3.1 Multispan Statically Determinate Beams 43
second support of the suspended beam. This procedure is called as distribu-
tion of influence lines within the suspended beam.
Step 4.The beam distribution procedure should be applied for the following sus-
pended beam.
To illustrate this procedure for statically determinate multispan beams we will
consider a structure as in Fig3.6. It is necessary to construct the influence lines
for reactions, bending moment, and shear for indicated sections. We are starting
from kinematical analysis of a structure: this beam is statically determinate and
geometrically unchangeable structure.
Inf. line
Mn (m)
1.5
1
+
Inf. line RD
1
0.333
+
Inf. line Qn
1
0.5 1
0.5
+ 5
−
0.333
1
Inf. line Qs
+
0.4
2
Inf. line
− Ms (m)
0.8
5m 2m 3m 3m 2m 3m
A
H 1
B C D
H 2 H 3
P= 1
3m
s k n
2m
BH^2 H^3 C D
A H 1
Fig. 3.6 Multispan statically determinate beam. Influence lines for reactions, bending moment
and shears at some sections
Influence Line forRD
The structural element is beamH 3 CD. Influence line for reactionRDwithin the
spanCDis a straight line with ordinate 1 at supportD, zero at supportC,and
extended within left-hand and right-hand overhangs.