STEEL - Materials for Civil and Construction Engineers - page 109

situation. In conventional reinforcing, the stresses fluctuate with loads on
the structure. This does not place any special requirements on the steel. On
the other hand, in prestressed reinforcement, the steel is under continuous
tension. Any stress relaxation will reduce the effectiveness of the reinforce-
ment. Hence, special steels are required.
Reinforcing steel (rebar) is manufactured in three forms: plain bars, de-
formed bars, and plain and deformed wire fabrics. Plain bars are round,
without surface deformations. Plain bars provide only limited bond with the
concrete and, therefore, are not typically used in sections subjected to ten-
sion or bending. Deformed bars have protrusions (deformations) at the sur-
face, as shown Figure 3.10; thus, they ensure a good bond between the bar
and the concrete. The deformed surface of the bar prevents slipping, allow-
ing the concrete and steel to work as one unit. Wire fabrics are flat sheets in
which wires pass each other at right angles, and one set of elements is par-
allel to the fabric axis. Plain wire fabrics develop the anchorage in concrete
at the welded intersections, while deformed wire fabrics develop anchorage
through deformations and at the welded intersections.
Deformed bars are used in concrete beams, slabs, columns, walls, foot-
ings, pavements, and other concrete structures, as well as in masonry con-
struction. Welded wire fabrics are used in some concrete slabs and pavements,
mostly to resist temperature and shrinkage stresses. Welded wire fabrics can
be more economical to place, and thus allow for closer spacing of bars than
is practical with individual bars.

FIGURE 3.10 Steel rebars used to reinforce PCC columns.