Civil Engineering Reference
In-Depth Information
(a)
Differential tie dapping (notched shear strength
may govern depth of dap)
(b)
Variable deck support elevation (small wedge
or angular dap required)
(c)
Tie shimming
(d)
Tie tapering
FIGURE 3.9
Track superelevation on open deck bridges.
large cranes) and to preclude uplift that may occur due to the large railway live load
to superstructure dead load ratio. Nevertheless, curved girders are often effectively
utilized for light transit applications.
3.2.4.1.3 Skewed Bridges
Skewed bridges have been considered as a necessary inconvenience to an abomination
(Waddell, 1916) by bridge designers. There are many salient design and construction
reasons for avoiding skewed bridge construction. Torsional moments and unequal
distribution of live load occur with larger skew angles and compromise performance.
Also, skewed spans generally require more material than square spans and include
details that increase fabrication cost. However, on occasion, and particularly in con-
gested urban areas or where large skew crossings exist, skewed construction may be
unavoidable.
Many railroads have specific design requirements regarding skew angle and type
of construction for skewed railway bridges. Skew connections and bent plates may be
prohibitedrequiringthatthetracksupportattheendsofskewedspansbeperpendicular
to the track. This can be accommodated many ways depending on bearing and span
types.
Figure 3.10
shows examples of two types of floor systems in skewed spans
over a pier.
