Erection Of Cables Of Suspension Bridge
The cable erection of a suspension bridge has two methods - namely, the Air Spinning (AS) method and the Pre-fabricated Parallel Wire Strand (PPWS) method.
Unlike other manufacturers, IHI has experience in the erection of overseas suspension bridges using the AS method. Through long experience, IHI has developed and established know-how on the AS method, including quality control, high-speed erection, adaptation to longer span bridges, and improved AS erection machineries which enable 24 hours seamless operation.
The Air Spinning Method is a method to erect cables, by spinning small 5mm dimension wires one by one. To span these wires, firstly the wire is reeled onto a U/R Winch, then it is pulled out from the U/R Winch (Unreeling / Reeling Winch) by a carrier, making round trips over the catwalk. The wire is placed around the strand shoe and fixed to anchorages on both sides. By repeating the above process, the cluster of wire thickens, and in uniting them together, a cable is made.
We use the low tension control method, in order to ensure quality and workability.
The picture below shows reeling devices, comprised of a Uncoiler, Wire Tensioner, and U/R Winch. The wire coil (2 ton) is reeled to the U/R Winch for spinning work.
A device to pull out wire from the U/R Winch. It is comprised of a Counter Balance Tower (to introduce tension to the wire), and Driving Devices (for the traveling carrier).
A wire makes loops on the carrier, and is pulled out over the catwalk. The lower wire is laid down on the way over, and the upper wire on the way back. The wires are laid down onto a supporting structure called a "cable former".
Wires are laid down on the tower top saddle and splay saddle, in an orderly manner. When the carrier arrives at the anchorage, wires are placed around the strand shoe during tensioning.
When the wires accumulate to form a strand (approx. 500 wires), then both ends are connected so that the strand forms a circle. This strand-making process is repeated, and the strands are again compacted to form one cable.