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What
is Vulcan?
Vulcan
is a three-dimensional frame analysis program, which has been developed
mainly to model the behaviour of skeletal steel and composite frames,
including the floor slabs, under fire conditions. Temperature distributions
across members can be non-uniform, causing differential thermal expansion
and a spread of elastic and inelastic properties across the section,
and a range of cross-sections can be defined, allowing different shapes
and materials to be represented.
The
structure is modelled as an assembly of finite beam-column, spring,
shear connector and slab elements. It is assumed that the nodes of
these different types of element are defined in a common fixed reference
plane, which is assumed to coincide with the mid-surface of the concrete
slab element. The beam-columns are represented by 3-noded line elements.
The cross-section of each element is divided into a number of segments
to allow variations in the temperature, stress and strain through
the cross-section to be represented. Both geometric and material
non-linearities are included. To represent the characteristics of
steel-to-steel connections in a frame, a 2-noded spring element of
zero length, with the same nodal degrees of freedom as a beam-column
element, is used. The interaction of steel beams and concrete slabs
within a composite floor is represented using a linking two-noded
shear-connector element of zero length, with three translational and
two rotational degrees of freedom at each node.
The
analysis includes geometric non-linearity in the slabs, using a quadrilateral
9-noded higher-order isoparametric element. This includes a modified
layered orthotropic formulation based on Mindlin/Reissner theory,
and using an effective stiffness model to model the ribbed nature
of typical composite slabs. The temperature and temperature dependent
material properties can be specified independently. A maximum-strain
failure criterion has been adopted for the concrete, and a smeared
model has been used in calculating element properties after cracking
or crushing. After the initiation of cracking in a single direction,
concrete is treated as an orthotropic material with principal axes
parallel and perpendicular to the cracking direction. Upon further
loading of singly cracked concrete, if the tensile strain in the direction
parallel to the first set of smeared cracks is greater than the maximum
tensile strain then a second set of cracks forms. After compressive
crushing, concrete is assumed to lose all stiffness. The uniaxial
properties of concrete and reinforcing steel at elevated temperatures,
specified in EC4, have been adopted in this model.
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