Shantilal shah Engineering College, Bhavnagar

Civil Engineering Department

Building & town planning

Topic: planning of earthquake resistant building

Contents

Introduction General Planning and Design Aspects Location of Staircase Water Tank Sensitivity of building

Introduction Today the world is facing the problem of natural calamities like

earthquakes, landslides and many other which harm the construction done by us.

Most of the loss of life in past earthquakes has occurred due to the collapse of buildings constructed in traditional materials like stone, brick, adobe and wood, which were not initially engineered to be earthquake resistant.

Earthquake: A sudden movement of the earth’s crust causes by the release of

stress accumulated along geologic fault or by volcanic activity is called earthquake.

Earthquake damage depends on many parameters, including earthquake ground motion characteristics (intensity, duration and frequency content of ground motion), soil characteristics (topography, geologic and soil conditions), building characteristics, and quality of construction, etc.

Let us understand the concepts of reducing the effect of earthquake.

General Planning and Design Aspects

1)Lightness: Since the earthquake force is a function of mass, the building shall be as light as possible. Heavier structure means large inertia force and collapse of these structure result in heavier damage and and loss of lives. Thus, roof and upper storeys of building, in particular, should be designed as light as possible.

2)Symmetry: The building as a whole or its various blocks should be kept symmetrical about both X and Y axes. Asymmetry leads to torsion during earthquakes and is dangerous (see Fig). Symmetry, as far as possible, is also desirable in the placing and sizing of door and window openings.

3) Regularity: Simple rectangular shapes (see Fig. 3.2 a) behave better in an earthquake than shapes with projections (see Fig. 3.2b). Torsional effects of ground motion are pronounced in long narrow rectangular blocks. Therefore, it is desirable to restrict the length of a block to three times its width. If longer lengths are required two separate blocks with sufficient separation between should be provided (see Fig. 3.2 c).

4) Separation of Blocks: Separation of a large building into several blocks may be required so as to obtain symmetry and regularity of each block. For preventing hammering or pounding damage between blocks a physical separation of 30 to 40 mm throughout the height above the plinth level will be adequate as well as practical for up to 3 storey buildings (see Fig. 3.2 c). The separation section can be treated just like expansion joint or it may be filled or covered with a weak material which would easily crush and crumble during earthquake shaking. Such separation is more practical in larger buildings since it is less convenient in small buildings.

5) Simplicity: Ornamentation involving large cornices, vertical or horizontal cantilever projections, facia stones and the like are dangerous and undesirable from a seismic viewpoint. Simplicity is the best approach.

Where ornamentation is insisted upon, it must be reinforced with steel, which should be properly embedded or tied into the main structure of the building.

6)Continuity: The earthquake forces developed at different floor levels in a building need to

be brought down along the height to the ground by the shortest path; any deviation or discontinuity in this load transfer path results in poor performance of the building.

Some buildings have reinforced concrete walls to carry the earthquake load to the foundation. Building, in which these walls do not go all the way to the ground but stop at an upper level, are liable to get severely damaged during the earthquakes.

7)Size of the building: Buildings of great length or plan area may not respond to earthquakes in the way calculated. Buildings that are too long in plan may be subjected to different earthquake movements simultaneously at the two ends, leading to disastrous results. As an alternate such building can be broken into a number of separate square buildings .

In tall buildings with large height –to-base size ratio (slenderness ratio > 4), the horizontal movement of the floors during ground shaking is large, The more taller a building, the worse the overturning effects of a an earthquake.

In buildings with large plan area like warehouses, the horizontal seismic forces can be excessive to be carried by columns and walls.

Location of Staircase

The staircases in structure may be vulnerable if not detailed properly. When attached rigidity to the floors, the flights of the staircase act like braces and cause damage.

There are three types of stair construction:

1)Separated staircase

2) Built-in staircase

3)Staircase with sliding joints

Separated Staircase:

One end of the staircase rests on a wall and the other end is carried by columns and beams which have no connection with the floors. The opening at the vertical joints between the floor and the staircase may be either covered with a tread plate attached to one sided of the joint and sliding on the other side, or covered with some appropriate material which could crumble or fracture during an earthquake without causing structural damage.

The supporting members, columns, or walls are isolated from the surrounding floors by means of separation or crumble sections. A typical example is shown in figure.

Separated staircase

Built-in Staircase:

When stairs are built monolithically with floors they can be protected against damage by providing rigid walls at their stair opening. An arrangement in which the staircase is enclosed by two walls, is given figure.

Built-in Staircase

Staircase with sliding joints:

In case it is not possible to provide rigid walls around stair openings for built in staircase or to construct separated staircases, the staircase should have sliding joints so that they will not act as diagonal bracing.

Water Tank Elevated water tank contain huge mass at height supported on

columns or circular RCC shaft. It is an example of single degree of freedom.

As large mass is supported at height, centroid of mass will be higher. During earthquake inertia force produced due to mass of water and earthquake acceleration may cause overturning of the tank.

Inertia force = mass * acceleration

Higher the mass, more will be the inertia force acting on the water tank. Attempts should be made to reduce the capacity of tank, i.e. mass of water.

The columns or RCC shaft acts as stiffening member, providing stiffness resistance during earthquakes.

Water Tank

The location of water tank on roof slab should be carefully decide. It should be centrally located on the building. Water tank on edge or corner of a building may cause imbalance of mass, resulting in overturning of tank. For small residential buildings, light weight PVC tanks are preferred to reduce mass of the building.

Sensitivity of building Construction work should be carried out by qualified civil

engineer.

Plan of building should be square or rectangle.

Flat concrete roof is preferred.

The thickness of wall should not be less than 230mm.

The proportion of cement : sand mortar should not be weaker than 1:4.

The total height of the building should not be exceed 15 m.

Vertical reinforcement must be provided at corners of wall and at door jambs.

Site investigation must be carried out. Bearing capacity of soil should be more than the required safe bearing capacity.

Proper R>C>C bands should be provided at plinth level, lintel level, caves level.

THANK YOU FOR BEARING

Presented By, Roll No.1061-1070