Defining the Temperature Patterns
Having defined how the key temperatures vary with time, it is now necessary to define the temperature distributions across the members. It is most important to get these right at the end of the required fire resistance time and less important during the earlier stages.
Again a number of common cases are included with Vulcan and can simply be selected from the library. The simplest is the case of uniform temperature which applies in the case of fully exposed sections (4-sided attack from the fire) or cold elements (which are not exposed to the fire at all). A factor enables similar temperature patterns to be defined in relation to the same temperature curves, but allowing a different rate of heating. The factor applies to the reference temperature.
In this example, we wish to assign a linear temperature distribution through the slab elements.
To do this:
1. Open the "Properties | Temperature Patterns" dialog box. You will notice that the entire structure has the same initial temperature pattern (pattern '1' - a uniform distribution).
2. Select the 'Add' tab. A new pattern (pattern '2') will be generated - initially, this will be uniform, as with pattern 1.
3. In the 'Type' drop-down menu, select '1D Linear'. This temperature pattern assumes that the temperature varies linearly with depth through the slab.
4. As the model we are creating assumes that the fire will be positioned below the slab, the bottom face should be the hottest part. With this in mind, the 'multiplier' options should be set at '1.00' for the bottom and '0.30' for the top, as shown:
5. Select the 'Attach' tab and choose to attach 'Pattern 2' to 'slab' elements using the menu and check boxes provided.
6. Using the mouse, select all of the slab elements (you may wish to switch to a plan view of the structure first) and click the 'attach' button.
N.B. You may generate your own temperature patterns in a text file...however, this should only be done once you are fully aware of the way in which Vulcan works.