mfstructural
Structural
- Feb 1, 2009
- 229
I looked at a CMU wall the other day that was leaning. The roof structure of the building consisted of bowstring trusses and the subject wall was an exterior wall parallel to a bowstring truss. The spacing between the wall and truss was about 20'. The CMU wall is about 11' in height from the interior floor to its top. The wall is 100' long and was relatively plumb near its ends, which makes sense since the corners stiffen the wall. Away from the corner, the wall leaned more and more, about 4.5 degrees and was worse at the middle third. The wall hadn't been painted in a long time per the owner and there were no cracks in the mortar joints or CMU....essentially the wall appeared to rotate as a unit.
The rafter from the adjacent bowstring truss came down on an angle and bore on the CMU walls....No anchorage just set on the wall. Furthermore, there was a mansard roof system that the maintenance personnel said was "bolted to the exterior CMU wall". from the exterior, there is a short section of flat roof between the angled rafters and mansard. I'm thinking that the thrust from the rafters and weight of mansard caused the wall to rotate as a whole....It's possible the footing rotated but I personally don't think that contributed much, at least at this point.
Wanted to get people's opinions on what they think caused the leaning....I am debating having the soil excavated to verify foundation conditions, and more importantly what are options to repair/stabilize the wall? I want to avoid anchoring any members to the top of the wall and tying back to bowstring truss, since they are fragile to begin with. I thought about installing some steel WF sections against the wall and have horizontal WF sections along the top of the wall to brace it but they would need to be tied back to something for that to work. The other option is installing vertical steel from the outside to support the leaning wall, but at that point it might be cheaper to replace the wall in sections. but that all depends on how the mansard roof is connected to the CMU wall.
I've included some photos.
The rafter from the adjacent bowstring truss came down on an angle and bore on the CMU walls....No anchorage just set on the wall. Furthermore, there was a mansard roof system that the maintenance personnel said was "bolted to the exterior CMU wall". from the exterior, there is a short section of flat roof between the angled rafters and mansard. I'm thinking that the thrust from the rafters and weight of mansard caused the wall to rotate as a whole....It's possible the footing rotated but I personally don't think that contributed much, at least at this point.
Wanted to get people's opinions on what they think caused the leaning....I am debating having the soil excavated to verify foundation conditions, and more importantly what are options to repair/stabilize the wall? I want to avoid anchoring any members to the top of the wall and tying back to bowstring truss, since they are fragile to begin with. I thought about installing some steel WF sections against the wall and have horizontal WF sections along the top of the wall to brace it but they would need to be tied back to something for that to work. The other option is installing vertical steel from the outside to support the leaning wall, but at that point it might be cheaper to replace the wall in sections. but that all depends on how the mansard roof is connected to the CMU wall.
I've included some photos.
