Boundary conditions that MIDAS/Civil allows include
General Spring Supports,
which are capable of representing lateral stiffness
of piles. Compression-only
and Tension-only elements are also provided
to represent the compression characteristics of foundation
and tension members respectively.
Boundary Condition
Surface Spring Supports
can represent the boundary conditions of foundation
mats or tunnels that are in contact with sub-soils.
It auto-calculates equivalent
spring stiffness based on the modulus of subgrade reactions
and effective contact areas of plate or solid elements.
Elastic Link, on the
other hand, can be applied to simulate
elastic bearing pads when analyzing bridge
structures. It eliminates the need for modeling the
pads as fictitious beam elements. Specifying the stiffness
in the relevant directions is all that is required to
calculate the reactions. Similarly, Rigid Link is used
to represent infinitely stiff elements. Plate
End Release together with Beam End Release
is used to represent pinned conditions of elements'
ends. Node Local Axis
is used when the directions
of the supports are skewed from the global
coordinate system. An example may be an arch bridge
having inclined supports at abutments.
Skewed boundary conditions on a curved bridge with lane
expansion
Rigid Link representing a bearing pad separation between
the bridge
box girder and support pier
Main tunnel lining attached to an emergency access,
modeled
by auto-generation showing equivalent soil springs
