The Earthquake Tips to make Safe Built Environment
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The Earthquake Tips to make Safe Built Environment

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Simple Tips to make building earthquake resistant

Simple Tips to make building earthquake resistant

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The Earthquake Tips to make Safe Built Environment The Earthquake Tips to make Safe Built Environment Presentation Transcript

  • Dr. J.N.Jha Dean (Testing & Consultancy Cell) Guru Nanak Dev Engineering College, Ludhiana Punjab The EQ Tips for Creating Safe Built Environment
  • Latest in the Series of Natural Disasters: Earthquake in Indian Ocean on 26 th December 2004 Generating Huge Tsunami Waves Killing Thousands
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  • 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 ~1290 km ), the Outer Core (thickness ~2200 km ), the Mantle (thickness ~2900 km ) and the Crust (thickness ~5 to 40 km ).
  • Local Convective Currents in the Mantle The Circulations Convection 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 fault
    • The earthquake focus is its point of origin along a fault plane
    • Its epicenter is the vertical projection of the focus to the surface
  • So here’s the big picture of what we’re living on
  • Schematic of Early Seismograph
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    • 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
  • What are the Seismic Effects on Structure
    • 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
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  • What are the Seismic Effects on Structure
    • 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
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  • What are the Seismic Effects on Structure
    • 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
  • What are the Seismic Effects on Structure
    • 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 bet n 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.
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  • 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
  • Affect of Architectural Features on Bld during EQ
    • 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
  • Affect of Architectural Features on Bld during EQ
    • 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
  • Affect of Architectural Features on Bld during EQ
    • 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………
  • Affect of Architectural Features on Bld during EQ
    • 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
  • Affect of Architectural Features on Bld during EQ
    • 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
  • Affect of Architectural Features on Bld during EQ
    • 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………
  • How building twists during Earthquake
    • Why a building twist
    • 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………
  • How building twists during Earthquake
    • Why a building twist
    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
  • How building twists during Earthquake
    • 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
  • How building twists during Earthquake
    • 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
  • 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
    Seismic Design Philosophy for Building
    • 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 bet n vertical columns and masonary fillers is acceptable and diagonal cracks running through column is not acceptable
    Seismic Design Philosophy for Building
    • 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
    Seismic Design Philosophy for Building
    • 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
    Seismic Design Philosophy for Building
    • 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
    Flexibility of Building Affects their EQ Response
    • 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
    Flexibility of Building Affects their EQ Response
    • 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
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    • 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
    Simple Structural Configuration required for 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 bet n such blocks
    • Gap not necessary if horizontal projections in Bld are small
    • An integrally connected inclined stair case slab acts like a cross brace bet n floors
    • It transfers large horizontal forces at the roof and the lower level (Area of Potential Damage)
    Simple Structural Configuration required for 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
    • Roll of Horizontal Bands
    Horizontal Band necessary in Masonary Building 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
    • Roll of Horizontal Bands
    Horizontal Band necessary in Masonary Building 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.
    • Roll of Horizontal Bands
    Horizontal Band necessary in Masonary Building
    • Design of Lintel Bands
    Horizontal Band necessary in Masonary Building
    • 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
    Horizontal Band necessary in Masonary Building
    • 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(bet n Roof & Lintel)
    • --- Wall Pier Masonary(bet n Lintel & Sill)
    • --- Sill Masonary(bet n Sill & Plinth)
    • Response of Masonary Wall
    Vertical Band necessary in Masonary Building
    • 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
    • Response of Masonary Wall
    Vertical Band necessary in Masonary Building
    • 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)
    • Response of Masonary Wall
    Vertical Band necessary in Masonary Building
    • 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 Band necessary in Masonary Building
    • 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
    Vertical Band necessary in Masonary Building
    • 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
    Effect of Earth Quake on RC Building
    • 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
    Effect of Earth Quake on RC Building
    • In fill walls- Vertical space bet n 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
    Effect of Earth Quake on RC Building
    • 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
    Effect of Earth Quake on RC Building
    • 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
    Effect of Earth Quake on RC Building
    • 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
    • Reinforcement and Seismic Damage
    How do Beams in RC Bld resist EQ
    • Two basic types of failure in beams:-
      • Flexural (Bending) failure
      • Shear failure
    • Reinforcement and Seismic Damage
    How do Beams in RC Bld resist EQ
    • 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
    • Reinforcement and Seismic Damage
    How do Beams in RC Bld resist EQ
    • 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
    • Reinforcement and Seismic Damage
    How do Beams in RC Bld resist EQ
    • 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
    How do Beams in RC Bld resist EQ
    • 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
    How do Beams in RC Bld resist EQ
    • 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
    How do Beams in RC Bld resist EQ
    • 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
    How do Beams in RC Bld resist EQ
    • Φ of Stirrups – 6 mm minimum
    • Φ o f 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
    • Requirements related to stirrups in RC Beams
    How do Beams in RC Bld resist EQ
    • 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
    • Requirements related to stirrups in RC Beams
    How do Beams in RC Bld resist EQ
    • 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
    How do Columns in RC Bld resist EQ
    • 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 ties
    beyond hook bend must be atleast 10d of steel bar ( close ties) but not less than 75 mm.
    • Possible EQ Damage
    How do Columns in RC Bld resist EQ
    • 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
    • EQ behaviour of Joints
    How do Beam Column Joins in RC bld Resist EQ        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  
    • EQ behaviour of Joints
    How do Beam Column Joins in RC bld Resist EQ           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
    • EQ behaviour of Joints
    How do Beam Column Joins in RC bld Resist EQ        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.
  • How do Beam Column Joins in RC bld Resist EQ
    • EQ behaviour of Joints
     Three stage procedure for providing horizontal ties in the joints
  • How do Beam Column Joins in RC bld Resist EQ
    • 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
    Why are Soft storey building vulnerable in EQ    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
    Why are Soft storey building vulnerable in EQ
    • The Problem
    Why are Soft storey building vulnerable in EQ        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.
    • Short Column Behaviour
    Why are Short Columns more Damaged During EQ      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
    • Short Column Behaviour
    Why are Short Columns more Damaged During EQ     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)
    • Short Column Behaviour
    Why are Short Columns more Damaged During EQ     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)
    • Short Column Behaviour
    Why are Short Columns more Damaged During EQ     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
    Why are Short Columns more Damaged During EQ     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
    • What is a Shear Wall Building
    Why are Bld with Shear Walls preferred in Seismic 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
    Why are Bld with Shear Walls preferred in Seismic Regions
    • What is a Shear Wall Building
    Why are Bld with Shear Walls preferred in Seismic 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 are a) 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
  • 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
  • How to reduce EQ effects on Building
    • 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
  • How to reduce EQ effects on Building
    • 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/
  • Thank You !...