Vaddamani, Varun Teja and Agarwal, Anil
(2017)
Modelling Thermal Insulation Effect of the Interface
between Steel Deck and Concrete Slab in Composite Slab
Systems in Fire Conditions.
Masters thesis, Indian institute of technology Hyderabad.
Abstract
Steel-concrete composite slabs are gaining importance, due to the ease of construction
without heavy lifting machinery and also the performance of steel decking as a
permanent formwork and external reinforcement. At elevated temperatures, steelconcrete composite slabs experience debonding of steel deck from the concrete slab.
This debonding creates a layer of air which offers thermal resistance to the rise of
temperature in the concrete slab. There is very limited numerical or analytical work
in the literature that provides a rational framework for thermal resistance offered by
this intermediate layer. Experiment data to support the modelling research is also very
sparse.
As a consequence of de-bonding of steel deck from the concrete slab, the heat
transfer from the steel deck to the concrete slab is through radiation and conduction
of the intermediate air layer. Preliminary structural analyses of the composite floor
systems reported in the literature showed that a proper temperature calculation of the
steel deck as well as concrete slabs is of great importance for the thermal gradient of
the slab and thus for global load redistribution. The temperatures have a simultaneous
effect on mechanical behaviour; and also the mechanical behaviour has a direct effect
on temperatures, which can be understood through a fully coupled thermal-stress
analysis. ABAQUS software is used for performing numerical simulations. However,
there are certain limitations while defining the parameters of radiation.
The present work addresses a way to include the radiation
effect due to debonding of steel deck in steel concrete composite slab, under standard
fire conditions. The factors influencing the radiative heat transfer are studied in detail.
As a first step, an uncoupled heat transfer analysis has been performed over a section
of steel-concrete composite slab taking into account the radiation and conduction
properties using interface elements. The radiation properties are accounted for, using
equivalent conductance for the interface elements as a function of temperature. The
concrete slab, the interface element and the steel deck are modelled using DC2D4
elements. Material properties for steel and concrete are adopted from Eurocode.
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