Approximate and refined analysis methods - Computational Analysis and Design of Bridge Structures - page 20

Column: Moments + axial forces
Deck: Moments

Column: Axial forces
Deck: Moments

(a) (b)

Column: Moments + axial forces
Deck: Moments

Column: Moments + axial forces
Deck: Moments + axial forces

(c) (d)

Figure 2.4 Frame-type bridges and internal forces under main loads.

is orthotropic if its stiffness properties are different in two perpendicular
directions. The slab bridges based on their composition can be divided into
the following types:

1. Solid Slab (Figure 2.5a). Concrete solid slabs are commonly used where
the spans are less than 15 m (50 ft). A solid slab is acting and can be
assumed as an isotropic plate, even though the reinforcement may be
different in two perpendicular directions.

2. Void Slab (Figure 2.5b and c). For spans greater than 15 m (50 ft),
the dead load of solid slabs becomes excessive and the structure can
be lightened by incorporating cylindrical or rectangular voids. It acts
as an orthotropic plate and is treated customarily as one unit. If the
void size exceeds 60% of the depth, the deck is generally considered as
cellular (box) construction. For the type with large void, the distribu-
tion of the loads transversely is by transferring vertical shear through
webs; the cross section distorts like a Vierendeel truss.

3. Corrugated (Coffered) Slab (Figure 2.5d) or Precast Beam Slab
(Figure 2.5e). Precast beams of various cross-sectional shapes of

(a) (b)

(c) (d)

(e) (f )

Figure 2.5 Slab bridge types: (a) solid slab; (b) circular void slab; (c) rectangular void slab;
(d) corrugated slab; (e) precast beam slab; (f) shear-key slab.