USG Cavity Wall Shaft Systems Page 5

USG Cavity Shaft Wall Systems

Flexing Resistance Provides Life-Safety
Shaft walls are subjected to both positive and negative pressures as elevator cabs rise and descend. This piston-effect of elevators in a shaft causes continual flexing in the shaft wall. In tests, USG Cavity Shaft Walls were subjected to over one million full oscillation cycles to check wall performance through the life of the building. These tests showed that a 25 ga. J-Runner is inadequate at the top or bottom of a shaft wall. As the long runner leg is continually flexed from wall deflection, it can rupture and screws strip out and fracture from the flexing. Oscillation tests showed 24 ga. runners minimize these problems and are essential to safety over a long time period.

Limitations

1. Non-load-bearing.
   
2. Elevator door operating equipment must be independently mounted.
   
3. Exposure to excessive or continuous moisture and temperatures exceeding 125 °F (52 °C) must be avoided.

Elevator Shaft Pressures
The air pressure load on shaft walls depends upon the elevator cab speed and the number of elevators per shaft.  The following recommendations are derived from United States Gypsum Company tests conducted in three high-rise buildings ranging in height from 17 to 100 stories.

Recommended Elevator Shaft Pressure Load

Limiting Heights
Maximum partition heights are shown for four different intermittent air pressure loads and three allowable deflections. The applied pressure load is selected by the designer based on elevator cab speed and the number of elevators per shaft. Instead of using only deflection criteria, United States Gypsum Company design data consider several additional factors in determining limiting partition heights.

A Bending stress — the unit force exerted which will break or distort the stud.

B End reaction shear — determined by the amount of force applied to the stud which will bend or shear the J-Runner or cripple the stud.

C Deflection — the actual deflection under a load. Allowable deflection is based on the amount of bending under load that a particular wall can experience without exceeding a prescribed ratio related to partition height.

Thickness— Steel Components⁽¹⁾

(1) Uncoated steel thickness; meets ASTM A568. Studs and runners meet ASTM C645. Base metal meets ASTM A924 standards for structural performance. Coatings are galvanized per ASTM A653; aluminized per ASTM A463, or aluminum-zinc per ASTM A792.
(2) Conforms to AISI Specification for the Design of Cold-Formed Steel Structural Members, 1986 edition.

Structural Properties—Steel Components

Component
& size

Stud
designation

Avg. weight
(lb/lin ft)

Area (in²)

I_x (in⁴)

S_x* (in³)

Allow. design
stress (ksi)

2-1/2" C-H stud

212CH25

0.5186

0.1524

0.129

0.093

19.8

212CH22   

0.861

—

0.208

0.1519

24.0

212CH20   

0.998

—

0.239

0.1741

24.0

4" C-H stud     

400CH25

0.6118

0.1798

0.383

0.162

19.8

400CH20

1.243

—

0.730

0.318

24.0

6" C-H stud     

600CH20

1.366

0.4227

1.998

0.569

24.0

double 6" E-Stud    

600ES25

1.546

0.3982

2.004

0.628

20.00

600ES20

2.372

0.0840

3.400

1.094

20.00

2-1/2" J-Runner  

212JR24

0.448

—

0.117

0.085

3.00

212JR20

0.670

—

0.192

0.130

4.96

4" J-Runner     

400JR24

0.573

—

0.351

0.163

3.00

400JR20

0.857

—

0.574

0.251

4.96

6" J-Runner     

600JR24

0.740

—

0.937

0.295

3.00

600JR20

1.107

—

1.523

0.457

4.96

2-1/2" Jamb Strut     

212JS20

0.818

—

0.226

0.143

3.00

4" Jamb Strut    

400JS20

1.006

—

0.647

0.270

3.00

6" Jamb Strut     

600JS20

1.256

—

1.673

0.485

3.00