Memory is often short lived. We have forget the lesson learned that Earthquakes don’t kill people, buildings do. Destructive earthquakes has tried to teach us hard lessons in designing safe buildings. although buildings of brick and stone masonry performed very badly during recent earthquakes. Still most of the buildings are being constructed with same very casual approach as shown in the Fig-1. Attention was focused on weaknesses in building construction, especially poor building standards and the lack of any provision for earthquake resistant element in structure. Indian Building Codes recommend standards of design and construction so that buildings could resist the horizontal motions created by ground shaking. Masonry buildings had to be firmly bonded, with parts tied together so the structure would move as one unit. The main aim is to protect a building from structural damage. For a major earthquake, however, the goal is to protect life by ensuring a building will not collapse and people can escape from it, even if the building itself is badly damaged. India is among the most earthquake prone countries in the world and in the last 15 years, we have experienced six earthquakes of moderate intensity. Although moderate in intensity, these earthquakes caused considerable losses to human life and property, highlighting the extreme vulnerability of the population and infrastructure to earthquakes. While earthquakes are natural hazards, the disasters are man-made.

The most of the domestic buildings constructed in recent past do not have minimum required wall thickness. Bad Construction practices (Some of them shown in the figure) have cropped up in the construction industry due to rising construction cost, the lack of trained masons. And over confident petty contractors. 115 mm thick brick walls with horizontal electric wire conduit pipe, water supply pipes are uses as load bearing walls. Hidden beam culture. Spacious rooms double height porch and lobby with difference in floor levels, big over head tanks and heavy RCC slanting roofs all such components has devastating effects on building performance during ground shaking, and should be avoided at least needs technical design and supervision to make them stable enough.

Fig-1

Fig- 3 Fig-2

Some Guidelines excerpt from codes:

· Box System -The box system utilizes. walls which support vertical loads and also resist seismic forces. There may be other elements, such as a partial simple frame system. which support a portion of the vertical loads.

· Band (Fig- 2) - A reinforced concrete or reinforced brick runner provided in the walls to tie them together, so that the structure acts as one unit to resist the earthquake effects. These bands are generally provided at plinth, lintel or roof level. The most common among these is the lintel band.

· Joints between exterior columns and adjoining beam members shall be confined by transverse column reinforcement through the joint as shown in Fig-3. This is required because exterior columns the joint core in not confined by beams on all sides.

· Extra care should be given to vertical and horizontal projections like towers, tanks, chimneys, balconies and other cantilever projections or appendages in buildings. Experience from past earthquakes has shown that such appendages get damaged considerably and many lives are lost due to their collapse. Such systems are subject to larger motions than the building to which they are attached. Therefore. the Code recommends that the seismic coefficient for the design of vertical cantilever projections attached to the building should be taken as five times that specified for the main structure.

· Continuous rows of openings in a load bearing wall makes it weak and hence it should be preferably a voided or otherwise the openings should be staggered. The openings should also be reinforced all round.

· If a new structure is built by the side of care should be taken to reinforce them and anchor an existing structure adequate precaution should them to the main structure adequately. be taken to provide separation between them to avoid hammering during seismic vibration.

· Ceiling plaster should be as thin as possible Projecting Parts and the suspended ceiling should be avoided as far as possible. Light weight suspended ceiling Overhanging parts, such as projecting in any building should be adequately fastened. cornices, balconies, parapets and chimneys are the Such ceilings often used for aesthetic reasons are first to fall during an earthquake.

· Unsymmetrical buildings usually develop torsion due to seismic forces. Hence the building should have a simple rectangular plan and be symmetrical both with respect to mass and rigidity, so that the centre of mass and centre of rigidity of the building coincide with each other and there is no eccentricity. Since zero eccentricity is very difficult to achieve in design, efforts should be made to have minimum eccentricity in the building with suitable provisions for torsional effect. Irregular shape buildings may be designed as a combination of few regular shapes with suitable construction joints.

· The foundations founded on soils liable to liquefy need design considerations to avoid damage to the structure due to foundation failure. The Code recommends that as far as possible entire building should be founded on the same type of soil in order to avoid differential settlement. Loose fine sand, soft silt and expansive clays may give rise to large differential settlements and should generally be avoided. However. a raft foundation in such soils is less vulnerable and may be used. Alternatively, a pile foundation would also obviate such a problem. If the structure is light (where a pile/raft foundation is not required), the Code suggests some methods for improving the foundation soil.

· To avoid sudden collapse of the structures during an earthquake and to enable them to absorb energy by deformation beyond yield point, the main structural elements and their connections should be so designed that the failure is of a ductile nature. From earthquake considerations a ductile structure is preferable as it has enough energy to absorb the shocks. Therefore. detailing of the member (including minimum reinforcement) should be such that the sudden collapse of structure is avoided in the event of any failure.

· It has been observed that fire frequently follows an earthquake and. therefore, the buildings should be constructed to make them fire resistant in accordance with the provisions of relevant Indian standards for fire safety. If fire breaks out. the components of the building should be able to retard the. fire for a few hours, that is the material used in construction should have fire resistance ratings specified in the National Building Code.

· The information provided in this article is for general awareness. It is advised that buildings should be structurally designed and constructed in the supervision of qualified and experienced civil engineer.

Er. Daljeet S Sidhu

M.E.Civil;, Memb. I.E., Memb.I.R.C.

House No. 624 Phase 2,

Dugri Road Urban Estate

Ludhiana

+919872094720

For Further Information Please Click the Following Links

FIRE SAFETY OF BUILDINGS

In order to reduce spread of fire, it is necessary that:

a) the fire should not spread rapidly from one room to another through the floors, partitions between rooms, and particularly between rooms and passages and staircases, that is, the structural elements should have adequate fire resistance,

b) the materials which are exposed to possible ignition, that is, wall and ceiling linings should not easily ignite, nor should the fire spread rapidly over the surface of the materials.

Fire Resistance

Ability of an element of building construction, component for structure to fulfill, for a stated period of time, the required stability, fire integrity and/or thermal insulation and/or other expected duty in a standard fire resistance test

Fire Separation

The distance in metres measured from any other building on the site, or from other site or from the opposite side of street or other public space to the building for the purpose of preventing the spread of fire.

Fire Resisting Wall

The wall, either load bearing or non-load bearing. capable of specifying the criteria of fire resistance with respect to collapse, penetration and excessive temperature rise.

Separating Wall

The wall provides complete separation of one building from another or part of a building from another part of the same building to prevent any communication of fire or any access or heat transmission to wall itself which may cause or assist in the combustion of materials of the side opposite to that portion which may be on fire.

Venting Fire

The process of inducting heat and smoke to leave a building as quickly as possible by such paths that lateral spread of fire and heat is checked, fire fighting operations are facilitated and minimum fire damage is caused.

General Design

The design of any building and the type of materials used in its construction are important factors in making the building resistant to a complete burn-out and in preventing the rapid spread of fire, smoke or fumes, which may otherwise contribute to the loss of lives and property. The types of construction according to fire resistance are classified into four categories, namely, Type I, Type 2, Type 3 and Type 4 construction. The fire resistance ratings for various types of construction for structural and non-structural members should be as given in Table 1.

HIGH RISE BUILDINGS

For high rise buildings, the following additional provisions of means of access to the building should be ensured:

The width of the main street on which the building abuts should not be less than 12 m and one end of this street should

join another street not less than 12 m in width; The road should not end in a dead end; The compulsory open spaces around the building should not be used for parking; and Adequate passageway and clearances required for fire fighting vehicles to- enter the premises should be provided at the main entrance; the width of such entrance should be not less than 4.5 m. If an arch or covered gate is constructed, it should have a clear head-room of not less than 5 m.

For Detail Study

IS 1641 : 1988 IS 1642 : 1989 IS 1643 : 1988 IS 1644 : 1988

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