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Introduction

One of the most popular design issue.

Terror attacks and accidents.

Subject is popularly applied in modern and

important buildings.

Emerging branch in the field of structural

engineering

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Principles of blast resistant design 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 ofbroken glass

and blast induced debris.

Facilitate rescue and recovery operation with

adequate time of evacuation of occupants.

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Stand-off zones

Blockades, planters, fountains, fences as

obstacles to ramming vehicles/truck bomb.

Allow only emergency vehicle access.

Raise the building 2m above ground level

(provide Ramps for barrier free access)

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Blastload

Thermalenergy

radiation

Audibleblast

Air blastDynamicpressure

Overpressure

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Effects of shock-waves

This travels away from explosion faster than the

speed of sound poses threat in close location.

Shock front is similar to moving wall of highly

compressed air accompanied by blast wind. It causes sudden rise in ambient pressure. This is

called over-pressure. Pressure caused by blast wind

is called dynamic pressure.

Both these pressure decay rapidly with time.

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Air blast This can penetrate basement areas that are open

causing high internal pressures and causing highvelocity jet of air through openings.

Window glass and debris shattered by shockwave

acts as missiles in the air jet.

High pressure causes lungs damage and ear drum

rupture.

Air-jets can pick people and hurl them to fixed

objects.

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Secondary fires

These are triggered by blast damages.

Damaged gas pipes

Flammable building materials. Electric short circuits.

Overturned appliances.

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2. Analysis using finite element methods It includes calculation ofnon-linear dynamic

single degree freedom of member i.e. blastpressure/load and then comparing withcalculated single degree of freedom response (i.e.calculation of blast load within response limit ofthe trial member)

Here balanced design of beams is doneconsidering beam is weaker than column andfailure of beam is desired first.

Sufficient shear transfer is provided to even slabsand transfer girders avoided near blast threatregions.

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3. Redistribution of loads from removed column

Here column from structural frame is removed.

Missing column loads are distributed. The frame is proportioned with sufficient

strength to resist twice the D.L and L.L .

Procedure may be conceptually incorrect butprovides desired solution.

Beams and columns assumed to distribute twicethe vertical loads.

Based on theory related to instantaneousapplication of loads.

To prevent progressive collapse

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Ductile detailing of reinforcements

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 muchmore energy than a brittle structure of the

same static strength.

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Acceptable Damage Levels

Minor: Non-structural failure of building

elements as windows, doors, and cladding.Injuries may be expected, and fatalities arepossible but unlikely.

Moderate: Structural damage is confined to a

localized area and is usually repairable. Structuralfailure is limited to secondary structuralmembers, such as beams, slabs and non-loadbearing walls. However, if the building has beendesigned for loss of primary members, localized

loss of columns may be accommodated withoutinitiating progressive collapse. Injuries andpossible fatalities are expected.

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Major: Loss of primary structural components

such as columns or transfer girders

precipitates loss of additional adjacentmembers that are adjacent or above the lost

member. In this case, extensive fatalities are

expected. Building is usually not repairable.

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CONCLUSION

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.

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References Blast safety of the building envelope by Eve Hinman ,PE hinman engg report.

Structural design for external terrorist bomb attack by Jon A. Schmidt structuremagazine 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 Whittaker

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 dmccann@exponent.com

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