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Load cases

Load cases are collections of loads, that have the same basis with regards to the standard and appear in the same time. Examples are self-weight of the structure or snow load. The loads, that have different properties according to the standard (e.g. permanent and variable loads), cannot be included in one load case. Load case properties are described by code, type and partial nd combination factors.

Code of load case

The program uses four different load case codes: "Self-weight", "Force", "Deformation" and "Temperature".

Load cases with the code "Force" can contain point or linear loads, forces or moments. Loads can be assigned to joints or members. The code "Deformation" is dedicated for enforced movements or rotations of supports. "Self-weight" is a special type of load case, it contains automatically generated self-weight of the structure. These loads can't be modified, only one load case with this code is permitted in the project. The code "Temperature" is used for actions induced by thermal changes.

It isn't possible to combine different types of load (e.g. self-weight and thermal action) in one load case. The change of load case code isn't permitted for existing load cases.

Type of load case

The load case type describes the load duration in time. This parameter is required by certain design standards (verification of timber or RC structure).

Factors

Any load case has own values of partial load factors and combination factors.

Partial load factors are used for the calculation of design values of loads according to the following expression

Where is:

Fd

  • The design value of load

γf

  • The partial factor, that takes into account deviations from representative values

Frep

  • The representative value of load

Two different values of partial factor are used::

γf,Sup

The factor for unfavourable effect

  • The partial factor for loads, that induce unfavourable effects in structure

γf,Inf

The factor for favourable effect

  • The partial factor for loads, that induce favourable effects in structure. This factor is equal to 0 for variable loads

Combination factors are used for the calculation of representative values according to the following expression

Where is:

Frep

  • The representative value of load

ψ

  • The combination factors ψ0, ψ1 or ψ2 or value 1.0. The choice of appropriate factor depends on the combination type and load (permanent, main variable, variable, accidental).

Fk

  • The characteristic value of load

The combination factors takes account of simultaneous occurrence of more variable loads in load combinations and may be used for the calculation of long-term effect for serviceability limit states.

ψ0

Factor for combination value

  • This factor is used in combinations for ULS and for non-reversible SLS.

ψ1

Factor for frequent value

  • This factor is used in combinations for ULS (with accidental loads) and for reversible SLS.

ψ2

Factor for quasi- permanent value

  • This factor is used in combinations for ULS and for reversible SLS. The value is also used for calculation of long-term effects on structure.

The reduction factor ξ is parameter of permanent loads. This factor is used in combinations for ULS according to the expression 6.10b of EN 1990.

Category

Categories of load cases are used for correct choice of combination factors ψ for variable loads and the factor ξ for permanent loads. Categories are based on the table A1.1 of EN 1990.

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