August 31, 2010
How Are Wind Loads Generated for Sloped Roofs?
RISAFloor is capable of automatically generating the wind loads on sloped roofs. Let’s look at an example of this with the model below:
Note that all of the roof members are defined as lateral. This is optional, as only the ridge beams truly need to be defined as lateral. However, by defining the rafters as lateral they will transfer into RISA-3D, and will be designed for wind load and uplift, which is a bonus. When transferring the model to RISA-3D make sure that the Generate Roof Wind Loads box is checked in the wind loads dialog.
Once in RISA-3D you can review the four basic load cases that have been generated by the program (WLX+R, WLX-R, WLZ+R, WLZ-R). A positive and negative load case is created for each wind direction, as the windward load magnitude is different from the leeward. Be sure to generate reversible load combinations for these roof wind loads to account for this in the Load Combination Generator.