Concrete rebar placement factor
Concrete rebar placement factor
(OP)
In the Canadian concrete code, there is a modification factor for the development length that is dependent on whether or not the rebar is "top" tension steel or "bottom" tension steel. I understand how to differentiate between the two, but what is the reason for this modification factor?
The code simply states that the factor was reduced from a previous edition, but gives no explanation as to why "top" steel requires a larger development length.
Thanks,
Mike
The code simply states that the factor was reduced from a previous edition, but gives no explanation as to why "top" steel requires a larger development length.
Thanks,
Mike






RE: Concrete rebar placement factor
The reason is the top 30 cm of the members be thought less compact than the lower concrete and hence the bond there being as well lesser.
RE: Concrete rebar placement factor
"so placed that more than 300mm of fresh concrete is cast in the member below the development length or splice."
So in a wall, the horizontal rebar could be 12" above the footing (with say 7 ft of concrete above it)and be considered top bar, thereby requiring extra development length.
I think someone said once that it had something to do with air bubbles genereated in the curing process, but I can't remember the exact reason.
RE: Concrete rebar placement factor
DaveAtkins
RE: Concrete rebar placement factor
RE: Concrete rebar placement factor
With extra concrete below the bar, there is the potential for the semi-set concrete to sluff downward, creating small voids directly below the bar, thus reducing its bond.