huangyhg

grade beam construction joints
anyone know of a code mandated construction joint distance? i have a typical wall construction joint distnace not to exceed, and now the question has come up - "what about the grade beams, then?".

i've never used any mandated spacing of construction joints in concrete grade beams. the spacing of cj's are left up to the contractor which depends upon crew size, availability of concrete, etc.
in the past, i have specified a limit of 400 cy of concrete in one day's placement - but haven't done that for a while as i think it invades the means and methods of the contractor.
in terms of controlling cracks, etc., i wouldn't think it necessary to use cj's at all unless the grade beam is some kind of wall system where large areas of concrete were exposed to view. in that case, i'd probably specify vertical formed goove joints near midspan.
i know of no code mandated requirements for spacing of joints. in aci 350, there used to be a chart or table that gave recommended percentages of steel for different joint spacing. keep in mind that this is for sanitary engineering structures, not buildings but it can give you some guidelines. i do not know if the chart or table is in the latest version of that code.
the larger amount of longitundinal steel, the farther apart the spacing of the joints can be. the steel helps reduce the cracking. since a grade beam typically has more longitundinal steel than a wall, the spacing between joints can be further apart than walls.
during the wpa programs of the 30's, many gravity retaining walls (railroad grade separation projects) were poured with no longitudinal steel. if i recall correctly, they limited the joint spacing to 20 feet. this, therefore, could be considered as a lower bound for joint spacing with no longitudinal steel.

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