Role of Cover and Bar Spacing in Reinforced Concrete


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Title: Role of Cover and Bar Spacing in Reinforced Concrete

Author(s): Peter Gergely

Publication: Special Publication

Volume: 72


Appears on pages(s): 133-148

Keywords: building codes; corrosion; cover; crack width and spacing; fire resistance; re --- reinforcing steels; thickness. cracking (fracturing); inforced concrete;

Date: 12/1/1981

The effects of the thickness of concrete cover on corrosion, crack width, fire protection, and development length are examined. Increased cover thickness and concrete with low permeability are necessary for corrosion protection, though the former leads to wider surface cracks. However, transverse crack-ing and the width of cracks usually do not aggravate the corrosion problem. Thus it is not advisable in most structures to limit the surface crack width in order to avoid or reduce corrosion. Longitudinal cracks along the bar can cause rapid corrosion. The only reason for surface crack width limitation in buildings is appearance; fortunately recommended limits can usually be met even with heavy covers unless the beam is wide and the bar spacing is large. Fire damage to most indeterminate structures is dictated by thermal forces not as much by temperature rise of the steel. Determinate structures fail when a section loses its capacity but moderate covers are usually sufficient for fire protection of the steel. Crack width limits and cover requirements in current codes should be examined.