Each environment aims to simulate real world loading scenarios by considering a combination of loads experienced by a network.
Load Factors compensate for the uncertainties and assumptions involved in calculating individual loads. Loads can vary significantly along the length of a line, and they affect different line components in different ways. Design and engineering standards therefore tend to take a conservative approach, ensuring the worst-case variation of each load is considered during analysis.
Note that load factors are applied to structures, not conductors — changing a load factor will not affect conductor clearance.
In FEA simulations, all load factors are set to 1.0 and the system is simulated until it reaches equilibrium. The conductor loads at equilibrium are then transferred to the structures as point loads, and the load factors are applied to those point loads. As a result, when non-unity load factors are used, structure deflection will not visually match the conductor positions.
Load and Resistance Factor Design (LRFD) is a specification for structural design and assessment that evaluates safety at the Ultimate Limit State using the inequality below.
Load Factor x Nominal Design Loads < Strength Factor x Nominal Design Strength
The right-hand side is covered in Strength States. The left-hand side is described below.
Nominal design loads are the base loads acting on a structure: conductor tension, wind load on the conductor and structure, and the mass of the structure itself (pole, assemblies, plant, and so on). These loads are scaled by load factors, and different design standards specify different load factors for the same nominal design load.
Setting up load factors
Open the Environments tab
Navigate to the Load Factors section of the Environments table and update the values required.
There are three load types for cables and two for structure as per below.
Load Factors on Conductors:
Longitudinal (Ft): scales loads acting along the direction of the span, i.e. conductor tensions. This load equals the horizontal component of the conductor tensions.
Transverse (Fc): scales loads acting perpendicular to the direction of the span. Sources include transverse wind pressure on the conductors, imbalanced tension from uneven sag or broken conductors, and deviation in the line's direction
Vertical (Gc): scales loads acting in the vertical direction. This covers the vertical load of the conductors and cables, the weight of any ice or snow on them, and attachments such as marker balls, spacers, and dampers.
Load Factor on Structure:
Wind (Wn): scales loads from wind acting on structural components such as poles, cross arms, insulators, and fittings.
Self Load (Gs): scales loads acting in the vertical direction on the structure. This equals the combined mass of the poles, cross arms, insulators, fittings, and counterweights, plus all ancillaries and attachments.
PLS-CADD Mapping
Neara uses the same load factor concepts as PLS-CADD, with slightly different naming. The table below maps between them.
Neara Load Factor | PLS-CADD Load Factor |
Ft | Wire Tension Load Factor |
Fc | Wire & Structure Wind Load Factor (1) |
Gc | Wire Vertical Load Factor |
Wn | Wire & Structure Wind Load Factor (1) |
Gs | Structure Weight Load Factor |
(1) PLS-CADD combines wire and structure wind into one load factor. Neara splits these into two: Fc (wire) and Wn (structure).
Example Standards
Below is a list of suggested load factors for various standards: