Structural Engineers' eBook

Cold-formed Steel Joists

Input
Example

Output
Example

Worksheet

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The worksheet performs design checks as per AISI 1996 (Addendum 1999) for single, two or three span cold-formed steel simply supported joists subjected to uniform dead and live loads based on the following criteria:
  • Flexure
  • Shear
  • Combined flexure and shear
  • Deflection

The underlying assumptions and limitations are listed below:

  • Flexural-torsional buckling is prevented by suitable bracings
  • Web crippling is prevented by stiffeners at all supports
  • Web punchouts are not considered for shear calculations
  • Strength increase due to cold work of forming is ignored

Joists are investigated for the following load combinations:

  • dead and live loads on all spans
  • dead load on all spans and live load on odd numbered spans
  • dead load on all spans and live load on even numbered spans

Two items of input require some explanation:

Allowable deflection:

By default, allowable deflections are span/360 for live load and span/240 for total load. Modify these values for a different deflection criterion.

Section Designation:

The five part section designation is adapted from the industry standard product identification code, where: 

Overall
depth in 
1/100 
inch		 Flange 
width in 
1/100 
inch		 Base
metal
thickness
in mils		        Yield
Stress
in ksi		 Configuration
[ = single channel
][= back to back channels
[]= boxed channels

Example: 
362 =>
362/100 
=3.62"
Example: 
125 => 
125/100
=1.25"
Example: 
33 =>
33/1000
=0.033"


Prefix S on flange width stands for Stud with a lipped channel cross-section which is commonly used for joists.

For calculations,  centerline bend radius is taken as greater of 2 times the design thickness or 3/32" and stiffening lip lengths are obtained from industry standard catalogues as follows:

Flange

    Flange   

Lip
Code      Width    Length


S125


1-1/4"


0.188"

S137

1-3/8"

0.375"

S162

1-5/8"

0.500"

S200

2"

0.625"

S250

2-1/2"

0.625"

Only those values of depth, flange width and metal thickness, considered as structural are included in this worksheet.  Please consult vendors' catalogues for availability of sections with a specific combination of these values.

© 1999-2009 Rudra Nevatia