Prestressed/post-tensioned concrete bridges - Computational Analysis and Design of Bridge Structures - page 130

Stage 1: Tensioning of prestressing strands in stressing bed before casting concrete.

1 2

Stage 2: Placement of concrete in forms and around tensioned strands.

2

1

Stage 3: Release of strands causing shortening of member.
Stage 4: Member placed on piers and/or abutments and deck slab, if any, cast.

Stage 5: Full-service load after all prestress losses.

(a)

1 2 3 4 5

Tensioning of
prestressing
strands

Concrete
placement

Release of
strands

Member
installation

Stage Full load

Location 1
(at transfer
length)

Location 2
(at midspan)

(b)

Figure 5.1 (a) Prestress loading stages. (b) Stress distribution at various loading stages.

Different from pretensioning, post-tensioning is the application of a com-
pressive force to the concrete at some point in time after casting. Post-
tensioning tendons may be installed through voids formed by ducts cast
into the concrete—in which case, they are internal tendons—or they may
be installed outside the concrete itself—in which case, they are external