split face cmu lintel options 1

[eng003]

With an exposed split face CMU construction what are the options & pro/cons for lintels. Are there any masons who still form up U block and pour? How abour power steel products??

 

[hokie66]

Depends on where you are and what the block supplier can provide. Where I am, split face blocks are available in pretty much the full range of shapes, including lintel blocks.

 

[AELLC]

Split face weighs a bit more.

 

[UcfSE]

Almost all of the split-face I have done in my area (FL) have used the powers steel lintel (the double-T shape, not the box). Other than that you need to shore and use appropriate block shapes such as lintels. One other option I have seen that works well if the architect likes it is to provide a regular cmu "band" at header height. Then you can use typical precast lintels.

 

[concretemasonry]

Every market area has different preferences and practices.Consequently, a local CMU supplier must respond to the customer's requirements and the customers are the architects, engineers and contractors.

Since a split face unit(any type/style) the appearance is important. Very often, several colors and patterns are used in the same structure. Very often the choice of the method is dictated by the architect that may require a contrasting material (typically smooth precast lintels) to contrast with the texture and color of the field of CMUs.

In the latter case, when the requirement is a uniform or complete CMU exposure, there are several choices.

To maintain bond, a lintel can be designed by using a colored split face bond beam (U shape) CMUs as the first course over the opening (supported by temporary bucks and then follow with subsequent courses (as required for the span) of the same face that can be reinforced and filled as required. Larger opening may require 1 to 6 courses. Then, the choice is up to the contractor to either saw units as required to be filled as required or have the CMU supplier make special split face CMUs that require no extra sawing. If the job has many openings with lintels it is cheaper for a contractor to order a special run of "pour-through" bond beams to eliminate the sawing, while others with smaller jobs or lower costs, just saw because it is cheaper.

Architecturally controlled masonry projects are rarely supplied by the ma and pa supplier companies because good architects and engineers usually contact a major supplier as an aide to find out what is possible in the local area.

Do not change the strength requirements unless absolutely necessary because the colors of the units will no match perfectly.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[jayrod12]

We just had an issue on a job using split face blocks.

We had clearance issues in the columns as there was not enough space in the core to put the rebar cage so we had to find a work around for that involving a steel section mounted to the exterior of the column (The contractor never notified us that the rebar wouldn't fit, we found out he didn't install it when we did a pre-pour inspection.

We also had clear cover issues for the lintel. This was solved by sawcutting the inside of the faces a little bit to give us more room in the u-blocks. This method actually worked quite well. There were still thick faces, and more than enough room in the u-block for the rebar plus clear cover.

 

[concretemasonry]

The specification for CMUs (ASTM C90) specifies the MINIMUM thickness and there is a wide range of actual configurations, face shell thicknesses, web thickness, number of webs, different tapers of the interior face shells and the location of the webs. Units like bond beams and lintels have somewhat greater face thicknesses for manufacturing purposes and dimensional stability since a CMU is only in the mold for 6 to 10 seconds. - The extra weight is not a factor for CMU producer, but contractors are a different problem. Most contracts do prefer CMUs with a wider mortar bed for spreading mortar and ease of handling.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[eng003]

Thanks all for the great responses...I am heading towards U-block and shoring as this near coast and don't like the idea of exposed steel i.e. power steel products. Its an 18 ft span supporting a 26 ft simp. supp. span of 2nd floor and roof loads...the numbers look like a 24" deep 8" thick cmu beam using lintel blocks at the bottom w/ (2) number #6's in the bottom should make it happen...as I am dialing in this one...looking for references on typical lintel dimensions to establish the right "d" distance though and can't find one?...and I just need an add'l 1/4" for grout cover after the shell thickness as I recall correct?..Does code require you consider placement tolerances too?..Plan on contuing reinforcement as it it a multi-span lintel using bond beam blocks inverted to allow vert. reinforcing to pass through...any thoughts on this approach?

New topic somewhat associated: in evaluating a slender shearwall element can one summarize the appropriate interaction analysis for in plane shear + vertical gravity loads + out of plane loading (wind in this case) for a cmu masonry wal element...all of the design references I have analyze in plane and out of plane seperately...where is this addressed in the governing codes i.e. ASCE 530 & IBC? I assume the answer will be just apply the unity equation for shear and compression on the masonry? can any one provide a good example. Thanks