Insights into the Complexity of Structural Fire Response from Repeated Heating Tests on Post Tensioned Concrete
This paper extends discussion of previous research presented by the authors on post tensioned (PT) concrete flexural elements in fire. Tests on two monostrand, continuous PT concrete slabs (one with an unbonded tendon and the other bonded) exposed to constant incident heat fluxes while under sustained load are reviewed and discussed. During testing these slabs demonstrated a distinct time deflection response in heating and cooling consisting of five phases. For the first time, this paper gives the results from these unique slab tests during a second thermal cycle. The novelty of this study is that it was performed in an attempt to observe and better understand the thermal straining effects that contributed to the observed five phase deflection response under first heating illustrating many inter related mechanisms that contribute to the complexity of the observed deflection responses. The resulting discussion is provided to advance the overall understanding of the response of real concrete structures (as opposed to isolated elements) in fire, and will hopefully assist structural fire modellers to validate (or otherwise) their modelling capabilities.