The structural response of industrial portal frame structures in fire.

A number of recent
fires in
single-storey warehouses have drawn attention
to a
current
lack of understanding about the structural response of
industrial
portal
frame
structures to elevated
temperatures. This
research project has investigated the
subject by conducting
fire tests on a scaled model and by computer modelling using
the non-linear
finite element program VULCAN. This program has been developed
in-house by the University of Sheffield and
is capable of modelling
the behaviour of
three-dimensional steel and composite
frames at elevated
temperatures. It has been
validated throughout its development. An initial investigation was conducted to
validate the program
for analysing
inclined members, which
form part of a pitched-
roof portal
frame, but for which
it was not
initially developed. Additional features
were
implemented into the program where necessary.
A series of
indicative fire tests was conducted at
the Health and Safety Laboratories,
Buxton. A scaled portal
frame model was designed and built, and
three major
fire
tests were conducted
in this structure.
In the third of
these tests the heated
rafters
experienced a snap-through
failure mechanism,
in which
fire hinges could clearly be
identified. The experimental results were
then used
for validating the numerical
results produced by VULCAN analyses. The correlations were relatively close, both
for predictions of displacements and
failure temperatures. This gave
increased
confidence
in using VULCAN to conduct a series of parametric studies. The
parametric studies
included two- and
three-dimensional analyses, and a number of
parameters were
investigated, including
the effects of vertical and horizontal load,
frame geometry, heating profiles and base
rotational stiffness. The influence of
secondary members was
investigated in the three-dimensional studies using different
fire
scenarios.
A simplified calculation method has been developed for estimating the critical
temperatures of portal
frames in fire. The
results compare well with predictions
from
VULCAN. The current guidance document for portal
frames in boundary
conditions
has been
reviewed, and
the concept of performance-based design for portal
frame
structures has been discussed.