Fire exposure critically compromises the structural integrity and load-bearing capacity of concrete buildings, posing severe risks for people inside the building and rescue workers. Under high thermal loads, concrete undergoes nonlinear damage processes particularly cracking and thermal spalling that can weaken substructural components such as walls, columns, and slabs. This localised deterioration often leads to progressive collapse at the structural scale, emphasising the need for integrated multiphysics simulations to inform fire safety assessments and engineering design. This study examines the multifaceted interactions between fire-induced damage in concrete and the overall stability of a structure. Specifically, it investigates the influence of local spalling and crack propagation on global load redistribution, and how these phenomena contribute to progressive collapse under extreme thermal conditions. A multiscale, multiphysics approach was developed in previous work of the authors to capture the complex behavior of concrete structures subjected to fire. In this work, an emphasis is placed on extending the simulation framework to three-dimensional settings, thereby enabling more realistic and detailed predictions of the evolving damage state. Herein, an external solver provides the thermal conditions, while a FEniCS-based solver employs a unified phase-field method to describe localised damage mechanisms. This substructural analysis is coupled with a global structural-scale simulation in ABAQUS, wherein load redistribution and collapse are investigated. The open-source coupling library preCICE facilitates the exchange of temperature, damage, and geometric data between the solvers. An illustrative example showcases how localised thermal spalling can culminate in progressive collapse, highlighting the necessity of a robust fire-structure framework to guide both safety assessments and engineering design.