DESIGN OF BLAST RESISTANT STRUCTURES
Sneha
09011A0135
AGENDA:
NeedTypes of blastsPrinciples Effects on the structurePreventive measures: (i) Measures to be taken while planning (ii) Measures to be taken while constructionInstallations Bomb shelter areas conclusion
Need:
Increase in number of terrorist attacks.
To minimize damage to the assets
To minimize the loss of life.
To protect historical monuments and important buildings
To subside social panic
Moving vehicle attack
Stationary vehicle bomb
Exterior attack
Arsons
Others
Ballistic attacks
Types of blasts
Maintain safe separation of attackers and targets i.e. STAND-OFF zones.
Design to sustain and contain certain amount of bomb damage. Avoid progressive collapse of the building.
Allow for limited localized damage of members Minimize the quantity and hazard of broken glass and
blast induced debris. Facilitate rescue and recovery operation with
adequate time of evacuation of occupants.
Principles of blast resistant design:
Effects of blast on the structure:
An explosion is a rapid release of potential energy characterized by eruption enormous energy to the atmosphere.
A part of energy is converted to thermal energy radiation(flash) and a part is coupled as air blast and shock waves which expand radially
How to safeguard the structure from these effects
Planning and layout:
Sufficient stand-off distance must be provided.
In case of congested areas where there is no provision for stand off distance, bollards, trees or street furniture are to be provided as obstacles.
Structural Solutions for Blast Resistant Buildings:
Roof: Arches and domes are the types of structural forms that reduce the blast effects on the building compared with a cubicle form.
Flooring: They must be prevented from ‘falling off' their supports. Pre-cast flooring is to be avoided in case of blast resistant structures
Beam-to-column connections:
Frame structures are deficient in 2 aspects:
failure of beam to column connections
Inability of the structure to tolerate load reversal
providing additional robustness to these connections can be significant enhancement.
Side plate connection for a steel structure
Beam to column connection in Reinforced concrete structure
The use of extra links and the location of the starter bars in the connection reduce the collapse and damages.
In critical areas full moment-resisting connections are made in order to ensure the load carrying capacity of structural members after an explosion
The need for fire resistance, strength and ductility favors reinforced concrete as a construction material for floors. Blast-resistant design philosophy allows structural elements to undergo large inelastic (plastic) deformations in response to blast loading.
• A ductile structure that undergoes large deformations without failure can absorb much more energy than a brittle structure of the same static strength
Ductile detailing of reinforcements:
Tensile reinforcement between 0.5 and 2 percent of the cross-sectional area of the concrete element will usually insure ductile behavior while providing the required strength.
Compression steel in flexural members serves two purposes. After a structural member is deflected by blast loads, it attempts to spring back or rebound. Dynamic rebound causes load reversal and, under certain circumstances, can result in catastrophic failure
Wrapping of columns:
Wrapping is done to done for external protection of columns and also to protect the column from shock waves. Two types of wrapping can be applied. Wrapping with steel belts or wrapping with carbon fiber-reinforced polymers (CFRP).
Miscellaneous measures:
Partially or fully embed buildings are quite blast resistant.
Projected roofs and floors are undesirable
Single story buildings are more blast resistant than multi story buildings
Double-Dooring should be used.
Installations:
Gas, water, steam installations, electrical connections, elevators and water storage systems should be planned to resist any explosion affects.
Bomb shelter areas:
The bomb shelter areas are specially designated within the building where vulnerability from the effects of the explosion is at a minimum and where personnel can retire in the event of a bomb threat warning.
Glazing and cladding:
Glass from broken and shattered windows could be responsible for a large number of injuries caused by an explosion in a city centre. The choice of a safer glazing material is critical and it has been found out that laminated glass is the most effective in this context.
It is not practical to design buildings to withstand any conceivable terrorist attack.
It is possible to improve the performance of structures should one occur in the form of an external explosion.
Design process to ensure that appropriate threat conditions and levels of protection are being incorporated.
Conclusion:
References:
Structural design for external terrorist bomb attack by Jon A. Schmidt structure® magazine march issue (2003)
Structure to resist the effects of accidental explosions U.S army nov 1990
Blast resistant design technology by Henry Wong WGA Wong Gregerson architects Inc.
Constructing and deigning blast resistant buildings by G. Gehring and P. Summers MMI engg Texas
Design of structure for blast related progressive collapse resistance by Ronald Hamburger and Andrew
Blast and progressive collapse Kirk A Marchand and Farid Afawakhiri AISC Inc.
Blast resistant design of R C structures by Dennis M. McCann and Stevan J. Smith an internet webpage in [email protected]
Thank you