huangyhg

masonry wall opening
can anyone help me with the following as to how should i proceed: the owner wants to have a 6'x8' opening on the existing masonry block commercial (load-bearing) 12 ft tall building. this opening will be used as a loading dock and has to be located next to (within 1') an existing exit door (42"x7'). thanks in advance.
try searching the forums. masonry wall openings have been discussed fairly recently already.
bashabo,
you basically have two options: steel lintel or bond beam.
when using a steel lintel, i usually specify angle(s), tees, or wide flanges. the disadvantage is that for exterior applications, they are subject to corrosion unless encased in masonry which requires additional labor. i like to use bond beams for exterior applications. at the ends, be sure to have a flexible joint such as caulk or silicon with a backer rod. this will help prevent ugly cracks in the masonry at the upper corners of the door.
in either case, be sure to take advantage of the arching action of the masonry. if you don't, you could end up with an enormous lintel. check the masonry code, it clearly explains the limitations of the arching action.
we rarely design lintels. in fact, for most jobs we include a standard lintel schedule in the specs. the reason for this is that because of the arching action, there is a theoretical maximum load on the lintel regardless of wall height.
good luck.
my main concern would be with the remaining cmu between the two doors. the overhead door and the "man" door will load this 1'-0" strip of cmu with a lot of wind. i doubt it will work unreinforced. if you cannot add some reinforcing to this existing cmu (by breaking it out from behind, for example), i would add a w6 or something like that, spanning from floor slab to roof structure.
daveatkins
these are some basic considerations:
1) load bearing or non-load bearing wall
2) fire rated wall or not
3) running bond or stack bond
4) adequate masonry each side of opening to develop
arching action (if used in analysis)
5) location of control joints
6) jamb strength to transfer wind loads (as dave atkins
mentioned)
7) deflection limited to l/600 or 0.3"
wouldn't the location of masonry control joints at the end of the lintel affect arching action?
assume 60 degree triangular loading on lintel and design your lintel for this load.but if load triangle is not completd and roof slab comes across then take the weight of slab for lintel design.use pre-cast lintel or steel section,place it in position and gradually make the opening.
if looks were not a problem, i would use what i call a "pinch beam". basically you can install two c8 or c10 channels (one on each side of the masonry wall) of course with the backs to the wall. use through bolts and space as required. then cut opening above the channels and fill solid with grout.
once all is set, proceed to cut the opening. keep in mind to extend the channels at least one foot passed the jamb on both sides.
i would also hot dip galvanize the steel and use ss bolts.
lutfi

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