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|Title: ||Damaged reinforced concrete structures in fire|
|Authors: ||Ervine, Adam|
|Supervisor(s): ||Gillie, Martin|
|Issue Date: ||25-Jun-2012|
|Publisher: ||The University of Edinburgh|
|Abstract: ||It is crucial for a building to maintain structural stability when subjected to
multiple and sequential extreme loads. Safety and economic considerations
dictate that structures are built to resist extreme events, such as a earthquakes, impacts, blasts or fires, without collapse and to provide adequate
time for evacuation of the occupants. However, during such events, some
structural damage may be permissible. Design codes do not account for the
scenario where two extreme events occur consecutively on a structure nor
do they address the situation of the structure having some initial damage
prior to being subjected to a fire load.
This work begins by detailing the major inconsistancies between designing
reinforced concrete structures for extreme mechanical loads and designing
for fire. The material behaviour and traits of the constitutive parts (i.e.
the concrete and the steel), including post yielding behaviour, thermal relationships and their interaction with each other are all explored in detail.
Comprehensive experimental and numerical investigations are undertaken
to determine whether, and to what extent, phenomena such as tensile cracking and loss of the concrete cover affect the local and global fire resistance
of a member or structure.
The thermal propagation through tensile cracks in reinforced concrete beams
is examined experimentally. A comparison is made between the rate of thermal propagation through beams that are undamaged and beams that have
significant tensile cracking. The results show that, although small differences occur, there is no significant change in the rate of thermal propagation
through the specimens. Consequently, it is concluded that the effects of tensile cracking on the thermal propagation through concrete can be ignored
in structural analyses. Significantly this means that analyses of heated concrete structures which are cracked can be carried out with heat-transfer
and mechanical analyses being conducted sequentially, as is currently normal and fully-coupled thermo-mechanical analyses are not required.
The loss of concrete cover and the impact on the thermal performance is
examined numerically. A comparison is made of the thermal propagation,
beam deflections and column rotations between structures that are undamaged and structures that have partial cover loss in a variety of locations
and magnitudes. Results show that any loss of cover can lead to unsymmetrical heating, causing larger deflections in both vertical and horizontal
directions, which can result in a more critical scenario. It is concluded
that the effect of cover loss on the thermal performance of the structure is
A new approach to numerically simulating the loss of cover by mechanical means from a member is developed. This new approach provides the
user with an extremely flexible yet robust method for simulating this loss
of cover. The application of this method is then carried out to show its
A large experimental study carried out at the Indian Institute of Technology, Roorkee and separately numerically modelled at the University
of Edinburgh. Unfortunately, due to unforseen circumstances, the experimental data available is limited at this time and as a result the validation
of the numerical simulation is limited.
Through these investigations it is clear that it is necessary to develop a
method in enhance the stability and integrity of the concrete when subjected to the scenario of a fire following another mechanically extreme event.
Therefore, finally a method is proposed and experimentally investigated into
the use of fibres to increase the post crushing cohesiveness of the concrete
when subjected to thermal loads. Results show that the fibrous members
display an increased thermal resistance by retaining their concrete cover
through an enhanced post crushing cohesion. From this investigation, it is
concluded that the use of fibrous concrete is extremely beneficial for the application of enhancing the performance under extreme sequential mechanical
and thermal loading.|
|Sponsor(s): ||Engineering and Physical Sciences Research Council (EPSRC)|
|Keywords: ||reinforced concrete|
|Appears in Collections:||Engineering thesis and dissertation collection|
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