Civil Engineering Reference
In-Depth Information
Fountain Hills, Arizona Wastewater Treatment Plant. (Courtesy of Economy Forms Corporation.)
This ACI equation (10-3) for the minimum amount of flexural reinforcing can be
written as a percentage, as follows:
c
3
f
200
f
y
min
for flexure
f
y
Values of
min
for flexure have been calculated by the authors and are shown for several
grades of concrete and steel in Appendix Table A.7 of this text. They are also included in
Appendix Tables A.8 to A.13. (For SI units, the appropriate tables are B.7 to B.9.)
Section 10.5.3 of the Code states that the preceding minimums do not have to be met
if the area of the tensile reinforcing furnished at every section is at least one-third greater
than the area required by moment. Furthermore, ACI Section 10.5.4 states that for slabs
and footings of uniform thickness, the minimum area of tensile reinforcing in the direc-
tion of the span is that specified in ACI Section 7.12 for shrinkage and temperature steel.
When slabs are overloaded in certain areas there is a tendency for those loads to be dis-
tributed laterally to other parts of the slab, thus substantially reducing the chances of sud-
den failure. This explains why a reduction of the minimum reinforcing percentage is
permitted in slabs of uniform thickness. Supported slabs, such as slabs on grade, are not
considered to be structural slabs in this section unless they transmit vertical loads from
other parts of the structure to the underlying soil.
