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Structural Engineering and Mechanics
  Volume 50, Number 6, June25 2014 , pages 755-772

Prediction of post fire load deflection response of RC flexural members using simplistic numerical approach
Hitesh Lakhani, Tarvinder Singh, Akanshu Sharma, G.R. Reddy and R.K. Singh

    A simplistic approach towards evaluation of complete load deflection response of Reinforced Concrete (RC) flexural members under post fire (residual) scenario is presented in this paper. The crosssection of the RC flexural member is divided into a number of sectors. Thermal analysis is performed to determine the temperature distribution across the section, for given fire duration. Temperature-dependent stress-strain curves for concrete and steel are then utilized to perform a moment-curvature analysis. The moment-curvature relationships are obtained for beams exposed to different fire durations. These are then utilized to obtain the load-deflection plots following pushover analysis. Moreover one of the important issues of modeling the initial stiffness giving due consideration to stiffness degradation due to material degradation and thermal cracking has also been addressed in a rational manner. The approach is straightforward and can be easily programmed in spreadsheets. The presented approach has been validated against the experiments, available in literature, on RC beam subjected to different fire durations viz. 1hr, 1.5hrs and 2hrs. Complete load-deflection curves have been obtained and compared with experimentally reported counterparts. The results also show a good match with the results obtained using more complicated approaches such as those involving Finite element (FE) modeling and conducting a transient thermal stress analysis. Further evaluation of the beams during fire (at elevated temperatures) was performed and a comparison of the mechanical behavior of RC beams under post fire and during fire scenarios is made. Detailed formulations, assumptions and step by step approach are reported in the paper. Due to the simplicity and ease of implementation, this approach can be used for evaluation of global performance of fire affected structures.
Key Words
    fire; residual capacity; load deflection; simplistic numerical approach
Hitesh Lakhani, Tarvinder Singh, G.R. Reddy and R.K. Singh : Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai, 400085, India
Akanshu Sharma : Institute of Construction Materials, University of Stuttgart, 70569 Stuttgart, Germany

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