Removing Masonry prtitons
Removing Masonry prtitons
(OP)
The architect requested our opinion in removing a number of masonry partitions from the second floor of a 2-storey steel framed building built in the sixties. I reviewed the existing drawings and found no lateral resisting system. The beam/column connections were shear connections, no bracings, no shear walls except for the masonry ones.
The base plates for all columns have 2 bolts.
Some of the partitions to be removed are only in the second floor.
I assumed all the columns are fixed. Checked whether they can resist the lateral loads if they act as cantilevers. Analyzed the building and found that the building would conform to the current code. The base plates can resist all of the forces.
Question: can you assume columns to act as cantilevers to resist lateral loads?
The base plates for all columns have 2 bolts.
Some of the partitions to be removed are only in the second floor.
I assumed all the columns are fixed. Checked whether they can resist the lateral loads if they act as cantilevers. Analyzed the building and found that the building would conform to the current code. The base plates can resist all of the forces.
Question: can you assume columns to act as cantilevers to resist lateral loads?






RE: Removing Masonry prtitons
RE: Removing Masonry prtitons
Then again, I have assumed that there is a lateral load resisting system at the ground floor level. Is that correct?
RE: Removing Masonry prtitons
my initial impression would be to keep the masonry walls. Determine if all of the walls are needed and if not, how much of the walls can safely be removed?
RE: Removing Masonry prtitons
RE: Removing Masonry prtitons
RE: Removing Masonry prtitons
JAE:
I assumed a 2-bolt base plate has a moment capacity equals to the force in anchor bolt/compression block times the distance between center of bolt to compression block.
Hokie66:
Your assumption is correct. We are not touching the structure in the first floor.
JLNJ and csd72:
What I am worried about is the effect of removing the masonry walls in the second floor, which changes the configuration of the lateral resisting system. When you say that enough sway will not happen to prompt a cantilever action, is it correct even when all the masonry walls in the second floor are removed?
RE: Removing Masonry prtitons
I you remove ALL the masonry walls on the second floor then what you say should work.
I have designed buildings similar myself.
But keep in mind that the cantilever action will amplify the reaction at second floor. You will therefore need to check the connections,diaphragm and the lower walls for the additional loads.
csd
RE: Removing Masonry prtitons
I just can't believe that a whole building can be laterally braced with only two bolt connections at the base of some steel columns with no beam-column moment connections.
Yes, you can certainly use the method you describe to get some sort of max. moment capacity, but remember that you probably don't know how deep the anchor bolts are embedded, the bolts are probably A307/A36 type bolts (not high strength) and the stiffness of these columns has to be pretty low - thus allowing very high lateral deflections in the building.
RE: Removing Masonry prtitons
From the post, I am assuming that they are double floor height columns and the two bolts are at the ground floor. The column is then a continuous cantilever supported at the second floor level.
The two bolts at ground floor then act as a pinned connection.
csd
RE: Removing Masonry prtitons
RE: Removing Masonry prtitons
RE: Removing Masonry prtitons
In addition though, if the CMU walls do prove to be shear walls, then would you not be creating a "soft story" laterally by removing them?
Mike McCann
McCann Engineering
RE: Removing Masonry prtitons
RE: Removing Masonry prtitons
Mike McCann
McCann Engineering
RE: Removing Masonry prtitons
If you actually do have shear walls still at the first floor and do a propped cantilever column system, then you should be focusing on the horizontal reactions at the first and second floor level and not justifying a fixed base condition.
RE: Removing Masonry prtitons
But how is the Second Floor framing attached to the First Floor CMU walls? The lateral loads cannot magically get into these shear walls.
DaveAtkins
RE: Removing Masonry prtitons
RE: Removing Masonry prtitons