When temporary structures are provided to support platforms for workers, the structural materials and equipment required during construction to be constructed at a height (usually more than 1.5 m) is called scaffolding,
Scaffolding is necessary in the following situations.
- To support working platforms where masons can stand and perform their duties such as plastering, brick laying or painting etc.
- Scaffolding is also provided where the building is to be demolished or maintenance work is to be done.
Key points to consider during scaffolding
- The construction and design of scaffolding falls under the safety regulation of the building site. For example when a person is liable to fall more than 2 m, scaffolding platforms should be provided with a guard rail up to a height of 1 m and a tie board at least 200 mm above the platform.
- About 35 to 40 percent of all accidents at building sites are caused by faulty scaffolding. Hence strict supervision should be followed as per standard practice during scaffolding construction.
- All scaffolding must be properly fixed so that they do not fall away from the wall later. Similarly it should also be longitudinally stable.
- The platform should be wide enough to accommodate the person working on it. When the height exceeds 1.8 m, its width shall not be less than 425 mm.
- When the material is to be deposited on the platform, the width of the platform should not be less than 850 mm.
- Employees should not work under scaffolding.
types of scaffolding
The following different types of scaffolds are in common use.
- Single Scaffolding Or Brick Scaffolding
- Double Scaffolding Or Masons Scaffolding
- cantilever or needle scaffolding
- bird cage scaffolding
- Ladder or Trestle Scaffolding
- suspended scaffolding
The construction of temporary structures to support an unsafe structure is called shoring.
applications of shoring
Shoring is provided in the following situations
when the wall of a building appears protruding or sloping outwards
At the time of demolishing or reconstruction of a defective building wall, shoring is provided to support the floors or roofs attached to that wall.
Shoring is also provided to support the super structure when large openings are required to be made in the walls.
Key points to consider during shoring
Temporary support may be given externally or internally through coasts for unsafe structures or may be from both sides.
To maintain balance, it is necessary that the lines of action of the reverse forces in the floors and ceilings, the forces in the walls and the reactions of the coasts meet at the same point.
Shoring can be made of wood or steel, depending on the load it has to withstand.
The shoring must be strong enough to resist the forces acting in accordance with the economy
types of shoring
Based on the supporting characteristic or their position in space, shorings are classified into the following 3 types.
- raking or sloping edge
- flying or horizontal edge
- dead or vertical edge
The structures provided under an existing foundation to maintain its stability are called underpinnings. Underpinnings are used to repair, strengthen or refurbish an existing building foundation.
During the underpinning, the existing structure is required to be temporarily supported by means of raking shores.
Applications of underpinnings
Aadhar is required in the following situations.
- When a defective wall foundation is to be replaced with a new foundation or when it is necessary to strengthen the existing wall foundation to enable it to carry more load.
- To strengthen the shallow foundation of the existing building when a building with deep foundation is to be constructed adjacent to it.
- To guard against the danger of excessive or differential settlement of the existing structure’s foundations.
- To increase the depth of the foundation to increase its bearing capacity so as to sustain the heavy load.
- During the construction of the basement of the existing building structure.
Key Points to Consider When Underpinning
- The building should be first examined for the presence of any weaknesses such as poor brickwork or masonry and for the effects of settlement that may arise during the underpinning operation.
- Temporary support should be provided by adequate shoring and by enlarging the inside of the opening and floor.
- In case of underpinnings under tall buildings, any movement of the building through the plumb bob or total station should be probed to measure it.
types of underpinnings
There are many methods of reinforcing the foundation, of which three popular methods are as follows.
- pit method – This includes reinforcement by digging and building under the existing foundation.
- stack method – This includes supporting the building on a variety of newly constructed piles without excavation.
- wharf method It is a combination of pit and pile method where first excavation is done under the foundation and a pir is made for the new foundation.