D1.A.5.8 Design of I-Section with Cover Plates

STAAD.Pro can design I-sections with cover plates per AISC 360-05 and AISC 360-10.

According to B4.2(c) (p.16.1-15) of the AISC 360-05 specification, the cover plate is taken as a stiffened element and the width of a flange plate in a built-up section is taken between as the distance between lines of fasteners or welds. For the compression flange, the appropriate classification in Table B4.1 is that of case 12, which explicitly includes "flange cover plates and diaphragm plates between lines of fasteners or welds." The section classification limits for this case are:

 λ = b/t

$λ p = 1.12 E F y$
$λ r = 1.40 E F y$
where
 b = width of the cover plate t = thickness of the cover plate

Similarly, according to B4.2(c) of the AISC 360-10 specification, the cover plate is taken as a stiffened element and the width of the flange plate in a built-up section is taken as the distance between lines of fasteners or welds. For the compression flange, case 7 is used.

 λ = b/t

$λ r = 1.40 E F y$

For flexure, case 18 is used.

 λ = b/t

$λ p = 1.12 E F y$
$λ r = 1.40 E F y$

The section classification is included in the STAAD.Pro output listed as UNSTIFFENED / STIFFENED elements of the shape, along with the classification limits calculated as above and the element slenderness ratio, λ.

In addition to the limit states described elsewhere in this section, I-sections with cover plates have the following considerations for code checking per AISC 360-05/10:

• For Section E4, the program determines if the section is doubly or singly symmetric. Based on this, E.4-4 or E.4-5 is used for the compression code check, respectively. An I-section with the same cover plate top and bottom remains doubly symmetric. An I-section with differing top and bottom plates or only a top or a bottom cover plate is singly symmetric.

• For lateral-torsional buckling calculations, the values of rt and aw are calculated as described in F4.2 for the effective radius of gyration in section ii.
• For shear, the minimum of all b/t ratios - including the flanges and top and bottom cover plates - is used for the web slenderness in the horizontal direction.
• For shear, the cover plates are checked for tension field action.
• The cover plates are considered in the seismic classification of the section.

It is assumed that the section classifications are for I-section flanges, web, and cover plates but not for parts of elements (i.e., outstanding flange).

Note: The following two items are not checked for I-sections with cover plates:
• The effects of the cover plates for flange local buckling of the section. Only the I-section flanges are considered in the FLB calculation.
• AISC Design Guide 9 is not incorporated.