pair of wear pads 28 peripheral straps are joined by horizontal tie bars.