huangyhg

do existing unreinf cmu walls need to follow tms 530 seismic
i'm working on an old unreinf cmu wall in a renovation job and it looks like there is no reinf in the wall, in the whole building...it's not load brg or part of the lateral system...just backup to brick...
it's an old bldg but it's located in sdc c in alabama...
the masonry tms code has min vert and horiz reinf requirements for masonry walls in sdc c...
can i get out of this since it's existing, or do i tell the owner he has to knock down the wall to install new horiz and vert reinf? or do externally applied reinf?
thanks
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the building official has to make the call about whether upgrading to current codes is required. most jurisdictions have ordinances based on the value of the remodel project.
if you think it is a life-safety hazard, as a pe you should recommend appropriate mitigation measures to protect the public regardless of the ordinances.
we follow the ibc existing building in chapter 34. unless the b.o. stipulates otherwise.
the asce 31 has established a method for the "seismic evaluation of existing buildings". i purchased that lovely book for a single job only to find that in washington with a sdc d there was little i could do for that particular condition. could we have a bit more info like wall thickness and height? additionally, is the top connected to the diaphragm above?
when you say backup to the brick, is it possible that the brick was meant as a veneer and the cmu is the main support?
"if you think it is a life-safety hazard, as a pe you should recommend appropriate mitigation measures to protect the public regardless of the ordinances." by taro
well said...
i just took a quick look at aci530-02 - chapter 5 for empirical design of masonry.
5.1.2 - limitations
5.1.2.1 seismic - empirical requirements shall not apply to the design of construction of masonry for buildings in seismic design categories d, e or f as defined in asce 7-98, and shall not apply to the design of the seismic-force-resisting system for structures in seismic design categories b or c.
the following sections got into the 110 mph winds and other items such as heights.
empirical design does not use reinforcement for the purposes of carrying loads, but may use some for continuity and some details (bond beams and vertical steel at some openings).
check out chapter 5 and see how that applies to your structure. often retrofitting some structures can create unexpected results. it sounds like you may have block infill as a back-up for a brick exterior.
dick
rvswa, it's a 3-story concrete slab-and-concrete beam framed dormitory built in the 50s. the partition walls and perimeter walls are 4" thick cmu (apparently unreinforced)...and the attic level is a stick-framed hip-and-gable deal anchored into the concrete slab below. currently if you go into the attic and look at the inside face of the cmu gable walls (which serve as backup to some ornate brick veneer on the gable) they are cracking pretty badly along the mortar joints, which makes us this the cmu is unreinforced and is probably cracking under wind loads on the face of the gable.
anyway so it appears that these cmu walls are not part of the overall lateral system, but still 1.13.5.2.3 says all these walls need min vert and horiz reinf for sdc c.
where can i get this asce 31 book? it sounds like it may get me out of this.
thanks
since you have 4" cmu walls it is very unlikely (or maybe impossible) for the walls to be reinforced. the dimensions of those units to not permit grouting under current codes.
you may find that all of the exterior 4" cmu back-up walls do not comply with the current codes. a 6" wall can easily and efficiently be reinforced and grouted.
dick
thanks dick...however, do you know if i have to upgrade all these existing walls to the min reinf required by current tms provisions for sdc c?
the question of tearing out all the main exterior walls would be a question for the local building official and would be influenced by the scope and extent of the renovation. the 4" cmu back-up walls may have met whatever code that existed at the time of construction. many areas have been placed in higher seismic zones in the past few years. the new reinforcement requirements are based on continuity and crack control and not a structural item.
much will depend on the present condition of those walls. bringing it up to code could require total reconstruction to build to the new standards.
the brick in the gable area could be a different problem since it is probably due to the lack of horizontal support from the roof system - a common problem with gable ends.
i would suggest you try to isolate the two areas (gable, other exterior walls), especially if there is a desire to maintain the exterior appearance.
dick
i've had a great deal of luck with construction books express, i have ordered from them a number of times and once when i transposed an old street address over a current zip, they worked quickly to help me get it figured out and get the book to me.

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