RECOMMENDATIONS OF INDIAN STANDARD CODE ( 4326: 1993)

 

RECOMMENDATIONS OF INDIAN STANDARD CODE (18 4326: 1993)

General principles

The general principles given in para 1 to 9 shall be observed in construction of earthquake resistant buildings.

1. Lightness:

Since the earthquake force is a function of mass, the building shall be as light as possible consistent with structural safety and functional requirements. Roofs and upper storey’s of buildings, in particular, should be designed as light as possible.

2. Continuity of Construction:

2.1. As far as possible, the parts of the building should be tied together in such a manner that the building acts as one unit.

2.2. For parts of building between separation or crumple sections or expansion joints, floor slabs shall be continuous throughout as far as possible. Concrete slabs shall be rigidly connected or integrally cast with the support beams.

2.3. Additions and alterations to the structures shall be accompanied by the provision of separation or crumple sections between the new and the existing structures as far as possible, unless positive measures are taken to establish continuity between the existing and the new construction.

3. Projecting and Suspended Parts:

3.1 Projecting parts shall be avoided as far as possible. If the projecting parts cannot be avoided, they shall be properly reinforced and firmly tied to the main structure, and their design shall be in accordance with IS 1893 2002.

3.2. Ceiling plaster shall preferably be avoided. When it is unavoidable, the plaster shall be as thin as possible.

3.3. Suspended ceiling shall be avoided as far as possible. Where provided they shall be light, adequately framed and secured.

4. Building Configuration:

4.1. In order to minimize torsion and stress concentration, provision 4.2 to 4.4 should be complied with as relevant.

4.2. The building should have a simple rectangular plan and be symmetrical both with respect to mass and rigidity so that the centres of mass and rigidity of the building coincide with each other in which case no separation sections other than expansion joints are necessary.

4.3. If symmetry of the structure is not possible in plan, elevation or mass, provision shall be made for torsional and other effects due to earthquake forces in the structural design or the parts of different rigidities may be separated through crumple sections. The length of such building between separation sections shall not preferably exceed three timers the width.

4.4. Buildings having plans with shapes like, LTE, and Y shall preferably be separated into rectangular parts by providing separation sections at appropriate places. The building with small lengths of projections forming LTE or Y shapes need not be provided with separation section. In such cases the length of the projection may not exceed 15 to 20 percent of the total dimension of the building in the direction of the projection. Similarly for buildings with minor asymmetry in plan and elevation separation sections may be omitted.

5. Strength in Various Directions:

The structure shall be designed to have adequate strength against earthquake effects along both the horizontal axes. The design shall also be safe considering the reversible nature of earthquake forces.

6. Foundations:

The structure shall not be founded on such loose soils which will subside or liquefy during an earthquake, resulting in large differential settlements.

7. Ductility:

The main structural elements and their connection shall be designed to have a ductile failure. This will enable the structure to absorb energy during earthquakes to avoid sudden collapse of the structure. Providing reinforcing steel in masonry at critical sections, as provided in this standard will not only increase strength and stability but also ductility.

8. Damage to Non-structural Parts:

Suitable details shall be worked out to connect the non-structural parts with the structural framing so that the deformation of the structural frame leads to minimum damage of the non-structural elements.

9. Fire Safety: Fire frequently follows an earthquake and therefore, building shall be constructed to make them fire resistant.