Scaffolding is a temporary structure erected during construction for supporting labourand materials in order to execute masonry, plastering and other items of work. It isvery essential that scaffolding should be strong enough and safe so that accidents donot occur due to its failure.
- A scaffold consists of upright members called standards, longitudinal horizontal members parallel to the wall called stringers and cross horizontal members at right angle to the wall called putlogs. Over the putlogs, planks are provided to form a platform which serves as working space for workers and stacking space for materials.
- In order to distribute concentrated loads from standards on the ground, these are supported on base plates of suitable size. On the other side of the platform, plank on edge called ‘toe board’ is provided to prevent falling down of materials, and also a guard rail is provided for safety of workers.
- Sometimes, it is necessary for workmen to execute certain items of work – such as application of finish coats to external walls at a height which cannot be reached by ladders and it is not economical to go in for normal scaffolding for that purpose. In such situations, a cradle with working platform, suspended by ropes from the roof terrace, is provided. The cradle is held in position or moved sideways or up and down by a few workers stationed on the terrace.
There are two systems of scaffolding, namely ‘single scaffolding’ and ‘doublescaffolding:
- In case of single scaffolding there is only one row of standards at some distance from the wall and putlogs are supported by stringers on one end and on wall masonry at the other end.
- In case of ‘double scaffolding’ two rows of standards are provided and two ends of putlogs rest on stringers only.
Two types of scaffold namely ‘timber/bamboo scaffold’ and ‘steel scaffold’ are mainly used in construction.
- Steel tubes for individual component type scaffolding shall be heavy class welded or seamless tubes of 40 mm nominal bore conforming to IS: 1161.
- For other types of scaffoldings, the individual tube or tubes forming part of the unit frame shall conform to the requirements of IS: 1161.
- The sizes of such tubes shall be governed by the design requirements stated below and the minimum thickness of metal for such tubes shall conform to IS:806.
All types of scaffoldings shall be capable of carrying and transmitting to the ground,all resultant loads by themselves or jointly with load carrying parts of the building,which have achieved adequate strength for this purpose.
- The loading on the scaffoldings shall comply with the appropriate requirements of relevant Indian Standards regarding loading on temporary structures and scaffoldings.
- All scaffoldings shall be adequately stiffened, both longitudinally and transversely to take up horizontal loading due to wind pressure on the scaffolding or tensioning ropes, if any, or both; and the forces resulting from inclined supports or support derived from the parts of a structurally stable building, lifting tackle, etc.
- The scaffoldings shall be adequately rigid at all stages of erection and dismantling.
- Where the supports cannot be fixed vertically due to any reason, the eccentricity of the loading so carried should also be taken into account.
- The braces should be designed to carry, in addition to any applied horizontal loads, and the horizontal loads induced by the non-vertical supports, an additional horizontal load equal to 1/100 of the vertical loads carried by each platform and applied on its upper surface, and 1/100 of vertical loads carried by the ground applied at the base of scaffolding.
- The permissible stresses and other design considerations shall comply with the appropriate requirements of relevant Indian Standards on structural design of tubular steel scaffolding.
All fittings shall be manufactured from steel which when analysed in accordance withthe relevant part of IS: 228 shall not indicate more than 0.06% of sulphur, 0.06% ofphosphorous and shall also conform to steels of schedule II of IS: 1570.
1 Steel sections, bars and rivets
a) Steel sections and bars shall conform to IS: 226.
b) Rivet bars shall conform to IS: 1148.
2 Bolts and nuts
Bolts and nuts shall have mechanical properties not less than those specified in IS:1367 and shall also conform to the requirements of IS: 1362.
- If not galvanized and unless otherwise specified, the tubes and frames shall be painted or varnished externally throughout their exposed surface.
- The steel sections shall also be suitably painted or otherwise treated for protection against rust and corrosion.
- All fittings shall be suitably treated so as to render them resistant to corrosion.
DISMANTLING OF METAL SCAFFOLDS
Dismantling sequence should be planned and that sequence of dismantling sectionsof the scaffold should be logical and determined with due consideration of the safetyof the labourers carrying out the work.
- Dismantling work should proceed generally from the top in horizontal sections.
- Scaffolds should not be dismantled in vertical sections from one end towards the other unless special consideration is given to ties and bracings.
- All materials should be lowered to the ground and not stored on the scaffold.
RELATED CODES :
- Hand book on masonry design and Construction (First revision) published by Bureau of Indian Standards.
- Code of practice for metal scaffolding safety by Occupational Safety and Health branch of Labour Department (Hong Kong).
- IS: 226-Specification for structural steel.
- IS: 228-Methods of chemical analysis for steel.
- IS: 806-Code of practice for use of steel tubes in general building construction.
- IS: 1148-Steel rivet bars (medium and high tensile) for structural purposes.
- IS: 1161-Steel tubes for structural purposes.
- IS: 1362-Dimension for screw threads for general purposes.
- IS: 2750-Specification for steel scaffoldi