Scaffolds are independent structures only in rare cases. For reasons of stability the frame work ties of a scaffolding are fixed to the building, framework, or steelwork to which they are adjacent. Mobile aluminium tower scaffolds are hard to get ahold of but please see here!
On traditional scaffolding, as part of general practice, the ties are attached on alternate lifts or every 4m. If the scaffold system is prefabricated, structural connections are required on all frames, and can be at every 2-3 m, with the tie patterns being provided by the supplier or manufacturer. The junction of standards and ledger make for node points and the ties need to be coupled to the scaffold as close to these nodes as possible. Regulation have changed recently, and these require scaffolding ties to support both positive tie and butt holds and negative lateral shear loads.
Structures have different natures, and this makes it necessary for a variety of ties that can take advantage of opportunities.
Ties are put through structural openings like windows. The opening is crossed by a vertical tube and this is attached to the scaffolding structure with a transom and a bridle tube which is a horizontal tube that crosses outside. To ensure a solid fit, use is made of timber sections to close the gap between tubes, by packing or wedging them in the gap.
Box ties can also be used to connect the scaffold and attach it to pillars or other features that are suitable. Shorter tie tubes are used to join two additional transoms that are put across the lift that is one each side of the feature. If it is not possible to make a complete box tie, use may be made of a lip tie that is l-shaped so that it hooks the scaffold to the structure. For limiting inward movement, a butt transom is additionally placed hard against the structure’s outside face.
At times it may be possible to use bolt or anchor ties, which are ties that fit into holes made in the structure by drilling. Common ties of this kind are ring bolts that have an expanding wedge, that is then tied to node points.
Refurbishment of Waverley Station Roof in Edinburgh with Scaffolding by Balfour & Beatty, in 2011
Reveal ties are ties that are the least invasive. They make use of an opening in the structure but use tubes that are wedged horizontally into an opening. These reveal tubes are kept in their place by the use of threaded bars that can be adjusted, or reveal screw pin, as well as packing that acts as protection at either end. The scaffold and reveal tube are linked to each other by a transom tie tube. These reveal tubes are not very well thought of, as they are dependent on friction and need to be checked frequently. It is recommended that not more than half of the ties used are reveal ties.
When this does not become possible use should be made of a safe number of tie rakers. These rakers are single tubes that are securely founded and at an angle that is less that 75° and attached to a ledge that extends out from the scaffold. A transom then completes the triangle that goes back to the base of the main scaffold.
Scaffolding Components
Base jacks or plates act as bearing areas for scaffolds.
A standard, which is a upright component that has connector joints.
Horizontal braces or ledgers.
The transom is a load bearing component that has a horizontal cross section and holds the decking unit, board or batten.
Cross-section component for bracing or brace diagonal.
Working platforms are made with board or batten components.
Couplers that are fittings that join various components together.
Scaffold ties that tie the structure and the scaffold.
Widths of working platforms are extended though the use of brackets.