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Civil-Comp Proceedings
ISSN 1759-3433 CCP: 79
PROCEEDINGS OF THE SEVENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and C.A. Mota Soares
Paper 179
The Effect of Creep on the Behaviour of RC Frames in Fire S. Bratina, F. Saje, M. Saje and I. Planinc
Faculty of Civil and Geodetic Engineering, University of Ljubljana, Slovenia Full Bibliographic Reference for this paper
S. Bratina, F. Saje, M. Saje, I. Planinc, "The Effect of Creep on the Behaviour of RC Frames in Fire", in B.H.V. Topping, C.A. Mota Soares, (Editors), "Proceedings of the Seventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 179, 2004. doi:10.4203/ccp.79.179
Keywords: fire resistance, non-linear planar frames, strain-based finite element method, heat conduction, reinforced concrete, creep, thermal strain, transient strain.
Summary
Fire resistance presents an important part of the safety
of structures. It is well known that the temperature increase in fire
conditions decreases load-carrying capacity of concrete, and increases
its deformability. Due to the structural and chemical changes in
material, caused by the elevated temperature, due to the internal
stresses implied by the temperature gradient, and due to high pore
pressures caused by the evaporation of the unbound pore water, internal
microcracks or damages appear in concrete. Further on, at the elevated
temperature, the decomposition process of cement stone in concrete
begins, which is the consequence of the dehydration of cement binder.
Physical-chemical changes appear also in the stoneware, which leads to
the decomposition of aggregate grains. For this reason the decrease of
compressive strength in concrete at the elevated temperature depends
also on the type of aggregate used. Abrams [1] discovered that
compressive strength of concrete made of limestone aggregate is at
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The magnitude of concrete creep at elevated temperatures is much bigger
than at room temperature. According to the experimental research
[2], the concrete creep at
The paper presents a computational model and a computer program developed for the non-linear analysis of the response of plane reinforced concrete frames simultaneously exposed to fire and external mechanical loads up to the failure. The analysis takes into account the geometrical and material non-linearities of the structure and includes the influence of elevated temperature on the mechanical and rheological properties of materials. The time response of a structure exposed to fire and mechanical external loads is obtained by the finite element method. Here we use an original beam finite element. The element is based on Reissner's theory of beams and is designed in such a way that only deformation variables of the centroidal axis of the beam need to be interpolated [6]. In numerical examples, a special attention is paid to the influence of creep in concrete and steel reinforcement onto the behaviour of the structure. With the help of the developed computational model and the related computer program, we analyse a number of reinforced concrete frames in fire. We compare our numerical results to the ones obtained in experiments in a fire laboratory, and prove that the effect of creep in concrete can not be neglected in the fire analysis of structures. References
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