cycones - 3

Structural mitigation measures

Structural mitigation measures

• (i) buildings, including multi-purpose cyclone• shelters;• (ii) road links, culverts and bridges;• (iii) canals, drains, and surface water tanks,

etc.;• (iv) saline embankments; and• (v) communication towers and power• transmission networks.

Design Considerations of StructuresGeneral Design Considerations for Buildings

• i) The design to be carried out for 1.3 times the basic wind speed as recommended in the IS 875 - 1987 part 3. The basic wind speed as per the code in most parts of the coastal zone is 50 m/s (180 km/hour) up to 10 m above ground level. Further, a number of corrections are to be applied based on the importance of the structure (risk assessment), topography, size and shape of the building.

ii) The design will also be able to withstand seismic forces in regions which are additionally vulnerable to earthquake hazard, such as Kandla, etc

iii) The local community will be encouraged to construct houses which will be cyclone resistant. Urban Local Bodies (ULBs) and Panchayati Raj Institutions (PRIs) will be asked to ensure this.

Road Links, Culverts and Bridges

3) Canals, Drains, Surface Water TanksDesign and Maintenance Considerations for Canals, Drains and Tanks

• i) The reinforcement cover of the foundations, substructure locking gates/sluices will be at the level specified in IRC: SP: 33-1989 to achieve the expected level of durability. For steel structures, IS-800 will be followed.

• ii) To ensure proper functioning of canals/ drains/tanks during storm surge due to cyclone, the following measures are required:

• a) Branches to the canal drain are to be closed.• b) The embankments will be strengthened.• c) The condition of the passage-bridge and channels will be

checked.• d) Obstructions in the canals/drains will be removed periodically

to enable free flow of water.

• e) The blocks and shutters of the canals are to be checked for satisfactory performance.• f) The instruments and materials required for attending to immediate repairs, breach of

closures, etc., will be stacked in advance at places where they may be required.• g) Navigation in the canal will be stopped.• h) Water supply into canals will be cut out off by closing the sluices.• i) The canals and drains will be free from constructions and they will be made available

for free discharge of drain water.• j) The link drains will be lined to minimize maintenance and overflowing during the

monsoon.• k) The water tanks used for drinking water supply are likely to become saline and will

even get contaminated during a cyclone. Adequate embankment of atleast 0.5 m above the flood level will

• be provided to such tanks.• l) The growth of water hyacinth, etc. is a major problem in many areas as they obstruct

and affect the carrying capacity of drains, canals and tanks. A regular maintenance mechanism will be institutionalised.

4. Saline Embankments

• Construction of ‘saline embankments’ is one of the structural mitigation measures to protect habitation, agriculture crop and important installations along the coast. These embankments are designed to protect the coastal population and property from regular phenomena such high tides, low intensity cyclone and normal rainfall but, are not adequate or suitable to protect the coast from high intensity cyclones generating high surge.

5. Communication Towers and Power Transmission Networks

• Communications and power transmission towers will be designed on the basis of 100-year return period wind velocity of cyclone.

Design and Maintenance considerations of Communication and Transmission Line Towers

• i) Transmission line and communication towers and elevated water tanks located in the cyclone prone areas will be designed with wind speed 1.3 times that specified by IS: 875/(part 3)/1987. The open area in the zone and its topography will be given due consideration in selecting the correction factors.

• ii) The towers will be designed using their dynamic analysis with suitable wind gust loading.

• iii) The structural steel used in the towers will be galvanized to withstand the corrosive exposure condition.

• iv) The foundation depth will be taken at least 1 m below the scour level and the stability of the towers will be standalone without depending on the filling weight of the soil.

• v) The design of a communication/transmission tower, including its foundation, is checked by a competent authority.

The relevant BIS Codes are:

• i. IS 456 : 2000 Plain and Reinforced Concrete – Code of Practice (reaffirmed 2005).

• ii. IS 875 : Part 3 : 1987 Code of Practice for Design Loads (other than Earthquake) for Buildings and Structures - Part 3 : Wind Loads (reaffirmed 2003).

• iii. IS 800 : 1984 Code of practice for general construction in steel (reaffirmed 2003) IS 8237 : 1985 Code of Practice for Protection of Slope for Reservoir Embankment (reaffirmed 2002).

• iv. IS 10635 : 1993 Freeboard requirements in embankment dams – guidelines (reaffirmed 2003).

• v. IS 11532 : 1995 Construction and maintenance of river embankments (levees) – guidelines (reaffirmed 2005).

• vi. IS 12094 : 2000 Guidelines for Planning and Design of River Embankments (Levees) (reaffirmed 2005).

• vii. IS 12169 : 1987 Criteria for design of small embankment dams (reaffirmed 2002).

Cyclone disaster management plan:

• Before the event– Timely accurate warnings– Community preparedness to meet the eventuality– Awareness about the disaster / crisis or education about

natural disasters– Construction of cyclone shelters– Protection barriers against floods, storm surges, lightning– Plantation of shelter beds– Stocking of food, emergency medicines and potable water– Evacuation of the people, who are likely to be affected to

safer places

• During the event– Organizing the affected people to be shifted the cyclone

shelters or camps– Motivate the people to be bold and organize them to help

one another• After the event– Conduct survey of the affected area to asses loss of life an

damage to property. Recommend assistance– Organise the affected people staying in the camps / cyclone

shelter to send them back to their places– Render help / assistance to the affected to rehabilitate