Civil Engineering Reference
In-Depth Information
s
y
estimate for
t
max
is
p
, where
s
y
is the Mises yield stress of the material adja-
cent to the surface. It should be noted that ABAQUS [1.29] offers the option
of specifying an infinite coefficient of friction (
m¼1
). This type of surface
interaction is called “rough” friction, and with it, all relative sliding motion
between two contacting surfaces is prevented (except for the possibility of
“elastic slip” associated with penalty enforcement) as long as the correspond-
ing normal-direction contact constraints are active. Rough friction is
intended for nonintermittent contact; once surfaces close and undergo
rough friction, they should remain closed. Convergence difficulties may
arise in ABAQUS if a closed contact interface with rough friction opens,
especially if large shear stresses have developed. The rough friction model
is typically used in conjunction with the no separation contact pressure-
overclosure relationship for motions normal to the surfaces, which prohibits
separation of the surfaces once they are closed. It should also be noted that in
ABAQUS [1.29], the sticking constraints at an interface between two sur-
faces can be enforced exactly by using the Lagrange multiplier implementa-
tion. With this method, there is no relative motion between two closed
surfaces until
t¼t
crit
. However, the Lagrange multipliers increase the com-
putational cost of the analysis by adding more degrees of freedom to the
model and often by increasing the number of iterations required to obtain
a converged solution. The Lagrange multiplier formulation may even pre-
vent convergence of the solution, especially if many points are iterating
between sticking and slipping conditions. This effect can occur particularly
if locally, there is a strong interaction between slipping/sticking conditions
and contact stresses.
5.3 CHOICE OF FINITE ELEMENT MESH FOR THE BRIDGES
AND BRIDGE COMPONENTS
The brief survey of the different finite elements mentioned earlier, available
in ABAQUS [1.29] element library, provided a useful background to help
beginners to choose the best finite element types to represent the different
components of steel and steel-concrete composite bridges. After choosing
the best finite element type, we need to look into the geometry of the bridge
and the bridge components to decide the best finite element mesh. Now, we
need to differentiate between modeling the individual bridge components
and modeling the whole bridge. To make it clear for readers, if we, for
example, model the shear connection of headed stud shear connectors in
solid concrete slabs, we will include the exact dimensions of the connection
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