The behaviour of steel and composite beam-to-column connections in fire.

Recent fire tests on the Cardington full-scale test frame and observations
from
real
fires
have demonstrated the significance of connections
in fire, when
they can have
beneficial effects on
the survival time of the structure. The lack of experimental data on
the behaviour of steel and composite connections
in fire means
that this is insufficiently
addressed
in current design codes and also
limits the effective use of numerical models.
However,
recent experimental
tests on small-scale specimens have shown that it is
possible
to derive accurately the moment-rotation relationships at elevated
temperature
and have established the principles by which
this could be achieved.
In order to extend the scope
to include further parameters,
five series of tests have been
carried out
in a portable connection
furnace at
the Building Research Establishment.
The test series
includes flush and
flexible end-plate bare-steel connections, and
flexible
end-plate composite connections. The testing procedure and the resulting behaviour are
described. The fire test temperature profiles across the connections are detailed and
the
connection
failure mechanisms are discussed. From the test results, moment-rotation-
temperature curves
for different
connection
types are derived. The degradation of
connection characteristics
is compared with
that of structural steel. The experimental
behaviour is also compared with the results obtained
from an existing
finite element
analysis developed to model connection response
in fire conditions.
The experimentally derived connection characteristics have been incorporated within a
parametric study of a typical sub-frame, to study
the effect of connection type, end-plate
thickness, concrete strength,
load
ratio, and connection
temperature. Analysis is
extended to a three-dimensional sub-frame.
The patterns of behaviour observed
in the connection
tests is compared with
that of the
connections
in the large-scale fire tests on the composite building at BRE's Cardington
laboratory.
Based on
knowledge about the behaviour of connections at elevated
temperature, a
component-based model
is developed for the elevated
temperature response
for flexible
end-plate connections, both as bare-steel and composite. This is based on the response
of constitutive parts of connection. The model
is easy
to use, and capable of modelling
the entire non-linear range of connection behaviour. The predicted response
is
compared with that recorded experimentally.