When using SPIDAsilk, a key component to performing sag and tension calculations is the set of environmental conditions that must be considered to satisfy safety code requirements or adhere to internal design standards. These are referred to as weather cases and can be defined and modified by the user within the Design Scenarios section.

Design Scenario Toolbar

Load Case Dropdown: Choose from a selection of pre-configured load cases, as well as any user-configured custom load cases.

Load Case Information (Info Icon): Displays the selected load case's weather cases, including temperature, ice, wind pressure, and constraints.

Save: Save any updates to the currently selected load case.

Delete: Delete the currently selected custom load case. Preconfigured load cases cannot be removed.

Table Columns Setting: Enable or disable attributes that appear as column headers. Enabled attributes will appear in the Design Scenarios table and in the Wire Report.

Load Settings - Creep and Bi-Metal Conductor Handling: Define the Creep Condition to be used in calculations by defining the temperature, ice thickness, and wind pressure. The Creep Condition will be remembered and retained between SPIDAsilk sessions.

• Permit outer strand to go into compression at high temperatures: Outer stranding (typically aluminum) will expand faster than the inner core (typically steel), which at very high temperatures may result in the outer stranding going into compression. This means the inner core of the wire bears all of the tension and load of the conductor, or that the outer standing has become a 'birdcage' around the core. When this happens, the outer stranding can be thought of as being 'overlashed' to the core - contributing to the linear weight, but not providing any tensile support. This effect can impact the sag and tension of the wire at these very high temperatures.

Initial Tension Checkbox: Set the initial tension and temperature of a wire directly and override all other design constraints.

Preconfigured Load Cases

SPIDAsilk includes 10 preconfigured load cases: CSA Medium A, CSA Medium B, CSA Heavy, CSA Severe, NESC Light, NESC Medium, NESC Heavy, NESC Warm Island – Below 9000', NESC Warm Island – Above 9000', and GO95. Selecting one from the Load Case Dropdown will populate the table with individual weather cases associated with the selected safety code.

Creating Custom Load and Weather Cases

The Add Weather Case button is always available to users to supplement an existing load case or define a new load case. When selected, a new row will be added to the table where a new weather case can be defined.

The Toggle Edit Mode button can be selected at any time to switch the Weather Case Table between edit and view modes. When editing, users can modify the name, temperature, ice, wind, constraint, and additional load for any weather case(s).

The Remove Component button will only appear active when a row in the Weather Case Table has been selected. When clicked, the selected weather case will be removed from the table.

The Remove All Components button is available at any time. When clicked, all rows will be removed from the Weather Case Table.

Definitions

Weather Case

Load: The name of each weather case, as defined in the selected load case.

Temp: The temperature of the wire being used in calculations; this is not the ambient, or surrounding air, temperature.

Ice: The thickness of radial ice being applied.

Wind: The wind pressure or wind speed being applied. The Wind Pressure/Wind Speed button on the main toolbar controls which mode is displayed in the Weather Case table.

Constraint: The boundary conditions, minimum or maximum, that can be established for each weather case to reflect design parameters used to determine the wire state. The controlling constraint for a wire appears in bold font. If the "Initial Tension Checkbox" is enabled in the Design Scenario Toolbar, the constraint will be overridden.

Additional Load: Any additional loads that are being applied. This includes special logic for gust response factors and exposure factors due to the height of the wire (NESC Extreme Wind), or additional linear conductor constants (NESC Zone Loading).

Linear Force: The total force per length of the wire, including its weight, any overlashed components, and any effects of ice or wind.

Tension Methodology

Initial: Wire tension immediately after stringing; this method assumes there is no plastic deformation of the wire.

Final without Creep: Tension calculated when accounting for plastic deformation due to high tension. The high tension is determined using all weather cases that are configured to be considered in the Edit Sag and Tension Constraints dialog.

Final with Creep: Wire tension that accounts for plastic elongation due to both high tensions and time at the tension produced by the specified Creep Condition.

Elastic: Wire tension that is calculated using a perfectly elastic modulus (linear stress-strain relationship); this is the legacy type of wire tension calculation in SPIDAcalc.

Table Settings

Max Tension: The maximum tension of the wire including weight, wind, and horizontal tension forces. When maximum tension is calculated, it is the tension along the length of the wire and is inclusive of the weight of the wire and acting downward forces.

Hor. Tension: The horizontal tension that is calculated for the wire based on the given weather case.

RTS: The percent loaded of rated tensile strength of the wire.

Sag: The maximum separation between the wire and the line of sight. This is not strictly vertical sag, as it includes a horizontal component when the weather case includes wind.

Max Hor. Sag: The maximum horizontal sag of the wire, typically due to wind.

Max Ver. Sag: The maximum vertical sag of the wire.

Distance to Lowest Point: The horizontal distance to the lowest point in the catenary curve from the attachment point. This point is not at the same location as the sag point for spans with elevation differences.

Lowest Point Below Attachment: The lowest point of the wire below the attachment point.

Cat. Con.: The catenary constant of the wire under the given weather condition, measured as Horizontal Tension / Linear Force.

Graphic View

Users can see a visual model of the wire in Graphic View of SPIDAsilk by clicking on any weather case. If using a nonlinear stress-strain wire, there will be a catenary for each wire state (Initial, Final without Creep, and/or Final with Creep), along with sag measurements from the line of sight. Legacy wires will only show a single catenary for the elastic model.