On the effect of thermal strains in slender prestressed concrete beams

In construction sector, prestressed concrete beams are commonly used, even in ordinary buildings; as a consequence, their exposure to various risk factors, including fires or high thermal gradients, is quite high. Extensive research has focused on concrete structures under extreme loading conditions, but slender prestressed members have proven unique and challenging in the understanding of mechanical response and their numerical modelling, particularly regarding the interaction between thermal gradients and prestressing forces. In fact, unlike ordinary concrete beams and columns, these structures are particularly sensitive to temperature changes and temperature gradients. In addition, their thermo-mechanical response is further complex due to the interaction of thermal loads with pre-existing prestressing stresses, which vary over time as a function of temperature field. This work explores this dual behavior by means of numerical simulations including temperature-dependent material properties, focusing on the thermal expansion coefficient (alpha) and thermal transient creep. Using a staggered scheme finite element modelling, the analysis applies a coupled thermo-mechanical approach. The model has been validated on a series of experimental tests carried out at Polytechnic of Bari. The comparison showed the model capability to capture the influence of temperature-dependent strains on these slender structures. The results highlight how even minor variations in thermal properties can affect the mechanical response, providing insights essential for the safe design of prestressed concrete elements under thermal loads.