On the structural behaviour of prestressed concrete members subjected to heating and subsequent cooling

Prestressed concrete members are very popular solution in variety of structural applications. Naturally, their performance in fire became a popular topic, yet not completely investigated and not even to the same extent as reinforced concrete members. Studying the thermo-mechanical response of prestressed members in fire implies the cooling phase to be taken into account, as real fires are characterized not only by an ascending branch, where the temperature is monotonically increasing until it reaches its maximum value, but also by a decay phase, where the temperature tends to go down, back to the ambient temperature. While the behaviour of P/C members at elevated temperatures was the main topic of few research studies, its behaviour during and after cooling still remains an open issue. Most of the engineering codes and common engineering practices do not explicitly take into account the residual material properties, which are certainly different from the, so-called “hot” properties. Lack of experimental data on the residual and post-fire properties makes it more difficult to build up a comprehensive and reliable numerical approach, but also to define material properties and constitutive laws which can accurately represent the behaviour of a material that is heated and subsequently cooled down. Sequentially coupled thermo-mechanical sectional analysis was conducted on four prestressed concrete simply supported beam sections, aiming to study the mechanical response, caused by thermal gradients as well as externally applied loads, at elevated temperature but also during the subsequent cooling phase. For that purpose, Visual Basic codes were developed by the Author. The influence of different parameters was investigated, and the maximum temperature in the strands and the load level were recognized as the most important ones, in view of the accurate interpretation of the failure in the heating or cooling phase, as well as the residual behaviour.