Whether you are using SUMO’s Portal Frame Wizard or the Wind Analysis module, you will find that the program generates four load cases (in SUMO) and four cases in Wind Analysis for your 0° wind direction. Initially, this can be very confusing, and it may not make sense why there is a difference in the first place.
These four cases represent four Cpe combinations as per SANS 10160-3:2019. Table 10 in the code lists all of the Cpe factors for duo-pitch roofs with a range of pitch angles. For some of the pitch angles, you will note that there are both negative and positive Cpe factors. A note at the bottom of the table explains what needs to be done under these circumstances:
The four cases are thus formed from these negative and positive Cpe factors. These four cases will then later become four separate load cases (as shown above). The code does not state in which order these cases must be, but SUMO helps us by indicating in the Notes cell of each load case exactly which combination is being considered.
In conclusion, understanding the origin and significance of the four load cases generated by SUMO or the Wind Analysis module can alleviate confusion during structural analysis. By recognizing that these cases correspond to different Cpe combinations as outlined in SANS 10160-3:2019, we can navigate the process more effectively. SUMO’s helpful notes further clarify the specific combinations considered. With this understanding, tackling structural design becomes a more manageable task, empowering engineers to create robust and efficient solutions.
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