Design Examples of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 239

moment is decreased towards the supports. Therefore, we can stop the top
flange plate at a certain distance to get the most benefit from the material.
This process is commonly called as curtailment (transition) of flange plates.
It should be noted that, theoretically, curtailment (transition) of flange plates
can be conducted by reducing the flange plate width, thickness, or both.
However, in practice, fabricators prefer to keep the flange widths constant
and vary the thickness because this option costs much less than reducing the
flange width that might require a very heavy grinding work. To avoid lateral
torsional buckling of the compression top flange at the reduction zone, it is
recommended practically to reduce the width or thickness by 40% of the
original with a smooth transition zone sloping at 1 (vertical) to 10 (horizon-
tal). It is also recommended that bridges with lengths of 20-30 m are cur-
tailed (transitioned) in one step. While for bridges with spans greater than
30 m, two steps of curtailment (transition) are recommended. For the inves-
tigated design example, we can conduct one-step curtailment (transition) by
reducing the top flange plate of the upper and lower flanges, as shown in
Figure 4.18 . To classify the reduced cross section,

s

235
f y

r

235
275

e ¼ ¼ ¼ 0 : 924

3

38

55

57

y y

y 1 y 1

1.6

150

y 0

y 0

60

Figure 4.18 Calculation of properties of area for curtailed main plate girder.