earthquake ravi

7/30/2019 Earthquake Ravi

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Basic Design Consideration for Earthquake Resistant Techniques inSmall Scale Buildings


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Shape of plan

The shape of the plan of the house might have an important influence on its stability. The

following rules must be considered:

The more compact a plan, the better the stability. This means a square plan is better than a

rectangular one, and a circle is better than a square.

L-shaped plans are less stable. The best solution in this case is to separate the Elements.


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Placement of house in the case of slopes

In earthquake-prone areas, where the site is inclined, the following

rules must be taken into account:

a) The house should not be cut into the slope, as the adjacent wall

might collapse due to the horizontal forces of the earth.

b) The house should not stand on the slope a sit might slip down.

c) The house should not stand near steep slopes as it mightcollapse due to falling rocks or earth avalanches.

d) If a slope is given, a platform has to be formed and the house

has to be placed at sufficient distance from the slopes.

e) It is recommended that massive and heavy houses stand on softsandy soils, whereas light flexible structures can stand on rocky

soils.

f) Different floor levels should be avoided. If it is necessary, the

rooms should be separated.


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Typical failures, typical design mistakes

diagonal cracks lead from the edges of windows to the bottom of the wall.

the lintel often destabilizes the walls, especially if it is not long enough and does not have

sufficient bond with the wall.

if the wall between window and door or between opening and corner is not long enough, it

might break.

if the wall has no ring beam at the top it breaks easily when suffering perpendicular loads

which produce bending.


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Typical design mistakes which might lead to the collapse of the house

1. Ring beam is lacking.

2. Lintels do not reach deeply enough into masonry.

3. The distance between door and window is too small.

4. The distance between openings and wall corner is too small.

5. Plinth is lacking.

6. The window is too wide in proportion to its height.

7. The wall is too thin in relation to its height.

8. The quality of the mortar is too poor, the vertical joints are not totally filled, the horizontal

joints are too thick (more than 15 mm).

9. The roof is too heavy.

10. The roof is not sufficiently fixed to the wall.


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Good features of earthquake resistant construction


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Corner solution Expedient proportion of wall


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Structural design aspects

1. Walls and roof are well interconnected and so rigid that no deformation occurs in the

earthquake.

2. Walls are flexible enough, so that the kinetic energy of the earthquake is absorbed by

deformation. In this case a ring beam, which is able to take bending forces, is necessary and

the joints between wall and ring beam and ring beam and roof must be strong enough.

3. the roof is fixed to columns separated from the wall, so that both structural systems canmove independently as they have different frequencies.


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Joint with lateral stability Internal reinforcement

5 cm diameter


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Ring beams

able to take bending loads when there are

lateral forces against the wall.

prevent the walls from buckling and falling.Can also act as a support for the roof structure.

stiffening the corners for ring beams


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Ring beams which act as roof support

positioned centrally over the wall.

a top layer of burnt bricks be built for better

stress distribution.


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Gables

If gables are part of the wall, they are very weak against perpendicular forces.

build a roof with four inclined planes (pyramidal shape), with which no gables appear.

build a light gable which is fixed only to the roof.

build a gable wall and to stabilize it with a buttress. If a concrete skeleton structure is used,

which is the most expensive solution, the gable also has to be stabilized by reinforced concrete

elements.

Stabilization by reinforced

concrete structureStabilization by buttressesGable fixed roof


17/38Strengthening of long walls by buttresses

R f S t d f


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Roofs

should be built as light as possible.

Roofs with tiles or stone plates are not re-

commended, as they are heavy and in case of

an earthquake the tiles or plates might fall

into the house. a pyramidal roof with 4 inclined planes,

which rest on a horizontal ring beam, is the

best solution.

Separated roofs

due to their different moment and weight,

the safest solution is to separate the roof from

the wall and have it resting on columns which

are positioned inside or outside the wall. Then

the roof and wall systems can moveindependently of each other.


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Roof Overhangs Must Be Kept Short

Openings in Long Overhangs Help Reduce Wind Pressure


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Openings for doors and windows

Openings within the walls destabilize the wall

system.

Lintels have to penetrate into the wall for at

least 40 cm in order to achieve a good bond. use the lintel as a ring beam on which the

roof structure rests.

part below the window be built as a light

flexible structure

The length of the windows should not be

more than 1.20 m and not more than 1/3 of the

length of the wall.

The length of walls between openings must

be at least 1/3 of their height and not less than

1 m. Doors must be opened towards the outside.

Opposite the entrance door there should be a

large window or another door, which acts as

emergency exit.

Stabilized openings


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Stabilized openings

Recommendable dimensions of openings

Recommendable positions of openings


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Reinforcing around openings


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Vertical reinforcement in walls


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Stone masonry

Random rubble masonry withthrough stones or other bonding

elements

through stones one -per m2 of wall area, e.g. one every 1.2 m horizontally in every 0.9 m

height.


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Random rubble masonry with through stones or other bonding elements

Foundations Masonry footing for load bearing walls


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Foundations Masonry footing for load bearing walls

Masonry footing for load bearing walls

Depth of footing should go below the weathering zone. Usually a depth of 75 to 90 cm below

ground level will be adequate.

footing width for safe bearing pressure.

Storey 1 2 3

width 75cm 1m 1,2m


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Plasters and paints

Adobe walls have to be plastered by mortars made of earth or lime, or by earth stabilized

with cement, lime or bitumen.

A pure cement plaster should never be used, as it is too brittle and tends to crack under

thermal loads (through expansion and retraction) and under mechanical impacts.

If water penetrates through these cracks, the earth underneath will expand creating more

cracks, or even burst off.

If an earth mortar is used for plastering, it is recommended that the surface be made

waterproof by applying a paint of lime or limecasein.

Rammed earth walls do not need plastering. It is better to smoothed the surface with a

trowel while it is still humid and then add two or three layers of thin lime or lime-casein paint.

The first layer must have a high water content, so that it penetrates 2 or 3 mm deep into the

wall.


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Quality of construction

Materials should conform to appropriate specifications e.g. properly fired bricks ofuniform

sizes, seasoned or dried heart wood.

Proper mortar should be used in construction, filling all horizontal and vertical joints. The

masonry units should be laid with proper bond avoiding continuation of vertical joints

particularly at the intersection of walls.

Stone masonry walls must have appropriate mortar filling in the hearting and use of

through stones or bonding elements is a must.


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Ground Floor Soft Story Columns Must Be

Braced

Diagonal Bracing Chevron Bracing


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EARTHQUAKE-RESISTANT CONFINED MASONRY CONSTRUCTION

WHAT it is ??

a building technology that offers an alternative to both unreinforced masonry and RC frame

construction.

suitable for one to four storey high.

consists of masonry walls (made either of clay brick or concrete block units) and horizontal

and vertical RC confining members built on all four sides of a masonry wall panel.

Vertical members, called tie-columns

Horizontal elements, called tie-beams,

Enhancing the stability and integrity of masonry walls for in-plane and out-of-plane

earthquake loads (confiningmemberscaneffectivelycontaindamagedmasonrywalls).

Enhancing the strength (resistance) of masonry walls under lateral earthquake loads.

Reducing the brittleness of masonry walls under earthquake loads.


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A typical confined masonry building


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Confined Masonry Different from RC Frame Construction

Confined masonry construction RC frame construction

Gravity and

lateral load resistingsystem

Masonry walls are the main load

bearing elements and are expected toresist both gravity and lateral loads.

Confining elements (tie-beams and tie

columns) are significantly smaller in

size than RC beams and columns.

RC frames resist both gravity

and lateral loads through theirrelatively large beams, columns,

and their connections. Masonry

infills are not load-bearing walls.

Foundation

construction

Strip footing beneath the wall and the

RC plinth band

Isolated footing beneath each

column

Superstructure

construction

sequence

1. The frame is constructed first.

2. Masonry walls are

constructed at a later stage and

are not bonded to the frame

members; these walls arenonstructural, that is, non-load

bearing walls.

Confined Masonry Construction: a Guideline


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Co ed aso y Co st uct o : a Gu de e

Building Layout - The building plan should be of a regular shape.

Building plan aspect ratio - The building should not be excessively long relative to its width;

ideally, the length-to-width ratio should not exceed 4.


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P iti f i i b ildi


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Position of openings in a building

Confining Elements

Tie-beams should be placed at every floor level. Vertical spacing of tie-beams should not

exceed 3 m.

Tie-columns should be placed at a maximum spacing of 4 m, as well as at the following

locations:

a) at wall-to-wall intersections.

b) within the wall if necessary to ensure that 4 m spacing between the adjacent confining

elements is not exceeded.

c) at the free end of a wall.


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Horizontal reinforcement in confined masonry walls


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a) Toothed wall construction;

b) horizontal dowels at the wall-to-column

interface.


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