When temporary structures are provided to support platform for workmen, structural material and appliances required during construction at raised height (normally more than 1.5 m) it is called scaffolding.
Applications of Scaffolds
Scaffolding is necessary in following situations.
To support the working platforms where masons can stand and carry on their duties such as plastering, brick laying or painting etc.
Scaffolding is also provided where demolition or maintenance work of the building has to be carried out.
Key Points to Consider During Scaffolding
Construction and design of scaffold comes under safety regulation of building site. For example when a person is liable to fall from more than 2m, the platforms of the scaffolds are to be provided with a guard rail to a height of 1m and also a tie board at least 200 mm above the platform.
About 35 to 40 percent of all the accidents that takes place in building construction sites is due to faulty scaffolding. Therefore strict supervision should be followed according to standard practice during scaffolding erection.
All scaffolding should be properly fixed so that they do not fall away from wall laterally. Similarly it should be stable longitudinally also.
The platform should be wide enough to accommodate a person working on it. It should not be less than 425 mm in width when the height is more than 1.8 m.
When materials are to be stored on the platform then the width of the platform should not be less than 850 mm.
Workmen should not work under the scaffolding.
Types of Scaffolding
The following different types of scaffolding are in common use.
Single scaffolding or bricklayers scaffolding
Double scaffolding or masons scaffolding
Cantilever or needle scaffolding
Birds cage scaffolding
Ladder or trestle scaffolding
Construction of temporary structures to support an unsafe structure is called shoring.
Applications of Shoring
Shoring is provided in following situations
When a building wall shows sign of bulging or leaning outward
At the time of dismantling or reconstructing a defective building wall, shoring is provided to support the floors or roofs connected to that wall.
Shoring is also provided to support super structure when large openings are required to be made in the walls.
Key Points to Consider During Shoring
Temporary support by means of shores to unsafe structures may be given externally or internally or may be from both sides.
To maintain equilibrium, it is essential that the lines of actions of overturning forces in floors and roofs, the forces in walls and the reaction of the shores must meet at a single point.
Shoring can be made of timber or steel considering the load it has to withstand.
Shoring should be strong enough to resist the acting forces, consistent with economy
Types of Shoring
Depending on the supporting characteristic or their positions in the space, shorings are classified into following 3 types.
Raking or inclined shores
Flying or horizontal shores
Dead or vertical shores
Structures provided underneath of an existing foundation to maintain its stability is termed as underpinning. Underpinning is used to repair, strengthen or renewal of the foundation of an existing building.
During underpinning, the existing structure is required to be temporary supported by means of raking shores.
Applications of Underpinning
The following situations demand underpinning.
When defective foundation of wall is to be replaced with new foundation or when existing foundation of a wall is required to be strengthened to enable it to carry more loads.
To strengthen shallow footings of the existing building when a building with deep foundation is to be constructed adjoining to it.
To safe guard against the danger of excessive or differential settlement of foundations of existing structure.
To increase depth of foundation to increase its bearing capacity so as to sustain heavier loads.
During construction of basement of an existing building structure.
Key Points to Consider During Underpinning
Building should be first examined for presence of any weakness such as poor brickwork or masonry and for effects of settlement which may arise during the underpinning operation.
Temporary support should be provided by adequate shoring and by strutting up of openings and inside of floors.
In case of underpinning below high rise buildings, check must be made to measure any movement of the building by means of plumb bob or total station.
Types of Underpinning
There are several methods of underpinning of foundation of which the three popular methods are as follow.
Pit method – it involves strengthening by excavation and building below the existing foundation.
Pile method – it involves supporting the building on newly built piles of various types without excavation.
Pier method – this is a combination of pit and a pile method where first excavation is done below the foundation and a pir is built up for the new foundation.