Blast Loadings - Industrial Buildings.

This section deals only with blast loadings from industrial processes and not with any generalized design requirements to survive blast loadings from unspecified sources or of unspecified values.

Varying requirements exist for blast loadings. Typical examples are:

(1) transformers, where the requirement is usually to deflect any blast away from other vulnerable pieces of plant but where frequently one or more walls and the roof are open, serving to dissipate much of the energy discharged
(2) dust or fine particle enclosures, which are often wholly inside enclosed  buildings.

The decisions to be made are as follows.

(1) Can the potential source of the blast be relocated outside the building  altogether, in a separate enclosure?
(2) If not, can it be placed against the external wall with arrangements to have a major permanent vented area or a specially designed blow-off panel, both of which will limit loadings on the remaining structure?
(3) Where the location cannot be controlled, it must be established which direction or directions require full protection against damage and which  can tolerate certain degrees of damage.

Loading data given by plant designers are usually stated in terms of peak pres- sures to be applied to projected areas in line with the potential source of the blast.

The validity of the data must be treated as being highly suspect since blast loadings are classic examples of true dynamic loading where the time-dependent response of the structure actually determines the loading that is imposed. Quoted blast pressures, which are probably derived from theoretical considerations of high-rigidity high-mass targets fully enclosing the source, may be invalid for steel structures which have tremendous capacity to deform rapidly, absorbing energy and thereby reducing and smoothing out peak blast pressures. Whatever results are obtained from analysis or calculation, it is good practice to use a grade of steel which has good ductility, a lower yield stress from which to commence ductile behaviour and a long and reliable extensibility prior to fracture.While this will ensure reasonable material behaviour, overall ductility of the structure also depends on stability against premature buckling and the ductile behaviour of connections.

Steelwork designers should acknowledge the very imprecise nature of most blast loading data, even when the potential source of the blast is precisely located and specified. They should thus direct their attention to ensuring that collapse does  not occur until major deflections and rotations have occurred, following normal guidelines for achieving plastic behaviour.

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