huangyhg

seismic retrofit of unreinforced cmu
i am working on an existing unreinforced masonry building. the building's use is changing form residential to state use. with that the building has to be retrofitted to meet the seismic code. i am considering saw-cutting a vertical slot and inserting one leg of an angle at certain intervals. the angle would be fastened to the cmu with epoxy anchors. is that a good approach?thanks!
eric mcdonald, pe
mcdonald structural engineering, pllc
frp is worth considering depending on what seismic actions you need to upgrade for (in-plane shear, out-of-plane flexure etc).
significantly easier to do surface prep and frp application than to saw cut and install steelwork and anchors.
i would strongly consider frp - the first structural uses of frp were seismic upgrades on brick walls in europe. you may be surprised how effective frp strips will be on a cmu wall - in terms of strength with relatively low material quantity. i would contact fyfe company (858-642-0694) - they are the leaders in retrofit work using frp.
the overall concept includes a composite fabric being adhered to the cmu with a high-strength epoxy. it is relatively easy and clean with a very unobtrusive finish. i suggest you contact fyfe company to discuss.
one option for installing vertical reinf is to sawcut an opening one cmu-cell wide on one side of the wall and grout a bar in. lots of labor required. the grout has to be field-formed on the cut side of the wall, and installed in lifts. this probably won't work if you are dealing with older, three-cell blocks.
second possibility is reinforced shotcrete on one or both faces of the wall.
third possibility is to drill from the top of the wall down with special machines and grout rods into the resulting cavities. have not done this myself. hear it is very popular in california when dealing with older unreinforced masonry building retrofits.

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