FIGURE 45. Moment distribution.
- Calculate the unbalanced moments
Computing the unbalanced moments at B and C yields the following: At B, +54.0 - 48.0 =
- 6.0 ft-kips (8.14 kN-m); at C, +48.0 - 78.8 = -30.8 fit-kips (-41.76 kN-m).
- Apply balancing moments; distribute them in proportion to the
stiffness of the adjoining spans
Apply the balancing moments at B and C, and distribute them to the two adjoining spans
in proportion to their stiffness. Thus MBA = -6.0(15/31) = -2.9 ft-kips (-3.93 kN-m);
MBC = -6.0(16/31) = -3.1 ft-kips (-4.20 kN-m); MCB = +30.8(16/25) = +19.7 ft-kips
(26.71 kN m); MCD = +30.8(9/25) = +11.1 ft-kips (15.05 kN-m).
5. Perform the "carry-over" operation for each span
To do this, take one-half the distributed moment applied at one end of the span, and add
this to the moment at the far end if that end is considered to be fixed during moment dis-
tribution.
F.e.m., ft • kips
(klM-m)
1st distribution
Carryover
2nd distribution
Carryover
3rd distribution
Carryover
4 th distribution
Carryover
Final moments
Length (N.T.S.)
