PJHudson
Structural
- Dec 3, 2007
- 6
This is not a new question. See thread507-178618 February '07 and thread507-139345 November '05.
I am in California where we just adopted the ASCE's hurricane region wind code (we only have gentle breezes and its always sunny). Does anyone have a clear understanding of the ASCE 7-05's intent regarding wind uplift and All-Heights Load Case 3 in Figure 6-9. There is a 1.5 times increase in the design load for uplift on interior columns if one interprets the code's "Load Case 3" to mean 0.75*(Longitudinal+Transverse) for uplift (not just lateral loads). In a low rise metal building this translates into big differences in footing size and cost. I found this language being stricken from a code revision proposal on an NCSEA meeting agenda on the IBC "torsional effects resulting from full and partial wind load combinations identified in ASCE 7 Figure 6-9." at Note the use of "partial" to descibe wind load combinations. Also Figure 6-9 of the ASCE 7 uses the language "Full design wind pressure acting on the projected area perpendicular to each principal axis" , and the notes 1-3 below have no mention of a "z" or vertical axis, only the "x,y" principal axes.
Is this a deliberately vague presentation in the code which is so precise about the values for Cp?
I sent a note to the ASCE wind committee and hope I get a response. Perhaps someone knows where to get an authoritative and clear interpretation of the code's intent even if it is to leave it up to engineering judgement.
Thanks in advance.
I am in California where we just adopted the ASCE's hurricane region wind code (we only have gentle breezes and its always sunny). Does anyone have a clear understanding of the ASCE 7-05's intent regarding wind uplift and All-Heights Load Case 3 in Figure 6-9. There is a 1.5 times increase in the design load for uplift on interior columns if one interprets the code's "Load Case 3" to mean 0.75*(Longitudinal+Transverse) for uplift (not just lateral loads). In a low rise metal building this translates into big differences in footing size and cost. I found this language being stricken from a code revision proposal on an NCSEA meeting agenda on the IBC "torsional effects resulting from full and partial wind load combinations identified in ASCE 7 Figure 6-9." at Note the use of "partial" to descibe wind load combinations. Also Figure 6-9 of the ASCE 7 uses the language "Full design wind pressure acting on the projected area perpendicular to each principal axis" , and the notes 1-3 below have no mention of a "z" or vertical axis, only the "x,y" principal axes.
Is this a deliberately vague presentation in the code which is so precise about the values for Cp?
I sent a note to the ASCE wind committee and hope I get a response. Perhaps someone knows where to get an authoritative and clear interpretation of the code's intent even if it is to leave it up to engineering judgement.
Thanks in advance.
