Lateral drift for outdoor open steel structures, what to consider ?

[gasma1975]

Hi,

I'm working on a project for an outdoor structure, basically its a roof on columns. It will be used in a park. In such non standard structure, how much drift (lateral wind force) can you accept ? The code says normally h/400, but I don't think it will apply in this case and it will cost too much.

Any idea ?

Gasma1975

 

[DST148]

ASCE 7-05, Commentary to Appendix C - Serviceability Considerations: Drift limits of 1/600 to 1/400 of building or story height. But this appendix is not a mandatory part of the standard, and moreover your structure may not qualify strictly as a building structure.
ASCE 7-05 Chapter 15, Seismic Design requirements for nonbuilding structures, section 15.4.5 Drift Limitations - The drift limitations of building structures need not apply to nonbuilding structures....P-delta effects shall be considered where critical to the function or stability of structure.
Assuming that the structure qualifies as a nonbuilding structure with no cladding, I would worry only about P-delta effects under wind & seismic loads.

 

[JAE]

Assuming you deal with the PDelta issues, I would go with L/240 as a max.

 

[DST148]

Source - Metal Building Systems - UBC 1997 made exemption from any drift limitations for single story steel-framed building for factory, business workshop, and certain occupancies.
Drift limits in AISC - Design Guide No. 3
H/60 - H/100 for metal panels
H/100 for precast concrete
H/200 for reinforced masonry - can be reduced to H/100 with proper detailing.
All the above criterion are for a 10-year wind loading.

I feel one should not get too hung up on the drift criterion for a single story steel-framed open structure in a park. The designer will have to set his own deformation limits for P-delta analysis. The limits are subjective based on the designer's comfort level.