Tornado loadings

For structures which are to be designed for tornado loading, the applied forces due to wind are calculated to determine if they are less severe than the applied forces due to tornado loading. The applied tornado force magnitude and distribution are determined as discussed in Section 3.3.2. Appropriate stress levels and load factors discussed in Section 3.8 of this PSID are considered in the determination of the governing loads. 

Loading combinations, the methods employed to convert tornado loading into forces, and the distribution across the structures are consistent with... 

Effect of Failure of Structures or Components Not Required to be Designed for Tornado Loads... 

Tornado loads (W. ), including wind pressures, differential atmospheric pressures, and missile spectrum, are given in Sections 3.3.2 and 3.5. 

Loads and loading combinations as delineated in Section 3.8.2 are considered. Wind loads, tornado loads, and accident loads are converted to equivalent static loads and are applied to the structure as uniform or concentrated loads. 

Section strength for reinforced concrete based on the strength design method Severe wind loads Tornado loads... 

Fabreeka pads (size and thickness) were designed based on Fabreeka Structural requirements. At the lower connection a plate, with a vertical slotted hole, and pin system limits the vertical movement to 100 mm in either direction md also restrcuns the ropeway from puHing away from A-frame. The connection system is designed for a tornado load equal to 2.2 times the 1 in 50 year wind load specified in the NBCC (2010). 

Whether tornado loadings is considered in the design or not is a conditioninal item for site permit, which is under investigation and analysis by applicant. 

Structures for the nuclear facility shall be designed to resist the maximum tornado load for a given plant site. The basis of the design shall be such that the safety class equipment remains functional even a safe shutdown of the facility is accomplished in totality without endangering the plant. The AEC Regulatory Guide 1.76 recommends the design basis tornado. 

Wt = tornado loadings including missiles as defined in the General Design Criteria. 

Tornadoes, Hurricanes, and High Winds - the design basis tornado produces the most severe wind loads assumed in the plant design. The design basis tornado is assumed to have the following characteristics ... 

Tornado criteria furnishing data, formulae, and procedures consistent with those currently employed for LWR design are used for determining the maximum wind loading on Standard MHTGR structures and parts of structures. (Ref. 3)... 

For factored loads, including earthquake (QBE or SSE), tornado and pipe break effects, etc., the following load combinations are satisfied ... 

Combinations 5, 7, and 8 are first satisfied without the tornado missile load in 5 and without Y, Yj, and Yjjj in 7 and 8. When considering these loads, however, local section strengths may be exceeded under the effect of these concentrated loads, provided there is no loss of function of any "safety-related" system. If non-linear concrete behavior is considered in the design of concrete missile barriers, ACI 349-76 and its 1979 Supplement, as modified by Regulatory Positions 10 and 11 of Regulatory Guide 1.142, Revision 1, will be utilized in the design of such barriers. 

These loads include extreme environmental conditions, such as tornadoes and the safe shutdown earthquake postulated to oeeur during the life of the faeility. Also included are effeets resulting from a postulated rupture of a high-energy system during normal operation, startup or shutdown of the plant or other postulated design basis aeeident. 

Tornado missiles (Tm) Tornado-generated missiles carry objects which are accelerated by the forces induced by the extreme wind speeds of the tornado. The parameters specified in the design basis tornado are translated into pressures and forces acting on the structures and its components. The important case is the real analysis that would be necessary to perform on the structure. The analysis is known as tornado structure interaction. In this analysis the load evaluated using a specific path width of the tornado field that experiences wind velocities >75 mph (120 km/h) is generally considered. 

In general, full 3-D finite element analysis of the fluid domain (impulse, in the case of wind or explosions) or full impact analysis (impact, in the case of aircraft crash or tornado missiles) are not used in the design process for the derivation of a suitable load function. Very detailed research programmes have been carried out in the engineering community and in some cases simplified engineering approaches are now available for a reliable design process, on the basis of the interpretation of test data or data from numerical analysis. 

A prehminary screening of the external events to be considered in the design of a research reactor can be done on the basis of a detailed hazard categorization. For facilities in the lowest category (hazard category 3) some extreme scenarios (aircraft crash, blast loads, tornado) may be screened out either by virtue of the selection of the site or on the basis of a low probabihty of occurrence. 

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