huangyhg

strengthening masonry wall
i have a shipping warehouse that has some problems with its masonry bearing wall. the front of the building has 3 overhead door openings. the wall is 12 inches thick, 8" cmu and 4" brick. the doors are 12 feet wide. two doors have a loading dock bumper height of about 3 feet high. a third door opens on grade and is 14 feet high. all door heads are same height. the masonry pier between doors is 5 feet wide. the remaining front of the building is a full height masonry wall for about 100 feet in length. the wall height above the doors is about 9'-8".

it appears that a truck has caught the side of the tall opening. the masonry piers are out of plumb. i dropped a plumb bob from the roof to the door head and the top of door head is about 3/4" out of plumb to the exterior face. i dropped the plumb bob from the door head down to the ground and the wall went back in about 3/4". the adjacent door was similar, slightly less. the pier between the last 2 doors was about 1/2" out of plumb, same curvature as the first one. as i progress away from the 14' high opening the out of plumb decrease, so it appears to radiate from this one door. that's why i think a truck must have pulled out one door jamb. the top of this jamb has severely cracked brick.

my fix first is to repair the cracked brick. the steel lintel above the door bears 8" on the jamb, the first 4" being on the cracked brick. then i think i should stabilize the masonry piers. my thought is to use a steel 'strongback' on the inside face. i envision a steel wide flange column bolted to the cmu wall. i expect the top course to be a bond beam since steel bar joist bear on it. i can attach the bottom to the concrete floor or a concrete wall at the base. i would guess i could connect to the masonry wall at about 2' o.c. vert. with adhesive anchors.

i want to get some feedback on what to design this 'strongback' for. perhaps some of you have done this before. the strongback will not be as stiff as the cmu wall so i don't believe it will take the lateral loading. i guess it would just be for buckling stabilization so the wall does not get worse. what kind of forces would this be? would one strongback per 5' wide pier be enough?

thanks for your help. i really appreciate all the wisdom from your input!

rich
it may be sounder to shore the loads to the slab on the ground and then replace anything in bad state. this is not so big masonry work as to not do this, and you will get a final sounder status. you may then add jamb reinforcement in the way that pleases you.
upon pertinent shoring you might even push the wall back to verticality and straightness for further refurbishment, but this is really quite an extreme intent again no worth avoiding its demolition.
now, on how your attached column may be working, well, the whole thing will act composite for any work to be developed from installation, and this with the limits to composite action that the interlock may supplementarily enforce (that may be little if the connection is thoroughly done). hence, for example, it might add entirely composite action for any new wind (and orthogonal to the plane) action.
respect your worries on the integral working of the 5 feet width with a single column, most likely such should be the case for any sound masonry properly tied to your inner backup, except that of course thermal actions etc dissolve the composite action by rupture of the masonry by the stiffer column (this happens a lot for exposed metalic attached long parts in masonry).
so if you plan composite action, and due to the imposed curvature by the truck impact, i would thoroughly check its status and reinstate any lack of integrity that there i might see, guess or divine, for otherwise the composite action would be with a part unable by itself (or code) to take any load.
you of course may add parts that ensure the lateral loads are passed to your new column, composite or not. this is acceptable practice, since there are lot of instances where masonry walls are surmised to be stabilized by some backup structure, even if it is clear that lacking composite action first the actual of the then purportedly non composite masonry will be working and only after partial destruction the backing structure may develop its strength in its intent ... yet if attached the composite action would be from the start.

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