Impacts Of blasts on buildings. civil engineering.

2. IMPACT OF BLASTS ON
BUILDINGS
Presented By : Umar Farooq

3. BASIC TERMS
• Explosion :-
An explosion is a swift release of energy, taking the form of
sound, heat, light, and shock waves.
• Blast :-
A blast generally means something more specific: It’s the initial
shock wave (or movement of air) created by the explosion.

4. STEPS OF AN EXPLOSIVE EVENT
• The explosive material “detonates”, which means it gets converted
from its original state into a hot, high-pressure gas

5. STEPS OF AN EXPLOSIVE EVENT
• In order to reach equilibrium with the surrounding air, the product of
the explosion expands rapidly, creating a shock wave made of highly
compressed air.

6. STEPS OF AN EXPLOSIVE EVENT
• This shock wave travels radially outward from its source (the
explosive material) at supersonic speed. As it expands, pressure drops
rapidly due to the energy dissipating. This typically happens in
milliseconds.
• The initial shock wave is only one third of the total chemical energy
release. The remaining two thirds are released more slowly, as
products of the detonation create an “afterburning” process, slower
than the original blast and detonation.

7. STEPS OF AN EXPLOSIVE EVENT
• These secondary shock waves (or “stress waves”) also carry a huge
amount of energy, and will pass through surfaces, organs and tissues,
creating tremendous damage.
• At the site of the explosion, a vacuum (or blast wind) will also be
created, due to the rapid expansion of the blast. If the blast can be
seen as a “push” effect, then the vacuum is more of a “pull”, since it
pulls in the surrounding atmosphere. This high-intensity vacuum can
cause objects, glass, or debris to be draw back towards the explosion
site.

8. FACTORS THAT DETERMINE THE EFFECTS
OF A BLAST
• Amount of explosives used :
Higher quantities of explosive materials tend to
lead to a bigger, more destructive event.
• Type and Composition of the material :
(e.g., TNT, C4, Semtex, HMX) will also dictate the
strength of the explosion.

9. FACTORS THAT DETERMINE THE EFFECTS
OF A BLAST
• The Stand-off distance :
The distance between the detonation and the
structure (the “stand-off” distance) also plays a critical role.

10. FACTORS THAT DETERMINE THE EFFECTS
OF A BLAST
• The building’s architecture and construction materials :
Blast-resistant buildings will generally withstand explosions
better than “regular” buildings. It is not a guarantee, of course.

11. BLASTS DAMAGE TO BUILDINGS AND
PEOPLE
The threats from explosive events should be broken down into two major
parts:
damage mechanisms to buildings, and injury mechanisms to people.
• For buildings, there are three major damage mechanisms:
1. Direct air-blast effects :
The detonation, the shock waves, vacuum, the quantity
and type of explosives, and the pressure created by the explosive event.
The direct air-blast may also result in flying debris damaging the
structure even further.

12. BLASTS DAMAGE TO BUILDINGS
2. Collapse:
Once a building has been hit (either directly or indirectly),
parts of its structure are at risk of collapse. This is the most severe
building response to an attack. This collapse may be immediate (e.g.,
a wall or beam being destroyed by the blast) but it may also be a
progressive collapse. This happens when localized structural failure
spreads to other elements of the buildings, leading to a chain-
reaction that leads to more damage and/or collapse.

13. BLASTS DAMAGE TO BUILDINGS
• The Head of Explosion Protection for the London-based Special Services Group
(SSG) described how a truck bomb would affect a building if detonated at varying
distances; this is displayed in the table below:
Local collapse of building 10-20 m
Structural damage 50 m
Damage to blast resistant glazing 100 m
Damage to glass with film 200 m
Damage to glass without film 400 m

14. BLASTS DAMAGE TO BUILDINGS
3. Damage to nearby structures:
Blasts targeted one building often have an impact on
neighboring buildings. Either the explosion itself is powerful enough
to reach nearby structures (e.g., a shock wave causing windows to
shatter), or the collapse of the main target will damage surrounding
buildings, or debris will be propelled with enough force to hit those
buildings.

15. EXPECTED DAMAGE LEVELS
• Minor :
• Non-structural failure of building elements such as windows,
doors & cladding.
• Injuries may be expected and deaths are possible but unlikely.

16. MINOR

17. EXPECTED DAMAGE LEVELS
• Moderate :
• Structural damage is confined to a localized area and is usually
repairable.
• Structural failure is limited to secondary structural members,
such as floors , roofs & non load bearing walls.
• Injuries and deaths are expected.

18. MODERATE

19. EXPECTED DAMAGE LEVELS
• Major :
• Failure of primary structural members such as columns , beams
etc.
• In this case, extensive deaths are expected.
• Building becomes non repairable.

20. MAJOR

21. RESPONSE OF STRUCTURES TO BLAST
LOADING
• The response of structure due to blast loadings can be as follows :
1. Impulsive
2. Quasi-static
3. Dynamic

22. RESPONSE OF STRUCTURES TO BLAST
LOADING
• Impulsive :-
If the positive phase duration of the blast pressure is shorter
than the natural period of vibration of the structure, the response is
described as impulsive. In this case, most of the deformation of the
structure will occur after the blast loading has diminished.

23. RESPONSE OF STRUCTURES TO BLAST
LOADING
• Quasi-Static :-
If the positive phase duration of the blast pressure is
longer than the natural period of vibration of the structure, the
response is defined as quasi-static. In this case, the blast will cause the
structure to deform while the loading is still being applied.

24. RESPONSE OF STRUCTURES TO BLAST
LOADING
• Dynamic :-
If the positive phase duration of the blast pressure is close to
the natural period of vibration of the structure, then the response of
the structure is referred to as dynamic. In this case, the deformation
of the structure is a function of time and the response is determined
by solving the equation of motion of the structural system.

25. HOW TO PROTECT PEOPLE AND STRUCTURES
AGAINST THIS GROWING THREAT???
• While we can’t always prevent terrorists from reaching their destination but we can
prepare our buildings to better withstand explosions.
For example:
• By increasing the stand-off distance.
• By improving our structures strength and make it more flexible.
• Roofs.
• Wrapping of columns.
• Beam to column connection.
• Double dooring should be used.
• Shear walls etc..

26. HOW TO PROTECT STRUCTURES AGAINST THIS
GROWING THREAT???
• Stand Off Distance :
• Blockades, planters, fountains, fences as obstacles to ramming vehicles or truck
bomb.
• Allow only emergency vehicle access.
• Raise the building 2m above ground level

27. STAND OFF DISTANCE

28. HOW TO PROTECT STRUCTURES AGAINST THIS
GROWING THREAT???
• Roofs :-
• Arches and domes are the types of structural
forms that reduce the blast effects on the
building compared with a cubicle form.

29. HOW TO PROTECT STRUCTURES AGAINST THIS
GROWING THREAT???
• Floorings :-
• They must be prevented from
‘falling off' their supports. Pre-cast
flooring is to be avoided in case of
blast resistant structures.

30. HOW TO PROTECT STRUCTURES AGAINST THIS
GROWING THREAT???
• 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).

31. WRAPPING OF COLUMNS

32. HOW TO PROTECT STRUCTURES AGAINST THIS
GROWING THREAT???
• Shear Walls :-
• Use a well distributed lateral load resisting mechanism in the horizontal
floor plan.
• Shear plan around the plan will improve the overall seismic as well as blast
behaviour of the building.

33. SHEAR WALLS

34. HOW TO PROTECT STRUCTURES AGAINST THIS
GROWING THREAT???
• 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.

35. HOW TO PROTECT STRUCTURES AGAINST THIS
GROWING THREAT???
• 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.

36. THANK YOU