Load groups

To define, edit or remove load groups:

• Click on .
  The following dialogue appears:

Standard (“Load factors for”)

• Using the drop-down menu, select the standard for the partial safety coefficients, combination factors and the composition of combinations.
• You can find an overview of all the available standards here.

Consequence class and design lifetime

• For Eurocode (and related standards), you have to impose a consequence class.
  Depending on the consequence class, the partial safety coefficients will be adjusted (more info).

• For Eurocode (and related standards), you have to define the design lifetime.
  Depending on the design lifetime, the magnitude of some variable loads will be adjusted (more info).

Service class

• For the design of timber, you have to specify the service class.
  The service class takes the humidity rate into account. Together with the load duration and timber type, it determines the modification factor k_mod.

Defining or deleting load groups

To add a new load group:

• adds a new load group at the end of the table.
  adds a load group between two existing load groups.
  
  On both cases a new line will be added to the table. All partial safety coefficients and the combination factors will be set to 1. That’s wrong!
• Choose the correct load group type form the drop down menu.
  Now all safety coefficients and the combination factors will jump to their correct values.
• The more load groups you use, the more combinations you will need to prepare and the longer the calculations will take.

To delete a load group:

• deletes the selected load group from the list

• Before each load group there’s a green check .
  This means the load group is active and will be taken into account when generating the combinations (on the condition it contains loads).
• If you click on the icon , it changes to .
  This means that the load group, even if it contains loads, will not be taken into consideration when generating the combinations!

Partial safety coefficients γ

• γ_ULS- is the parial safety coefficiënt for the ultimate limits state when the load as an unfavourable effect.
• γ_ULS+ is the parial safety coefficiënt for the service limits state when the load as an unfavourable effect.
• γ_SLS- is the parial safety coefficiënt for the service limits state when the load as an favourable effect
• γ_SLS+ is the parial safety coefficiënt for the service limits state when the load as a favourable effect.

Combination factors ψ

• ψ₀ is the combination factor
  It takes into account that it is unlikely that multiple independent variable loads reach their maximum value at the same time.
• ψ₁ is the frequent value factor.
  It plays a role in the repeated occurrence of life loads.
  It represents the typical upper value of a variable load that occurs often but not continuously.
• ψ₂ is the quasi-permanent value factor
  It also plays a role in the repeated occurrence of variable loads.
  It represents the sustained portion of a variable load that stays present on the structure for a long time.

Correlation coefficient φ

The modal parameters of a structure (eigenmodes and – frequencies) are calculated based on the stiffness and mass distribution within the structure.

• The stiffness of the structure only depends on the geometry of the structure itself.
• But for the mass distribution, masses are related to the vertical loads (point loads, line loads, surface loads) (0,981kN -> 100kg) using the correlation coefficient φ (and also multiplied by the combination factor Ψ₂ for what EN 1990-1-1 is concerned).

Diamonds will set the correlation coefficient to 1 for all load groups, except for temperature loads and dynamic loads (set to 0). For standards in which no Ψ₂ is mentioned, the correlation coefficient φ of only the self-weight and the dead loads is set to 1.

More info on modal analysis here.

Reduction factor ξ

This factor is used when the fundamental combinations (ULS FC) are generated using equations 6.10a and 6.10b from EN 1990. The formula 6.10b contains a reduction of dead loads according to the factor ξ. The recommended value is ξ = 0,85.

Combination for cracked calculations and parameter t₀

Both parameters are only used when calculating the cracked deflection in time .

• Column ‘t₀‘
  Note the moment (in days) when loads will be applied after concrete is cast.
• Column ‘Combination for cracking’
  This is the combination used to determine the cracked stiffness of the cross-section.

Columns ‘Load’ and ‘Action’

The final two columns ‘Load’ and ‘Action’ indicate the character of the load groups.

• The column ‘Load’ will determine which load-buttons are active.
  For example: if you select a load group for wind, the buttons for snow will be disabled so the Diamonds interface doesn’t get too heavy.
• The column ‘Action‘ describes if a load is static or dynamic.
  For ‘Life loads’ you can choose between a static or a dynamic load. You switch between both by click on the icon in the column ‘Action’. A seismic load groups always has a dynamic character.

Modification factor k_mod

• The modification factor k_mod takes the effect of the humidity rate (defined by the climate class) and the load duration on the strength properties of the timber quality into account.
  In the column ‘k_mod‘ you define the load duration category of each load group (more info).

Load type (only for ASCE 7-10)

When defining combinations according to the American standard ASCE 7-10, you have to choose the load type in this column. Then Diamonds knows which safety factors he should use. Diamonds contains these types of loads:

• Dead load [D]
• Live load [L<]: ≤ 100psf
• Live load [L>]: > 100psf
• Roof live load [Lr]
• Snow load [S]
• Wind load [W]
• Wind load [Wa]: wind for service limit state
• Earth, groundwater, bulk materials with a permanent character [H-]
• Earth, groundwater, bulk materials with a variable character [H~]
• Rain load [R]
• Fluid [F]

Linked load groups

Diamonds can link load groups that have the same favourable or unfavourable effect on the structure. This will reduce the number of load combinations, since the case where one load group works (un)favourable will be eliminated by Diamonds (more info).

Incompatible load groups

You can ban the simultaneous presence of several load groups in a combination using ‘incompatible load groups’ . When load groups are indicated as incompatible, Diamonds will never generate combinations in which these load groups appear at the same time (more info).

Sub load groups

Sub load cases is a tool to organize loads that have the same origin, like wind or snow. The sub load cases can be activated by checking the option “Several load cases per group”.

3 columns will be added to the table:

• Column “#”
  Define the number of sub load cases in the column #.
  Note: it is not possible to add sub load cases for Self weight.
• Column “Name load case”
  Diamonds gives the newly added sub load a default name in the column ‘Name load case’, but you’re free to change it.
• Column “Type”
  The icon , which changes to when you click on it and visa versa.
  • The icon stands for ‘always together’. The logical ‘AND’.
    All the sub load cases in the load group are expected to always apply simultaneously.
    A practical example of this scenario would be a dead load of a floor whose components (coating, insulation, finishing, …) are defined using sub load cases.
  • The icon stands for ‘always separate’. The logical ‘OR’.
    All the sub load cases in the load group are expected to never act simultaneously.
    A practical example of this scenario would be wind loads acting in different directions.
• Using the button you can merge existing load groups into a series of sub load groups (more info).
• Using the button you can ungroup a load group containing sub load groups into separate incompatible load groups (more info).

Sub load groups are an alternative for Linked load groups and Incompatibel load groups (both are explained above). However, there are some pro’s and con’s to using either of these methods (more info).