Integrated Buildings & Structures

IBC 2015 Chapter 5 presents provisions for building heights and story limits for building frames over podiums of Type I to Type IV construction materials, ASCE 7-10 contains provisions for Seismic and Wind Loading considerations, and AISI S240 Section B1.1 allows LIVE LOAD REDUCTIONS of the framing alone for CFS part of the MWFRS resisting wind loading conditions, "IS THERE ANY SIMILAR PROVISIONS IN THE NDS FOR MASS TIMBER OR WOOD FRAMED SYSTEMS" of multistory buildings over podiums for live load reductions of the framing (no shear walls taking lateral loads, only the wood framed system)?

See recent article of Cold-Formed Steel Framing for Podium Structures in Structure Magazine March 2019
https://www.structuremag.org/?p=14285



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[Pedro R.] [Munoz] [Ph.D., P.E.]
[Principal Engineer]
[PRM Engineering, LLC]
[Methuen] [MA]
[(978) 738-8001]
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That article references AISI S240-15, B1.1. B1.1-B1.1.2 read as follows:

B1.1.1 Application of Live Load Reduction on Wall Studs

For the purpose of calculating the design axial load on a wall using floor live load reduction requirements in accordance with the applicable building code, the tributary area of the wall shall be limited to the floor area assigned to the individual wall framing members.

B1.1.2 Application of Wind Loads on Wall Studs in the United States and Mexico

In the United States and Mexico, the design of the wall studs shall be based on the following design wind loads:

(a)  Combined bending and axial load effect based on Main Wind Force-Resisting System (MWFRS) wind loads.
(b)  Bending load effect based on Components and Cladding (C&C) wind loads.
(c)  Deflection limits based on 42% of Components and Cladding (C&C) wind loads with no axial loads.

AISI S240 B1.1.1 refers to the applicable building code, usually the IBC in the US. The IBC allows the live load reductions for any material. This is not a special case applying only to steel studs.

In paragraph B1.1.2, AISI is not creating any special consideration for steel stud walls. They are just summarizing the load cases that need to be checked and how the relevant ASCE 7 and IBC provisions apply to stud walls. The effects of the wind on the MWFRS need to be checked on any studs that are part of the MWFRS (often shear walls). But also because the exterior wall studs are part of the curtain wall system, those studs also need to be checked for Component and Cladding wind loads. The 42% factor is used because wind loads after ASCE 7-10 are strength level loads and comes from IBC 2018 Table 1604.3, footnote f.

These provisions apply equally to wood construction or any other material, where elements of the structure are both part of the MWFRS and are the building "curtainwall" or exterior. (Its typical to refer to steel studs on building exteriors as curtainwall but I have not heard it applied to wood construction.)

I teach both wood and CFS design class at the graduate level and I am Chair of the ASCE/SEI Committee on the Performance of Wood Structures. I was in full-time design practice for 20 years before entering academia.

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William Kirkham Ph.D. Ph.D.,M.ASCE
The University of Kansas
Overland Park KS
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Thank you so much for the comments and expanded references to the AISI applications of live and wind loads son stud walls. Mainly I was curious to know if the NDS which is the National Standard for Wood Construction contains similar language in reference to the same items of the AISI. It seems logical to think that it should be the same for both steel and wood studs. If anyone can shed some light on the specific NDS requirements for live and wind loads on wood stud walls and permitted reductions of live load, it would be great to know the specific applicable section of the NDS. If there are none in NDS then we could certainly refer to ASCE 7 and apply the corresponding applicable provisions and treat the studs as studs, regardless of the material, but using the applicable allowable bending, axial, and shear  stresses and the applicable live and wind loads. Interesting situation, Great to hear from an authority in the subject. Thank You!

------------------------------
[Pedro R.] [Munoz] [Ph.D., P.E.]
[Principal Engineer]
[PRM Engineering, LLC]
[Methuen] [MA]
[(978) 738-8001]
------------------------------

Original Message:
Sent: 03-29-2019 15:19
From: William Kirkham
Subject: Multistory CFS and Wood Framing over Podiums

That article references AISI S240-15, B1.1. B1.1-B1.1.2 read as follows:

B1.1.1 Application of Live Load Reduction on Wall Studs

For the purpose of calculating the design axial load on a wall using floor live load reduction requirements in accordance with the applicable building code, the tributary area of the wall shall be limited to the floor area assigned to the individual wall framing members.

B1.1.2 Application of Wind Loads on Wall Studs in the United States and Mexico

In the United States and Mexico, the design of the wall studs shall be based on the following design wind loads:

(a)  Combined bending and axial load effect based on Main Wind Force-Resisting System (MWFRS) wind loads.
(b)  Bending load effect based on Components and Cladding (C&C) wind loads.
(c)  Deflection limits based on 42% of Components and Cladding (C&C) wind loads with no axial loads.

AISI S240 B1.1.1 refers to the applicable building code, usually the IBC in the US. The IBC allows the live load reductions for any material. This is not a special case applying only to steel studs.

In paragraph B1.1.2, AISI is not creating any special consideration for steel stud walls. They are just summarizing the load cases that need to be checked and how the relevant ASCE 7 and IBC provisions apply to stud walls. The effects of the wind on the MWFRS need to be checked on any studs that are part of the MWFRS (often shear walls). But also because the exterior wall studs are part of the curtain wall system, those studs also need to be checked for Component and Cladding wind loads. The 42% factor is used because wind loads after ASCE 7-10 are strength level loads and comes from IBC 2018 Table 1604.3, footnote f.

These provisions apply equally to wood construction or any other material, where elements of the structure are both part of the MWFRS and are the building "curtainwall" or exterior. (Its typical to refer to steel studs on building exteriors as curtainwall but I have not heard it applied to wood construction.)

I teach both wood and CFS design class at the graduate level and I am Chair of the ASCE/SEI Committee on the Performance of Wood Structures. I was in full-time design practice for 20 years before entering academia.

------------------------------
William Kirkham Ph.D. Ph.D.,M.ASCE
The University of Kansas
Overland Park KS
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