Structural vulnerability analysis of civil infrastructure facing seismic hazards - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 209

3

3

3

3

1 2

1 2

1 2

1 2

4

4

(a) (b)

3

3

1

1

2

1 2

2

1 2

(c) (d)

8.1 Structural rings: (a) a just-stiff ring; (b) a mechanism; (c) an over-
stiff ring; and (d) an open ring.

4

4

3

4

D

1

3

3

D C

3 4

1

A

A

4

3

1

1

2

C

2

B

B

1 2

2 2

Ball-jointed structure 2D rings 3D round

(a)

1

2

2
3

2

1 B 2

A

1 A B

1 3

4

4 3

3
4

1 C

1

1

C

4

Rigid jointed structure 2D rings 3D round

(b)

8.2 Structural rounds: (a) a ball-jointed round and (b) a rigid-jointed
round.

over-stiff ring is obtained (Fig. 8.1c). A fl exural member can be represented
as a ring with a cut (Fig. 8.1d).
A structural round is composed of 2D structural rings described above.
It can resist loads from any arbitrary direction in space. Figure 8.2(a) shows
the simplest ball-jointed structural round (a tetrahedron) which has four
rings. It is called a basic round, because many trusses can be built by adding