Design of Steel Tower

DESIGN OF STEEL TOWERS Presented By,

U. C. T. Warnakulasuriya

Design of Steel Towers :         

Introduction Type of towers Tower configuration Tower loading Analysis of tower members Design of tower members Bolt Connection Testing of Towers Design Example

1.0 – Introduction : The tower types used in the industry are 1.0 Transmission towers 2.0 Telecommunication and broadcasting towers Why do we need transmission towers Interconnection of scattered power generating locations to the national grid and power distribution requires transmission lines.

2.0 – Type of Transmission Towers : Tower types used in the transmission line work are Straight Line Towers – Line deviation angle is zero 100 angle Towers – Line deviation angle varies from 00 to 100 degrees 300 angle Towers – Line deviation angle varies from 110 to 300 degrees 600 angle Towers - Line deviation angle varies from 310 to 600 degrees Terminal towers or dead end towers.

3.0 – Tower Configuration Tower configuration depends on the following main factors, a. Length of insulator assembly

3.0 – Tower Configuration b. Minimum clearance from conductors to the tower steel c. Mid span clearance under dynamic conductor behavior d. Geometric mean distance between conductors e. Economic use of tower material

Tower Figures

Tower Figures 1. Tower height considered from ground level Minimum ground clearance Maximum sag of lowermost conductor Height and Location of Ground Wires 2. Length of cross arms and horizontal spacing between conductors

Tower Figures

Tower Figures 3. Tower width at base and top width Tower base width to height taken in the range of 2.4 to 4.0 Tower top width to base taken in the range of 1/3 to 1/3.5 4. Bracing pattern used in the tower configuration

Tower Bracing Patterns

Tower Bracing Patterns

4.0 - Tower Loading

The loading applied on transmission line towers are as follows, a. Vertical loads b. Transverse loads c. Longitudinal loads

Vertical Loads Dead weight of tower structure Vertical Loads due to conductors and ground wire

Vertical Loads

Transverse Loads Wind on conductors and ground wire Transverse component of cable tension in case of angle tower Wind on tower body

Longitudinal Loads Unbalance pull due to broken wire condition Pull of conductors and ground wire in case of dead-end tower.

5.0 – Analysis of Tower Members A computer software STAAD PRO is used for the analysis of tower members

6.0 – Design of Tower Members The designing of tower members are carried out according to ASCE 10-97 standard (American Society of Civil Engineers) Permissible Axial Stress in Tension Permissible Axial Stress in Compression

6.0 – Design of Tower Members

6.0 – Design of Tower Members

7.0 – Bolt Connections Bolt connection shall be designed as per ASCE 10-97 standard. Shear capacity of bolts Bearing capacity of bolts

8.0 – Testing of Towers Transmission line tower remains as one of the few structures in structural engineering which is tested full scale to destruction.

9.0 – Design Example Design calculation could be carried out in the following steps, Step 01 - Collection of design information Step 02 - Load Calculation Step 03 - Preparation of loading trees Step 04 - Calculation of wind load on tower after completion of tower geometry - Wind Diagram

9.0 – Design Example Step 05 - Transfer of tower geometry to computer program and load application (with computer software) Step 06 - Analysis of tower (with computer software) Step 07 - Grouping of analyse tower member forces Step 08 - Tower member design Step 09 - Completion of final tower line diagram for detailing