Working with foundation reaction axis systems
- Local Support (default)
- Building Direction
- Angle to Global (X and Y)
The method for setting the axis system varies depending on whether you want to display the reactions in a graphical results view, a tabular data view, a report, or a drawing. Instructions for each method are provided below.
Also given below in the 'Understanding the axis system options' section are details of the sign conventions applicable along with some examples.
Set the axis system in a graphical results view
Set the axis system for a tabular data view
Set the axis system for a report
Set the axis system for a drawing
Understanding the axis system options
Local Support (default)
The sign convention for support reactions using this axis system is as shown below, with positive moments about an axis acting in a clockwise direction when viewed in the direction of the axis:
For columns and walls the support local axes are determined by the column/wall orientation.
Column | Wall |
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Special case - intersection of two connecting walls | |
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For more details, see: Case study (connecting walls) below. |
Building Direction
The Building Direction arrows can be displayed by selecting Show Building Direction Arrows in the Structure Properties window. These Dir1 and Dir2 arrows indicate the orthogonal horizontal reaction directions when the Building Direction axis system for reporting reactions is selected. The third reaction direction is aligned to the Global Z axis.
The sign convention for support reactions using this axis system is as shown below, with positive moments about an axis acting in a clockwise direction when viewed in the direction of the axis:
Angle to Global (X and Y): when angle = 0 degrees

The sign convention for support reactions using this axis system is as shown below, with positive moments about an axis acting in a clockwise direction when viewed in the direction of the axis:
Angle to Global (X and Y): for any other angle
While they are not actually displayed, the dir1 and dir2 arrows that apply when an angle to global has been specified are as follows:
- dir1 is at an anticlockwise angle θ from Global X when looking down in plan.
- dir2 is at 90 degrees to dir1
- The third reaction direction is aligned to the Global Z axis.
The sign convention for support reactions using this axis system is as shown below, with positive moments about an axis acting in a clockwise direction when viewed in the direction of the axis:
Columns example
Consider the following structure consisting of a slab supported on eight columns. The building direction has been defined at an angle of 30 degrees to the global axes. We will investigate the reactions resulting from a wind load which has been applied to one side.
The total wind load is 1.0kN/m2 * 14.5m * 3m = 43.5kN
When viewed from above you can see how the local axis system of each support is determined by the rotation angle of the column being supported.
In the Results View, Foundation Reactions can be displayed in each of the axis systems.
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In the Local Support axis system the Fx and Fy reactions would be displayed as follows:
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In the Building Direction axis system the Dir1 and Dir2 reactions would be displayed as follows:
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In the Angle to Global axis system (with angle set to 0 degrees) the FX and FY reactions would be displayed as follows:
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In the Angle to Global axis system (with angle set to 45 degrees) the F1 and F2 reactions would be displayed as follows:
The reactions can also be displayed in a Tabular Data View.
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In the Local Support axis system the tabular reactions would be displayed as follows:
Because the local axes are all in different directions, there is nothing to be gained from summing the above reactions.
- In the Building Direction axis system the tabular reactions would
be displayed as follows:
When the above reactions are summed, FDir1 equates to -43.5kN, and FDir2 equates to 0kN.
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In the Angle to Global axis system (with angle set to 0 degrees) the reactions would be displayed as follows:When the above reactions are summed, FX and FY equate to the Total Reaction figures given in the Project Workspace Loading Summary, (as the Total Reaction is always reported according to the Global Axis system.
Walls example
Consider the following structure consisting of a slab supported on two connected walls and a column. The building direction has been defined at an angle of 30 degrees to the global axes.

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The Building Directions (Dir 1 and Dir 2) are not aligned to the Global Axis System.
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Wall W1’s major axis is aligned with Building Direction Dir 1
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Wall W2’s major axis is aligned with Building Direction Dir 2
We will investigate the reactions resulting from a wind load of 18kN is applied to the front face of the building so that it acts in Building Dir 2.

When Support > DOF is switched on in Scene Content it can be seen that they are aligned as follows:

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Shared support at the point where the walls connect:
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Local x is aligned to global X
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Local y is aligned to global Y
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Remaining supports:
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Local x is aligned to each wall’s major axis
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Local y is aligned to each wall’s minor axis
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After analysis the total global X,Y, and Z reactions can be obtained from the Project Workspace Loading Window.

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In the Local Support axis system the Fx and Fy reactions would be displayed in the Results View as follows:
At the shared support the local Fx and Fy reactions align with the global axes, whereas all the other supports they align to the wall major and minor axes.
When the same results are displayed in a tabular data view, the reaction at the shared support (Reference 28 in the table below) is split equally and then converted to the local axis system applicable to each wall. -
In the Building Direction axis system the FDir1 and FDir2 reactions would be displayed in the Results View as follows:
When the same results are displayed in a tabular data view, the reactions at the shared support are output in a single row. (All rows are output in the Building Direction axis system).In the tabular data view, the sum of the reactions (FDir1 = 0kN, FDir2 = 18kN) equate to the applied load.
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In the Angle to Global axis system (with angle set to 0 degrees) the FX and FY reactions would be displayed in the Results View as follows:
When the results are displayed in a tabular data view, the reactions at the shared support are output in a single row. (All rows are output in the Global Axes system).
The sum of the reactions (FX = 9kN, FY = 16.6kN, FZ = 0kN) equate to the global reaction values in the Project Workspace Loading Window.