Civil Engineering Reference
In-Depth Information
(a)
Timber tie
Deck girder
Cross brace
(b)
hrough girder
Knee brace
Stringer
Timber tie
Floorbeam
FIGURE 3.13
(a) Open deck plate girder (DPG) span. (b) Open through plate girder (TPG)
span.
3.3.2.1.3 Ballasted Bridge Decks
Closed or ballasted steel plate and concrete slab deck bridges are common in new
railway bridge construction. On ballasted or closed bridge decks, track ties are laid
in stone ballast that is supported by steel or concrete decks (
Figures 3.14a
and b).
The deck design may be composite or noncomposite. Dead load can be considerable,
but dynamic effects are reduced and train ride quality is improved due to a relatively
constant track modulus.
Steel plate decks are usually of isotropic design as orthotropic decks are often
not economical for ordinary superstructures due to fabrication, welding, and fatigue
design requirements. However, steel orthotropic plate modular deck construction is
an effective means of rapid reconstruction of decks on existing steel railway bridges.
Cast-in-place reinforced concrete and reinforced or prestressed precast concrete con-
struction can also be used for deck slabs. Composite steel and concrete construction
is structurally efficient (see Chapter 7), but may not be feasible due to site constraints
(i.e., need for falsework and site concrete supply). Noncomposite precast concrete
deck systems may be considered when site and installation time constraints exist in
the particular railroad operating environment. However, precast concrete decks may
be made composite with steel superstructures by casting recesses for shear connection
