Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 137

5.2.2 tendon modeled as load-resisting elements
The tendon is not considered to be removed from the concrete member.
Rather, it is modeled as a distinct element linked to the concrete mem-
ber (Figure 5.10). The change in the prestressing force is automatically
accounted for in the equilibrium equations set up for the analysis of the
segment.
For tendons modeled as resisting elements, four post-tensioning analysis
types are shown in Figure 5.11: (1) beam type, (2) tendon type, (3) plane
stress type, and (4) solid type. The former two are used in routine bridge
analyses, whereas the latter two with more detailed modeling technique
are used more in research or forensic analysis (LUSAS 2012). For post-
tensioning, the tendons can be either external or internal where internal
tendons can be either bonded or unbonded (Figure 5.12).

5.2.3 2d and 3d modeling
Based on the discussion in Section 2.4.5, two-dimensional (2D) or three-
dimensional (3D) models can be generated based on the project's needs.
For a 2D model, only one beam is considered and section properties of
that beam are based on the locations of their respective neutral axes. Two
2D beam models representing two different stages of noncomposite and

Tendon truss element

Tendon initial
length (force)

Rigid link

Node I
(b)

Beam frame Node J

(a)

Continuity tendon
truss element

Cantilever tendon
truss element

Rigid link

Beam frame element

(c)

Figure 5.10 Tendon modeled as an element linked to the concrete member. (a) Tendon
as element. (b) Tendon element geometry. (c) Finite element modeling of
the segmentally erected bridge with post-tensioning tendons.