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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 construction

InstallationsBomb shelter areasconclusion



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



Movingvehicleattack

Stationaryvehiclebomb

Exteriorattack

Arsons

Others

Ballisticattacks



Maintain safe separation of attackers and targets i.e.STAND-OFF zones.Design to sustain and contain certain amount of bombdamage. Avoid progressive collapse of the building.Allow for limited localized damage of membersMinimize the quantity and hazard of broken glass and

blast induced debris .

Facilitate rescue and recovery operation withadequate time of evacuation of occupants.



Effects of blast on the structure:

An explosion is a rapid release of potential energycharacterized by eruption enormous energy to theatmosphere.

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 fromthese effects



Planning and layout:

Sufficient stand-off distancemust be provided.

In case of congested areas

where there is no provisionfor stand off distance,

bollards, trees or streetfurniture are to be providedas obstacles.



Structural Solutions for Blast Resistant Buildings:

Roof : Arches and domes are the typesof structural forms that reduce the

blast effects on the building comparedwith a cubicle form.

Flooring : They must be preventedfrom ‘falling off' their supports. Pre -cast flooring is to be avoided in caseof blast resistant structures



Beam-to-column connections:Frame structures are deficient in 2aspects:

failure of beam to columnconnectionsInability of the structure totolerate load reversal

providing additionalrobustness to these

connections can be significantenhancement.

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 theconnection reduce the collapse and damages.

In critical areas full moment-resisting connections aremade in order to ensure the load carrying capacity ofstructural members after an explosion



The need for fire resistance, strength and ductility favorsreinforced concrete as a construction material for floors.Blast-resistant design philosophy allows structural

elements to undergo large inelastic (plastic) deformationsin response to blast loading.

• A ductile structure that undergoes large deformationswithout failure can absorb much more energy than a

brittle structure of the same static strength



Tensile reinforcement between 0.5 and 2 percent of the cross-sectional area of the concrete element will usually insureductile behavior while providing the required strength.

Compression steel in flexural members serves two purposes.After a structural member is deflected by blast loads, itattempts to spring back or rebound. Dynamic rebound causesload reversal and, under certain circumstances, can result incatastrophic failure



Wrapping of columns:

Wrapping is done todone for external

protection of columnsand also to protect thecolumn from shockwaves. Two types ofwrapping can beapplied. Wrapping

with steel belts orwrapping with carbonfiber-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 toresist any explosion affects.

Bomb shelter areas:

The bomb shelter areas are specially designated within the

building where vulnerability from the effects of the explosionis at a minimum and where personnel can retire in the eventof a bomb threat warning.



Glazing and cladding:

Glass from broken and shattered windows could beresponsible for a large number of injuries caused by an explosion ina city centre. The choice of a safer glazing material is critical and ithas been found out that laminated glass is the most effective in thiscontext.



It is not practical to design buildings to withstandany conceivable terrorist attack.It is possible to improve the performance ofstructures should one occur in the form of anexternal explosion.Design process to ensure that appropriate threatconditions and levels of protection are beingincorporated.

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 nov1990

Blast resistant design technology by Henry Wong WGA WongGregerson architects Inc. Constructing and deigning blast resistant buildings by G. Gehringand P. Summers MMI engg Texas

Design of structure for blast related progressive collapse resistanceby 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 andStevan J. Smith an internet webpage in [email protected]



Thank you

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