Earthquake is produced by sudden release of tremendous amount of energy with in the earth by sudden movement of Earth's various layers. Earthquake strikes suddenly, very fast and violently without any warning. It may harm badly designed and constructed buildings which may injure or kill its inhabitants. The following factors affect the building safety during the earthquake.
Factors affecting building during earthquake
Poor quality building material, weak foundation or structure may be harmful during earthquake.
Old or leaning trees, electrical wires and power line close to the house or building are harmful and cause damage at the time of earthquake.
Irregular balconies and cantilever structure may be dangerous during earthquake.
Reservoirs, water tower and other weak or poorly constructed buildings adjoining to your house or building can be harmful at the time of earthquake.
Nature of soil also has great effect on the safety of the building during earthquake. Poor deep loose sand, silt clay, gavel, soft and saturated granular soils are not able to resist the earthquake motion in the ground and lead to foundation damage.
Sandy soil can be easily affected by earthquake; it may make ground incapable of supporting foundation. The ground may crack or heave which may cause settlement of building. The building may even collapse due to this settlement problem.
Water saturated soil changes its behavior during earthquake and becomes slushy which may lead to the failure of foundation of the building.
Type of building structure whether R.C.C. frame, steel frame, wooden frame or load bearing masonry walls also affect the building structure during earthquake.
Irregular shaped and high buildings may be affected easily during earthquake.
However, if the structure has ductile behavior, it may increase the strength of building. RCC structure, steel structure and timber structure have ductile nature so this material is suitable for construction. Timber based construction requires good quality timber and some safety factors such as fire safety, termite control, and moisture should also be considered so that the timber retains strength for a long period. The brick masonry structure is less resistant to earthquakes where as RCC frame structure building and brick structure with re-enforcement at all the meeting joints provide earth quake resistant structure. Qualified engineer, good quality material and construction may minimize the damage during earthquake.
Earthquake resistant construction and building material
Foundation of the building should be constructed on the hard strata soil by using earthquake safety measures as directed by design Engineer. Soil test must be performed before designing the foundation of the building.
Minimum depth of foundation should be one meter.
Deep and unbroken rock foundation of good quality and stiff soil are best for foundation as it allows less transfer of vibrations to the building.
Foundation of building should be re-enforced by using M .S bars and cement concrete mix not less than the ratio of 1:1.5:3
Building should be frame structure with re-enforced columns, beams and slab with less use of brickwork or stone work in walls and roof.
The shape of building should be square or compact rectangular.
Building should be closed shape, it is preferred to construct in U or L shape building.
The parts of the building should be tied together firmly and braced at corners stiffly in such a way that the whole structure tends to move as single unit. In RCC frame structure building, tie beams are provided for such purpose.
Keep minimum balconies and cantilevers during construction of building.
Parapets, cornices, cantilevers and projections should be re-enforced and attached to the main structure firmly.
Keep minimum height of parapet and other unsupported walls.
The structure should be made as light as possible because the force of earthquake is a function of the mass.
Particularly the roof and upper stories of building should be designed as light as possible.
The thickness of any load bearing wall should not be less than 23 cm.
Keep minimum height as far as possible in multi-story building.
If there are roof trusses, fix these with wall using bolts in pockets made in the wall and it should be filled with cement concrete.
Use light sheet material for roofing such as G I sheet or A C sheet. And fix them with the purlins and J hooks.
Do not use loose dry brick when using false ceiling below the trusses.
All the joints of purlins and other supporting members should be properly bolted with each other.
Make plinth protection around the house or building wide enough, so as to prevent water going under the foundation.
R.C.C band with the size 75 mm to 100 mm thick should be provided at plinth level, lintel level and roof level.
Provide R.C.C. band in case of trusses or rafter to connect all the columns and walls for protection against earth quake.
Bricks should be first class bricks and should have minimum crushing strength of 105 Kg. per sq. cm.
Sand used for making cement mortar should be clean, free from silt, vegetable matter, and other foreign material.
The ratio of cement sand mortar in brick work should be 1:4 but not less than 1:6 in any case.
The material used in cement concrete should be according to the specification and the mix should be 1:1.5:3.
Mild steel used in R. C. C. work should be tor or ribbed and properly tested in the testing laboratory.
All the doors, windows and cabinets should be properly fixed with proper hold fast that should be embedded in cement concrete.
The cement used in construction work should be fresh not affected by moisture and manufactured by reputed firm and not from local plant.
The bricks used in masonry should be properly soaked in water.
All construction work should be done by skilled mason, carpenter and blacksmith etc.
All the building members should be properly connected with each other.
R.C.C. unit should be laid with proper steel plates not by wooden planks or temporary bricks etc.
Proper curing should be done during construction work for maximum strength of building.
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