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 |
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γf |
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Frep |
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Two different values of partial factor are used::
γf,Sup | The factor for unfavourable effect |
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γf,Inf | The factor for favourable effect |
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Combination factors are used for the calculation of representative values according to the following expression
Where is: | Frep |
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ψ |
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Fk |
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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 |
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ψ1 | Factor for frequent value |
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ψ2 | Factor for quasi- permanent value |
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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.