Toward coupled fire‐structure simulations for forecasting smoke leakage in case of concrete structures under fire

Abstract

AbstractComputational modeling of the fire‐structure interaction demands the coupling between several models typically implemented in independent simulation software describing distinct physical processes. For instance, in the event of a fire breakout or building on fire, the fire not only increases the temperature of the immediate area but also initiates structural damage, leading to the spalling of the concrete along with the propagation of the smoke, heat, and radiation originating from the fire. As a result of the progressive structural damage caused by the fire such as macro cracks or breakthroughs in the wall, smoke and other hazardous gases begin to disperse and spread into previously unaffected zones. Thus, it represents a coupled multi‐physics problem, which is not well addressed in the scientific community, yet. Therefore, the investigation of such fire‐structure interactions requires a comprehensive computational modeling and simulation framework that couples the consequences of various phenomena with minimal invasive solver modifications. In this work, the structural model treats concrete as a multi‐phase porous material exposed to high temperatures resulting from the fire. For this purpose, the structural solver is at the moment manually coupled with a computational fluid dynamics (CFD) solver to setup a computational framework for such fire‐structure simulations. Herein, the combustion process of the fire and the smoke propagation is carried out using the open‐source software denoted as Fire Dynamics Simulator (FDS) and the thermo–hydro–mechanical fracture is computed using a FEniCS‐based solver. The finite‐difference method based FDS solves the filtered Navier–Stokes equations using the large‐eddy simulation technique to describe the turbulent flow and heat transfer including radiation and combustion inside the fluid domain. The concrete damage such as cracks, holes, or spalling is computed using a phase‐field method in a separate solver based on the thermal boundary conditions from the fire simulation. Subsequently, both solvers are coupled using the open‐source coupling framework preCICE. Based on the rate at which the crack or spalling is developing, the computational domain of the fluid solver has to be adapted taking the generated holes in the wall structure into account for the ongoing CFD simulation. It allows for the leakage of smoke gases through the concrete wall structure and thus the spreading of the fire scenario. The proposed model is illustrated by an exemplary case that forecasts the leakage of smoke and hazardous gases from the successive damage caused by the thermal spalling induced on a concrete wall structure.