Concrete Design Ali N. Attiyah, Ph.D.
Fourth Year 2015-2016
1
Lecture four
Direct Design Method
The first step of DDM is calculating the total static factored moment.
The span lengths in Eq. 8.10. are defined as follows:
Concrete Design Ali N. Attiyah, Ph.D.
Fourth Year 2015-2016
2
If the column is not square or rectangular, the equivalent area is used to find its face.
The second step of DDM is distributing M
o
to positive moment at the middle of span and
negative moments at supports. The degree of restraining to rotation at supports will
govern the distribution, so, if the supports are fully retrained, the negative moment will
2/3 M
o
.
Concrete Design Ali N. Attiyah, Ph.D.
Fourth Year 2015-2016
3
According to ACI 8.10.4, the positive and negative moments are:
Concrete Design Ali N. Attiyah, Ph.D.
Fourth Year 2015-2016
4
Example: