Basement framing-thermal considerations 3

[mrengineer]

I am designing a steel framed building, approx 120'x215' in plan, with full basement, poured walls. In the past I have used pilasters in the basement walls to support exterior steel columns, which then obviously start at ground level. This results in interior beam lines framing into the pilasters (double angle connection welded to embed plate in pilaster).The only thing that bothers me is that the steel is subject to thermal movement during construction (midwest location) and may cause distress at the beam to pilaster connection. I am considering eliminating the pilasters and running the steel columns down to basement level, altho this is not quite as clean. Any thoughts would be appreciated. It seems like the longer I am in this business, the more things I find to worry about.

 

[ishvaaag]

If you want to stay within your practiced ways you may use ordinary bolts on slotted holes, designed to slip before any damage may happen to the beams. Since you count with a quite stiff background, the wall with the pilaster, these connections should be feasible.

 

[AlohaBob]

Isn't the thermal gradients more stable at the basement level? The sun shining on a roof would make greater expansion at the top of column level. Slotted connections and axpansion joints at opportune points allow for movement there.

You refer to the difference in thermal expansion of concrete and steel, right? That's 15%.

Or is it the process that induces the thermal effects. Certainly a 500 degree difference effect would raise trouble with the supports. The foundries have troubles like this during shut down this time of year.

 

[jheidt2543]

Did you calculate the thermal induced stress? This is such a common detail that I find it hard to believe that the thermal stress is high enough to worry about. I agree that sometimes "It seems like the longer I am in this business, the more things I find to worry about.", BUT, if I sit down and dream about it - it generally goes away.

I really think you would have more of a problem dropping the columns at the exterior wall down to the basement level. IF IT WORKS DON'T FIX IT!

 

[mrengineer]

Thanks for all your comments. I think what I need to do is look at the stiffness of the basement walls that the beam lines frame into.