Parametric studies on the temperature dependent behaviour of steel structures within a fire context.
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Date
2012
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Abstract
The mechanical and material properties of structural steel at elevated temperatures play
an important role in structural fire design. The South African 350W and S355 structural
steels are common in building structures with S355 slowly replacing the older 350W. The
cost and feasibility of full scale fire tests are some of the causes for the lack of
experimental data on the behaviour of steel structures when exposed to fire. Therefore
excessively conservative design codes based on isolated laboratory experiments are used
in practice which leads to increased material costs. Another area of concern with respect
to building safety is the reusability of structural steels post fire exposure, which is not
effectively addressed within these codes.
This study aims to establish greater insight into structural fire design and simulation on
which further research can be built. Experimental programs on the temperature
dependent behaviour of these steel members loaded axially are conducted and compared
with theory and the Eurocode 3 standard [1]. The reusability of steel exposed to fire and
after being cooled down is investigated and compared to the findings by Outinen [2].
Further testing on material to determine the relationship between remaining life and
hardness degradation after cooling down was conducted.
Experimental data from various external studies are used to develop novel computer
models using the finite element analysis software, SimXpert [3]. These are verified against
the original data and compared to existing design codes. A parametric approach is used
with these models to demonstrate the advantages of computer simulations in structural
fire design. Different cross sections and slenderness ratios are evaluated for their
susceptibility to buckling at elevated temperatures.
The results of this study show that as temperature and exposure time increase the
integrity of steel members decrease. The current design codes accurately predict the
behaviour of isolated specimens but lack data on real situations where the specimen is
part of a complex structure. It was found that steel members can be reused if their
exposure temperature does not exceed 700°C, after which their strength can reduce to
90%. This temperature dependant behaviour was successfully modelled using basic
computer simulations and then demonstrated the ease in which they can be used in place
of experimental regimes. The parametric advantages of these simulations were
demonstrated by predicting the effects of slenderness ratios and geometry cross sections
on the buckling behaviour.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2012.
Keywords
Steel, Structural--Testing., Steel, Structural--Fatigue., Building, Fireproof., Fire protection engineering., Fire resistant materials., Theses--Mechanical engineering.