Previous posts in the New Narrows Bridge Series:
- The Two Towers I: Introduction
- The Two Towers II: History of the Narrows Bridges
- The Two Towers III: The Caissons
- The Two Towers IV: Anchor Management Class
- The Two Towers V: The Tour Begins
- The Two Towers VI: Struttin’ My Stuff
- The Two Towers VII: To the Top
- The Two Towers VIII: Stairway to Heaven
- The Two Towers IX: Spinning Beginning
- The Two Towers X: Wheels Over Water
- The Two Towers XII: Compacting the Cables
The cables, whose spinning progress was interrupted by problems of premature corrosion of the galvanized steel wire mentioned in my previous post, have now been completed. The North cable has been compacted and banded, and the infrastructure supporting cable spinning has been dismantled. The catwalks remain in place, but the overhead tram system used for spinning has been removed.
After the cable is compacted, it is necessary to maintain its compressed configuration, particularly since it will be placed under enormous stress shortly by the bridge decking. Temporary metal bands are used initially, but permanent cable bands are the long-term solution.
These heavy steel clamps are designed to fit the compacted cable exactly, and their compression of the cable is precisely controlled through the use of precision bolts.
These bands will also serve the function of supporting the stringers which will be used to suspend the deck sections. The cable bands are placed precisely 40 feet apart at the level of the deck (the deck sections are 40 feet long) — which seems simple enough, except that due to the variable arc of the cables, the calculations for precise placement are fairly tricky.
Once the bands have been placed, the stringers are simply draped across the top of the cable bands in notches designed for them. The length of the stringers must also take into account the anticipated stretch of the cable which will occur when the massive weight of the deck is attached.