Reinforced concrete bridges - Computational Analysis and Design of Bridge Structures - page 109

A

Abutment

Skew angle

Abutment A

Bridge clear span
Section A-A
Figure 4.6 Description of a skew angle using a skewed bridge over a highway. (Data from
Menassa, C. et al., Journal of Bridge Engineering , 12, 205-214, 2007.)

A nonskewed bridge deck behaves in flexure orthogonally in the lon-
gitudinal and transverse direction. The principal moments are also in the
traffic direction and in the direction normal to the traffic. The slab of this
type of bridges bends longitudinally leading to a sagging (or called positive)
moment as it is shown in Figure 4.7. The load from the slab is transferred
to reaction line directly through flexure. There will be a small amount of
twisting moment because of the bidirectional curvature, and it will be
negligible.
The force flow between the support lines in skew slabs is through the
strip of area connecting the obtuse-angled corners, and the slab primarily
bends along the line joining the obtuse-angled corners. The width of this
primary bending strip is a function of skew angle and the ratio between the
skew span and the width of the deck (aspect ratio). The areas on either side
of the strip do not transfer the load to the supports directly but transfer the
load only to the strip as cantilever as shown in Figure 4.8c. Hence the skew
slab is subjected to twisting moments. This twisting moment is not small
and hence cannot be neglected (Rajagopalan 2006). Because of this, the
principal moment direction also varies, and it is the function of skew angle