Enhanced Fujita scale damage indicators and degrees of damage, chapter 26
C-1 Electrical Transmission Lines (C-ETL)
Typical Construction:
- Single wood poles with wood cross arms, 7-35 metres (m) in height and 15-60 centimetres (cm) in diameter (at 2 m above ground)
- Single steel or concrete poles with metal cross arms
- Metal trussed towers
Notes:
- Whether poles go down is related to size, composition (wood / concrete / steel) and load (wire tension, number of transformers)
- For small diameter (~15-20 cm) or very old wood poles, decrease toward lower-bound wind speed; for large diameter (~45-60 cm) wood poles, increase toward upper-bound wind speed
- Keep in mind - one weak or overloaded pole going down can cause other poles along the line to break due to wire tension
- Trees falling on lines can bring down poles - do not use this DI if this is the case
- Metal truss towers where lines change direction are often more strongly reinforced, increase toward upper-bound wind speed
DOD | Damage Description | EXP* | LB* | UB* |
---|---|---|---|---|
1 | Threshold of visible damage | 130 | 110 | 155 |
2 | Broken wood cross member | 155 | 125 | 175 |
3 | Wood poles leaning | 175 | 135 | 200 |
4 | Broken wood poles | 195 | 145 | 220 |
5 | Broken or bent steel or concrete poles | 210 | 180 | 240 |
6 | Collapsed metal truss towers | 220 | 185 | 255 |
*All wind speeds in km/h
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