A Treatise On The Principles And Practice Of Dock Engineering

WOODEN GATES. 333 exception of the two topmost connecting pieces and a rubber on the front of the gate, which are of pitchpine, the whole of the framing and of greenheart, fastened with galvanised iron bolts and straps. panelling is The data for calculation are as follows : — Ft. Width of waterway, ..... 60 Span of gates (between heel-post centres), . 63 Rise or versed sine of sill,* .... 10 Rise or versed sine of gates,* ... 10 Radius of heel-post, ..... 0 Length of leaf (water-bearing surface), . . 34 Distance from centre of heel-post to centre of meeting faces of mitre-posts, ... 33 Ins. 0 8 0 6 12 6 6 The gates are segmental in form, and so designed that the curve of pressure coincides with the back of the gate at the centre of each leaf. The thickness of the middle head is 2 feet. The total height of each leaf is 34 feet 3 inches, of which 9 inches forms a sill abutment, leaving a height of 33 feet 6 inches capable of sustaining water pressure. Adopting first the approximate formula (47) for the resultant, we obtain— „ wh2I (I - p) — ------3---- 4 r 64 x 33-5 x 33-5 x 34-5 x 33-5 , -----------3 -----------------= 1,976,442 Ibs. 4 x 10-5 This may be checked by drawing in the diagram of stresses as illustrated in fig. 256, from which it will be found that the radius of curvature is 55 feet. Hence 55 x 64 x 33-5 x 33-5 1,975,160 Ibs. R = 2 The agreement is very close. Let the result be taken in round numbers at 882 tons. Now, the maximum bending moment is at the middle head, where the curve of pressure is situated 12 inches outside the longitudinal axis of the gate. At this point its direction is normal to the back of the gate, so there will be no shearing stress along the joints on either side of the middle head. In the preliminary investigation it will be recollected that when the curve of pressure lay upon the outer edge of a horizontal rib the intensity of stress in the outermost fibres was found to be four times that of the simple compression due to a resultant acting along the gate axis. The 882 compressive intensity is tons, the gate being 24 inches in thickness. .,. 882x4 Accordingly the maximum stress intensity is —— — = 147 tons over the whole depth of the gate. * The versed sine is measured in each case from the line through the centres of the heel-posts and extends to the point of the sill and the centre of the meeting faces of the mitre-posts respectively.