Document: NUREG-0800
Document ID: 274f0789-5956-4979-b7da-3b44ddf985d4
Document Type: srp
Title: TORNADO LOADS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070570002.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.3.2
CFR Part: 
CFR Title: 

Content:
Regulatory Guide (RG) 1.76 for the contiguous United States into three geographical regions and by (1) maximum wind speed, (2) translational speed, (3) maximum rotational speed, (4) radius of maximum rotational speed, (5) pressure drop, and (6) rate of pressure drop for each of the three regions. Tornado effects are subdivided into three groups: i. Tornado wind effects caused by the direct action of air flow on structures, ii. Atmospheric pressure change effects caused by the differential pressure between the interior and exterior of a structure during the passage of a tornado, and iii. Tornado-generated missile impact effects. Tornado effects considered in design should include combinations of tornado wind effects, atmospheric pressure change effects, and tornado-generated missile impact effects. B. Tornado Wind Effects Procedures delineated in American Society of Civil Engineers/ Structural Engineering Institute (ASCE/SEI) 7-05, “Minimum Design Loads for Buildings and Other Structures” are acceptable for transforming tornado wind speed into pressure-induced forces applied to structures. In particular, the following shall apply: i. The maximum velocity pressure, qz, should be based on the applicable maximum tornado wind speed, V, using the following equation from ASCE/SEI 7-05, Section 6.5.10: qz = 0.00256 KzKdtKdV2I (lb/ft2) where: Kz = velocity pressure exposure coefficient equal to 0.87 Kdt = topographic factor equal to 1.0 Kd = wind directionality factor equal to 1.0 V = maximum tornado wind speed (mi/h) I = importance factor equal to 1.15 The maximum tornado wind speed, V, is the resultant of the maximum rotational speed and the translational speed of the tornado. 3.3.2-5 Revision 3 - March 2007 ii. Wind speed is assumed not to vary with the height above ground. iii. Design tornado wind loads should be determined in accordance with the following sections in ASCE/SEI 7-05, as applicable. (1) 6.5.12 Design Loads on Enclosed and Partially Enclosed Buildings