Precast Inc. - November/December 2008 - (Page 60) whichever number is greater. Any strand ends that have been nicked by chucks should be cut off before they can be placed on another vise or chuck. Chucks must be inspected and lubricated before each use; discard any that show signs of wear, distortion or slippage. Prior to applying tension, all strands must be checked to assure that they are not tangled or crossed. Cable restraining devices should be securely attached in place in the forms to prevent employee injury in the event that a cable snaps. Pushdown and hold-up devices must be used following the manufacturer’s recommendations, and they must be inspected before use. Stretching operation The stretching or stressing operation is the act of applying force to the cables to achieve the desire calculated prestressed condition. It is achieved by pulling the cables with hydraulic rams at predetermined forces. During this operation, one end of the cable is attached to a stationary abutment and the other end is attached to the pulling mechanism, or jack. All jacking equipment must be inspected by a qualified employee before and during each day’s stretching operations, and any defects or deficiencies found must be corrected before the operation begins or continues. During stressing operations all personnel not involved must be kept away from the area. Audible and visual alarms should be turned on during these operations, and no employee should approach that area until they are turned off. In some cases an employee can be posted in a safe place within view of the designated area to warn employees who approach the area. The stressing-designated area should include the whole length of the bed, both ends and the sides for a distance of about 20 feet. Only stressing personnel should be within this designated area. The stressing personnel should not stand directly behind the jack or in line with the stressed cables, because a rupturing cable will tend to follow the direction of the line of tension. Employees must not attempt to relocate or shift strands while under tension. The measurement of elongation should be made by means of mechanical devices attached to the jack, which can be viewed from a safe distance. No personnel should measure elongation by entering the jacking area or approaching the BOOTH 1551 THE PRECAST SHOW 60 NOVEMBER/DECEMBER 2008 | PRECAST INC. http://www.penntechindustrialtools.com http://www.penntechindustrialtools.com
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.