Thermomechanical Behaviour of Axially Restrained Prestressed Hollow-Core Slabs in Fire: A 3D Nonlinear Finite Element Investigation of Thermal Lag during Fire Decay

Abstract

Precast prestressed hollow-core (PHC) concrete slabs are widely utilized in modern construction for their material efficiency, yet their thermomechanical response during the critical fire decay phase remains insufficiently quantified. This study aims to evaluate the structural resilience of PHC slabs under realistic fire scenarios by developing a high-fidelity 3D nonlinear finite element (FE) framework in ABAQUS. The methodology explicitly accounts for the "cavity effect" - incorporating internal radiation and convection within longitudinal voids - and utilizes a sequentially coupled thermal-structural approach. Data was collected through the validation of the numerical model against established experimental benchmarks, achieving high predictive accuracy with thermal error margins below 2%. A parametric investigation was conducted to quantify the influence of axial restraint stiffness and varying fire exposure types, including ISO 834 and Eurocode parametric curves. Findings demonstrate that Compressive Arching Action (CAA) in restrained slabs significantly mitigates deformation, reducing peak mid-span deflections by up to 78.7% compared to simply supported configurations. Critically, the study identifies a "thermal lag" where maximum structural demand occurs during the cooling phase rather than at peak gas temperatures. It is concluded that traditional fire design, which focuses solely on the heating phase, may underestimate the risk of shear failure during decay. It is recommended that performance-based fire design frameworks incorporate axial restraint effects and cooling phase assessments to ensure the structural integrity of precast infrastructure.