Engineering for 18' Steel Column

[IAmNotVerySmart]

I have a steel beam in the roof framing of my 2-story building. I am using a HSS post to carry it on both ends. One of the HSS posts spans 18' down to the foundation. I was wondering if there was a better way to engineer this than to have a single post span the 18' feet. Is there a detail where the column would break between the floor joists level? or will I just consider this a single cantilevered post but braced by the floor framing?

I also want to preface that this beam & post is only taking an axial load.

 

[BAretired]

I believe you meant to say the HSS posts are loaded axially. The steel beam is either horizontal or sloping and is spanning between posts.

To answer your question, each HSS can be one piece or two, depending on which is easier to erect. In either case, it will rely on the floor system and roof system for lateral bracing.

BA

 

[IAmNotVerySmart]

@BAretired - So this is not a moment frame. The beam at the top are sitting on the HSS columns. I would imagine it is easier to have 2 HSS columns to construct than it is to erect one tall one. I just do not know how the detail for connecting the 2 separate columns would be. Are the columns just welded together with stiffeners?

I actually just searched up on column splicing details and I believe I answered my own question.

Thank you!

 

[BAretired]

What detail did you use?

BA

 

[IAmNotVerySmart]

The first image that comes up on google when typing 'HSS column splicing detail'

 

[BAretired]

That is not a common detail and is not recommended. It requires either proprietary blind bolts or field welding.

If a single column can be installed without clearance problems, that would be a better choice. If a double column is necessary, it would be simpler to use end plates bolted together.

In either case, the column must be laterally braced by the floor system. The floor framing has not been shown, so the connection detail between column and floor system is still to be resolved.


BA

 

[IAmNotVerySmart]

In this instance a double column is necessary because it is not a new building construction but rather addition to existing building. Having end plates on the end of each column and bolting them together would be acceptable? I imagined some sort of welding would have been necessary but if end caps are all that are needed then that does make it easier. Also the floor framing on one side of the column has joists that brace it but the other side of the column they run parallel to it. The column does fall within a shear wall but I do not know if that makes a difference.

 

[BAretired]

If there are clearance issues with a single column, a two-piece column is necessary.

If the column is laterally braced at both floor and roof, the column connection can be pinned. Otherwise, it must be designed to resist a calculated moment.

Falling within a shear wall could have implications for the shear wall, which will have lost some of its shear strength unless its continuity can be restored by adequate fastening to the column. The foundation under the column may be problematic.

A floor framing plan may be helpful.


BA

 

[IAmNotVerySmart]

Spoke to some people and seems like we are using a single 18' HSS column. Here is a floor framing plan. The column I am talking about is the one directly above the column that FB-17 is connected to. As you can see the floor framing on one side is perpendicular to it while the other side it is parallel to it.

 

[BAretired]

I have a steel beam in the roof framing of my 2-story building. I am using a HSS post to carry it on both ends. One of the HSS posts spans 18' down to the foundation. I was wondering if there was a better way to engineer this than to have a single post span the 18' feet. Is there a detail where the column would break between the floor joists level? or will I just consider this a single cantilevered post but braced by the floor framing?

I also want to preface that this beam & post is only taking an axial load.

Nothing wrong with a single 18' long column if it can be installed without clearance problems; in fact it is preferred.

It cannot be considered a cantilevered column, even if laterally braced by the floor framing. The column must be braced by the roof framing. Depending on the load it is carrying, it may or may not need to be braced by the floor framing. In other words, the column could work with an unsupported length of 18' if the axial load is not too large.



BA

 

[IAmNotVerySmart]

The beam that will be connected to the top of this column will have ceiling joists and roof rafters connected to it. Does that mean that the column will be considered a pin pin connection?

In my calculations I have considered it a cantilevered column braced by the floor system. Is this not more conservative than to consider a column with 2 pin connections and no bracing?

 

[BAretired]

BA[/color]]The beam that will be connected to the top of this column will have ceiling joists and roof rafters connected to it. Does that mean that the column will be considered a pin pin connection?
It might mean pin/pin, provided that the roof framing can provide lateral bracing to the top of column. Are the rafters tied? Can the upper storey resist lateral forces without the aid of the column in question?

In my calculations I have considered it a cantilevered column braced by the floor system. Is this not more conservative than to consider a column with 2 pin connections and no bracing?
If the 18' column height consists of two 9'-0" tiers, then the effective unbraced length of a cantilever is greater than 18', so that would seem to be more conservative, assuming only axial load on the column. If the cantilever column is needed to provide wind resistance, then it may be less conservative.

You are asking questions which nobody here can answer without more knowledge of the structure. You are being niggardly with the information, and some of your information is poorly described or inconsistent.







BA