Warehouse Renovation 1

[McQSE]

I am involved in a renovation on a warehouse that is about 60+ years old. The lateral system consists of x-bracing in one direction & a rigid truss system in the opposite direction. I attached a drawing showing the floor plan and side view showing the x-bracing locations. The drawing also shows a section. The client wants to remove the 2nd floor (dotted lines in the section view). The 2nd floor consists of heavy timber girders and joists supported by timber columns. The heavy timber girders are supported by the steel columns at the edge of the 2nd floor. I have been studying the effects of removing the timber 2nd floor and have come the conclusion that the building should be fine without it. I am still nervous about removing it though. While my analysis has shown that the building is stable without it, it has to add a lot of stiffness to the structure. Does anyone have any insight on this issue? I appreciate your input.

 

[vandede427]

I agree with the first reply of the thread. I would be hesitant to remove the floor and would fully consider the effects the floor has.

For example, lateral loads applied to the lower elevation of the frame "stay" in the lower elevation. The floor diaphragm acts like a strut and connects the left lower truss to the right lower truss. The high framing only has to resist it's own lateral loads and dumps them down into the lower framing.

If you remove the floor, then lateral loads have to "travel up" to the high diaphragm and then back down again. Before, the high framing was only accountable for it's own loads, it now has more lateral load traveling through it.

 

[McQSE]

Thanks for all the comments.

I have narrowed my problem down some. I am convinced that the 2nd floor diaphragm is not required to transfer lateral forces in the building. I am now considering two issues:

1. The possibility of removal increasing the column effective length
2. The possibility of the 2nd floor acting as a strut and the effects of removing that strut

I modeled an interior frame with and without a beam at the 2nd floor level. It is a simplified model without the trusses exactly modeled, but I think it serves its purpose. See the attached file that shows moment diagrams on the members (wind load right to left). It seems that vandede427 was on to something about the strut issue. The forces in the upper truss connection do increase without the 2nd floor. I suppose I will have to do a more exact model to see if the upper truss can take the extra forces.

Any more thoughts?