B1.5.1     Design Loads

Applied basic wind pressures shall be in accordance with those specified in B2.5.8 above. The design shall be based on the following considerations:-

B1.5.13.1        Normal Conditions

Vertical loads (V) consisting of:

• Weight produced by the effective portion of the adjacent conductors and earth wire spans including weights of warning spheres (if specified for supply).
• Weight of insulator strings and linesmen with tackles.
• Weight of solar aircraft warning light system (if specified for supply).
• Weight of tower.

Transverse loads (T) consisting of:

• The transverse horizontal component of the maximum line and earth conductor tensions.
• Wind loads produced by the effective portion of the adjacent conductor and earth wire spans including wind loads of aircraft warning spheres (if specified for supply).
• Wind loads produced by insulator strings.
• Wind loads produced by solar aircraft warning light (if specified for supply).
• Wind loads on tower.

Two wind directions shall be considered:

• Perpendicular to the line direction.
• Under the angle of 45° (“Quartering wind” according to IEC 60826).

Maximum angle pulls, corresponding to type of towers.

Longitudinal loads (L):

• Resultant forces produced by the maximum tension of conductors or earth wire in the direction perpendicular to cross-arms.
• The maximum out of balance longitudinal component of loading, taken as 15% of the actual maximum line conductor and earth-wire tensions.
• The design of the dead end tower shall consider conductor and earth wire tension without any offset for slack-span connections.
• Wind loads on tower for “Quartering wind”.

In case of conductor uplift, the cross-arm of tension towers shall be designed accordingly and proven by calculations. Counterweights may be permitted on suspension towers.

B1.5.13.2        Broken wire conditions

SuspensionTower

• Angle Tension tower and TerminalTower
• As specified under sub-clause B1.5.8 (g) above.
• As specified under sub-clause 2.5.8 above.

Vertical loads (V) consisting of:

• 75% of weight produced by the effective portion of the adjacent conductor and Earth wire spans.
• Weight of insulator strings and linesmen with tackles.

Transverse loads (T) consisting of:

• 75% of normal condition for wind loads.
• 50% of normal condition for maximum angle pulls.

Two wind directions shall be considered:

• Perpendicular to the line direction.
• Under the angle of 45° (“Quartering wind” according to IEC 60826).

Longitudinal loads (L) consisting of:

• 70 % of maximum working tension of one phase bundle, 100 % of max. tension of Earth wire for suspension towers.
• 100 % of maximum working tension of conductors or earth-wire for angle tension and terminal towers

The decrease in the vertical and transverse loads above refers only to phases where conductor is broken.

Towers shall be designed so that all members will withstand normal and broken wire conditions with safety factors as specified.

The total loading for the tower shall include the dead weight of the tower plus transverse wind load on tower plus the simultaneous application of loading as specified above for each tower type. Wind loads on tower leg extension shall be taken into consideration.

Terminal towers shall be designed to face the direction of the incoming line, and shall withstand the load of all conductors and earth wire.

The Contractor shall submit the stress analysis calculation for tower members of all tower types and for each of the specified load conditions. An explanation shall be submitted along with the computer calculation.

B1.5.13.3        Erection and Maintenance Loads

For all members which can be climbed and are inclined with an angle less than 30° to horizontal an erection and maintenance load of 1.5 kN acting vertically in the center of a member shall be assumed, however, unfactored and without any other loads.