In addition to seismic effect on tank, oscillation of water and induced waves produce additional risk; particularly when baffle plates are not designed properly. Seismic damage may range from minor to major including total collapse. Major damage of large tank results large volume of water runoff.
• Quality of construction• Design standard
• Maintenance of structure and tanks
• Site amplification
At first we will discuss about small elevated tank.
Small Elevated Tanks:
Small tanks are used to store water for individual dwelling, schools, small industries or group of houses. Various materials are used to construct these and supporting structures are also constructed of different materials like wood, reinforced concrete, structural steel etc. Smooth corrugated iron, fiber glass, reinforced concrete, asbestos concrete etc. are used to construct tanks. The ill-effect of asbestos is now well-known to all and gradually replaced by other materials.
Type of Damage and Recovery:
Tanks made of CI sheet often collapse during earthquake. Previous experiences show us that poor maintenance is the main cause of failure but some instability cases were also found.
• Damage in tank and/or support often may require light repair. But if supporting structure collapses, tank also has to be replaced.
• In many cases, a portion can be salvaged where metal and wooden structures are used except corroded portion.
Partially Buried Water Tanks:
These types of tanks are used for storage or regulation purposes for towns and cities which are usually constructed of concrete may be of reinforced or unreinforced concrete, stonework or other materials. They may be damaged such as
• Cracks in covering, floor, walls or at the joint of these elements like at entrance or exit pipes which may be repaired easily or total reconstruction is required.
• Cover, part of walls or interior columns may be caved-in; sometimes minimal repair is enough but may require total reconstruction.
• Total destruction of structure.
Large elevated tank:
Medium to large elevated tanks are generally constructed of reinforced concrete or steel.
Damage in steel tank:
• Damage of supporting structure with/without storage tank can become minor to severe; severe damages are often observed in connection between pipes and supporting structures.
• Total collapse of structure.
Damage in concrete tank:
Following forms of damages are observed in concrete tank due to earthquake:
• Cracks may formed in
• At the point of pipe passing through concrete walls• At the joint between supporting structure and water tank
• Region of overlap of excessive reinforcements
• Foundation failure, or leaving or topping of structure
Comparison between steel and concrete tank:
This disaster broke water main resulting flooding nearest commuter station, rail tunnels and telecommunication vaults (containing cables).