Advanced Methods of Structural Analysis

3.4 Trusses with Subdivided Panels 59

and (2). However, for modification (3) thisstructure becomes geometrically change-
able and cannot be used as an engineered structure. Unfortunately, some modern
software will work out a numerical analysisfor any structure, even if the structure
is changeable. Therefore, in order to avoid structural collapse, each engineer must
complete a kinematical analysis as the very first step.
The entire structure in Fig.3.18can be represented as a combination of main
and secondary trusses. A feature of this subdivided Warren truss is the following:
if the load is located on joints 10 , 30 , 50 , etc. of the secondary trusses on thelower
chord, then the reactions of the secondary trusses are transmitted as active loads to
the joints of thelowerchord of the main truss.

Inf. line U5–5′

+

3 d

h

3 d

h

1

2 tana Right-hand portion

1

2 sina

− Inf. line D^4 ′−^7 =D^4 ′−^5

1

1 ′ 357

0

13

911

264128 10

3 ′ 5 ′ 7 ′

0 ′ 10 ′

9 ′ 11 ′

Entire 2 ′ 4 ′ 6 ′ 8 ′

structure h

a

+ 2 tana Inf. line U 5 ′−7=U 5 ′−5

1

1

Inf. line V2–3

+

Inf. line D 4 ′–5

1

(^1) 2 sina
sina
−

• Connecting line for D 5 − 6
  Right-hand portion
  Left-hand portion
  4 ′
  5 ′ d
  1 ′
  (^357)
  4 ′
  5 ′
  5 a 7
  Main truss Secondary truss
  Combination of main and secondary trusses
  sec
  sec sec
  main
  Connecting line for Umain
  5 − 7
  Fig. 3.18 Influence lines for internal forces for subdivided Warren truss
  Now we will consider the construction of influence lines for reactions and in-
  ternal forces of elements belonging to three different groups, i.e., to the main truss
  only, to a secondary truss only, and to both trusses simultaneously. These elements
  are indicated in Fig.3.18.