Effects of Flooding

DOE-STD-1020-2002

of the structure is overloaded. Ductility allows the structure to undergo large deformations

without sudden and catastrophic collapse. The structure also must have sufficient strength and

stiffness to resist the applied loads without unacceptable deflection or collapse.

Cladding forms the surface of the structure envelope. Cladding includes the materials

that cover the walls and roof of a structure. Cladding failure results in a breach of the structure

envelope. A breach develops because the cladding itself fails (excessive yielding or fracture);

the connections or anchorages are inadequate; or the cladding is perforated by windborne

missiles. Cladding is sometimes relied upon to provide lateral support for purlins, girts or

columns. Cladding may be an integral part of shear wall construction. If the cladding or its

anchorage fails, this lateral support is lost, leaving the elements with a reduced load-carrying

capacity.

Most cladding failures result from failure of the fasteners or the material in the vicinity

of the fastener. Cladding failures initiate at locations of high local wind pressures such as wall

corners, eaves, ridges, and roof corners. Wind tunnel studies and damage investigations reveal

that local pressures can be one to five times larger than overall external pressures.

Breach of structure envelope resulting from cladding failure allows air to flow into or

out of the building, depending on where the breach occurs. The resulting internal pressures

combine with the external pressures, both overall and local, to produce a worse loading

condition. If the structure envelope is breached on two sides of the building, e.g. the windward

and leeward walls, a channel of air can flow through the building from one opening to the other.

The speed of flowing air is related to the wind speed outside the building. A high-speed air flow

(greater than 40 mph) could collapse interior partitions, pick up small pieces of equipment or

transport unconfined toxic or radioactive materials to the environment. A breach can also lead to

water damage due to rain.

Systems, consisting primarily of piping, utilities, and distribution configurations, are

more susceptible to wind damage when located outdoors. Electrical lines, transformers,

overhead pipe bridges, steam lines, storage tanks are examples of wind vulnerable systems. Net

wind forces are calculated for each element of the system. Channeling and shielding may be a

factor in complex facilities. Windborne missiles also pose a threat to systems. Collapse or

failure of less vulnerable SSCs could cause damage to more critical ones.

Components, consisting primarily of equipment such as fans, pumps, switch gear, are

less vulnerable to wind than earthquake forces, but can be damaged if exposed to flying debris.

E.3

Effects of Flooding

E.3.1 Causes and Sources of Flooding and Flood Hazards

There are a number of meteorologic and hydrologic phenomena that can cause flooding

at a site. For each cause or source of flooding, a facility may be exposed to one or a number of

E-8