Building Directions

Question

When applying Equivalent horizontal forces (EHF’s) or reviewing Analysis or Tabular results such as Deflections, Storey Shear or EHF’s there are references to Dir 1 and Dir 2. What are these?
 
 

 


 

Answer

In Tekla Structural Designer buildings are set out in the Global X, Y and Z co-ordinates. For the majority of models you would probably model the building such that the “principal axis” of the building aligns with the global X and Y directions as the screenshot below.

 

A building may however, have its "principal axes" oriented at any angle to the global axes (in plan).

 

There are certain processes that require this knowledge in order to orientate themselves correctly for the building - these include:

• Slenderness calculations
• Direction of continuous beams
• Equivalent horizontal forces/notional loads
• Seismic loading
• Natural frequencies
• Deflection results
• Drift results
• Story shear results

If you highlight the Structure branch at the top of the Project Workspace Structure window you can see the Structure properties in the Properties window.

This includes Show Building Direction Arrows and the Building Direction Rotation.

The default Building Direction rotation is 0 degrees which aligns the building Direction 1 arrow with the global X axis and the Direction 2 arrow with the global Y axis.

In the screenshot below, the model has not been created such that the principal axis correspond to the Global directions. In order to obtain results in the principal directions, the Building Direction Rotation has been amended so that the building directions - Dir 1 and Dir 2 align with the principle axis of the model.

Entering a positive value rotates the Building Direction arrows anti-clockwise. A negative value rotates anti-clockwise. The limiting values are +45 degrees and -45 degrees. (If you enter larger values they will be capped at these limits).

The building direction arrows are always at 90 degrees to each other.

 


When reviewing results, such as deflections you can then review the deflection in the principal axis of the model - Dir 1 and Dir 2 which are more useful than the global directions.