Loading on the Roof

Dead load = snow load + finishes + dead load (adverse) 

Dead load = finishes + self-weight (benifidal) 

The downward loading is chosen for this is the worse case. The negative value in the second calculation shows when blasting occurs. The load is balanced by the downward imposed load, dead load and self-weight of the roof slab. 

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EPDM roof sheet is one of the lightest roof membrane materials because of its low specific gravity. It is highly suitable for lightweight structures and puts negligible extra load on the roof to be waterproofed. It is serviceable over a wide range of temperatures -50 °C to 150 °C, and the membrane does not embrittle in freezing condition nor soften in hot weather. 

For a building with a flat roof (pitch less than 10°) it is normally assumed that reflection does not occur when the blast wave travels horizontally. Consequently, the roof will experience the side-on overpressure combined with the dynamic wind pressure, the same as the side walls. The dynamic wind force on the roof acts in the opposite direction to the overpressure (upward). Also, consideration should be given to variation of the blast wave with distance and time as it travels across a roof element. The resulting roof loading, as shown in Figure 3.8, depends on the ratio of blast wave length to the span of the roof element and on its orientation relative to the direction of the blast wave. The effective peak overpressure for the roof elements are calculated using Equation 3.11 similar to the side wall. 

The rear wall is proportioned the same as the front and side walls, spanning vertically from foundation to roof. Because the highest loads are on the front wall, a rear wall analysis would only be. necessary to determine a net loading on the overall building. The analysis will be for a wall segment 1 foot wide. 

Another possible protective scheme, although rarely used in the petrochemical industry, is a blast resistant barrier wall. A barrier wall can be used to provide protection from fragments and reduce reflected wall loads. However, it will not reduce overpressures on the roof and unprotected side walls. 

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. 

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. 

For primary members (external walls, roof slabs, etc.), the load computation is performed in accordance with Chapter 3. Loads on supporting, or interior members, are determined either by I. the tributary area method or 2, from a computed dynamic reaction. In the tributary area method, external blast pressures are multiplied by the exterior surface area tributary to a support location. The resulting force is then applied to the next member. Dynamic reactions result from a numerical time history analysis (refer to Section 6.5.3) and provide a more accurate time-varying load on the supporting member. 

In most Nordion irradiators the pencils of cobalt-60 are mounted vertically in a source rack. The configuration is formally described as laminar. The source rack is suspended from a hoist mechanism on the roof of the cell such that it is movable between two locations. One of these locations is in the center of the cell in a position where product can be moved around the source during its irradiation. The other location is below floor level. This is for safe storage of the source when product irradiation needs to be interrupted for loading or maintenance work within the cell. 

Many of the workers on the eighth floor were able to squeeze through the doorway and found refuge either on the street or, after that passageway had been cut off, on the roof. Others crowded into the two elevators which ferried dangerously heavy loads to safety. Those who climbed on to the fire escape, however, found that the narrow, flimsy structure was blocked by an open shutter locked into place. As more and more women piled on to it the structure buckled from the heat and collapsed, sending dozens of workers to their death eight stories below. Most of those on the tenth floor were able to escape either to the roof or by one of the elevators, which made its first stop for the executives. It... 

A major use of PVC in the building industry is for roofing sheets. These sheets are produced on calenders and contain in most cases two plasticized PVC foils that are reinforced by glass fiber or polyester fabrics. The used sheets show different properties, depending on whether they are applied under direct influence of light and weather conditions and on the fact that in some cases these sheets on the roof are loaded with... 

Roof mounted hoods A hood is fixed on the furnace roof and collects fumes through a gap between die furnace shell and the roof. In addition, fumes arising from the working door and the tap-hole are also captured. Roof mounted hoods are heavy and subject to distortion from heat. If fitted to an existing EAF, problems may arise due to increased stmctural load of the roof lifting and rotating mechanism. Typical extraction rates for this system are 7500 to 15000 Nm /tonne... 

Many fundamental design criteria have nothing to do with the capacity equation. Evaluating their impact on building cost is therefore easier. They can vary independently of other design criteria. For example, as the snow load increases, the roof costs increase. 

Ice loading is not a concern because of the structural characteristics of the facilities (steel reinforced concrete roof/wails). Furthermore, any potential effects of ice loading on the facilities (i.e., coiiapse) are subsumed in the consideration of Earthquakes. 

Live loads consist of all loads except dead, accident, seismic, flood, and wind and include snow loads on the domed roof of the containment. Live loads are assumed for the design of internal slabs consistent with the intended use of the slabs. 

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