Open topic with navigation

Deflection limits & Unity Checks

What are the SLS deflection limits?

The SLS deflection limits are a way to define a limit deflection for the relative deformations. They are used for obtaining the SLS unity checks which are explained further.

Where to define the SLS deflection limits?

The SLS deflection limits can be defined for two directions (in plane deflection and out of plane deflection) and for two types of relative deformations:

• SLS deflection limit for the total loads: the limit will be applied on the total relative deformation.
• SLS deflection limit for the variable loads: the limit will be applied only on the relative deformations coming from the variable load cases of the given combination/class.

The SLS deflection limits can be defined on two places within SCIA Engineer

• Steel setup:
  The defined SLS deflection limits in the steel setup are applied on steel members that are using the default buckling groups or are using a buckling group in which the setting "Deflection limits" = From setup.
  Eurocode:
  
  
  SIA-code:
  
  
• Buckling group (via system lengths and buckling settings):
  The SLS deflection limits can also be defined within a buckling group for deflection z and deflection y. All the members that are using that buckling group will use the same deflection limit.
  Via the setting within it called "Deflection limits" the user can choose from three settings:
  - From setup: the defined deflection limits from the steel setup are used. The defined deflection limits from the setup are displayed greyed out in a grid in which each row represents a span of that buckling group..
  
  - For all spans: deflection limits are inputted for all spans of that buckling group. The first row allows user input which is then applied on all the other rows (=spans) of that buckling group.
  
  - Per span: deflection limits can be inputted per span independently. Each span can have its own independent deflection limit by inputting it in its corresponding row of the grid.
  

How to display the deflection limits in the SLS-check?

Calculated deflection limit values Lim. u_y & Lim. u_z

The relative deformation limit (Lim. u_y and Lim. u_z) can be seen in the SLS-check as a result of the ratio span length divided by the inputted limit value:

• Out of plane deflection limits (def y)
  Type of values = Deformation u_y:
  - Lim. u_y,max: the deflection limit for the deflections due to total loads in u_y direction:
  
  - Lim. u_y,var: the deflection limit for the deflections due to variable loads in u_y direction:
  
  
• In plane deflection limits (def z)
  Type of values = Deformation u_z:
  - Lim. u_z,max: the deflection limit for the deflections due to total loads in u_z direction:
  
  - Lim. u_z,var: the deflection limit for the deflections due to variable loads in u_z direction:
  
  

SLS unity checks

The SLS-check is in fact the ratio of the relative deformation (due to total loads or variable loads) and the relative deformation limit (for total loads or variable loads). There is a clear difference on how to obtain the SLS unity check in case of a simply supported span and a cantilever span.

• Simply supported span: in case of a span in which both ends are fixed the unity check is obtained as follows:
• Cantilever span: in case of a span in which one end is fixed the unity check is obtained as follows:
  

There are five unity checks in the SLS-check, four unity checks of of the four relative deformations and one which is the maximum unity check of those four:

• Check u_y,max: unity check for the out of plane deflections due to total loads.
  
  
• Check u_y,var: unity check for the out of plane deflections due to variable loads.
  
  
• Check u_z,max: unity check for in plane deflections due to total loads.
  
• Check u_z,var: unity check for in plane deflections due to variable loads.
  
• Check_Overall: maximum unity check of the four previous unity checks.
  
  

Open topic with navigation