Residential: reducing baseplate thickness

[shacked]

Preface: The majority of my projects are residential, therefore the loading that I encounter for design purposes is relatively low.

I'm designing an attached 250sf open patio roof and I am using 2 steel cantilever columns to resist lateral seismic loading at the free edge, furthest from the house.

Knowns: HSS4x4x5/16 columns, Axial load = DL+Lr = 3.6kips, Design seismic moment at base of column = 11.0kip-ft.

Designing the column as fixed, therefore the baseplate design is to resist bending. Using AISC 360 requirements the required thickness is 1 inch. This seems excessive for a lightweight patio roof. I see that size of baseplate being used for traffic lights approximatelly 15ft tall that cantilever 10-15ft over the street width.

Is there a way, other than fully embedding the steel column in the footing, that could be used to reduce the bending in the baseplate?

Tie the column into the concrete slab?

Thanks.

 

[dauwerda]

that document says 50ksi is the new preferred material for rectangular HSS...that's news to me. Good to know

Yes, HSS has been supplied as dual certified as A500 grade B and grade C for a few years now - definitely take advantage of the grade C.

 

[dold]

The new steel construction manual - HSS column tables in chapter 4 - only lists strength for grade C now.

 

[BAretired]

TheDaywalker,

That has been the most common material for HSS in Canada for at least fifty years. What were you using in SC?

BA

 

[TheDW]

A500 Gr B, thats what my 14th edition SCM shows as preferred.

 

[TheDW]

Apparently I'm late to the 50ksi party!

 

[BAretired]

Welcome to the party.

Edit: While 50 ksi has been common for HSS shapes, ASTM A36 has been fairly common for base plate material, particularly for lightly loaded columns where a high yield was not necessary. Also some fabricators used to call up and request to use A36 because they had oodles of it in stock.

Of course, I've been retired for 12 years now, so their stock may be pretty much used up by now.

BA

 

[dik]

BART:
A36, although may be available, it isn't all that common.

Dik

 

[BAretired]

I'm sure you are correct, dik. I'm not current with the availability of structural materials any more. But it often happens that a lightly loaded column doesn't really require a base plate any bigger than the outline of the column, so when that is the case, the yield stress of the base plate is of little concern to the EOR and a lesser standard could be accepted if the fabricator requests it.

BA

 

[r13]

BA,

FYI - trend of steel producing (blog from AWS dated Jan. 2014).

And according to other articles it appears that the mills are actually phasing out the A-36 designation in many, if not all, shapes. The new products and specs meet the customer demand better and still cover anything previously accomplished by using A-36. As it is almost impossible to locate a pure A-36 Wide Flange beam, it will soon be of other shapes.

 

[dik]

BART:

I often use thin plates based on HSSt +2x PLt if it works on confined area for compression for lightly loaded BPL. This guy was predicated on the anchorage and the design moment.


Dik