Advice for drift allowance? Glass Curtain Walls & Ceramic Block Perimeter

[pwmiller54]

Looking for advice on how stringent the drift allowance should be against wind on a 2-story office building? Perimeter is mostly glass curtain wall and ceramic brick. I normally use L/240 at roof level for my buildings (usually not this much glass, many industrial). I know this should be more stringent but can't seem to find anything. Thanks in advance for any help.

 

[Hokie93]

I typically use H/400 for checking frame drift and use a wind pressure based on a 10-year mean recurrence interval (as opposed to the strength design wind pressure based on a 50-year MRI). If you are using ASCE 7-05 or 7-10, frame drift due to seismic load (which includes the deflection amplification factor, C_d) must be checked against the criteria in Table 12.12-1.

 

[pwmiller54]

Hokie93- Are ASCE 7-10 wind loads based on the 50-year occurrence as you mention above or 10-year? I can't seem to see it referenced anywhere in the book itself.

 

[johnbridge231]

I would say L/200

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[Hokie93]

No. The ASCE 7-10 basic wind speeds are provided on a strength-level basis, as opposed to a service-level basis in ASCE 7-05 (and earlier versions of ASCE 7). The mean recurrence intervals for Risk Category I, II, and III/IV structures in ASCE 7-10 are 300 years, 700 years, and 1700 years, respectively. The good news is that the Commentary to Appendix C (Serviceability Considerations) provides three wind speed maps (for 10-year, 25-year, and 50-year MRI) explicitly for serviceability-related purposes.

The wind speed 'calculator' on the Applied Technology Council website (

http://www.atcouncil.org)

provides the 10-year, 25-year, and 50-year MRI wind speeds as part of its output. The software is free and very user-friendly, if you aren't familiar with it.

As an aside, I have found that the design wind pressures for ASCE 7-10 are essentially equal to the ASCE 7-05 values for Risk Category II and III/IV structures in non-hurricane prone regions (areas where V=90 MPH for ASCE 7-05) and approximately 20% less for hurricane-prone regions.

 

[wannabeSE]

The commentary to appendix C of ASCE 7-10 has some discussion on wind drift limits.

 

[dhengr]

Why not talk this drift issue over with the/a window or glass facade designer and fabricator. After all, the building structure and the facade are ultimately going to have to fit and work together. A facade which is made up of two one story units will tolerate one drift value, while facade units which are made two stories high may tolerate less drift, for a given window unit width. The allowable drift and beam deflection are highly dependent upon the detailing of the facade units, or visa-versa.

 

[a2mfk]

Agree with other posts, but I also think brick will control as glazing manufacturers have lots of ways to deal with drift.

Good thread:

http://www.eng-tips.com/viewthread.cfm?qid=267575

From AISC's website, do you have access to Design Guide #3?

4.1.2. Why are deflection and drift limits not specified in the 2005 AISC Specification?

Deflection and drift are examples of serviceability criteria. Serviceability limitations are not mandated other than the requirement in the 2005 AISC Specification Section L3.1 that "Deformations ... shall not impair the serviceability of the structure." Summarizing from the 2005 AISC Specification Commentary Section L3.1, any specific serviceability limit would depend on the function and components of the structure. Guidance can be found in AISC Design Guide #3, Second Addition Serviceability Design Considerations for Low-Rise Buildings (West and Fisher,"Deflections In Structural Members And Structural Systems... Shall Not Impair Serviceability of the Structure" 2002).