Tsunami Draft Code

7/31/2019 Tsunami Draft Code

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39 - 16 15 10 2009

39

39 39

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39 (7545) 91.120.25

31 12 2009


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DRAFT IN

WIDE CIRCULATIONDOCUMENT DESPATCH ADVICE

Reference DateCED 39/T- 16 15 10 2009

TECHNICAL COMMITTEE: EARTHQUAKE ENGINEERING SECTIONAL COMMITTEE , CED 39

ADDRESSED TO :

1 Interested Members of Civil Engineering Division Council, CEDC2. All members of CED 39 and CED 39/AP/Tsunami3. All others interested

Dear Sir,

Please find enclosed the following document:

Doc No. Title

CED 39(7545) Draft Indian Standard Tsunami Resistant Design of Buildingsand Structures RecommendationsICS No. 91.120.25

Kindly examine the draft standard and forward your views stating any difficulties which you arelikely to experience in your business or profession, if this is finally adopted as Indian Standard.

Last date for comments : 31 12 2009

Comments if any, may please be made in the format as given overleaf and mailed to theundersigned at the above address.

In case no comments are received or comments received are of editorial nature, you will kindlypermit us to presume your approval for the above document as finalized. However, in case ofcomments of technical in nature are received then it may be finalized either in consultation with theChairman, Sectional Committee or referred to the Sectional Committee for further necessary actionif so desired by the Chairman, Sectional Committee.

The document is also being hosted on BIS website www.bis.org.in.

Thanking you,

Yours faithfully,

(A.K. Saini)Sc `F & Head (Civil Engg.)

Encl: as above email : [email protected]


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Doc : CED 39(7545)

DRAFT FOR COMMENTS ONLY(Not to be reproduced without the permission of BIS or used as an Indian Standard)

DraftIndian Standard

TSUNAMI RESISTANT DESIGN OF BUILDINGS AND STRUCTURES RECOMMENDATIONS

FOREWORD

The Great Indian Ocean Tsunami on 26 December 2004 caused massive damage and agreat deal of it was structural. Furthermore a large proportion of the loss of life could beascribed to this structural failure, since it had not planned for vertical evacuation, and theresulting debris became an added hazard. Although, structural failure was widespread,many structures did survive inundation by the tsunami, particularly if it was only partialinundation, suggesting that if communities are going to be built in tsunami prone areasthere may be structural solutions that could be expected to provide a safe refuge in all butthe most extreme events. There is also a need for critical infrastructure in tsunami proneareas to be resilient to tsunami inundation.

To date there has been very little research undertaken on the design of structures toresist tsunamis, primarily because major tsunamis were perceived as being so rare asnot to warrant attention from the point of view of public safety. However publicperceptions in this regard are changing. If suitable structural solutions are to be foundthey will need to be based on a fundamental understanding of the forces imposed onstructures by tsunami inundation, and the response of structures to them. This will requireconsiderable knowledge about the physical characteristics of the tsunamis as theypenetrate over land. Three important variables are penetration, depth and velocity. Some

information is available on penetration and depth, but very little is known about velocitiesduring inundation, and the effect of the entrained debris, which are critical to estimatingforces.

In the context of the above a need was felt to formulate a code, which can provide aguideline to professional engineers and government bodies for designing tsunamiresistant structures near coasts

Tsunami forces are so high that structures cannot be designed to resist the full impact oftsunami forces either elastically or in-elastically. Buildings subjected to tsunami are likelyto experience extensive damage even if designed to conform to the provisions of thiscode. Tsunami force could be 8-10 times the earthquake force. It will be difficult to design

the normal residential structures to sustain tsunami forces. Hence normal structures mustbe protected from design tsunami waves and need not be designed for tsunami forces.However the coastal protection structures such as walls, dykes, embankment and thestructures inside the sea (e.g. bridges, jetty etc) must be able to sustain the tsunamiforces. Though earthquake occurrence time is of the order of few seconds, the tsunamiarrival time on the coast may range from few minutes to few hours. The simultaneousimpact of both the phenomenon on a structure is not possible, hence, while combiningthe loads the effect of forces for earthquake and tsunami need not be takensimultaneously.


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The presence of suitable coastal protective measures have been found to mitigate theextent of damage to structures. Coastal protection measures include hard solutions likegroins, seawalls, break waters, bulk heads, water gates, etc. and soft solutions likeartificial beach nourishment, bioshields, mangroves etc. The presence of coastalprotection measures is an added advantage to safety and it should not be considered forreducing the design forces stipulated in this code.

With the availability of time gap between initiation of a tsunami event and of its striking aregion, it is recognized that installation of appropriate tsunami warning system plays avery important role to enable evacuation and prevent loss of life. In the aftermath of theDecember 2004 tsunami, India has developed its own tsunami warning system, whichincludes a seismic network and ocean bottom pressure recorders. This system enables awarning to be issued within 20-30 minutes of an earthquake

The effects of sea level variation due to climate change are beyond the scope of thisstandard and hence is not addressed.

This draft Indian Standard has been prepared based on studies carried out by variousresearch groups and the papers published in national and international journals. In the

preparation of this standard, assistance has been taken from the following documents :

Tsunami Glossary:International Tsunami Information Center (ITIC) IntergovernmentalOceanograhic Commission (of UNESCO): International Co-ordination Group for theTsunami Warning System in the Pacific (ICG/ITSU) , 2006.

Guidelines for Reconstruction of House affected by Tsunami in Tamil Nadu: RevenueAdministration, Disaster Management & Mitigation Department, Government of TamilNadu, 2005.

Development of Design Guidelines for Structures that Serve as Tsunami VerticalEvacuation Sites (52-AB-NR-20051) By Harry Yeh (Oregon State University), Ian

Robertson)University of Hawaii), Janes Preuss, Planwest Partners, 2005

Preventive / Protection and Mitigation from Risk of Tsunami, A Strategy Paper byAnand.S. Arya,Ministry of Home Affairs, Government of India, 2005.

Reducing Tsunami Risk-Strategies for Urban Planning and Guidelines for ConstructionDesign by Asian Disaster Preparedness Centre.

Designing for Tsunami by National Tsunami Hazard Mitigation Program SteeringCommittee, USA, March 2001

For the purpose of deciding whether a particular requirement of this standard is complied

with, the final value observed or calculated, expressing the result of a test or analysis,shall be rounded off in accordance with IS 2 : 1960 Rules for rounding of numericalvalues (revised). The number of significant places retained in the rounded off valueshould be the same as that of the specified value in this standard.


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Doc : CED 39(7545)

DraftIndian Standard

TSUNAMI RESISTANT DESIGN OF BUILDINGS AND STRUCTURES RECOMMENDATIONS

1 SCOPE

1.1 This standard deals with the strategies for protection against tsunami and the designof structures located on coastal sites to resist the forces induced due to tsunami.

1.2 This standard also includes special criteria for multistory buildings that may be usedfor vertical evacuation.

2 REFERENCES

2.1 The standards listed in Annex A contain provisions which through reference in thistext, constitute provisions of this standard. At the time of publication, the editions listedwere valid. All standards are subject to revision and the parties to agreements based onthis standard are encouraged to apply the most recent editions of the standards indicatedin Annex A.

3 TERMINOLOGY

3.1 Arrival Time

Time of arrival of the first wave of a tsunami at a particular location.

3.2 Crest Length

The length of a wave along its crest. Sometimes it is also called as crest width.

3.3 Datum

Reference level for measurement of elevation on land (mean sea level extendedlandward is considered as datum in the context of tsunami).

3.4 Dynamic Wave Pressure

The pressure that a moving mass of water associated with tsunami would induce whileencountering an obstruction.

3.5 Estimated Time of Arrival

Computed arrival time of the first wave of a tsunami at coastal zone after a specific majordisturbance in the ocean like, earthquakes, landslides or volcanoes that has occurred.


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3.6 Elapsed Time

Time interval between observed time of arrival of the first wave of a tsunami at a specificlocation on the coast and the time of reaching the normal water level conditions.

3.7 Evacuation Map

A drawing or representation that outlines danger zones and designates limits beyondwhich people must be evacuated to avoid any harm from tsunami waves.

3.8 Far-Field Tsunami

A tsunami capable of widespread destruction, not only in the immediate region of itsgeneration, but across the entire ocean basin.

3.9 Force

Pressure distribution integrated over a given area of the structure.

3.10 Hazard

A Hazard is a situation which poses a level of threat to life, health, property orenvironment. Most hazards are dormant or potential, with only a theoretical risk of harm,however, once a hazard becomes active, it can create an emergency situation.

3.11 Impact Standing Wave Pressure

The pressure that acts on the structure experiences due to formation of a standing wave.

3.12 Inundation depth

Depth of water measured at a given location inland at the time of occurrence of tsunami.

3.13 Inundation Distance

The distance that a tsunami wave penetrates inland, measured horizontally from theintersection point of mean sea level and the beach face (also known as shoreline).

3.14 Intensity

Intensity is the degree of damage to buildings.

3.15 Local Tsunami

A tsunami of which destructive effects are confined to coasts within a hundred km of thesource.

3.16 Mean Sea Level

The average height of sea surface, based upon hourly observations of the height of tideon the open coast or in adjacent waters which have free access to the sea.


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3.17 Mean Tsunami Height

Average height of a tsunami measured from the trough to the crest.

3.18 NearField Tsunami

A tsunami from a nearby source, generally less than 200 km or associated with a shorttravel time of less than 30 minutes.

3.19 Reference Sea Level

It is level of water at the time of tsunami occurrence.

3.20 Regional Tsunami

A tsunami capable of causing destruction in a particular geographic region, generallywithin about 1000 km of its source. Regional tsunami also occasionally have very limitedand localized effects outside the region.

3.21 Run up

Maximum vertical height of the water level inland, measured above mean sea level.

3.22 Sustained Wave Pressure

The pressure that a structure continues to experience for a short period to time.

3.23 Terrain Slope

The tangent of angle made by the ground surface with respect to the mean sea level(symbolically indicated as tan in the fig.1)

3.24 Travel Time

Time required for the first tsunami wave to propagate from its source to a given point on acoastline.

3.25 Tsunami

A Japanese term derived from the characters "tsu" meaning harbor and "nami" meaningwave. A tsunami is a series of waves with a long wavelength and period (time betweencrests) usually generated by disturbances associated with earthquakes/landslide orvolcanoes occurring below or near the ocean floor. Time between crests of the wave can

vary from a few minutes to over an hour. Tsunamis are often incorrectly called tidalwaves; they have no relation to the daily ocean tides. Tsunamis can occur at any time ofday or night.

3.26 Tsunami Amplification

Tsunami amplification is the increase in the height of tsunami as it travels from deepocean to near shore region.


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3.27 Tsunami Dispersion

Redistribution of tsunami energy, particularly as a function of its period, as it travelsacross a body of water.

3.28 Tsunami Height

It is the vertical distance between the crest (highest point over the water surface) andtrough (lowest point over the water surface) of a tsunami.

3.29 Tsunami Magnitude, Mt

A number characterizing the strength of a tsunami based on the tsunami wave height. Mt= log 2H, where H = maximum run-up height or amplitude on a coast line near thegenerating area Or, Mt = logH + a logR + D, where R is the distance in km from theearthquake epicenter to the tide station along the shortest oceanic Path, and a and Dare constants

3.30 Tsunami Period

Time that a tsunami wave takes to complete a cycle. Tsunami period typically rangesfrom 5 minutes to two hours.

3.31 Tsunami Wavelength

Wavelength is the horizontal distance between successive crests of a tsunami wave.

3.32 Wave Celerity

The speed with which a wave crest moves horizontally across the ocean surface isdefined as wave celerity (c) or phase speed, and is usually measured in meters per

second.

Note: Refer to Fig.1 for some of the important glossary of terms.


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4. TSUNAMI CHARACTERISTICS

4.1 Generation of Tsunamis

Tsunamis are generated by any large, impulsive displacement of the sea bed level(Fig.2). Earthquakes generate tsunamis by vertical movement of the sea floor. If the sea

floor movement is horizontal, a tsunami is not generated. Earthquakes of M > 6.5 arecritical for tsunami generation. Tsunamis are also triggered by landslides into or underthe water surface, and can be generated by volcanic activity and meteorite impacts.

4.2 Characteristics of Tsunamis

Tsunami velocity is dependent on the depth of water through which it travels (Velocityequals the square root of water depth h times the gravitational acceleration g, that

is hg=V ) (see fig.3). Tsunamis travel approximately at a velocity of 700 kmph in 4000

m depth of sea water. Thus, the tsunami from Sumatra coastal earthquake traveled toTamil Nadu coast in about two hours. In 10 m of water depth, the velocity drops to about

36 kmph. Even on shore tsunamis speed is 35 40 km/h, hence much faster than aperson can run.

Possible boreformation on shoreAs waves approach shore

they slow down, the waveslengths shorten andamplitudes become higher

Submarine faultmovement, landslide, orvolcanic activity

Tsunami wave trainformation

Fig. 2 Wave train of Tsunami*

3

4

2

*Source:- International Tsunami Information Centre Gerologic Hazard

**Source: http://www.prh.noaa.gov/pr/itic/library/pubs/great_waves/tsunami_great_waves_4.html


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Tsunamis range in size from few centimeters to over 30 m height. Most tsunamishowever are less than 3 m in height. In deep water (greater than 200 m), tsunamis arerarely over 1m high and will not be noticed by ships due to their long time period.

The scientific and technical studies carried out after Indian Ocean Tsunami haveprovided some lessons and guidelines for the construction of tsunami safe buildings and

structures and these have been covered in Annex B.

5 GUIDELINES FOR PLANNING OF BUILDINGS AND EVACUATION OF HUMANS

The tsunami waves always approach from the direction of sea towards the coast. Thegeneral guidelines for planning of buildings shall be as follows:

5.1Minimizing Tsunami Pressures

The buildings constructed on reinforced stilt columnswith sufficient clearance under the buildingsuperstructure, the tsunami wave will be able to passthough exerting only the minimum pressures on thecolumns (see Fig.4). For further reduction in suchhydrodynamic pressures, the columns may be madecircular, octagonal or square with chamfered/roundedcorners. The risers in stairs should be left open forwater to cross through.

Tsunami Max

Fig. 4 - House constructed on stilts

Possible

Bore

Fig.3 Tsunami Velocities**


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5.2 Providing Soft Breaking Obstructions

Buildings may be built as per5.1 but with infill/cladding wall panels which would breakeasily and give way to the tsunami wave to pass through under the upper structure of thebuilding. Such a lower level space may be used to perform functions like seating forprimary education schooling or community gathering purposes in the normal course.

5.3 Protecting the Building by Strong Walls

On the coastal side of the building, strong walls may be constructed by which the wavewater will be deflected back towards the sea (see Fig.5 a). The walls may be curvedconcavely towards the sea in vertical or the horizontal plane. Needless to say that thewalls will have to be designed for the resulting very large reactive forces.

NOTE Recommended heights of bund above high tide line (on the basis of Dec 2004 IndianOcean Tsunami) given in Annex C.

5.4 Use of Break Waters

On the coastal side of the building, appropriate energy dissipation blocks of concrete orstone may be arranged as under the canal falls or the spill way dams which will dissipatethe energy of the fast moving waters of the tsunami so that the impact on the buildingelements will be minimized to safe level (see Fig. 5 b).

5.5 Designing the Building Resistance

It is known that the tsunami forces can even be ten times larger than the maximumearthquake or cyclonic wind pressures. It will therefore require a very heavy wall structurein the lower storyes of the building to make it safe against tsunami impacts. The kind ofactions created on the building are shown in Fig. 6.

Blocking Wall

Fig. 5a Construction of Blocking walls for

deflection of tsunami waves.

Fig. 5b Construction of wave breakersfor slowing speed of waves.


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5.6 Evacuation of the Population

Evacuation of the people could be affected by vertical evacuation through raisedplatforms with proper staircase approach, or into multistoreyed upper floors, or toplatforms constructed at high enough elevation as part of elevated water towers, or bycreating safe areas at higher elevations provided with easy and direct approach to thenearby communities as shown in Fig. 7. The design approach for structures to be usedfor evacuation purposed should be chosen suitably for the sites under consideration.

6 TSUNAMI HAZARD MAP

The Tsunami hazard map at present may be empirically defined using a deterministicapproach based upon potential maximum Tsunami wave heights. The definition of thetsunami hazard zones, as preliminary estimates, is given in Table 1. For the terrestrialenvironment the hazard has been presented as inundation depths. Tsunami hazard mapindicating the elevation data of coasts (contour maps) is yet to be developed . However,Maximum Probable Storm Surge Height and Seismic Zone in Coastal Districts of Indiaare given in ANNEX C.For the marine environment (In water) Harbor, Bay and Reefs hazard has been specified in terms of potential tsunami amplifications.

Fi . 7 Vertical & Horizontal Evacuation

VERTICAL

EVACUATION

HORIZONTAL

EVACUATION

HIGH MOUND

WAVE

BREAK

OVERTURNING

SLIDING

SCOURING

Fig. 6 Actions on Structures created by

Tsunamis


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Table 1 Tsunami Hazard Zones Definition

Tsunami Hazard ZoneCharacteristics

Very high High Medium Low Very Low

On landstructures:Inundationdepth above GL(m)

> 9 6-9 3-6 1-3 < 1.0

In waterStructures:Tsunamiamplificationabove MSL (m)

- > 2 1-2 0.5-1.0 < 0.5

7 GENERAL DESIGN CRITERIA

Due to the effect of tsunami, structures are subjected to the following additionalpressures such as dynamic and sustained wave pressures in addition to the impact wavepressure. The effects of long term erosion, storm-induced erosion and local scour shouldbe considered in the design of foundations of buildings and structures.

7.1 Category of Structures

For tsunami resistant design of structures, the structures are classified into the followingcategories:

Category Description

I Load bearing or Non-engineered buildings.

II RCC & steel buildings which are not intended forvertical evacuation.

III Structures for vertical evacuation.

IV All near shore and on shore structures not covered in I,II & III categories.

7.2 Materials and Methodology for Category I Structures

No special analysis and design provisions are envisaged for category I structures.However, applicable clauses of IS 4326 / IS 13828 may be used as recommended in 8 ofthis standard.

7.3 Materials for Category II, III and IV Structures

The requirements in this clause are applicable to structures of category II, III & IV only.


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7.3.1 Concrete

Exposure condition for coastal environment shall be taken as defined in IS 456. Minimumgrade of concrete, cement content, maximum w/c ratio, maximum aggregate size andcover to reinforcement shall be as per the provisions of IS 456.

NOTE In case, prestressed concrete is used, it shall conform to IS 1343.

7.3.2 Reinforcement Steel

Reinforcement steel Fe 415 or TMT bars (Fe 500 or Fe 550) conforming to IS 1786 andhaving minimum elongation of 14.5 percent shall be used.

7.3.3 Structural Steel

Structural steel conforming to IS 2062 shall be used with suitable corrosion protectionmeasures. Provisions pertaining to durability and corrosion protection as given in IS 800

shall be complied.

7.4 Methodology for Designing Category II Structures

The provisions of IS 1893 and IS 13920 shall be applied for analysis and design ofcategory II structures as per seismic zone V requirements for the structures in thetsunami affected area of the district. However, for rest of the area, design of structuresshall be done as per seismic zones given in Annex C.

7.5 Forces due to Tsunami Impact on Category II Structures

7.5.1 Estimation of Tsunami Amplification Near the Shore

Tsunami amplification near the shore can be estimated from the following equation:

d)(g21

H)0

d(g20

H = (1a)

or

= (1b)

whereHo =Approximate height of tsunami in flat deep ocean floor (can be determinedfrom the fig. 8. For rugged deep ocean floor adopt fig. 9)H1 = height of tsunami near the shore (m)do = water depth in the deep sea (m)d = water depth near the shore (m)g = acceleration due to gravity (9.81 m/s2)


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Figure 8 Height of tsunami in flat deep ocean floor (depth more than 4000 m )

Figure 9 Height of tsunami in rugged ocean floor

7.5.2 Estimation of Impact Forces for Structures Located Near the Sea Front

7.5.2.1 For Structures Located Within 50 m from the Sea Front

The following procedure for estimating the design force for structures within 50 m fromthe sea front shall be adopted. For structures located beyond 50 m upland, proceduregiven in7.5.2.2 shall be adopted


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a) Determination of dynamic wave pressure

The following equation gives the dynamic wave pressure:

= (2a)

or

= (2b)

wherePdm = maximum dynamic wave pressure (N/m

2)c = wave celerity (m/s)h = initial water depth (m)

H1 = Height of tsunami near shore (m) = density of seawater (kg/m3)g = acceleration due to gravity (m/s2)K = kinetic wave coefficient (0.3 to 0.51)

b) Determination of Sustained Wave Pressure

( )+= (3)

where1 : structure slope (Fig. 10)Psm : maximum sustained wave pressure (N/m

2)Pdm : maximum dynamic wave pressure (N/m

2)c : wave celerity (m/s)g : acceleration due to gravity (m/s2)H1: Height of tsunami near shore (m)

Figure 10 Definition sketch for1


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c) Determination of Impact Standing Wave pressure

The relation between the sum of maximum dynamic wave pressure Pdm, maximumsustained wave pressure Psm and maximum impact wave pressure Pim is given by thefollowing equations.

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Tsunami Draft Code