Safe Built Environment

Dr. J.N.JhaDean (Testing & Consultancy Cell)

Guru Nanak Dev Engineering College, LudhianaPunjab

The EQ Tips for Creating Safe Built Environment

Latest in the Series of Natural Latest in the Series of Natural Disasters:Disasters:

Earthquake in Indian Ocean on Earthquake in Indian Ocean on 2626thth December 2004 Generating December 2004 Generating

Huge Tsunami Waves Killing Huge Tsunami Waves Killing ThousandsThousands

Inside the Earth

Long time ago, a large collection of material

masses coalesced to form the Earth

Inside the Earth (Contd.)

Large amount of heat was generated by this fusion,

and slowly as the Earth cooled down, the heavier

and denser materials sank to the center and the

lighter ones rose to the top.

The differentiated Earth consists of the Inner Core

(radius ~1290km), the Outer Core (thickness

~2200km), the Mantle (thickness ~2900km) and the

Crust (thickness ~5 to 40km).

Local Convective Currents in the Mantle

The CirculationsConvection currents develop in the viscous Mantle,

because of prevailing high temperature and pressure

gradients between the Crust and the Core, like the

convective flow of water when heated in a beaker

The Earthquake

Rocks are made of elastic material, and so elastic strain energy is stored in them during the deformations that occur due to the gigantic tectonic plate actions that occur in the Earth.

The material contained in rocks is very brittle.

Thus, when the rocks along a weak region in the Earth’s Crust reach their strength, a sudden movement takes place there;

Types of Inter-Plate Boundaries

Convergent Boundary

Transform Boundary

Divergent Boundary

The convective flows of Mantle material cause the Crust and some portion of the Mantle, to slide on the hot molten outer core. This sliding of Earth’s mass takes place in pieces called Tectonic Plates.

Opposite sides of the fault (a crack in the rocks where movement has taken place)

suddenly slip and release the large elastic strain energy stored in the interface rocks.

For example, the energy released during

the 2001 Bhuj (India) earthquake is about 400

times (or more) that released by the 1945 Atom

Bomb dropped on Hiroshima!!

Elastic Rebound Theory

Elastic Strain Build-Up and Brittle Rupture

The slip generated at the fault during

earthquakes is along both vertical and horizontal

directions (called Dip Slip) and lateral directions

(called Strike Slip) with one of them dominating

sometimes.

Large strain energy released during an

earthquake travels as seismic waves in all

directions through the Earth’s layers, reflecting

and refracting at each interface.

Arrival of Seismic Waves at a Site

Type of Faults

These waves are of two types

-- body waves and surface waves;

Body waves consist of

Primary Waves (P-waves)

Secondary Waves (Swaves),

Surface waves consist of

Love waves

Rayleigh waves.

- these are restricted to near the Earth’s surface

Direction of Energy Transmission

Motions caused by Body and Surface Waves(Adapted from FEMA 99, Non-Technical Explanation of the NEHRP

Recommended Provisions)

Direction of Energy Transmission

Motions caused by Body and Surface Waves(Adapted from FEMA 99, Non-Technical Explanation of the NEHRP

Recommended Provisions)

Earthquake generation along a Earthquake generation along a faultfault

The earthquake The earthquake focusfocus is its point of is its point of origin along a fault origin along a fault planeplane

Its Its epicenterepicenter is the is the vertical projection of vertical projection of the focus to the the focus to the surfacesurface

So here’s the big picture of what So here’s the big picture of what we’re living onwe’re living on

Schematic of Early Seismograph

Magnitude 4.0 Wyoming Earthquake of 7 April 2004

M6.6 earthquake of Hindu Kush Region of Afghanistan, 5 April 2004

Magnitude 6.4 Earthquake of North Coast of Morocco, 24 February 2004

M6.6 Earthquake of Southeast Iran, 26 December 2003

M6.5 San Simeon California Earthquake, 22 December 2003

Recent Earthquakes…

M 8.3 Hokkaido, Japan Earthquake of 26

September 2003

M 7.3 Kazakhstan-Xinjiang Border Region,

Russia Earthquake of 27 September 2003

M 6.5 Dominican Republic, 22 September 2003

The Boumerdes Algeria Earthquake of 21 May

2003

….Recent Earthquakes…

Some Past Earthquakes in India

Within the last two hundred years, India has

experienced five great earthquakes, each

with Richter magnitude exceeding 8. The

regions where these occurred are as follows:

1819 Kutch, Gujarat 1897 Assam 1905 Kangra, Himachal Pradesh 1934 Bihar-Nepal 1950 Assam-Tibet

What are the Seismic Effects on Structure

Inertia Forces in Structures Effect of Deformation in structures Horizontal and vertical shaking Flow of Inertia forces to foundation


Inertia Forces in Structures

• During EQ building experiences motion at its base

• Roof has a tendency to stay in its original position

• Wall and column drag the roof along with them

• Roof experiences a force (Inertia Force-IF)

• IF =M(mass)x a(Acceleration)

• Mass is more, IF will be more,

• Lighter building performs better in EQ shaking


Effect of Deformation in Structure

• Inertia force (IF) transfer to ground via column

• Column(Vertical) carry no horizontal EQ Force

• Band develop internal force(stiffness force)

& large deformation(u)

• Stiffness force = Stiffness x Displacement

• Internal force depends on the size of the column


Horizontal and Vertical Shaking

• EQ –Shaking of ground (X,Y & Z Direction)

--Random Shaking back & forth ( - & +)

• Structure Designed for gravity load (Mg)

• Vertical Acceleration adds or subtracts “g”

• FOS used in Design Adequate

against vertical Shaking

• Horizontal Shaking(+ & -)remains

a concern


Flow of Inertia Forces to Foundation

• Inertia force(IF) transferred from floor slab to foundation and finally to soil through wall/column

• Design of structural element and connections betn

them must be adequate to transfer this IF

• In traditional construction:-

- Floor Slab and beam receive more attention than wall/ column

- Wall/column relatively thin and often made of brittle material

- Poor in carrying horizontal EQ Inertia force along the direction of thickness

• Failure of masonry wall & poorly designed RCC Column have been observed in past earthquake.

Affect of Architectural Features on Bld on during EQ

Importance of Architectural Features

• Behavior of Bld during EQ depends on overall shape, size and geometry

• Late Henry Degenkoly noted EQ Engineer of USA summarised the configuration of building “If we have a poor configuration to start with, all the engineer can do is to provide a band aid improve a basically poor solutions as best as he can. Conversely, if we start off with a good configuration and reasonable framing system, even a poor engineer cannot harm its ultimate performance too much”

Affect of Architectural Features on Bld during EQ

Importance of Architectural Features

• Architecture conceive wonderful and imaginative structure which are aesthetic and functionally efficient

• Sometimes the shape of the building catches the eye of the visitors and other times the structural system appeals

• However each of these choices of shapes and structure has significant bearing on the performance of the building during earthquake


• Horizontal Movement is very large in tall building(Ht /Base)

• Damaging effects are many in long buildings

• Horizontal seismic force becomes excessive in case of building with large plan area (force to be carried by column/wall)

Size of the Building


• Bld. With simple geometry in plan performs well during EQ

• Bld. With U,V,H & +shape sustains significant damage

• L-Shaped Building- Can be converted in simple plan into 2 rectangular block using separation joint at the junction

• column/wall carries equally distributed load in case of simple plan

Horizontal layout of the building


• EQ force travels through the shortest path along the height of the building (Developed at different floor level of the bld.)

• Any discontinuity in this load transfer path results in poor performance of the bld

• Bld. With vertical set backs causes a sudden jump in earthquake force at the level of discontinuity

• Bld. With fewer column/wall in a particular storey or with unusually tall storey tend to damage or collapse

Vertical layout of buildings

Contd………


• Building with open ground story tends to damage during EQ (2001 –Bhuj EQ-Ahmedabad)

• Unequal height of the column along the slope caused ill effects like twisting and damage is more in shorter column

• Building with hanging and floating column have discontinuities in load transfer path

• Building with RCC Walls that stops at an upper level gets severely damaged

Vertical layout of buildings


• Two buildings too close pound on each other during the strong shaking

• If Bld. Heights do not match, shorter building may pound at the mid height of the column of the taller one which is very dangerous

Adjacency of Buildings


Suggestions• Architectural features detrimental to EQ response of building should be avoided. If not they must be minimised

• In case irregular features included in building higher level of engineering efforts is required in structural design

• Decision made at the planning stage on building configuration are very important

• Building with simple architectural feature will always behave better during EQ

How building twists during Earthquake

Why a building twist

• Building too are like this rope swings, just that they are inverted swings

• Wall/column are like ropes and flow like cradle

• All points on the same floor moves horizontally by the same amount

Contd………



• If mass on the floor of the building is more on one side, then that side of the building moves more under ground moment (horizontal movement & Twisting)

Contd………



Contd………

• Building with unequal vertical members(column/wall) floor twist about a vertical axis and displaces horizontally

• Building which have walls only on two/ one sides and thin column along the other twists when second at the ground level


Why a building twist• Buildings that are irregular shapes in plan tend to twist under earthquake shaking

• Overhanging portion swings on the relatively slander columns under it.

•The floor twists and displaces horizonally


What twist does to building members• Twist in a building is called torsion by engineers

• Different portion at the same floor level move horizontally by different amount during this twist

• Column/Wall on the side that move more tends to damage more

• Best to minimise the twist by ensuring symmetrical plan of Bld.

Severity of ground shaking at a given location during an earthquake can be minor, moderate and strong.

Relatively speaking, minor shaking occurs frequently, moderate shaking occasionally and strong shaking rarely.

For instance, on average annually about 800 earthquakes of magnitude 5.0-5.9 occur in the world while the number is only about 18 for magnitude range 7.0-7.9

Seismic Design Philosophy for Building


• Don’t attempt to make EQ proof building (Bld. Will be too robust and too expensive)

• Engineering intention shall be to make EQ resistant building

Earthquake Design Philosophy• Under minor but frequent shaking the main members of the building that carry vertical and horizontal forces should not be damaged, however the building parts that do not carry load may sustain repairable damage

• Under moderate but occasional shaking the main members may sustain reparable damage, while the other parts of the building may be damaged such that they may even have to be replaced after the EQ

• Under strong but rare shaking the main members may sustain severe damage but the building should not collapse


Earthquake Resistant Design

• Ensure that damage in building during EQ is of acceptable level

• Damage should occur at right place by right amount eg. RCC Framed Building (with masonary filler wall) cracks betn vertical columns and masonary fillers is acceptable and diagonal cracks running through column is not acceptable


Acceptable Damage:Ductility

• Identify Acceptable form of damage and desirable building behaviour during EQ

• EQ resistant buildings (Main Element) need to built with ductility in them

• Such building with stand EQ effects with some damage but without collapse


EQ Resistant Design of Building

• Seismic Inertia Forces generated at its floor level is transferred through its beam and column to the ground

• Failure of a column can affect the stability of the whole building

• Failure of beam causes localised effect

• Correct building components should be ductile

• RC building should be designed using strong column weak beam design method


Oscillation of Flexible Buildings

• Time taken for each complete cycle of oscillation is same and is called FUNDAMETNAL NATURAL PERIOD (T) of the building (Inherent property of the building)

• Value of T depends on the building flexibility and mass

• Any alteration made to the building will change its “T”

Flexibility of Building Affects their EQ Response

Contd………

Oscillation of Flexible Bld.

• Taller Bld. - more flexible and are having larger mass therefore have a larger “T”

• T of the building varies from 0.05 to 2 seconds


Importance Of Flexibility• Time taken by the wave to complete one cycle of motion is called PERIOD OF EQ WAVE (0.03 to 33 seconds)

• In a typical city Bld. Of different sizes and shapes exist ground motion under Bld. Varies across the city


• Short EQ wave have large response on short period buildings

• Long EQ wave have large response on long period buildings

Behaviour of Wall• Masonary Bld. Most vulnerable under EQ shaking(Brittle Structure)

• Wall is most vulnerable component of the Bld due to horizontal force (EQ)

• Wall offers greater resistance if pushed along its length (Strong Direction)

• Wall topples easily if pushed in a direction perpendicular to its plan(Weak Direction)

Behaviour of Brick Masonary Houses during EQ

Behaviour of Wall• All walls if joined properly to the adjacent wall ensures good seismic performance

• Walls loaded in weak direction take advantage of the good lateral resistance offered in their strong direction

• Walls need to be tied to the roof and foundation to reserve their overall integrity

Behaviour of Brick Masonary Houses during EQ

Box Action in Masonary Bld.• Good interlocking at jn provides good box action

• Opening too close to wall corners detrimental to good seismic performance

Simple Structural Configuration required for

Masonary Building

• Interlocking hampers the flow of forces from one wall to another wall

Contd………

Box Action in Masonary Bld.•Large opening weakens walls from carrying the inertia forces in their own plane


Masonary Building

Contd………

Box Action in Masonary Bld.• Separate block can oscillate independently and even hammer each other (If too close during EQ)

• Adequate gap required betn such blocks

• Gap not necessary if horizontal projections in Bld are small

• An integrally connected inclined stair case slab acts like a cross brace betn floors

• It transfers large horizontal forces at the roof and the lower level (Area of Potential Damage)


Masonary Building

Roll of Horizontal Bands

•Gable Band

• Roof Band

• Lintel Band

• Plinth Band

(Named after their location in the building)

Horizontal Band necessary in Masonary Building

Contd………

TYPES OF HOR. BANDS



Contd………

Lintel Band:--

---Most important needs to be provided in almost all buildings

--- Ties the walls together and creates a support for walls loaded along weak directions from walls loaded in strong directions

--- Bands also deduces the unsupported height of the walls and thereby improve their stability in weak direction



Roof Band:--

---To be provided in building with flat timber or GI Seats roofs only

--- This band is not required with flat reinforced concrete or reinforced brick roofs (Roof slab)

Plint Band:--

--- It is used when there is concern about uneven settlement.



Design of Lintel Bands


• Lintel bands undergo bending and pulling action during EQ

• Construction of band requires special attention to resist these actions

• Band can be Wooden band or RCC (best)

• RC bands minimum Thickness is 75 mm. Provide 2 bars of 8mm Φ with steel links of 6 mm Φ at a spacing 150 mm C/C

Contd………

Design of Lintel Bands


• Straight length of the band should be properly connected to the wall corner

• This allow the bend to support walls loaded in their weak direction by walls loaded in their strong direction.

• Adequate anchoring of steel links with steel bar is necessary for RC bands

• Wood spacer with proper nailing necessary to make the straight length of wood runner to act together

• Minimum X-section of runner(mm) is 75x38 and spacer(mm) 50x30

Response of Masonary Wall

Vertical Band necessary in Masonary Building

• Masonary building weakened by opening in the wall (Even in the presence of horizontal band)

• Masonary wall are grouped into three sub units (Even in the presence of horizontal band)

--- Spandrel Masonary(betn Roof & Lintel)

--- Wall Pier Masonary(betn Lintel & Sill)

--- Sill Masonary(betn Sill & Plinth)



• Eg. A hipped roof building with two window opening and one door opening in a wall• Inertia force (EQ) causes masonary wall pier to disconnect from the masonary above and below

• Masonary sub units rock back and forth (developing contacts only at the opposite diagonals)

• Rocking of masonary pier can crush the masonary at corners



• Eg. A hipped roof building with two window opening and one door opening in a wall• Rocking is also possible when masonary pier are cylinder

• Piers are likely to develop diagonal shear cracking (X-type)



• Opening reduces the X-sectional area of the masonary wall

• During EQ shaking building may slide

-- Just under the roof

-- Below the Lintel band

-- At the sill level

• Exact location of the sliding depends on factors like:-- Building Weight, EQ induced Inertia Force, Area of Opening, Type of Door Frame

How Vertical Reinforcement helps


• Vertical reinforcement bars forces the slender masonary piers to undergo bending instead of rocking

• In wider wall piers the vertical bars enhance their capability to resist horizontal EQ Forces and delay X type cracking

• Vertical bars also help in protecting the wall from sliding as well as from collapsing in weak direction

Protection of Opening in Walls


•Most common damage observed after an EQ is diagonal ex-cracking of wall pier, inclined cracks at corners of doors and window opening.

• A square opening become rhombus during EQ Shaking

• The corners that come closer develop cracks, Cracks are bigger when the opening sizes are large

• Steel bars provided all around the opening restrict cracks (corner)

RCC Building

Effect of Earth Quake on RC Building

• Structures of complex shapes are possible with RCC

• Typical RC building consist of horizontal members (Beam & Slab), Vertical members (column & Wall) and foundation resting on ground

• System comprising of RC Column & connecting beam is RC Frame

• In any multi-storyed bld, lower stories experience higher EQ induced forces, therefore has to be designed stronger than upper story

Role of Floor Slabs & Masonary Walls


• Floor Slabs are like horizontal plates facilitating functional use of building

• Beams & Slabs at one storey level are cast together

• When Beam bends in vertical direction, thin slab bends along with them

• When beams moves with column in horizontal direction, slab usually forces the beam to move together with it

• Geometric distortion of slab (though negligible) is known as Rigid Diaphragm Action, must be considered during design

Role of Floor Slabs & Masonary Walls


• In fill walls- Vertical space betn columns and floor filled with masonary walls and not connected surrounding RC Columns & Beams

• Columns receives horizontal forces at floor levels & try to move in horizontal direction

• Masonary walls tends to resist this horizontal movement

• Masonary is a brittle material, therefore develops crack once their ability to carry horizontal load is exceeded

• Placing in fills irregularly in the bld causes ill effects like short column effect

Horizontal EQ Effects


• EQ loading caused tension on beam and column faces at locations different from those gravity loading

• Steel bars are required on both faces of beam to resist reversal of bending moment

• Steel bars are required on all faces of column too

Strength Hierarchy


• Building to remain safe during EQ :--

--Column should be stronger than Beam

--Foundation should be stronger than Column

--Connection betn beams & Column and Columns & Foundation should not fail

Strength Hierarchy


• If this strategy adopted in design & beam detailing done properly

- Building as a whole can deform by large amount despite progressive damage caused due to consequent yielding of beams

- If columns are made weaker, it suffer local damage at the top and bottom of a particular storey

• This localised damaged can lead to collapse of building

Reinforcement and Seismic Damage

How do Beams in RC Bld resist EQ

• Long straight bars (longitudinal bars) placed along its lengh

• Closed loop of small diameter steel bars (Stirrups) placed vertical at regular intervals along its length



• Two basic types of failure in beams:-

a) Flexural (Bending) failure

b) Shear failure



• FLEXURAL (BENDING) FAILURE

• Beam can fail in two ways

a) Brittle failure (b) Ductile failure

• Brittle Failure:-

Relatively more steel is present on the tension face, concrete crushes in compression which is undesirable



• Ductile Failure:-

Relatively less steel is present on the tension face, steel yield first and the re distribution occurs in the beam until eventually concrete crushes in compression, is desirable

• Characterised with many vertical cracks starting from the stretched beam face and going towards its mid depth



• SHEAR FAILURE:--

- A shear crack, inclined at 45 degree to the horizontal, develops at mid depth near the support and grows towards the top and bottom face

- Closed loop stirrups are provided to avoid such shearing action

- Shear damage occurs when area of shear stirrup is insufficient

- A Brittle failure, must be avoided

Stirrup helps beam in three ways


• It carries the vertical shear force, thereby resist diagonal shear crack

• It protect the concrete from buldging outwards due to flexure

• It prevents the buckling of compressed longitudinal bars due to flexure

Longitudinal bars


• Provided to resist flexural cracking on the side of the beam that stretches

• Requires on both faces at the ends and on the bottom face at mid length

• As per ductile detailing code:--

- At least two bars shall go through the full length of the beam at the top as well as the bottom of the beam

- At the end of the beams, the amount of steel provided at the bottom is at least half that at the top

Longitudinal bars


• As per ductile detailing code:--

- At least two bars shall go through the full length of the beam at the top as well as the bottom of the beam

- At the end of the beams, the amount of steel provided at the bottom is at least half that at the top

Requirements related to stirrups in RC Beams


• Φ of Stirrups – 6 mm minimum

• Φ of Stirrups – 8 mm , if beam>5m.

• Both ends of a vertical stirrups should be bent into 135 degree hook and extend sufficiently beyond this hook to ensure that stirrups does not open out in an earthquake



• Max. spacing of stirrups is less than half the depth of beam

• For a length twice the depth of beam from the face of the column, the spacing should not be more than one fourth the depth of beam



• At the location of the lap, the bars transfer large forces from one to another

• Laps of the longitudinal bars are:-

a) Made away from the face of col.

b) Not made at locations where they are likely to stretch by large amounts and yield (eg. Bottom bars at mid length of the beam)

• At the location of laps, vertical stirrups should be provided at closer spacing

Possible EQ Damage

How do Columns in RC Bld resist EQ

• Column can sustain 2 type of damage:-

a) Axial Flexural (Combined Comp. Bending) failure

b) Shear Failure (Brittle Damage) & must be avoided by providing transverse ties at closer spacing

• Minimum width of the column = 300 mm, and if the unsupported length of column <4 meter and beam length< 5 m., width up to 200 mm is allowed

Possible EQ Damage


• Purpose of horizontal ties

a) Carry horizontal shear force induced by EQ and thereby to resist diagonal shear crack

b) Hold together the vertical bars and prevent them from buckling

c) Contain the concrete in the column within the closed loops

• The ends of the ties must be bent as 135 degree. The length of the tiesbeyond hook bend must be atleast 10d of steel bar ( close ties) but not less than 75 mm.

Possible EQ Damage


• In column where spacing between the corner bar exceeds 300 mm

“Additional links with 180 hook ends for ties to be effective in holding the concrete in its place and to prevent the buckling of vertical bars”

Lapping Vertical Bars

EQ behaviour of Joints

How do Beam Column Joins in RC bld Resist EQ

• Column beam joint have limited force carrying capacity when forces larger than these are applied during EQ, joints are severely damaged

• Repairing damage joints is difficult, so damage must be avoided

• Under EQ shaking, the beam adjoining a joint are subjected to moments in the same direction



Under these moments, the top bar in the beam-column joint are pulled in one direction & the bottom one in opposite direction.

The forces are balanced by bond stress developed between concrete and steel in the joint region

If there is insufficient grip of concrete on steel bars in such circumstances, the bar slip inside the joint region, the beam loose their capacity to carry load



Under this pull- push forces at top and bottom ends joint undergo geometric distortion

One diagonal length of the joint elongates and the other compresses. If the column cross- sectional size is insufficient, the concrete in the joint develops diagonal cracks



Problem of diagonal cracking & crushing of concrete in the joint region can be controlled by

a) Providing large column size

b) Providing closely spaced closed loop steel ties around column bars in joint region

Ties hold together the concrete in the joint and also resist shear force.


EQ behaviour of Joints Three stage procedure for

providing horizontal ties in the joints


Anchorage of beam bars in exterior joints

Anchorage of beam bars in interior joints

Basic Feature

Why are Soft storey building vulnerable in EQ

Relatively flexible in the ground storey, also called Soft storey.(Relative horizontal displacement is much larger as compared to the above storey)

Relatively weak storey in ground storey (Weak Storey)

Such buildings are extremely vulnerable under earthquake shaking

EQ Behaviour


Presence of walls in upper storeys make them much stiffer than the open ground storey

Upper storeys move almost as a single block and most of the horizontal displacement occurs in the soft ground storey itself

Basic Feature


The Problem


In the current practice, stiff masonry walls are neglected and only bare frames are considered in design calculation

After 2001 Gujrat EQ , IS : 1893 (Part –1)- 2002 has given special design provisions related to soft storey buildings

Special higher design forces for the soft storey as compared to the rest of the structure

Beam and column in the open ground storey are required to be designed for 2.5 times the forces obtained from bare frame analysis

Short Column Behaviour

Why are Short Columns more Damaged During EQ

Bld resting on sloped ground consisting of short & long column, when shakes, all column move horizontally by the same amount along with floor slab at a particular level

Short column effect also occurs in columns that support mezzanine floor or loft slabs that are added in between two regular floors.



A tall column & a short column of same cross section move horizontally by same amount during EQ

Short column is stiffer than long column(Stiffness of column means resistance to the deformation)

Larger is the stiffness, larger is the force required to deform it



If a short column is not adequately designed for such large force, it can suffer significant damage during EQ

Short column attracts several times larger force and suffer more damage as compare to taller ones.

This behaviour of short column is called short column effect and often the damage is in the form of X –shaped cracking (Shear Failure)



If a short column is not adequately designed for such large force, it can suffer significant damage during EQ

Short column attracts several times larger force and suffer more damage as compare to taller ones.

This behaviour of short column is called short column effect and often the damage is in the form of X –shaped cracking (Shear Failure)



Special Confining reinforcement is to be provided over the full height of column that are likely to sustain short column effect

Special confining reinforcement must extend beyond the short column into the column vertically above and below by certain distance

The Solution


In new building, short column effect should be avoided to the extent possible during Architectural design itself

For short columns in the existing building retrofit solutions can be employed to avoid damage in future Earth Quake

The retrofit solution should be designed by a Qualified structural Engineer with requisite background

What is a Shear Wall Building

Why are Bld with Shear Walls preferred in Seismic

Regions

Reinforce concrete (RC) Bld often have vertical plate like RC walls called Shear walls

Shear walls are generally start at foundation level and are continuous throughout the building height

Thickness range; 150 mm to 400 mm

Shear walls are usually provided along both length and width of Bld

Shear walls are like vertically originated wide beams that carry EQ load downwards to the foundation

Shear walls are efficient both in terms of const. Cost and effectiveness in minimizing EQ damage in Structural & Non-Structural Member



Regions

Shear walls in building must be symmetrically located in plan to reduce ill effects of twist in building

Shear walls are more effective when located along exterior perimeter of building

Different possible geometries of Shear Walls


Regions



Regions

Steel reinforcing bars are to be provided in walls in regularly spaced vertical & horizontal grids

Vertical and horizontal reinforcements in the wall can be placed in one or two parallel layers called curtains

Horizontal reinforcements needs to be anchored at the ends of wall

Minimum area of reinforcing steel to be provided is 0.0025 time the cross sectional area (Along each of the horizontal & vertical directions)

Why EQ effects are to be reduced

How to reduce EQ effects on Buildings

Lifeline structures like hospitals etc are remain to be functional in the aftermath of EQ

Special techniques are required to design such life line structures which usually cost more than normal bld do

Two basic technology area) Base isolation device

b) Seismic Dampers

Why EQ effects are to be reduced

How to reduce EQ effects on Buildings

a) Base isolation device

- Idea behind base isolation is to detach (isolate) the buildings from the ground in such a way that EQ motions are not transmitted up through the building or at least reduced

b) Seismic Dampers

- Special devices introduced in the building to absorb the energy provided by the ground motion to the building

How to reduce EQ effects on

Building

a) Base isolation device

- Idea behind base isolation is to detach (isolate) the buildings from the ground in such a way that EQ motions are not transmitted up through the building or at least reduced

b) Seismic Dampers

- Special devices introduced in the building to absorb the energy provided by the ground motion to the building

How to reduce EQ effects on Building

• Several commercial brands of base isolators are available

• A Careful study is required to identify the most suitable type of device for a particular building

• Base isolation is not suitable for all types of buildings

• Most suitable building for base isolation are low to medium rise building rested on hard soil underneath

• High rise buildings or building rested on soft soil are not suitable for base isolation


• Several commercial brands of base isolators are available

• A Careful study is required to identify the most suitable type of device for a particular building

• Base isolation is not suitable for all types of buildings

• Most suitable building for base isolation are low to medium rise building rested on hard soil underneath

• High rise buildings or building rested on soft soil are not suitable for base isolation


• Over 1000 blds across the world have been equipped with seismic base isolation

Base isolation in real buildings

• In India base isolation technique was first demonstrated after 1993 Killari EQ

• Two single storey bld (one school and another shopping complex bld) were built with rubber base isolators resting on hard ground

• The four storey bhuj hospital bld was built with base isolation technique after 2001 bhuj EQ


Seismic Dampers• Another approach for controlling

seismic damage in bld is by installing seismic dampers in place of structural elements such as diagonal braces

• These dampers act like hydraulic shock absorbers and absorbs part of the seismic energy transmitted through them, thus damps the motion of the building

• Commonly used seismic dampers are shown in figure

• 18 storey RC framed structure in Gurgaon (Friction dampers provided)

• The author wishes to gratefully acknowledge with thanks the various sources cited in the references which have greatly aided and enhanced the quality of presentation of the material either in the form of information, data, figures or tables

• The author also wishes to gratefully acknowledge with thanks to Mr. K.K.Sareen,Lecturer Department of Mech. & Prod.Engg. G.N.D.E.C. Ludhiana for rendering his help during the preparation of this presentation

Acknowledgement

Resource Material

EERI, (1999), Lessons Learnt Over Time – Learning from Earthquakes Series: Volume II Innovative Recovery in India, Earthquake Engineering Research Institute, Oakland (CA), USA; also available at http://www.nicee.org/readings/EERI_Report.htm.

Hanson,R.D., and Soong,T.T., (2001), Seismic Design with Supplemental Energy Dissipation Devices, Earthquake Engineering Research Institute, Oakland (CA), USA.

Skinner,R.I., Robinson,W.H., and McVerry,G.H., (1999), An Introduction to Seismic Isolation, John Wiley & Sons, New York.

IITK & BMTPC Earthquake Tips; available at http://www.nicee.org/

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