Bridge load combinations and design




The previous version of SCIA Engineer introduced bridge load combinations: the automatic generation of (envelope) load combinations for several types of bridges complying with EN 1990 and EN 1991-2. In addition to this, the first steps were taken for specific design rules and checks for reinforced and prestressed concrete bridges according to EN 1992-2.

We wanted to continue this effort, and therefore present you a list of improvements for both bridge load combinations and bridge design in SCIA Engineer 2013.

Improvements for Bridge Combinations according to EN 1990

Protection improvements
Bridge load combinations in construction stage analysis
'Modified' equation 6.10a for combinations


Protection improvements

Some protection improvements have been done, in order to correctly enable or disable the functionalities for bridge combinations.

A warning message is now shown when disabling the functionality ‘Load combinations’ in the Project data dialog, in case some bridge combinations were already created in the project. The reason is that this may affect both the content of combinations and the content of construction stages, if present.

What happens if the user chooses ‘Yes’ to continue:

  • Any previously created Load groups, which were set to the Bridge Structure type, will remain untouched until edited by the user. If edited, the Structure type is automatically set to Building and the Load type to category A.
  • Any previously created Combinations, which were set to the Bridge Structure type, will remain untouched until edited by the user. If edited, the Structure type is automatically set to Building.

What happens in case construction stages have been created before:

  • The Structure type will be set to Building in the Construction stages setup – and also in all previously created stages.
  • All variable load cases will be removed from these previously created stages.

This may lead to a possible loss of data in the construction stages!

Bridge combinations in construction stage analysis

A new option has been added to the Construction Stages setup, for the selection of the Structure type. By default this type is set to Building. In case the ‘Bridge design’ and ‘Load combinations’ functionalities have been activated, the 3 implemented types of bridges are available as well: Road bridge, Footbridge and Railway bridge.

The Structure type is used for all construction stages and influences the automatic generation of (envelope) load combinations per stage.

The list of variable load cases, which the user can select from and add to a stage, is filtered out according to the selected Structure and Combination type.

For each constructions stage, code combination(s) and envelope combinations are generated with respect to the rules defined in the Manager of National Annexes.

Equation 6.10a ‘modified’

The third improvement is a new equation for the generation of load combinations, which is in fact a general improvement not strictly related to bridge design. For ULS load combinations of type (STR/GEO) (Set B), the user can now also choose for the equation 6.10a ‘modified’ as described in EN 1990. The reason is that the National Annex may modify 6.10a to include permanent actions only, as is the case for e.g. Finland.

The choice between 6.10, 6.10a & 6.10b, or 6.10a ‘modified’ & 6.10b, can be made in SCIA Engineer in the Manager of National Annexes.

Improvements for Bridge Design according to EN 1992-2

Extension for calculation of minimum concrete cover
Global imperfection for columns
Modification in check of redistributed bending moments
Shear check adaptation in case of prestressing
Allowable concrete stress during execution

Sonja Asselbergh