special vs ordinary cantilevered column continued, still clear as mud

[Materofact]

this issue hasnt gone away for me... did i miss something?

the classic square tube steel column 2 legged carport problem, and im tasked with anchorage design on an existing sonotube concrete pillar.. you know the drill
2.5 overstrength will blow things out and using 1.25 ordinary vs 2.5 special for R last time i checked means double the loading.. no bueno...



thread507-290892

 

[Deker]

AISC 341 permits cantilever column bases to be designed for overstrength if designed per D2.6c. Overstrength is 1.25 for both special and ordinary cantilever columns.

 

[driftLimiter]

What is the issue exactly? I look at them as either cantilever columns or ordinary moment frames. Pin the base of the moment frame will help reduce anchorage demand.

 

[dauwerda]

I'm assuming by "issue" you are talking about what differentiates a Special Cantilever Column from an Ordinary Cantilever Column as is discussed in the referenced thread. This has been addressed in more recent code editions.

So starting in table 12.2-1:

We need to take a look at section 12.2.5.2 and 14.1 to see what the requirements are (for both special cantilever and ordinary cantilever)

Section 14.1 then kicks us to AISC 341:

AISC 341 Section E5 tells us the requirements for Ordinary Cantilever Column Systems (OCCS) and section E6 tells us the requirements for Special Cantilever Column Systems (SCCS).

The main deign requirements are:
OCCS:
-Column bases shall be designed in accordance with section D2.6

SCCS:
-Columns shall be braced to satisfy the requirements applicable to beams classified as moderately ductile members in section D1.2a.
-Column members shall satisfy the requirements of Section D1.1 for highly ductile members.
-Abrupt changes in column flange area are prohibited in the protected zone as designated in Section E6.5c
-Region at the base of the column shall be designated as a protected zone and shall satisfy the requirements of Section D1.3. The length of the protected zone shall be two times the column depth.
-Groove welds at column splices and welds at column-to-base plate are demand critical welds
-Column bases shall be designed in accordance with section D2.6