Repair/Stabilization of Leaning CMU Wall

[mfstructural]

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.

 

[dhengr]

Mfstructural:
That end roof surface btwn. the last bowstring truss and the end wall (gable end?), facing the street, is itself a warped surface, since the distance from the bowstring truss to the wall is constant, but the top end elev. of the rafters is max. at the center of the bldg and decreases as you move toward the two corners of the bldg. Secondly, is appears likely that you can get a fair amount of snow loading on those rafters, behind the mansard roof, with a max. at the bldg. center. Before you do any digging, stretch a string (maybe piano wire) at the top, mid-height and base of that wall, and measure in to the wall to get a picture of the wall surface shape. A surveyor could set up and shoot that wall from a vert. plane 4" in front of it, and again, measure in to the wall from that plane. I suspect that the base of the wall is fairly straight, and that probably means the ftgs. are not to blame, or a problem. You have to get up there and really understand how the rafter bearing is detailed at the top of the wall, and at the truss, your photos just don’t show that. Draw those details, and a section through that end wall, so we can all understand what’s going on. Finally, any deflection of the bowstring trusses is going to push that wall outward, that’s just a trig. problem, the rafter length doesn’t change, but its top drops 2" with the truss deflection, so its base must move out.

 

[EcoGen]

Like dhengr said I think you need to share some detail sketches of the general roof structure and the bearing detail for us to get a better idea of what's going on. In any case, you're saying the top of the wall is not tied into anything which could result in some of the rotation you're describing since I'd expect the ends of the trusses could push the walls outwards under heavy snow loads. The best way to arrest the rotation would probably be to tie the top of the wall back into the roof structure with tie back rods or something of the kind. I'm curious to know what the wall on the other side of the building is like and whether that is also rotating in the same manner?