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Notes on the Erection of the Illinois and St. Louis Bridge
L.—Mode of Setting and Adjusting the Skew-Backs.—The bedplates upon which the skew-backs were to rest were bedded into the masonry during the building of the piers and abutments. Great care was taken to get them into proper position, but it was found practically impossible, under the circumstances, to adjust them with perfect accuracy. A more accurate adjustment was there fore delayed until the skew-backs and their connected tubes (first tubes of the arches) were in place. After these were hoisted into position upon the bed-plates and anchor bolts and firmly screwed down to the bed-plates, the following measurements and observations were made to ascertain the amount and direction of variation from correct position. 1st. The angular inclination of the skewback tubes in a vertical direction was determined. 2d. The direction of the centre line of these tubes in reference to the centre of their opposing skew-backs (at other side of the span) or their horizontal deflection. 3d. A line was drawn through the pin-holes at extremities of the four tubes composing the upper or the lower set of skew-back tubes, to determine the variation in the resultant lengths of these tubes, due to variation in thickness of skew-backs or projection of the bed-plates. 4th. The vertical distances between the pins in the upper and lower set of skew-backs, which governed the depth of the arch rib. 5th. The horizontal distances between the centres of the skew-backs. 6th. The level of the centre line of each pin-hole at extremities of the skew-baek tubes. In addition to these, as additional checks upon the correctness of the adjustment, the distances of the pins in the upper skew-backs from the pins in the extremities of the lower skew-back tubes-the length of first main braces-were taken; also the vertical and horizontal distances between the centres of the pin-holes at extremities of the skew-back tubes.
Notes on the Erection of the Illinois and St. Louis Bridge
L.—Mode of Setting and Adjusting the Skew-Backs.—The bedplates upon which the skew-backs were to rest were bedded into the masonry during the building of the piers and abutments. Great care was taken to get them into proper position, but it was found practically impossible, under the circumstances, to adjust them with perfect accuracy. A more accurate adjustment was there fore delayed until the skew-backs and their connected tubes (first tubes of the arches) were in place. After these were hoisted into position upon the bed-plates and anchor bolts and firmly screwed down to the bed-plates, the following measurements and observations were made to ascertain the amount and direction of variation from correct position. 1st. The angular inclination of the skewback tubes in a vertical direction was determined. 2d. The direction of the centre line of these tubes in reference to the centre of their opposing skew-backs (at other side of the span) or their horizontal deflection. 3d. A line was drawn through the pin-holes at extremities of the four tubes composing the upper or the lower set of skew-back tubes, to determine the variation in the resultant lengths of these tubes, due to variation in thickness of skew-backs or projection of the bed-plates. 4th. The vertical distances between the pins in the upper and lower set of skew-backs, which governed the depth of the arch rib. 5th. The horizontal distances between the centres of the skew-backs. 6th. The level of the centre line of each pin-hole at extremities of the skew-baek tubes. In addition to these, as additional checks upon the correctness of the adjustment, the distances of the pins in the upper skew-backs from the pins in the extremities of the lower skew-back tubes-the length of first main braces-were taken; also the vertical and horizontal distances between the centres of the pin-holes at extremities of the skew-back tubes.
Notes on the Erection of the Illinois and St. Louis Bridge
Cooper, Theodore (author)
Transactions of the American Society of Civil Engineers ; 3 ; 239-254
2021-01-01
161874-01-01 pages
Article (Journal)
Electronic Resource
Unknown
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