Curved concrete bridges - Computational Analysis and Design of Bridge Structures - page 178

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(b)
Figure 6.5 Modeling of curved concrete box bridges. (Data from Nutt, R. and Valentine, O.,
“NCHRP Report 620—Development of Design Specifications and Commentary
for Horizontally Curved Concrete Box-girder Bridges,”Transportation Research
Board, Washington, DC, 2008.) (a) Typical spine beam model. (b) Typical grillage
model.

monolithically single-column bent where the super- and substructures
are tied together. This model uses frame elements, effective bending
stiffness, cap with large torsional and transverse bending stiffness to
capture superstructure (Caltran 2012). The calculation of bending and
torsional stiffness can be found in Chapter 2.

2. Grillage model. However, spine model cannot capture the super-
structure carrying wide-roadway, high-skewed bridges. In these cases
grillage model as shown in Figure 6.5b is recommended (Caltran
2012). Grillage models are used regularly for modeling steel compos-
ite deck superstructures. For complicated concrete structures where
superstructures cannot be considered stiff such as very long and nar-
row bridges and interchange connectors, grillage models can be used.
This analysis approach requires the structure to be modeled as a 3D
grid of frame elements in which the superstructure is comprised of
both longitudinal and transverse beams located at the vertical center
of gravity of the superstructure. Section properties are based on the
box section with equivalent effective width as shown in Chapter 2.

For bridges with single- or multicell box (or spread multiple boxes)
as shown in Figure 6.1, properties can be calculated as shown in