Load Categories 1

[arrass]

I have recently begun using Risa Foundation to design metal building foundations. Among some of the issues I have encountered, one in particular has me wondering...this is the matching of Risa load categories with the plethora of metal building load group designations. Please explain the configurations that yeild WL1, WL2, LWL1, LWL2, LWL3, LWL4, WL3, and WL4. I know these represent "Lateral Primary Wind Load" and "Longitudinal Primary Wind Load", however I can not seem to visualize how the wind is actually contacting the building to produce these loads. WL1 is always the negative of WL2, WL3 is negative for WL4. Likewise LWL1 is negative of LWL2, and LWL3 is negative for LWL4...this represents the wind direction and its reverse effect, but what do the pair of negative groups (WL1/WL2 & WL3/WL4 and LWL1/LWL2 & LWL3/LWL4) represent? And what is the best way to match them to Risa's load combinations?

 

[JoshPlumSE]

I do not understand where you are getting those load category descriptions. Those do not sound like standard RISA categories.

RISA usually uses the following terminology:
WLX, WLY, WLZ (Wind Load in the X, Y or Z direction)

WL+X, WL-X (Wind loads in the X and Z direction when the direction of the load changes the behavior of the structure).

WLXP1, WLXP2 (These corresponds to the partial wind load defined by ASCE-7 2005 figure 6-9. Essentially it's like an accidental torque or accidental eccentricity due to wind).

Josh

 

[arrass]

Josh,
First, allow me to express my appreciation for your response and your commitment to help those that utilize RISA. I have communicated with you via phone and email for a couple of years now and you are always helpful...you are to be commended.

No, those loads are not standard RISA categories and this is partly the trouble. Those loads are typical of the type of column reactions I receive from most metal building suppliers (others are absolutely baffling!). Transferring (and sometimes deciphering) the building supplier's loads to match RISA's limited list of load categories is the greatest demand on my time and the greatest opportunity for error. In a perfect world, the software utilized by the metal building manufacturer (how many programs can there be?) to generate column reactions would mesh with foundation software. Needless to say, I must arrive at generating a translation table that assigns OL1, OL2,... to some ambiguous load designation contrived by the building manufacturer. But I digress, the initial need and purpose of this post is to see if anyone knows what WL1, WL2, WL3, WL4, LWL1, LWL2, LWL3, and LWL4 represent. Are they referring to Fig 6-9 (ASCE7)? Fig 6-10? Could they be a throw back to UBC? Believe it or not, I have contacted the metal building suppliers to try to understand their tables and even they can't explain it! They often tell me to just use the greatest values, but not knowing is unsettling to me. I like to know that I know. Thanks

 

[JoshPlumSE]

Ah yes, I understand better now.... I have received a number of similar comments from guys who design foundations for metal buildings.

One thing that is one our development list for foundation is developing user defined load cases. Similar to RISA-3D where can call out a Basic Load Case based on it's number even if the load category is not defined. That way, you could create any weird load cases that you get from the metal building guys.

Unfortunately, that's a major development item and won't happen anytime within the 3 or 4 months.... though it is possible that it could happen this year.