Loads

Contents

• Colour schema for loads
• Automatic load assignment
• New load group management
  • New interface
  • Load groups
  • Examples
• Moving load for regions
  • Definition
  • Results
  • Miscellaneous

Colour schema for loads

Visual differentiation and check of loads is facilitated by the fact that the loads' basic colours can be overwritten by the so-called Colour schema.

Within Colour schema (Tools > Colours...) different display colours can be assigned to

• Point forces,
• Point moments,
• Line forces,
• Line moments, and
• Surface forces

based on their intensity values or user-defined comments.
 

The colour legend (Palette) displayed on the screen contains only the currently visible loads.
 

Automatic load assignment

With just one click, all or just a selection of Line and Surface loads can be assigned automatically to structural objects.
 

From now on, if we create the assignment of a Line load with an edge selection (Line by selection), it is enough to select only the proper edge, we do not need to select the host object too. Like the previous one, selection of a proper region (Pick existing region) is enough when assigning Surface load to an object's region.

New load group management

FEM-Design 20 introduces a new interface for managing load cases in groups. Thanks to the new functions listed below, loads can be systematized in any large and complex project (e.g. handling a large number of moving loads in bridge engineering).

Major new features and improvements:

• Load case definition and grouping in one common tree-view-based dialog
• Subgroup system within Groups for quick modeling of loads with different position in time: e.g. road/rail traffic on bridges, wind load, etc.
• "Master-Slave" system to fast generate and copy Load cases with same type and position within a Load group
• Relationships of Load cases: Alternative, Simultaneous, Entire and Custom
• Improved automatic Load combination generation
• Load groups can optionally participate in calculations for Maximum of Load group
• Easier and more transparent handling of seismic loads
• Fast input with shortcuts: Insert key for new Load case, Delete for removing selected item, Ctrl+Delete for removing group with its members, etc.
  
   

New interface

Load groups

Load group is a container and organizer of Load cases and Subgroups which are in a specific logical connection, in so-called "relation". According to definition of Eurocode: load group represents a group of similarly handled effects. For example wind loads which are modeled as alternative load cases for directions are used with the same combination factors in the EN 1990 combination formulas, if they are organized in a Load Group. Load groups are necessary for automatic Load combination generation and for Maximum of Load group calculation. 
A load group is defined by a name and a type. Depending on type, different properties can be set for a Load group.
 

Relations

We can choose from four types of relationship (that defines the relations between the members of a group):

• Alternative (default): all elements of the group are mutually exclusive.
• Simultaneous: each member of the group can be applied simultaneously. For "Temporary"-type groups, combination with zeros for all members is a valid case. For other group types, at least one member is always selected for combination.
• Entire: all members are compulsorily selected. Likely to be used in permanent groups with multiple load cases, when all cases should be handled together.
• Custom: we can create custom relations among the members with Setup:
   

Subgroups

Subgroups belong to a Load group and contain Load cases, which are wished to be handled together based on some logic (e.g. one load action with multiple load cases with different positions or directions).
 

"Master-Slave" system for Load case generation from one Subgroup to another:

• The system helps us with creating Subgroups (called "Slaves") based on a selected Subgroup sample (called "Master") by copying Load cases with the same knowledge (type, properties and "Position" (see later) as the "Master"s into the "Slaves".
• The system guarantees that only Load cases with the same "Position" (that represents e.g. a load direction) are matched during later automatic Load combination generation. Example: Load case with "Position X" from a "Master" Subgroup will only be combined with cases also having "Position X" in all "Slave" Subgroups.
• Load cases within "Master" and "Slave" Subgroups cannot be modified as long as their connection exists. Insertion of Load cases inside these subgroups are not allowed.
• "Position" is a custom tag or ID of a Load case; that should be unique within a Subgroup and controls the creation of "Master-Slave" relations between Subgroups.
   

Examples

Wind load:

• Wind force acting on the building is analysed with four different directions (X+, X-, Y+ and Y-).
• Wind force has an outer pressure, an inner pressure and a frictional part. All these parts can act individually, or combined with each other.
• Without Subgroups and the "Master-Slave" system, the Load group should contain 12 (=3x4) Load cases with "Simultaneous" relation, so the total number of generalized combinations would be 4090. However only those combinations are valid, where the directions are the same, therefore the user should manually select them.
• By using Subgroups and the "Master-Slave" system, only the proper directional combinations are generated, and the total number of combinations is only 28.
• Relationship type of the host Load group should be set to "Custom" to generate "simultaneous relations and cases" with the Add simultaneous button. (See the images above.)
   

Traffic loads on bridges (defined by EN 1991-2, table 6.11):

The table shows a guidance for combining different effects acting on a bridge. These load actions usually contain one moving load, with multiple load cases with different positions. Usually these moving load has several (>10) positions, and of course, only loads with the same positions needs to be considered in the load combination generation. The Load group hierarchy is the following in the case where there is only one track on the bridge and we examine 5 different "Positions" for each load action ("LM71" is generated automatically as a moving load, the rest of the subgroups are “Slaves” of "LM71"):
 

"Custom" should be chosen as the Load group’s relationship-type, and so the first 7 combinations defined by EN 1991-2 can be easily set:
 

This way, due to the relationship of Load cases 35 load combinations are automatically generated. (35=7 (number of relations) x 5 (number of "Positions"))

Seismic-type Load group:

• "Seismic" group type is a special case of Load groups. Only one "Seismic" type group can be defined.
• The relation in the "Seismic" group is always "Alternative" and cannot have Subgroups.
• Two group property variants define the behaviour of seismic calculation:
  • Seismic calculation results: equal to internal force-based increments in the combinations. This type of group can contain one indelible, non-movable and non-modifiable “(Automatic)” item. The previously created Load cases of this seismic group will be moved into the "Independent load cases". The contents can be set at both auto-generation of Load combinations and Analysis settings:
    • Signed results option applies EN 1998-1-1 4.3.3 (4.18-4.22) formulas (effect of highlighted direction multiplied 1.0; non-highlighted 0.3).
    • Unchecked Signed results applies the Seismic max case (absolute value of the seismic result ‘s component applied with the unfavourable sign).
  • User defined load cases: we can manually organize load cases into the seismic group. Allowed load case types: "Ordinary; +Seis load [component and direction]". For Load combinations and Load group max calculation, these Load cases are separated to X and Y directions (ordinary cases are presumed to be both X and Y directional), and the two groups of directional cases are combined to each other according to EN 1998-1-1 4.3.3 (4.18-4.19) formulas (effect of highlighted direction multiplied 1.0; non-highlighted 0.3).
     

Moving load for regions

From now on, region can be used to define moving loads to aid road bridge design tasks including influence surface evaluation.

Definition

The loads are generated automatically according to Grid and the Vehicle load settings.

Results

We can display and animate analysis results (such as for example the internal forces and displacement) by the load positions of a moving load case type.
 

The influence surface can be displayed by selecting a result component, an examined structural element and finally an examination point. 
 

Miscellaneous

Improvements for all moving load definition modes:

• The Moving load tool palette is extended with quick settings option, like Name, and division settings for Line moving load.
• At Vehicle settings, the selected and applied Vehicle item can be shifted in its local x' and y' directions.
• Available Vehicles is extended with the Unit load (with 1kN value).

Parent topic: FEM-Design 20 New Features