Building Blast Loading

A control building is located 125 ft (38 m) from a facility that handles highly reactive materials having the potential for explosion. The building can withstand a 12 psi (0.83 bar) side-on overpressure, 20 ms blast load. 

The company standards classify this facility as "high explosion potential," requiring control buildings that are located at this distance [125 ft (38 m)] from a potential explosion be designed to a minimum load of 10 psi (0.69 bar) side-on overpressure and 20 ms blast load. It was determined that this... 

Evaluation of Building Response and Tolerance Criteria Principles of evaluating building response to explosion loads are presented in Section 5.5.1. The resulting responses are to be compared to structural capacities in accordance with ultimate strength provisions of the governing material standards (e.g., Refs. 94,99, and 100). Blast loads are large compared to conventional loads and less likely to occur than are such conventional loads,... 

For biast resistant design of buildings, the principal parameters of the blast wave required to define the blast loading for a building s components are ... 

The shape of (he rear wall loading is similar to that for side and roof loads, however the rise time ami duration arc influenced by a not well understood pattern of spillover from the roof and side walls and from ground reflection effects. The rear wall blast load lags that for the front wall by L/U, the lime for the blast wave to travel the length, L, of the building. The effective peak overpressure is similar to that for side walls and is calculated using Equation 3.11 (Ph is normally used to designate the rear wall peak overpressure instead of P,). Available references indicate two distinct values for the rise lime and positive phase duration. 

This example illustrates the calculation of blast loading on the components of a building subjected to a shock wave traveling horizontally. The building dimensions... 

Windows should be designed to withstand the same blast loads as the walls. The engineer should define the structural design criteria and coordinate with the building s architect to assure the manufacturer s correct interpretation,... 

Determine the location and size of potential explosions, and establish blast loads on the building. 

Upgrade to the existing facility depends on the increase in blast capacity required. Level of blast protection is generally based on building category, function, risk level and blast loads. Structural assessment and cost evaluation are then made to determine the best alternative to use. 

Connections for precast panels can be a problem for blast loaded buildings. Typical connections for walls rely on direct bearing for support of the panel for positive loads, and weld plates for negative loads such as wind suction. Rebound of stiff panels due to blast toad can be very high, and the connections typically used in conventional design may be inadequate to resist this load. Substantial and expensive changes arc often required to develop the full capacity of precast panels. 

The dynamic pressure exerts the dominant blast effect on open frame structures, framed structures with frangible cladding, and on small structure or components such as poles, stacks, etc. The dynamic pressure also influences, but to a lesser extent, the net blast loads on the walls and roof of an enclosed building as discussed in Section 3.5. 

FIGURE 3.6 Blast Loading General Arrangement for a Rectangular Building... 

The plan (outline) and elevation profiles of a blast resistant building should be as clean and simple as possible. Reentrant comers and offsets, in particular, should be avoided. Such features, create local high concentrations of blast loading. The orientation of the building should be such that the blast induced loads are reduced as much as possible. This requires that as small an area of the building as possible should face the most probable source of an explosion. 

This type of construction uses precast concrete walls with steel or concrete frames (Figure 4.2). The frame resists all vertical loads and precast shear walls resist lateral loads. Ductile connections for precast panels are an important consideration. Precast panels are made with embedded steel connection devices attached to the building frame by bolting or welding. The roof is usually a concrete slab on metal deck. The metal deck is attached to steel framing by studs or puddle welds. Tins type of construction can be economically designed to withstand blast loading on the order of 7 to 10 psi (48 to 69 kPa) side-on overpressure. 

The primary failure mechanisms encountered in reinforced concrete buildings arc flexure, diagonal tension, and direct shear. Of these three mechanisms,. flexure is preferred under blast loading because an extended plastic response is provider prior to failure. To assure a ductile response, sections are designed so that the flexural capacity is less than the capacity of non-ductile mechanisms. 

Normally, the overall blast capacity of a building is not controlled by its foundation because there is usually adequate inherent strength to prevent a catastrophic failure. However, excessive dynamic movements from a blast load may result in unacceptable foundation damage, which because of inaccessibility, can be difficult and expensive to repair,... 

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