This document discusses the design of blast resistant structures. It covers types of blasts, principles of blast resistant design such as maintaining safe stand-off zones and minimizing debris, and guidelines for analysis including redundancy and ductile structure elements. It also describes procedures for analysis using pressure-impulse diagrams and finite element methods. Acceptable damage levels from minor to major are defined. The key differences between blast and seismic loads are outlined, and it is concluded that while withstanding any attack is impractical, performance can be improved through appropriate design processes.

1. Design of Blast resistant structures

2. 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

3. Types of blasts

4. 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 of broken glass and blast induced debris. Facilitate rescue and recovery operation with adequate time of evacuation of occupants.

5. 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)

6. Blast load definition 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

8. Thermal energy radiation Much of the thermal energy is absorbed . Combustible materials gets ignited. These act fuel for building materials to be burnt Life inside also get burnt.

9. 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.

10. Pressure and overpressure sinks below ambient pressure before equalizing back to atmospheric pressure.

11. Air blast This can penetrate basement areas that are open causing high internal pressures and causing high velocity 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.

12. Secondary fires These are triggered by blast damages. Damaged gas pipes Flammable building materials. Electric short circuits. Overturned appliances.

13. Guidelines for analysis Redundancy and alternate load paths. Ductile structure elements. Designing for load reversals. Shear capacities which prevent shear failure prior to flexural failure.

16. But both material linear and material non-linear capacities are considered and designed

19. Here balanced design of beams is done considering beam is weaker than column and failure of beam is desired first.

21. Missing column loads are distributed.

22. The frame is proportioned with sufficient strength to resist twice the D.L and L.L .

23. Procedure may be conceptually incorrect but provides desired solution.

24. Beams and columns assumed to distribute twice the vertical loads.

25. Based on theory related to instantaneous application of loads.

33. Explosion loads act directly on the exterior envelope.

34. Explosion loads generally cause localized damage.

35. Mass helps resist explosion loads.Seismic load The vibrational load of earthquakes which is acts over seconds. Earthquakes load acts at the base of the building. Seismic loads cause global response. Mass worsens earthquake response.

37. 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.

38. References Blast safety of the building envelope by Eve Hinman ,PE hinmanengg report. 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 Whittaker Blast and progressive collapse Kirk A Marchand and FaridAfawakhiri AISC Inc. Blast resistant design of R C structures by Dennis M. McCann and Stevan J. Smith an internet webpage in dmccann@exponent.com