How Earthquake Resistant buildings are Planned?
The earthquake resistant buildings are planned in the following ways:
(i) Symmetry: The building as a whole or its individual blocks should be kept symmetrical about both axes. Asymmetry leads to torsion during earthquakes and is very dangerous; symmetry is also desirable in the arrangement and size of door and window openings, to the extent possible.
(ii) Regularity: Simple rectangular shapes behave better in an earthquake than shapes with many projections. The torsional effects of ground motion are particularly pronounced in long, narrow, rectangular blocks. Therefore, it is desirable to limit the length of a block to three times its width. If longer lengths are required, two separate blocks should be provided with adequate spacing between them.
(iii) Division of blocks: Division of a large building into several blocks may be necessary to achieve symmetry and regularity of the individual blocks. To prevent damage from hammering or bumping between blocks, a physical separation of 3 to 4 inches across the entire height above the base is appropriate and practical for buildings up to three stories.
The separation section can be treated as an expansion joint, or it can be filled or covered with a weak material that is easily crushed and crumbled during earthquake shaking. Such a separation may be considered for larger buildings, as it may not be practical for small buildings.
(iv) Simplicity: Appearance involving large cornices, vertical or horizontal cantilever projections, facia stones are very dangerous and undesirable from a seismic viewpoint. It is the best approach.
(v) Enclosed Area: A small building enclosure with properly interconnected walls acts like a rigid box against earthquake. Therefore, structurally it will be advisable to have separately enclosed rooms rather than one long room.
(vi) Separate Buildings for Different Functions: In view of the difference in importance of hospitals, schools, assembly halls, residences, communication and security buildings etc., it may be economical to plan separate blocks for different functions to affect economy in strengthening costs.
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