Interpretation of fire load exposure directions in the model

User question  #

“I would like to understand how to interpret the exposure direction in the case of fire load. For example, in the “Fire Load Parameters” dialog box, how do the pictogram represents the external and internal sides of a reinforced concrete wall?”

Explanation #

For horizontal surfaces, interpreting the exposure to fire based on the pictogram is straightforward. However, for walls or surface elements that are not oriented horizontally, it may be more ambiguous. It’s important to know that for surfaces, the normal vector of the surface is used to position the exposure. The direction of the normal vector coincides with the positive ‘z’ direction of the local coordinate system of the surface element. The icon in the “Fire Load Parameters” dialog that represents surface exposure should be interpreted such that the upper half of the surface in the pictogram indicates the direction of the positive normal vector. With this understanding, the exposure of walls or non-horizontal surface elements can be clearly interpreted.

For line elements, interpreting the exposure to fire requires understanding the axes and orientation of the local coordinate system of the line element placed in the model. The icon representing exposure in the “Fire Load Parameters” dialog should be interpreted such that the local ‘x’ axis is facing us, while the local ‘z’ and ‘y’ axes follow the right-hand rule. Accordingly, the local ‘z’ axis points upward, and the local ‘y’ axis points to the right in the icon.

Example #

The following example shows how to interpret the exposure icon in the “Fire Load Parameters” dialog for a vertical wall surface with one-sided exposure. The positive normal vector of the surface points outward from the building, aligned with the local ‘z’ axis of the surface. The top half of the icon represents this direction. With these settings, the fire acts on the external side of the wall.

Position of fire load in case of a vertical wall using one sided exposure

In the case of a line element, to interpret the exposures in the “Fire Load Parameters” dialog, you need to be aware of the orientation of the local axes of the selected line element in the model. The exposure pictogram in the “Fire Load Parameters” dialog should be interpreted such that the local ‘x’ axis of the element points toward you, and the ‘z’ and ‘y’ axes are set accordingly. In the following example, according to the settings, the I-section is exposed to fire from below and from two sides.

Position of fire load in case of a beam using three sided exposure