Issue 46

S. Motsa et alii, Frattura ed Integrità Strutturale, 46 (2018) 124-139; DOI: 10.3221/IGF-ESIS.46.13 124 Developments in the fracture and fatigue assessment of materials and structures Failure behaviour of a fire protected steel element Siphesihle Motsa, Georgios Drosopoulos Structural Engineering and Computational Mechanics Group, Discipline of Civil Engineering, University of KwaZulu-Natal, Durban, South Africa 214580281@stu.ukzn.ac.za DrosopoulosG@ukzn.ac.za , https://orcid.org/0000-0002-4252-6321 A BSTRACT . In the present article the failure behaviour of a steel, beam type element supported against fire by protection boards, is studied. Three – dimensional, coupled temperature - displacement, non-linear finite element analysis models have been developed to simulate the unprotected and protected structure. A simple modelling approach is proposed for the investigation of the influence of the gradual failure of fire protection at elevated temperatures, on the structural performance of the system, under thermal and mechanical loads. Yielding of steel is depicted and force – displacement diagrams are used to evaluate the ultimate behaviour of the unprotected and protected models. It is shown that for the protected structure, yielding is less severe and the time period up to maximum strength is significantly longer. Eventually, is depicted how failure of the fire protection leads to a gradual reduction of the response, in fire conditions. K EYWORDS . Steel structures; Fire; Protection; Coupled analysis; Finite element analysis. Citation: Motsa, S., Drosopoulos, G., Failure behaviour of a fire protected steel element, Frattura ed Integrità Strutturale, 46 (2018) 124-139. Received: 21.05.2018 Accepted: 23.07.2018 Published: 01.10.2018 Copyright: © 2018 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION tructural steel, although is a widely used material, due to its high thermal conductivity rapidly loses its strength when exposed to elevated temperatures. The yield strength and stiffness of steel can be reduced drastically, when exposed to a temperature of 500°C or more [1]. To overcome these shortcomings, passive (among others) fire protection systems acting as insulators, are assigned to steel elements. Spray applied fire resistive materials (SFRM), gypsum and cement based, concrete boards are some of the options related to passive fire protection. Concrete, due to its low conductivity, acts as an insulator since it delays the transfer of heat to the steel elements when exposed to elevated temperatures. Several experimental research studies have shown that fire protection boards improve the resistant of steel when exposed to fire. Composite columns made of partially encased steel sections tested in [2] in fire conditions, failed under flexural buckling, while the concrete encasement played a significant role in preventing local buckling of the flanges. An investigation conducted in [3] concluded that the fire protection of steel columns can easily be damaged in ambient temperatures, and the risk of damage is higher when the protected steel is exposed to cyclic loading. From an S