huangyhg

cmu control joint spacing
i am designing a commercial building in northern nevada, 90' x 180' x 24' tall, with 8" lightweight cmu. what should spacing/size of expansion joints/control joints be? is there an industry reference? what is a common delta-t for temp. differential - 100 degrees f.? does that control the spacing, or does material drying/shrinkage control?
don't try to over-engineer a control joint. - there many good standards based on years of of history.
go to the national concrete masonry association (ncma) site at ncma.org. in the upper right section there is a square to click on to get access to the ncma tek notes. it is a series of over 100 documents written by engineers on various aspects of design and construction.
after you click to get to the tek note site, select a state(any state) and a producer/sponsor (any one) to get access to the tek notes that are indexed by subject and by key words.
you should find all the information you need with documentation to codes and standards. the staff engineers are
i always try to provide control joints every 8 metres (26') for reinforced corefilled masonry. provide control joints wherever you have change in heights of the masonry and near all returns. also to one side of a lintel beam.
if there is a control joint at one end of the lintel beam can you use arching action when designing the lintel? where will the required thrust come from?
enginerding:
there are a number of places that i do not use arching action for lintel design:
1) insufficient height over the lintel to develop arching
2) inadequate masonry on one or both sides of opening
3) stack bond
4) cj or exp. jt adjacent or near edge of opening
additionally, i design all steel or precast lintels to carry a minimum of 8 courses of green masonry before arching can happen. this is not necessary for block lintels in that they are normally shored.

thanks jike.
i completely agree - that was my point about the thrust. the only issue is that it seems as long as the top three issues don't apply, it is common to design with arching. if it is typical to use control joints at openings, then arching should rarely, if ever, be used in designing lintels.
enginerding -
you are correct about the first three items and that is why the roman aqueducts have performed and stood so well. they were pure masonry and not composite construction. the only joints were because of construction limits/processes or elevation changes.
if you have a veneer with dissimilar materials (brick with either concrete block, wood or steel), the control joints are required and the lintel must support the veneer dead load.
dick

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