huangyhg

bond beam location
i have seen a note on drawings that requires bond beams to be placed above openings and where shown on plans and shall be placed no greater than 10'-0" oc vertically. can anyone tell me where i can find anything that tells where bond beams should be placed, besides the top of the wall or when reinforcing is designed to span between bond beams. this note is a typical note and applies to all projects even though the reinforcing is designed for a span from foundation to roof.
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typically above openings, a lintel is used, not a bond beam.
as far as spacing, you need to follow the provisions of aci 530-02, section 1.13. it's dependent on your seismic design class. you get lower loads if you reinforce to the criteria of 1.13.2.2.5, special reinforced masonry shear walls which requires bond beams at 48 inch maximum spacing. the 10 ft. spacing is mentioned in section 1.13.2.2.2.1. it seems excessive to me and i've never seen it used. but i guess it's there.
as a minimum, bond beams should be placed at every bearing level (roof, floor, mezzanine, etc.) to help distribute gravity and lateral forces into the wall. additionally, i would place them at the top of walls to them everything together. it would also serve to anchor wood blocking for connecting the coping.
beyond this, there may be additional criteria for shear walls depending on the level of shear that you are trying to resist. there is also additional criteria for stack bond walls (48" oc). there may also be other structural reasons to add bond beams for special conditions.
twinnel,
as mentioned by jedclampett normally you would use lintels over opening rather than bond beams because they are cheaper. but there are a number of situations where a bond beam would be more suitable.
i imagine that this criteria is either for crack prevention, or for seismic ductility (is it in a high seismic area?).
i also agree with all jikes comments.
regards
csd
i believe that the wording of article 1.13 has changed over the years. when the seismic requirements were first introduced here in the east, they were not clearly understood. some designers would require both the horizontal joint reinforcing at 16 inches on center, and bond beams spaced at 10 feet on center. some of these old practices have carried over. if you have many windows lined up in a wall, it may be simpler to provide a continuous lintel rather than individual lintels over each window. some call this continuous lintel a bond beam.
there are also some difficulty in the nomenclature difference between bond beams and lintels. there is a major differences between the east and the west, where reinforced masonry is more established and common. the local differences compound this. unfortunately, codes write there own terminolgy in an effort to promote uniformity.
in general, bond beams provide vertical load distribution and continuity. lintels provide spanning strength over openings to cary the loads above that are not subject to arching action.
a bond beam is a horizontal course of block, usually the top course, but it may also be an intermediate course that replaces horizontal joint reinforcement or for code purposes. - jike's post reflects this classical use of a bond beam.
a masonry lintel is usually a course of block (usually 8" to 16"+) that is used over an opening.
in some cases (especially for smaller openings - less than 3' or so, the same block that is used in a bond beam with minimal reinforcement is a lintel.
for smaller openings and for architectural purposes and "bond beam" block is preferred for aesthetics and economy.
for longer spans, in many situations, a "bond beam" block with reinforcement is used on the first course of a lintel and the remaining courses above (1 to 3 or more) may be common block above for an aesthetic or economic purposes and the multiple couses of the lintel are filled together to construct the lintel. i have seen 4' high block lintels that project into the wall on the upper floor on 20 story buildings.
for good information on bond beams and lintels go to the national concrete masonry association site (ncma.org) and go to the tek notes area. they have over 100 tek notes that are prepared by engineers that serve on all national code and standards organizations.
dick
i have always used "lintel" to mean reinforced course(s) that span over openings, with a solid bottom required at the lowest course. everywhere else i call them "bond beams" where the webs are knocked out.
i believe fbc requires 10ft max spacing of "bond beams" or "tie beams" or whatever they call them in broward and dade county. you need to check your building code for special placings required other than what has already been mentioned.
jed,
you replied " it seems excessive to me and i've never seen it used. but i guess it's there."
do you mean that a bond beam every 10' is a bit excessive? if so, please explain.
i'm not trying to test you here, i'm trying to gather some insight on if a bond beam(s) is required in my design.
i've taken a glance at the masonry tek's as well, but i can't seem to find the bond beam location info i'm looking for.
unfortunately i'm not familiar with masonry, and i'm also from canada, so i'm not overly familiar with us codes, so bear with me if it's a bit of an obvious question.
thanks!
the 10' vertical bond beam spacing mentioned in 1.13.1 (seismic design requirements) is specifically noted in 1.13.2.2.2.1. this applies only when a bond beam is used to provide minimum reinforcing requirements in lieu of horizontal joint reinforcement at 16" o.c. (every other course of block). the purpose of the 10' spacing is to provide a reasonable distribution of steel in high walls instead of heavy bond beam steel at greater spacing.
a higher wall using joint reinforcement only needs a bond beam as the top course of the masonry for the purpose of continuity and load distribution. special loading conditions and load distributions could require other locations based on the geometry and loads.
dick
hunt007, i poorly worded that. to me, 10'-0" is too far between bond beams. we try to space them at no more than 4'-0" on center.
there's nothing in the code that says that you can't exceed the minimum.
jedclampett -
apparently you have very unusual conditions and applications to require 4' o.c. bond beams, unless you choose to eliminate horizontal joint reinforcement. the majority of masonry in the world is not even classified as "reinforced masonry" unless the design engineer is partial to that type of construction.
the special reinforced masonry shear walls (1.13.2.2.5) are not a very common occurance. when aci 530-20 was written, however, there was some concern that the reference to close spacing could easily be used out of context on common structures.
i have seen hundreds of up to 30 story load bearing masonry buildings built without "intermediate bond beams" because the situation never came up. - possibly because engineers dictate the structual wall layout and construction and not architects. - just basic meat and potatoes engineering to perform well.
dick

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