Earthquake ResistantEarthquake Proof. In normal construction this concept is incorrect, simply because We are aware that the forces resulting from the shaking in a strong Earthquake may be in excess of those required by the code;Earth sliding may occur unpredictably to cause damage;Unforeseen earthquake faulting may occur at any un predictable location, ad has already occurred in Bhuj and in LaturUnstable ground conditions, such as liquefaction or sliding could contribute to some phenomenon not presently being considered.

Purpose of earthquake resistant design.To protect human lives from the earthquake disaster and to prevent the damage to buildings during the EQ. For EQ which are not so big and encountered rather frequently, the structural element of building should not be damaged

AWARNESS IN ENGINEERS

Engineers have been aware of the effects of seismic force on the structures they build.

However, the recent spate of EQ in the country has brought into sharp focus the responsibility of this Engg. community in minimizing the loss of property and life during EQs.

CAUSES OF EARTHQUAKES

Earthquakes can be caused by volcanic activity, underground explosion, collapse of caves or slipping of geological faults.The most important cause from an engineering point of view, it is believed at present, is the movement of the faults, which are burried deep below the earths surface For the khilari event the focus was 5 km.For the Bhuj earthquake - 24 km

FOCUSEPICENTRE -FIG. 2MAGNITUDE (M) ------. RichterM = log10 (A/Ao)A- the max. amplitude recorded by a wood- anderson seismograph at a distance of 100 km form the centre of the disturbance.A0 is an amplitude of 1/1000 of a millimetre.

Generally, an average magnitude M is determined from a number of recordings.The magnitude can be related to the energy release during an EQ.log10 E= 11.8+1.5ME is the energy released in - ergs.

INTENSITY(I)

M - referred to the strength of EQ source, I - refers to the effect it produces on structures and human beings.[ Modified Mercali Intensity (MMI)]Table 2

Damages

Damages are more due to ground shaking than fault displacement Failure is not new to India alonesoil condition is very important

SIESMICITY OF INDIA

Roughly it may be stated that the southern region is less prone for shocks than northern region.

This does not mean in anyway that strong EQs are ruled out in south India.

Some of the past earthquake in IndiaThe Assam EQ 1897 (M 8.7,XII)The Bihar Nepal 1938 (M 8.4, X)The Quetta earthquake 1935 (M 7.6,VIII)Assam Tibet 1950 (M 8.7, X1)Koyma 1967 (M 6.5,VIII)(Koyma dam designed with a seismic coefficient of 0.05 with stood this earthquake well)6. The Bihar Nepal 1988 (M 6.6, IX)7. The Utter kashi (U.P) 1991 (M 6.6, IX)8. The latur 1993 (M 6.4, VIII - IX)9. Earth tremor at Kottayam, Idukki (Kerala) in 2001 (M 4.8)10. The Jabalpur EQ 1997 (M 6.0, VI - VIII)11. The Chamoli (U.P) 1999 ( M 6.8, IX )12. The Bhuj (Gujarat) 2001 (M 7.9)

Refer Fig. 1 epicentre map o India.Regions:- i. Kashmir and Western Himalaya.ii. Nepal Himalayasiii.a) Assam (N.E. India)b) Andaman Nicobar islandsiv. Gangetic basin and Rajastan v. Cambay and the Rann of cutch. vi. Peninsular India.

OCCURANCE OF EARTHQUAKE

The number of EQ of magnitude M > 5 recorded in the recent past in each of the six zones are

ZoneNo. of EQPeriodi.321828-1968ii.961803-1970iii. (a) (b)3131461822-19711917-1971iv.181720-1970v.101819-1965vi.411764-2000

EARTHQUAKES IN SOUTH INDIA

In Peninsular India, ie.; santh of 280 N latitude, about 380 earthquake have been reliably experienced in a period of 600 years,

For the 4 southern states taken together there have been same 152 EQ in this last 600 years.

SIGNIFICANT EARTHQUAKES IN PENINSULAR INDIA

1. Malabar CostYr. 1341VII5.72. Bombay26-5-1618IX6.93. Bellary31-03-1843VII5.84. Villupuram03-07-1867VII5.75. Coimbatore07-02-1900VII6.06. Koyna19-12-1967IX6.87. Bhadrachalam13-04-1969VII5.78. Coimbatore29-07-1972VI5.29. Koyma17-10-1973VI5.210. Shimoga12-05-1975V5.011. Khilari (Latur)30-09-1993VIII6.4

)F(tkxxcxm=++&&&)2()1(2220)sin()(xfwrrtkFtx+=--stkFd=0Tpw2=ww=rCcC=xDAFsttx=d)(tFotFwsin)(=SDOF

ESSENTIALS OF STRUCTURAL SYSTEMS FOR SEISMIC RESISTANCE

INFLUENCE OF BUILDING CONFIGURATION ON SEISMIC RESPONSE

HOW SEISMIC FORCES ARE DETERMINDED

IS1893 (part I) 2002

For the purpose of determining seismic forces, the country is divided into 4 seismic zones as shown in fig.

Design spectrumHorizontal seismic coefficient Ah=Z zone factor for the maximumConsidered earthquake (MCE)(0.1, 0.16, 0.24, 0.36) for 4 zones I- important factor R- response reduction factorR- the response reduction factorRgZISa2

Response spectrum fig.

Design lateral force

Design seismic base shear VB = Ah.WFundamental natural periodTa = 0.075h 0.75 for R.C framed building = 0.085h 0.75 for steel frame building for all other buildingsTa =

Distribution of design force

Vertical distribution of base shear to different flow levels

Qi = VB

Qi = the design lateral forces at floor i

n= number of storeys in the building

DYNAMIC ANALYSISDynamic Amplification REGULAR BUILDINGS>40 m in height in zone iv &v>90 m in zones ii & iiiIRREGULAR BUILDINGSAll framed buildings higher than 12 m in zones IV & V and those > 40m height in zones II & III.Analysis : - 1) Time history method 2) Response spectrum method

Free vibrationMode superpositionForce on1) Cantilever projection, Vertical & Horizontal

AmplificationsThe amount of amplification varies depending on the dynamic properties of the structure and the actual earthquake ground motion involvedThe important engineering properties of the structure are 1. The Natural frequency (or period) of vibration of the structure2. The ductility of the structure.3. The damping properties of the structure

LESSONS LEARNED FROM FAILURESUn reinforced and unanchored brick masonry should not be used in areas of seismic activity.Structures must be able to resist torsional action introduced into the structure by seismic ground motion.Ductility for concrete construction is essential.In an in filled frame, a strong possibility arises that the concrete columns will fail in shear when the weak masonry fails.The most rigid element in this structures will receive most of the lateral load.Concrete outside the column cage of columns should be ignored in design of columns that will be require to resist the shear forces and the subsequent bending..

Contd..reasonably well designed buildings perform wellThere is not apparent correlation between the intensity of earthquake damage and the earthquake magnitude or size.building should be separated to prevent pounding against one another an abrupt change in stiffness of vertical elements will create problems thorough construction review by the structural designer is necessary to ensure that the provisions of the plans and specification are incorporated in the final construction.

Design to behave in Serviceability limit state :- Structure will undergo little or no structural damage. Important buildings like hospitals, atomic power stations; etc., Should be designed for elastic behaviour under expected earthquake forces.Damage controlled (damageability) limit stateThere is some damage to the structure that can be repaired after the event and the structure can again be put in to use. Most of the permanent buildings should come under this category. For this purpose the structure is to be designed for limited ductile response only. Survival limit stateIn this case the structure may be allowed to be damaged extensively, but the support should stand and be able to carry the permanent loads fully so that in all cases there will be no caving in of the structure and no lose of life.

Current design practiceWe can design structure for the first two limit states by elastic or restricted ductile response of the structure using conventional methods of design and incorporating ductile detailing.Full ductile detailing is costly.Limited ductile response is cheaper and full ductile response is the cheapest. But will undergo large deformation under service earthquakes, and therefore reconstruction may not be possible.The current practice is to design structure for one of the first two limit states as full plastic design is still in the development stage.

Reinforcement Detailing

B.I.S codes for EQ designIS 4326 (1976): Code of practice for earthquake resistant design and constructing of buildingsIS 1893 (2002) : Criteria for earthquake design of structures (vth revision)

1962 Revision 1966, 1970, 1975, 1984, 2002.

IS 13920 (1996) Code of practice for ductile detailing of reinforced concrete structures subjected to seismic forces. This code was written to supplement IS 4326.SP 22: Explanatory handbook on codes of earthquake engineering needs revision