Simplified Frame Analysis - Simplified Design of Reinforced Concrete Buildings - page 39

˜

2

w a

A

˜

2

w a

6

12

˜

2

w a

B

C

4

L span

L column

Face of col .

Modified

2 a Computed

from analysis

˜

2

c
2

w a

=

12

L

(A) = Theoretical moment
(B) = Computed moment ignoring stiffening effect of column support
(C) = Modified moment at face of column

w

= uniformly distributed factored load (plf)
= span length center-to-center of supports
= width of column support
= c/

˜

c
a

˜

Figure 2-10 Correction Factors for Span Moments 2.2

2.4.4 Two-Cycle Moment Distribution Analysis for Gravity Loading

Reference 2.2 presents a simplified two-cycle method of moment distribution for ordinary building frames.
The method meets the requirements for an elastic analysis called for in ACI 8.3 with the simplifying assump-
tions of ACI 8.6 through 8.9.

The speed and accuracy of the two-cycle method will be of great assistance to designers. For an in-depth
discussion of the principles involved, the reader is directed to Reference 2.2.

2.5 COLUMNS

In general, columns must be designed to resist the axial loads and maximum moments from the combination
of gravity and lateral loading.

For interior columns supporting two-way construction, the maximum column moments due to gravity loading can be
obtained by using ACI Eq. (13-7) (unless a general analysis is made to evaluate gravity load moments from alternate
span loading). With the same dead load on adjacent spans, this equation can be written in the following form:

( ) + 0.5q Lu

⎣ ⎦ 2

M u = 0.07 q Du

2
n

− ʹ

2 2

n n