Advanced Methods of Structural Analysis

76 3 Multispan Beams and Trusses

3.11.A design diagram of a truss is presented in Fig.P3.11. Moving loads are
applied to the lower chord.

(a)Perform the kinematical analysis; (b) Construct the influence lines for the inter-
nal forces in the indicated members; (c) Using the constructed influence lines,
compute the indicated internal forces if external forcesP 1 andP 2 are placed at
joints 7 and 9, respectively.

h

d

a

3579

2

1

D2–5

U7–9

Fig. P3.11

Ans.U 7 - 9 D

9d

4h

P 1 C

d

h

P 2 ID 2 - 5 D

3

8 cos ̨

P 1 C

1

2 cos ̨

P 2

3.12.A design diagram of a truss with over-truss construction is presented in
Fig.P3.12. Pinned supportsAandBare located at different elevations. Panel block
1-2-3-4 has no diagonal member. The vertical members (links) are used only to
transmit loads directly to the upper chord of the truss. Provide kinematical analy-
sis. Construct the influence line for thrustH. Using the constructed influence line,
computeHif forcesP 1 andP 2 are placed at joints 10 and 20 , respectively. What
happens to the structure if supportsAandBare located at one level?

l

h

A

3 4

B

x 1 x 2

1 2

1 ′ 2 ′

Fig. P3.12

Ans.HD

l

2h

P 1 

3l

8h

P 2