PARTES DE EQUIPO
9 Sistema de enfriamiento
3.2 Proceso de fabricación de las películas delgadas
Table D-1 Examples of Similar Damage from Straight Winds, Hurricanes, and Tornadoes
Type of Damage Winds Hurricanes Tornadoes
Windward wall collapses
Inward Mobile home, Big Spring, Texas 1973 A-frame, Hurricane Diana 1984 Metal building, Lubbock Texas 1970 Leeward wall or side wall
collapses outward Warehouse, Big Spring, Texas 1973 Commercial building, Hurricane Celia 1970 Warehouse, Lubbock, Texas 1970
Roof Warehouse, Joplin,
Missouri 1973 Motel, Hurricane Frederick 1979 School, Wichita Falls, Texas 1979
Eaves Mobile home, Big Spring,
Texas 1973 A-frame, Hurricane Diana 1984 Metal building, Lubbock, Texas 1970 Roof corners Residence, Irvine,
California 1977 Residence, Hurricane Frederick 1979 Apartment building, Omaha, Nebraska 1975 Wall corners Metal building, Irvine,
California 1977 Flagship Motel, Hurricane Alicia 1983 Manufacturing building, Wichita Falls, Texas 1979 Internal pressure Not applicable Two-story office building,
Cyclone Tracey, Darwin, Australia 1974
High School, Xenia, Ohio 1974
A somewhat arbitrary, but quantitative approach is used to determine if a particular DOE site should be designed for tornadoes. Hazard assessments for both straight winds and tornadoes for each DOE site are presented in Reference D-2. The intersection of the straight wind and tornado hazard curves determines if tornadoes should be included in the design and evaluation criteria. If the exceedance probability at the intersection is greater than or equal to 2x10-5, tornadoes are a viable threat at the site. If the exceedance probability is less than 2x10-5, straight winds control the design or evaluation criteria. The concept is illustrated in Figure D-1 (using fastest mile basis for illustration). Straight wind and tornado hazard curves are shown for Oak Ridge National Laboratory (ORNL) and Stanford Linear Accelerator Center (SLAC). The SLAC curves intersect at an exceedance probability of approximately 2x10-7, indicating that tornadoes are not a viable threat at the California site. On the other hand, the intersection of the ORNL curves is at 6x10-5 suggesting that tornadoes should be included in the design and
evaluation criteria. Design wind speeds for the 25 DOE project sites were selected on this basis. However, this methodology is now superceeded by adopting latest information for straight winds and hurricanes in ASCE 7-98. However, at few sites previous site specific data still governs. For tornadoes, assessment is to be made by new methodology developed at LLNL (Reference D- 13).
D.3 Load Combinations
The ratios of hazard probabilities to performance goal probabilities (risk reduction factor) for the Performance Categories in Table D-2 are an approximate measure of the conservatism
DOE-STD-1020-2002
D-4
required in the design to achieve the performance goal. The ratio is largest for SSC Performance Categories 1 and 2, and is progressively smaller for Performance Categories 3 and 4 for winds and tornadoes. The trend is just the opposite from earthquake design. The reason for the decreasing trend in wind is because we use smaller hazard probabilities and thus need a lessor degree of conservatism in Performance Categories 3 and 4.
Conservatism can be achieved in design by specifying factors of safety for Allowable Stress Design (ASD) and load factors for Strength Design (SD). These factors for straight wind should be obtained from applicable material design standards. Consistent with the ratios in Table D-2, the loading combinations recommended for tornado design and evaluation of DOE SSCs are given in Table D-3.
DOE-STD-1020-2002
D-5
Table D-2 Ratio of Hazard Probabilities to Performance Goal Probabilities
Performance
Category Performance Goals Hazard Probability Performance ProbabilityRatio of Hazard to Straight Winds 1 10-3 2x10-2 20 2 5x10-4 10-2(1) 20 3 10-4 10-3 10 4 10-5 10-4 10 Tornadoes 3 10-4 2x10-5 1/5 4 10-5 2x10-6 1/5
Table D-3 Recommended Tornado Load Combinations for Performance Categories 3 and 4
ASD 1. 0 1. 6 D + W
[
t]
1. 33 1.6 0.75 D + L + L[
(
r+ Wt)]
1. 5 1. 6 0.66 D + L + L[
(
r+ Wt+ T)]
SD D + Wt D + L + Lr+ Wt D + L + Lr+ Wt+ T AS D= Allowable Strength Design
Use allowable stress appropriate for building material
Lr = Roof live load
SD = Strength Design
Userfactors appropriate for building material
W = Straight wind load
D = Dead load Wt = Tornado load, including APC if
appropriate
L = Live load T = Temperature load
The 1.6 denominator represents the factor of safety for material allowable stress,
effectively removing this unneeded conservatism. The 1.33 and 1.5 factors negate the 0.75 and 0.66 factors permitted in ASD.
DOE-STD-1020-2002
D-6
ASD is typically used for the design of steel, timber and masonry construction. Allowable stresses for the material and the type of loading (axial, shear, bending, etc.) are determined from applicable codes and specifications. The specified load combinations for ASD for Performance Categories 1 and 2 should be taken from the applicable material design standard (e.g. ACI or AISC) for straight winds. Load combinations for Performance Categories 3 and 4 can be less conservative than for Performance Categories 1 and 2. Because the ratio of hazard to performance probability is smaller by a factor of two, it is judged that the load combinations can be reduced by 10 percent. The load combinations for Performance Categories 3 and 4 for straight winds should reflect this reduction. The hazard to performance probabilities for tornadoes is more than satisfied by the hazard probability, as indicated by the ratio 1/5. The tornado load combinations for ASD Performance Categories 3 and 4 were somewhat arbitrarily chosen, based on engineering judgment.
Strength Design (SD) has been used for the design of reinforced concrete structures since about 1977 (Ref. D-4). Recently a strength design approach was introduced for steel
construction which is called Load and Resistance Factor Design (LRFD) (Ref. D-5). Strength
design concepts are currently being developed for use with timber andmasonry construction.
With SD, the nominal strength of the material is reduced to account for uncertainties in material and workmanship. The reduced material strengths must be greater than or equal to the factored loads in order to satisfy a postulated limit state. The required conservatism is reflected in the load factors for loads involving straight winds. In this case, the load factors for Performance Categories 3 and 4 are increased by ten percent. Load factors for Performance Categories 1 and 2 are recommended in References D-3, D-4 and D-5. Since the performance goals are satisfied by the tornado hazard probabilities, unit value of load factors can be used for SD. Unit values are justified in this case, because the material reduction factors account for uncertainties associated with materials. The load factors for tornadoes are consistent with recommendations for commercial nuclear power plants as given in ACI 349 (Ref. D-6) for concrete and
ANSI/AISC N690-1984 (Ref. D-7) for steel.