Specifies options for the Brazil NBR 6123 wind code.
Basic Wind Velocity (Vo)
Velocity from a three second gust, exceeded only once in 50 years. It is measured at 10 meters over smooth open ground and depends on the plant location. The wind may blow in any horizontal direction. This velocity is taken from Figure 1, and item 8 which shows the iso-velocities over Brazil. The referred to Figures and Tables are found in the Petrobras document BPE-500-P4-19i and the Brazilian Wind Code NBR 6123.
Topographical Factor (S1)
Accounts for the variations and profile of the land. For plain or slightly uneven ground, use a value of 1. The larger this value is, the greater the final computed wind pressure is. If the vessel is on a hill top, this value should be computed according to section 5.2 of NBR 6123.
Roughness Category (S2)
|
Category |
Description |
|---|---|
|
1 |
Plain ground with large dimensions (more than 5 km of extension) |
|
2 |
Plain (or slightly uneven) ground with few, and separated, obstacles |
|
3 |
Plain or uneven ground obstructed by obstacles (walls or separated low buildings) |
|
4 |
Ground with many grouped obstacles in industrial or urban areas |
|
5 |
Ground with many grouped and tall obstacles (such as developed industrial areas) |
Using Category I produces a higher wind load than Category II and so forth.
Dimension Class
|
Class |
Description |
|---|---|
|
A |
Greatest dimension is less than or equal to 20 meters |
|
B |
Greatest dimension is greater than 20m and less than 50 meters |
|
C |
Greatest dimension is greater than or equal to 50 meters |
Statistical Factor (S3)
Accounts for security and the expected life of the equipment. For industrial plants S3 is generally taken to be 1.0.
Pipe Surface Condition
Vessel surface condition can be classified as smooth or rough. A selection of rough results in an increased value of the shape coefficient. Using a rough classification generates a higher wind load on the vessel as there is more drag. The shape coefficient is computed based on the height to diameter ratio of the vessel.
Frequency
Specifies the natural frequency used to calculate the dynamic wind gust effect factor for dynamically sensitive structures. (f < 1 Hz.)
If the natural frequency is not defined, CAESAR II uses a gust effect factor 0.85.
Total Wind Height
Specifies the structural damping coefficient. This value is the percentage of critical damping and is used to calculate the gust factor for the wind load calculations.