The main cable wire is generally transported to site in coils and wound on to2 mdiameter reels capable of holding about 10-15 span lengths. The end of the wire is led round a tensioning wheel (which turns against a controlled brake) and on to the reel. Ends can be spliced together with swaged couplings.
The drums of wire are taken from the reeling area and set up on electrically powered unreeling machines (in the example shown a single reel is illustrated but often up to eight wires are simultaneously unreeled across the span). The end of the wire is passed over a series of pulleys housed in a high tower and led via a floating sheave to a strand shoe, where a temporary connection is made. The wire is then looped by hand over the spinning wheel and hauled with the endless tramway drive rope at 200-300 m/min to a strand shoe on the anchorage at the other bank. Thus two wires are simultaneously spun, one dead (i.e. that fixed to the shoe) and the other live. The dead wire is temporarily held in position with hooks spaced at approximately150 mcentres along the catwalk, while the live wire is run through sheaves to aid control. Meanwhile the empty wheel returns to the reeling side. Adjustment of sag for each wire generally takes place while spinning is in operation. As soon as the wheel passes over a tower the dead wire or) the side span is unhooked, pulled clear of the catwalk with an electric winch, lined up with a guide wire and clamped at the top of the tower, it is then manually lifted into the strand formers located along the catwalk at about150 mcenters. The procedure is then repeated in the main span after the wheel has passed the other tower. Adjustment of the remaining side span sag takes place after the wire has been looped over the strand shoe while the wheel is stationary in ready uses for the return journey to the reeling side. During this return period, the previously live wire is released from the sheaves and adjusted in a similar manner to the dead wire.
The process is repeated until a complete strand has been made, where after the loose end is spliced to the temporary connection initially provided for the start end of the wire. The wires are subsequently shaken out, temporarily banded into strands and any final sag adjustments taken up by the strand shoe. The remaining strands are spun in a similar manner until the whole cable is formed. Spinning can usually only take place when wind speeds are less than about50 km/h. The whole process typically takes up to 6 months for a1000 mspan bridge, with an average about 6 tonnes per day of spun strand (Bianculli, 2003). (more…)