FIMILARISATION WITH IS CODES RELATED TO

EARTHQUAKE AND IMPROVING EARTHQUAKE

RESISTANCE

CAUSES OF EARTHQUAKES• MAJOR EARTHQUAKES ARE CAUSED DUE

TO LARGE SCALE STRAINS IN THE CREST OF EARTH DUE TO IMPOSED LOADS. THESE ARE OF TECTONIC NATURE. IN THESE TYPES OF EARTHQUAKES DUE TO LARGE DEFORMATIONS OF EARTH CREST MOVEMENTS OF ADJACENT CREST OF THE EARTH TAKES PLACE WHICH CAUSES MAJOR EARTH QUAKES.

THE THEORY DESCRIBING THIS PHENOMENON IS TERMED AS ELASTIC REBOUND THEORY, ACORDING TO WHICH THE STRAIN ENERGY THAT ACCUMULATES DUE TO DEFORMATION IN THE EARTH MASS GETS RELEASED WHEN THE RESILIENCE OF THE STORING ROCK IS EXCEEDED. THE ENERGY RELEASED THROUGH RUPTURE IS PROPOGATED IN FORM OF WAVES WHICH ARE PASSED ON TO THE EARTH MASS THROUGH WHICH THEY PASS AND VIBRATE THE STRUCTRES STANDING ON IT(FIG 1)

• A MAJOR TECTONIC EARTHQUAKE IS GENERALLY PROCEEDED BY SMALL SHOCKS CAUSED EITHER DUE TO SMALL RUPTURES OR DUE TO PLASTIC DEFORMATIONS AND IS FOLLOWED BY AFERSHOCKS DUE TO FRESH RUPTURES OR DUE TO THE RE-ADJUSTMENTS OF THE FRACTURED MASS.

• A SHOCK MAY RESULT FROM A RUPTURE OF ROCK OVER A LENGTH OF FEW HUNDRED KILOMETRES AND SEVERAL KILOMETERS WIDE AND THICK. THE BIGGER IS THE MASS THAT RUPTURES AT A TIME , THE BIGGER IS THE EARTHQUAKE.

• SMALL EARTHQUAKES ARE CAUSED BY VOLCANIC ERRUPTIONS, ROCKS-BURSTS , BLASTS , MINING , IMPONDING OF RESEVIORS, PUMPING OF OIL ETC. THESE MAY CAUSE DAMAGE IN SMALL AREAS BUT AREAS ARE SHAKEN BY TECTONIC MOVEMENTS ACROSS ACTIVE FAULTS AS EXPLAINED ABOVE.

SOME MAJOR EARTH QUAKES IN INDIA • YEAR PLACE MAGNITUTE 1819

KUTCH 8.0 1869 NEAR CACHAR (ASSAM) 7.5 1885 SOPOR(J&K) 7.0 1897 SHILLONG 8.7 1918 SHRIMANGAL(ASSAM) 7.6 1930 DHUBRI(ASSAM) 7.1 1934 BIHAR-NEPAL BORDER 8.3 1941 ANDAMAN 8.1

• YEAR PLACE MAGNITUTE 1943 ASSAM 7.2 1967 KOYNA 6.5 1988 BIHAR-NEPAL BORDER 6.4 1991 UTTARKASHI 6.6 1993 LATUR 6.3 1997 JABULPUR 6.0 1999 CHAMOLI 6.8 2001 BHUJ 6.9 2005 J & K 7.4

• FEW PHOTOGRAPHS OF EARTHQUAKEAS ARE BEING SHOWN WHICH SHALL GIVE YOU AN IDEA ABOUT THE AMOUNT OF DAMAGE THAT CAN BE THERE IN AN EARTHQUAKE.

LACK OF SHEAR CONNECTIONS BETWEEN FLOORS AND THE ELEVATOR

FIVE STOREY R.C, COLLAPSE OF OPEN PLINTH, WATER TANK AT TOP DISLOCATED (BHUJ)

COLLAPSE OF R.C FRAME RAILWAY STATION BUILDING AT VONDH

FOUR STOREYED RC BULDING (AMDAVAD), TWO OF WHICH COLLAPSED

R.C BULDING COLLAPSE AT GANDHIDHAM

SOFT GROUND STOREY COLLAPSE (AMDAVAD)

ELEVATED SHAFT – WEAK SHEAR CONNECTION WITH FLOORS (AMDAVAD)

IN-FILLED WALL DAMAGE

VARIOUS IS-CODES RELATED TO EARTHQUAKES

• IS:1893 CRETERIA FOR EARTHQUAKE RESISTANT DESIGN OF STRUCTURES

• IS: 13920 DUCTILE DETAILING OF REINFORCED CONCRETE STRUCTURES SUBJECT TO SEISMIC FORCES.

• IS: 4326 EARTHQUAKE RESISTANT DESIGN AND CONSTRUCION OF BUILDINGS.

• IS: 13828 IMPROVING EARTHQUAKE RESISTANCE OF LOW STRENGTH MASONRY BUILDINGS- GUIDELINES.

• IS : 13827 IMPROVING EARTHQUAKE RESISTANCE OF EARTHEN BUILDINGS-GUIDELINES.

• IS: 13935 REPAIR AND SEISMIC STRENGTHENING OF BUILDINGS-GUIDELINES

THESE STANDARDS TAKEN TOGETHER COVER THE PROFESSIONAL DESIGN & CONSTRUCTION REQUIREMENTS QUITE ADEQUATELY.

IMPROVING EARTHQUAKE RESISTANCE OF BUILDINGS

THESE GUIDELINES COVER FOLLOWING FEATURES FROM EARTHQUAKE SAFETY POINT OF VIEW•SITING AND FUNDATIONS.•ARCHITECHTURAL FEATURES•STRUCTURAL ANALYSIS AND DESIGN•CONSTRUCTION AND STRENGHTHENING FEATURES IN LOAD BEARING WALLS.

• CONSTRUCTION AND STRENTHENING FEATURES OF ROOFS AND FLOORS.• REPAIR AND STRENGTHENING OF

DEMAGED BUILDINGS.• SEISMIC RETROFITTING OF EXITING

WEAK BUILDINGS.

TERMINILOGY• BAND• A REINFOCED CONCRETE, REINFORCED BRICK OR

TIMBER RUNNER PROVIDED IN THE WALLS TO TIE THEM TOGETHER IS CALLED A BAND. PLINTH BAND, LINTEL BAND, ROOF BAND,EAVES BAND ARE FEW BANDS PROVIDED IN THE BUILDINGS.

• CENTRE OF MASS• THE CENTRE OF GRAVITY OF ALL THE MASSES OF

ROOFS/FLOORS AND WALLS ABOVE ANY STOREY OF BUILDING

• DESIGN SEISMIC COEFFICIENT• THE VALUE OF HORIZONTAL SEISMIC

COEFFICIENT COMPUTED TAKING INTO ACCOUNT THE SOIL FOUNDATION FACTOR AND IMPORTANCE FACTOR AS SPECIFIED IN IS-1893.

• SEISMIC ZONE• INDIA HAS BEEN DIVIDED INTO FOUR ZONES

II TO V AS SPECIFIED IN IS-1893. ZONE I HAS BEEN OMITTED AND MERGED WITH ZONE II.

• SIESMOGRAPH• SEISMOGRAPH IS AN INSTRUMENT USED TO

MEASURE EARTHQUAKE MOTIONS.IT HELPS IN DECLARING INTENSITY OF EARTHQUAKE.

• EPICENTRE AND HYPOCENTER • THE POINT INSIDE THE EARTH MASS WHERE

TH FRACTURE BEGINS IS TERMED AS HYPOCENTRE AND THE POINT ABOVE ON EARTH’S SURFACE IS TERMED AS EPICENTRE. BOTH THESE POINTS HAVE BEEN SHOWN IN FIG. 1 .(SLIDE- 4)

• SEISMIC ZONE FACTORS• ZONE FACTOR(Z) IS A FACTOR TO OBTAIN THE

DESIGN SPECTRUM DEPENDING UPON AMOUNT SEISMIC RISK IN WHICH THE STRUCTURE IS LOCATED. AS PER IS-1893 THESE ARE

SEISMIC ZONE II III IV VFACTOR 0.1 0.16 0.24 0.36 • RESPONSE REDUCTION FACTOR• IT IS A FACTOR BY WHICH THE ACTUAL SHEAR

FORCE SHALL BE REDUCED TO OBTAIN THE DESIGN LATERAL FORCE.THE VALUES ARE DEPENDENT ON DUCTILITY OF STRUCTURE.

• RESPONSE REDUCTION FACTOR (R) FOR LATERAL LOAD RESISTING SYSTEM

• ORDINARY LOAD RESISTING SYSTEM(OMRF) 3.0

• SPECIAL RC MOMENT RESISTING FRAME 6.0• ORDINARY SHEAR WALLS 3.0• DUCTILE SHEAR WALLS 4.0• OS WALL WITH OMRF 3.0 • OS WALL WITH SMRF 4.0• DUCTILE SHEAR WALL WITH OMRF 4.5 • DUCTILE SHEAR WALL WITH SMRF 5.0

DESIGN LATERAL FORCE• DESIGN BASE SHEAR( Vh)• Vh= Ah X W • W= SEISMIC WIGHT OF BUILDING• DESIGN HORIZONTAL SEISMIC COEF.(Ah) • Ah = Z I Sa WHERE 2R g Z = ZONE FACTOR Sa g IS SPECIAL ACCELERATION

COEFFICIENT WHICH CAN BE OBTAINED FROM GRAPH AVAILABLE IN IS-1893.

• STOREY SHEAR(Qi)• Q1= Vh X W1xh1xh1 W1xh1xh1 + W2xh2xh2 + …………

ONCE THE STOREY SHEAR FOR ALL FLOORS ARE KNOWN THE ANALYSIS CAN BE DONE AND SUBSEQUENTLY DESIGN CAN BE UNDERTAKEN.

NOW AFTER THIS BRIEF DISCUSSION WE DISCUSS THE WAYS TO IMPROVE EARTHQUAKE IN BUILDINGS

SITTING AND SETTLEMENT OF BUILDINGS• EFFECTS OF SITE CONDITIONS ON

BUILDING DEMAGE • EARTHQUAKE STUDIES HAVE INVARIABLY SHOWN

THAT THAT THE ITENSITY OF SHOCK IS DIRECTLY RELATED TO THE TYPE OF SOIL LAYERS SUPPORTING THE BUILDING. THE STRUCTURES BUILT ON SOLID ROCK AND FIRM SOIL FARE BETTER THAN BUILDING THAT REST ON SOFT GROUND.

• IT IS ALSO SEEN THAT THE TOPOGRAPHY OF THE BUILDINGS SITE ALSO EFFECTS THE DEMAGE TO THE STRUCTURE. THE BUILDING BUILDINGS BUILT ON SITES WITH OPEN AND EVEN TOPOGRAPHY ARE USUALLY LESS DEMAGED THAN THE BUILDINGS ON HILL RIDGES , HIGH HILLS AND ON STEEP SLOPES.

• STEEP SITES MAY HAVE PROBLEM OF LAND SLIDES AND ROCK FALLS AND SHOULD BE AVOIDED OR EFFECTIVELY IMPROVED IF THERE IS NO CHOICE.

• PLAIN SOILS WITH LOOSE FINE SAND WITH HIGH WATER TABLE ARE LIABLE TO LIQUEFACTION. THESE SITES SHALL BE AVOIDED, UNLESS IMPROVED. SUCH AREAS SHOULD BETTER BE RESERVED FOR PARKS, PLAY GROUND ETC.

BUILDING SAFETY• BUILDING SAFETY STARTS BY CHOOSING A SAFE SITE.

SUCH A CHOICE IS NORMALLY NOT AVAILABLE WITH MANY PEOPLE WHO ARE CONSTRAINED TO BUILD ON WHATEVER SITE THEY ARE ABLE TO GET. UNSAFE SITES SHOULD BE IMPROVED AS FOLLOWS FOR ACHIEVING SAFETY OF BUILDING :

• A STEEPLY SLOPING SITE MAY BE IMPROVED BY TERRACING AND CONSTRUCTING BREAST AND RETAING WALLS.

• SITE LIABLE TO LIQUEFACTION MAY BE IMPROVED BY COMPACTION, STABILISATION OR SAND PILING.

FACTORS EFFECTING DEMAGE TO BUILDING• THE PRINCIPAL FACTORS THAT INFLUENCE DEMAGE

TO THE BUILDINGS AND OTHER MAN MADE STRUCTURE ARE LISTED BELOW :

• BUILDING CONFIGRATIONS• AN IMPORTANT FEATURE IS REGULARITY AND

SYMMETRY IN OVERALL SHAPE OF BUILDING. A BUILDING SHAPED LIKE A BOX, SUCH AS RECTANGULAR IN PLAN AND ELEVATION IS INHERENTLY STRONGER THAN L-SHAPED OR U-SHAPED BUILDING. AN IRREGULAR SHAPED BUILDIND WILL TWIST AS IT SHAKES, INREASING THE DEMAGE.

OPENINGS IN WALLS

• REGIDITY DISTRIBUTON • THE RIGIDITY DISTRIBUTION IN A BUILDING

ALONG THE VERTICAL DIRECTION SHOULD BE REGULAR , SINCE THE CHANGES IN THE STRUCTURAL RIGIDITY OF A BUILDING FROM ONE TO NEXT FLOOR SHALL CAUSE POTENTIAL AND SHALL THEREFORE BE AVOIDED.COLUMNS AND THE SHEAR WALLS SHOULD RUN CONTINUOUSLY FROM FOUNDATION TO ROOF.

• DUCTILITYDUCTIBILITY IS THE ABILITY OF THE BUILDING TO

BEND AND DEFORM BY LARGE AMOUNT WITHOUT SERIOUS DEMAGE OR COLLAPSE.

• THE ADDITION OF STEEL REINFORCEMENTS CAN ADD DUCTILITY BY PROPER USE OF REINFOFCEMENT STEEL.

• FOUNDATION• THE BUILDINS WHICH ARE STRUCTURALLY STRONG

TO WITHSTAND EARTHQUAKES SOMETIMES FAIL DUE TO INADEQUATE FOUNDATION DESIGN. TILTING, CRACKING AND FAILURE OF SUPPERSTRUCTURE MAY RESULT FROM SOIL LIQUEFACTION AND DIFFENTIAL SETTLEMENT OF FOOTINGS.

• CERTAIN TYPES OF FOUNDATIONS ARE MORE SUSCEPTIBLE TO DEMAGE THAN OTHERS. FOR EXAMPLE ISOLATED FOOTING ARE MOST LIKELY TO BE SUBJECTED TO DIFFERENTIAL SETTLEMENT PARTICULARLY WHERE THERE DIFFERENT TYPES OF SOIL SUPPORTING GROUND. ALSO MIXED TYPE OF FOUNDATION MAY ALSO LEAD TO DAMAGE.

• VERY SHALLOW FOUNDATION MAY LEAD TO DAMAGE BECAUSE OF WEATHERING PARTICULARLY AT PLACES EXPOSED TO FREEZING IN COLD CLIMATES AND PRESENCE OF BLACK COTTON SOIL.

QUALITY OF CONSTRUCTION AND MAINTENANCE

• IN MANY CASES THE FAILURES OF THE BUILDINGS IN AN EARTHQUAKE HAS BEEN ATTRIBUTED TO THE POOR QUALITY OF CONSTRUCTION, POOR WORKMANSHIP AND CARELESS MAINTENANCE. THIS MAY RESULT IN INADEQUATE BONDING OF MASONRY. LACK OF CURING MAY REDUCE THE STRENGH AND DURIBILITY OF CONCRETE.

ARCHITECTURAL DESIGN FEATURES• THERE ARE CERTAIN FEATURES WHICH IF

TAKEN INTO CONSIDERATION AT THE STAGE OF PLANNING AND DESIGN OF THE BUILDING, THEIR PERFORMANCE DURIND THE EARTHQUAKE CAN BE IMPROVED. SOME OF THESE ARE STATED BELOW :

• LIGHTNESS• SINCE EARTHQUAKE FORCE IS A FUNCTION

OF WEIGHT, THE BUILDING SHALL BE AS LIGHT AS POSSIBLE MEETING STRUCTURAL SAFETY AND FUNCTIONAL REQUIREMANTS.

• BUILDING CONFIGRATION• THE BUILDING PLAN SHOULD HAVE A SIMPLE RECTANGULAR

PLAN AND BE SYMMETRICAL BOTH WITH MASS AND RIGITY. IF, IT IS NOT POSSIBLE, THEN THE STRUCTURE HAS TO BE DESIGNED FOR TORSION AND OTHER EFFECTS DUE TO EARHTHQUAKE FORCES WHILE DESIGNING.

• SEPERATION OF WINGS • LARGE PLANS SHALL BE SEPERATED INTO RECTANGULAR

BLOCKS BY PROVIDING EXPANSION JOINTS. THIS SHALL AVOID TORSIONAL FORCES DUE TO EARTHQUAKE. WHERE SEPERATION IS NECESSARY , A COMPLETE SEPERATION OF PARTS SHOULD BE MADE EXCEPT BELOW PLINTH LEVEL. THE PLINTH BEAMS, FOUNDATION BEAMS AND FOOTINGS MAY BE CONTINUOUS. THE SEPERATION SHALL ALSO TAKE CARE THE MOVEMENT DUE TO TEMPERATURE CHANGES.

DETAILING FOR DUCTILITY • THE STRUCTURE SHOULD RESIST MODERATE

INTENSITY OF EARTHQUAKE SHAKING WITHOUT STRUCTURAL DAMAGE.

• THE STRUCTURE SHOULD BE RESIST EXCEPTIONALLY LARGE INTESITY OF EARTHQUAKE SHAKING WITHOUT COLLAPSE. SUCH AN INTENSITY COULD OCCUR NOT MORE THAN ONCE IN THE LIFE OF THE STRUCTURE. IT IS NOT CATERED FOR IN DESIGN BUT IS TAKEN CARE BY PROVIDING DUCTILE DETAILING.

RECOMMENDATION FOR DUCTILIY

• IS: 13920 LAYS DOWN THE REQUIREMENTS FOR R.C.C. MOMENT RESISTING FRAMES FOR DETILING OF BEAMS , COLUMNS, SHEAR WALLS AND THEIR JOINTS.

• CONCRETE AND STEEL GRADES • FOR MORE THAN THREE STOREYED BUILDINGS ,

THE MINIMUM CONCRETE GRADE SHALL BE M25 AND STEEL REQUIREMENT SHALL BE Fe 415.

• DETAILING OF BEAMS • MINIMUM WIDTH OF THE BEAM SHALL BE 200

MM AND OVERALL DEPTH SHALL NOT BE MORE THAN 0.25 OF CLEAR SPAN.

• TENSION REINFORCEMENT SHOULD NOT BE MORE THAN 0.25 PERCENT.

• THERE SHALL BE AT LEAST TWO BARS AT TOP AND BOTTOM OF THE BEAM FOR FULL LENGTH AND SHALL BE ENCHORED IN THE COLUMN FOR FULL BOND LENGTH PLUS 10xd WHERE d IS THE DIAMETER OF THE REINFORCEMENT BAR.

• NO SPLICE SHALL BE PROVIDED IN THE BAR UPTO ¼ OF SPAN. NOT MORE THAN HALF BARS SHALL SPLICED AT A SECTION.

• THE LAP LENTH SHALL BE Ld AND THE SPACING OF THE STIRRUPS IN THIS PORTION SHALL NOT BE LESS THAN 150 MM.

• SIDE FACE REINFORCEMENT SHALL BE PROVIDED IN THE BEAM.

• THE SPACING OF SHEAR REINFORCEMENT SHALL NOT EXCEED d/4 BUT SHALL NOT BE LESS THAN 75 MM. THE SPACING IN THE OTHER PORTION SHALL NOT EXCEED d/2.

• DETAILING OF COLUMNS • MINIMUM SIDE OF COLUMN SHALL BE 200 MM.

HOOPS AND ARE SHOWN IN THE NEXT SLIDE.• SPECIAL CONFINING REINFORCEMENT SHALL BE

PROVIDED FOR LENGTH h/6 DISTANCE AS SHOWN IN THE SLIDE.

• THE LOGITUDINAL BARS SHALL BE SPLICED WITH IN MIDDLE 2/3 rd HEIGH OF COLUMN AND THE SPACING OF THE TIES SHALL NOT BE LESS THAN 150 MM IN THE SPLICED PORTIONED. THE TYPICAL BEAM COLUMN JOINT DETAILS ARE GIVEN IN THE NEXT SLIDES.

SAFETY OF NON-ENGINEERING BUILDINGS

• AS PER DETAILS AVAILABLE , IN INDIA EARTHERN AND STONE HOUSES AND OTHER BRITTLE HOUSES(BURNT BRICK) ARE 84.7 % AND ARE HIGHLY VUNERRABLE. THE COLLAPSE OF THESE HOUSE TAKES PLACE DURING AN EARTHQUAKE OF MODERATE INTENSITY. THESE RESULT IN LARGE LOSS OF LIVES. FOR SAFETY OF HUMAN LIVES AND PROPERTY IT IS IMPORTANT THAT ALL THESE BUILDINGS ARE BUILT WITH EARTHQUAKE RESISTING FEATURES.FOLLOWING TABLE IS GIVES DETAILS TO BE ADOPTED