WIND LOAD PATTERN

[DabbRacing]

Hi,

Until now I used SAP the old way calculating the wind loads in an updated excel from my university days and then I put the loads to the walls and roof for every wind case X+ X- Y+ Y-.

I have no problems using auto lateral loads for earthquake loads. But I'm really mad about not making auto lateral wind loads work. I ask CSI and they repeat like parrots the same answer, my local dealer tells me he uses the program the same old fashioned way as I do since que mostly do RC buildings.

CSI tells me that when I create a new load pattern I choose for example ASCE7-10 auto load pattern, I choose the wind speed and some other coefficients and since I'm modeling a steel warehouse with a gable roof made of cold formed purlins and metal deck and magically microstep cases should appear at my load cases table.

Well I do exactly as they tell me and no microstep cases appear, there is just one case with the name of the load case I did.

To make it brief, can anyone tell me step by step how they do it. How many load cases and directions you make. How do you assign coefficients to windward and leewards walls, side walls and each half of the gable roof. CSI tells me to input coefficients without negative signs for example.. 0.8 for winward and 0.7 for side walls... but when I do that my results are crazy and exactly the same as when I input -0,7.

So please, give me a hint of how to set wind directions and load coefficients. I cant be that hard but I'm trapped. CSI does a great software but support in some far away countries isnt the best.


Thanks in advance!

 

[theshearstud]

Dabbs

I'm using V14 and SAP2000 generates all the cases for me (I believe 12). Under the "Cases" parameter, I make sure "Create all cases" is selected, I do not touch anything else except the "Wind Coeff" section inputs. Click OK and then click OK for the "define Load patterns" window.

When I open the load pattern window back up, all load cases are generated for every wind load direction case. I have not done a gabled roof model though, all mine are flat. I also use the "exposure from extents of rigid diaphragm" which is defined by the diaphragm constraint assignments to each node at each level.

 

[theshearstud]

I meant V16

 

[stressed]

If SAP2000 generates wind loads based on extents of rigid diaphragms, it will automatically add all the required torsional load cases for you. If you do not want to use rigid diaphragms, then for area objects like walls you have to manually assign wind load coefficients (Cp) under area load assignment for both windward and leeward directions. So for each direction the same wall would have a separate Cp for windward direction and in the opposite direction wind case that same wall would have a leeward wind coefficient assigned to it. Wind load coefficients are always input using + positive values according to CSI documentation. For area objects, wind load is always normal to the face.

For ASCE 7-10, SAP2000 can also automatically generate wind loads on open frame structures as a function of height based on wind direction (0 degrees direction default is X direction, Y is 90 degrees, etc.) section dimensions and local axis of each section relative to the wind load direction. Under frame load assignment you can assign different wind coefficients to override the SAP2000 defaults and assign other parameters like ice thickness. I believe the SAP2000 default for open frame wind loading is to consider all frames/beams unshielded, which is conservative.

A google search came up with this wind load FAQ from the CSI Wiki

https://wiki.csiamerica.com/display/kb/Auto+lateral+load+FAQ