Masonry structures upto three storeys or maximum four storeys are not very uncommon in India. Most of housing boards, Development Authorities construct housing flats upto three/four storeys and masonry is definitely economical. National Building Code of India (SP-7) provides all the required design tables, nomograms and description on masonry design.
Recommendations of IS 4326 for seismic detailing in masonry structures shall be seen. RCC bands at Plinth level and Lintel Levels is a must in masonry structures.The vertical bars at corners of rooms along with vertical bars around openings shall be provided as per details given in IS 4326.
Brickwork is generally available in three classes:
- 1st class Bricks have crushing strength not less than 105 Kg/cm2
- 2nd class Bricks have crushing strength not less than 75 Kg/cm2
- 3rd class Bricks have crushing strength not less than 35 Kg/cm2
For buildings over two storeys, 1st class brickwork is needed For buildings upto two storeys, 2nd class brickwork can be used. 3rd class bricks can be used in exceptional circumstances of non availability of good bricks , only for single storeyed.
Masonry structures must have system of walls with cross walls at regular interval( about 3.0m to 3.5m c/c). In case cross walls are not available, need for provision of RCC columns to laterally support the long wall arises. Opening in masonry structures must be properly planned in consultation with Architect. Zones of stress /load concentrations must be identified. Introduction of RCC columns may be resorted where stress is exceeding.
All beams must rest on PCC bed blocks/or extended bearing length on masonry to keep the stress on brickwork within limit.
Mortars for brick work:
This shall be provided as per design requirements. Very approximately:
CM 1:6 – single storeyed (can be 3rd class brick in exceptional cases if design permit)
CM 1:5 – Ground storey of Two storied( with min 2nd class brick)
CM 1:4 – Ground storey of Three storied( with First class brick)
CM 1:3 – Ground storey of Four storied( with First class brick)
Curing of brick work – This is very neglected area and 10 to 14 days curing must be emphasized.
Provision of plasters also help in strengthening the walls Free standing Boundary walls must be in CM 1:5 minimum.
SP20 of Indian Standard (IS) Code provides all the guidelines for design and construction of brick masonry.