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5/22/2018 ABB Structural Design of Steel Latticed Towers
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Structural design of steel latticed
towers
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Structural design of steel latticed towers
Specific criteria and design approaches recommended for steel
transmission towers
Self supporting and guyed structures
Suspension and tension towers
Tower outline definition
Geometrical and Mechanical checks
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Specific criteria and design approaches recommended for steel
transmission towers
It is recommended that the line designer provides at least the following informations:
Applied loads, including safety factor, at attachment point of insulator/earthwire
Wind load on support
Load combinations
Ultimate limit state for each load combinationDeformation of structure
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Self supporting and guyed structures
Towers could be designed as self-supporting or as guyed towers. The difference
between the two type of configuration is that the stability of self-supporting tower is
guaranteed by its foots with relative foundations, while the guyed tower use some
pretensioned wires connected between tower and relative foundations.
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Self supporting structures
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Guyed structures
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Suspension and tension towers
Three basic tower definitions are recommended:
1. Suspension the conductor phases pass through and are suspended from the insulator
support point at the tower
2. Strain the conductor attachment points are made by attaching the conductor to
a dead end clamp, a compression or bolted fitting and connecting the
clamp through the insulator string directly to the tower. In order to
connect electrically the adjacent span a jumper is looped through or
around the tower body
3. Dead end conductor attachment point is the same of strain tower, but this type of
tower has a permanent different tension on each side of tower
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Suspension tower
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Strain / Dead end
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Tower outline definition
The geometric configuration of latticed transmission tower is based on the overhead
ground wire shield coverage, number of circuits, conductor phase arrangement selected
to satisfy the electrical clearances and right-of-way requirements.
The development of tower configuration starts with the upper portion. This section of
the tower is designed for the selected vertical and horizontal phase spacing and
electrical clearance around each conductor.The configuration should be as compact as
possible around each conductor.
The lower portion of the tower is designed next and depend to useful height, clearance
to ground and extension or reduction of height request by tower spotting.
The wider the tower base gives smaller loads on foundation but increase the length and
the weight of bracing members. Therefore an economical balance must be reached
between the tower base width and the size of the bracing members.
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Geometrical configuration of structure
The geometrical configuration of the head of tower is characterized by:
Type of transmission line ( voltage, circuits, conductors)
Electrical clearance
The height of tower depend on:
Sag of conductor
Electrical clearance to ground
Loads on foundation are affected by:
Width of base of tower
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Geometrical and Mechanical check
The arrangement of tower members should keep the tower geometry simple by using as few
members as possible.
A tower is described by a design drawing which shows overall dimensions, joints, and
member locations.
For purpose of analysis a tower can be represented by a model composed of members
interconnected at joint. Members are normally classified as primary and secondary member.
Primary members form the triangulated system that carries the loads from their applicationpoints down to the tower foundations. Secondary members are used to provide intermediate
bracing points to the primary members and thus reduce unsupported length. Secondary
members can be easily identified on a drawings as members inside a triangle formed by
primary members.
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