Steel Column Reinforcing

[cuels]

Is it reasonable to reinforce a steel column by welding a plate to the flanged on the minor axis edges (essentially creating a boxed section - biaxial symmetry) to strengthen a column? In the past, we have always reduced the braced length by diagonal bracing or simply additional beams. In some cases, the plate welded to the flanges would not extend the full height of the column (i.e. anchor bolts at base plate, or sway bracing). Is this something that is common and if so, how do I consider the reinforcing plate to cut short of the full column height? Also, without a moment in the frame, is there any shear flow along the welded connection or is this specified based off of standard detailing?

Any discussion on this method of column reinforcement would be appreciated.

 

[ishvaaag]

See p. 5 of

http://www.google.es/url?sa=t&rct=j...source=web&cd=18&ved=0CHAQFjAHOAo&url=http://

http://www.harmangroup.com/articles...-YHICg&usg=AFQjCNGdUi_2roRwVIw2S2O2xrV7f9HDMQ

You consider the refurbished column strength by considering the member as of variable section both in xx and yy axes (a step increase in the area, moments of inertia in the central part of the column.

It is crucial for this reinforcement be fully sure of that the standing condition is not loading so severely the column that initiating weldment could start buckling or local failure of the member. At the lesser doubt, prop the structure in suitable way in order to perform the retrofit.

Respect shear flow at the weldments, you no doubt will have some locked shear stresses there from the weldments, and, since the new plates cut short of the column length, you will take some shear flow on introduction of further loads taken by the ends to the newly welded plates (to make them collaborate). And the same for further bending of the built-up member.

 

[ishvaaag]

Presently the Direct Analysis Method through division of the column in segments allows for easy normative account of stability effects. In the past we would have resourced to some buckling factors, there being tables for the cases with stepped inertia amidst the member.

 

[cuels]

A couple of questions:

1. Is there shear flow if the column loads are purely axial? (v=VQ/I) - There is no beam shear, just axial compression.

2. How do you segment a column between bracing? Obviously, there is a point where the existing column is adequate to support the loads if the mid area of the column is reinforced, but I have never come across any reference material or textbook that would walk me through that process. It makes sense in my mind, but how do I determine where that point is? I have an example in my textbooks for a built up column and a composite column, but nothing that changes moment of inertia along the column. What is my K for the segmented section (KL/r)?