Fire 2021, 4, 70. https://doi.org/10.3390/fire4040070 www.mdpi.com/journal/fire Article Numerical Analysis of Seismic Performances of Post‐Fire Scoria Aggregate Concrete Beam‐Column Joints Bin Cai 1 , Wen‐Li Hu 1 and Feng Fu 2, * 1 School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China; caibin@jlju.edu.cn (B.C.); hwl5275@163.com (W.‐L.H.) 2 School of Mathemaics, Computer Science and Engineering, City, University of London, London EC1V 0HB, UK * Correspondence: feng.fu.1@city.ac.uk Abstract: In order to analyze the post‐fire seismic performances of scoria aggregate concrete (SAC) beam‐column joints precisely and effectively, one finite element model (FEM) was developed to simulate the seismic behavior of SAC beam‐column joints. The FEM consists of two sequential parts: firstly, the heat transfer analysis of the beam‐column joints, and then the seismic analysis of the SAC joints by combining the temperature field distribution obtained from the heat transfer analysis with the mechanical properties of the SAC after fire, both of which were implemented in ABAQUS. In order to make the simulation results more accurate, spring elements were applied to simulate the bond–slip behavior with material degradation due to fire damage in the simulation of seismic anal‐ ysis. Moreover, in order to validate the FEM, the seismic behavior of the natural aggregate concrete (NAC) beam‐column joints after fire was simulated with the established FEM, and the simulation results were compared with the available test data. It is proved that the FEM we built was accurate and effective and provided efficient solutions for evaluating the seismic performance of post‐fire beam‐column joints so that the effects of various parameters, namely, fire time, longitudinal rein‐ forcement ratio, and axial compression ratio on the seismic performance of SAC beam‐column joints after fire were investigated in depth, which indicated the increase of axial compression ratio can improve the strength, initial stiffness, and energy dissipation capacity of SAC joints, while the in‐ crease of longitudinal reinforcement ratio can increase the strength and stiffness of SAC joints to a small extent, but too high reinforcement ratio will significantly weaken the energy dissipation ca‐ pacity of SAC joints. Keywords: scoria aggregate concrete; post‐fire; heat transfer analysis; beam‐column joints; seismic performance; finite element model; spring element 1. Introduction The rapid growth of the global economy has led to an increase in the density of urban buildings and of the facility circuits and gas pipelines in the city. When a city is hit by an earthquake, the fracture of public facility circuits and gas pipelines is apt to trigger fires. Moreover, the fire will last for a long time due to the breakdown of traffic, communica‐ tion, water, and other systems. Prolonged exposure to fire may significantly diminish the performance of structural materials, thereby affecting structural integrity. In this case, buildings are likely to suffer significant damage or even collapse in the subsequent after‐ shocks. Therefore, it is of great theoretical significance and practical value to systemati‐ cally research the seismic performance of structures after they have been subjected to fire [1,2]. So far, extensive experimental research has been conducted on the mechanical prop‐ erties and seismic performance of structural components after exposure to fire. Al‐Ameri conducted an experimental study to evaluate the effect of high temperatures on Citation: Cai, B.; Hu, W.‐L.; Fu, F. Numerical Analysis of Seismic Performances of Post‐Fire Scoria Aggregate Concrete Beam‐Column Joints. Fire 2021, 4, 70. https://doi.org/10.3390/fire4040070 Academic Editors: Alistair M. S. Smith and Chad M. Hoffman Received: 31 August 2021 Accepted: 9 October 2021 Published: 14 October 2021 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and institu‐ tional affiliations. Copyright: © 2021 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (http://crea‐ tivecommons.org/licenses/by/4.0/).