huangyhg

retrofit cmu wall openings
i need to add some window openings to an existing exterior 8" loadbearing cmu wall. does anybody have some thoughts on how to best accomplish this? i can't add any structural reinforcement, concrete or steel, on the inside of the wall (no room). i have specified breaking out the face of vertical cells before, to add reinforcing, but i'm not sure how practical this is. as far as a header goes, i've heard of people sawing out the bed joint at the head of the opening, and inserting steel angles, but i've never seen a good detail.
any thoughts would be appreciated.
find a job or post a job opening
how big is the opening and are there any reinforced cells nearby? i have done the bolted angle method several times. ugly but effective. have also had them cut out block and slip in a precast lintel. size of openng and location (i.e., exterior walls/wind forces) factor in whether the cells on each side need reinforcing or if you can just grout solid.
i don't understand if you can't put some structural element in the thickness of the wall due to the height of the window (ceiling, top floor) or it is in the interior room where you can′t. 8" certainly is more than the width required to install a competent structural lintel. if you can, do it, whatever the structural form it takes: maybe an rc beam lintel in u shaped lintel blocks, embedded w shapes or angles etc.
respect how to practide holes in bearing walls, ensuring the vertical load paths to foundation when working is the first concern. for normal window sizes the works need not be much important, normally.
to open significant holes in bearing walls one first makes a number of holes in the wall a bit under the lintel height, pass short beams through, and support such short beams on stable formwork. normally running beams in the interior and exterior sides support the short beams. then, on the short beams, you discharge the bearing wall load above through wedges of wood or mechanical jacks. then you can cut all the wall under the short beams, install the beam that will support the wall above and its columns etc. this is the process, assuming general stability can be taken as warranted when opening such holes.
i've had a lot of success with the following.
rake out mortar joints at top of opening for a length of the opening + 16". slide in two angles with lenghts of the opening + 16", one each side, into the wall. then remove the block. then weld a plate with a lenth of the opening to the bottom of the two angles. this serves to connect the two angles together for one larger composite flexural member and keeps loose material from dropping down through the wall above (coke cans and cigarette butts from masons during original construction).

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