Straight and curved steel I-girder bridges - Computational Analysis and Design of Bridge Structures - page 232

of small, refined submodels, or the local models, which are extracted from
the global model. When extracting local models, enough buffer zones sur-
rounding the focus area should be included in the refined local models so
that the effect of the notch stress concentration may be negligible. Local
model at midspan girder 3 is shown in Figure 7.39.
The interest of this project is to determine the location of fatigue crack,
crack path, and crack rate; the global model of the whole bridge cannot be
more refined, and therefore the local model of this critical region can be
facilitated for this purpose. It is a common issue and also crucial in modeling
a local refined model that the boundary conditions of a local model are set
up correctly to truly reflect its mechanical connections to the global model.
Boundary conditions of the local model —To set up the boundary condi-
tions, the following guidelines should be followed:
1. The boundary nodes should apply the same displacements obtained
from the global model.
2. The boundary nodes should apply the same external forces obtained
from the global model as internal forces.
In the local model to investigate the hot spot at the connection plates of
the K-type bracing, equivalent forces were applied at the other ends of the
K-type bracing. Results obtained from the local model can be used for the
calculation of SCF for fatigue study of the hot spots.