Yielding column

#This invention relates to a yielding column for use in mines or structures.

#Yielding columns are used in mines to provide indications of roof movement possibly leading to roof failure, while supporting the roof. A portion of the column is designed to provide a visible indication of yielding at a load somewhat below the ultimate strength of the column. A good column absorbs a lot of strain before it fails. FIG. 6 shows the characteristics of various roof-supporting arrangements. Wood cribs are excellent in this regard, as they have a long, flat stress-strain curve.

#An object of the invention is provide a yielding column providing an improved visible indication of load indicative of potential roof failure.

#In the accompanying drawings,

#FIG. 1 is a front elevation of a yielding column embodying the invention, partly broken away to show a cross-section thereof on a vertical bisecting plane;

#FIG. 2 is a cross-sectional view thereof, taken on the line 2-2 in FIG. 1;

#A yielding column embodying the invention comprises a steel tube 10 having foot and head plates 12, 14. The head plate 14 is welded to a screw pipe 16. The external threads of the screw pipe engage internal threads on a collar 18. The collar is circumferentially undercut to the inner diameter of the tube at its bottom, leaving an external circumferential shoulder 20 at the top. The undercut portion has a circumferential groove 21 in its outer surface for receiving a set screw 22 which is received in a threaded hole 24 extending through the wall of the tube near its upper end 26. The collar shoulder bears against this upper end. The hole 28 at the collar end is for receiving a wrench (not shown).

#A number of slots 30 are formed in the wall of the tube. Preferably, each slot has a fixed width, except at its rounded ends 32, and extends entirely through the tube wall. The slots are preferably arranged in two or more circumferential rows “R”, the spacing of slots within each row being uniform and extending around the entire circumference. The row-to-row spacing is preferably uniform as well. Alternating rows are staggered so that the slots are misaligned between adjacent rows, preferably by one-half of the slot-to-slot pitch within a given row.

#The height “H” and width “W” of the slots may be varied according to the desired predetermined axial load; the geometry shown in the drawings is merely preferred. The drawings show four slots in each row. Each slot has a width about twice the wall thickness “T”, and a height about three times the slot width. The load-supporting pillars 34 remaining between the slots thus have approximately equal height and width, each about three times the wall thickness. The combined load bearing capacity of the pillars is reduced in proportion to the width of the slots.