Study of the Behaviour of Steel Angle Tension Connections in Fire
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Date
2026
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
KADA Abdelhak / LAMRI Belkacem
Abstract
teel braced frames are considered one of the most effective strategies for ensuring structural
resilience in earthquake zones such us Chlef (Algeria). However, structural safety under fire
conditions remains a critical concern in civil engineering, particularly for steel structures,
whose mechanical properties deteriorate significantly at elevated temperatures. This doctoral
research focuses on the behaviour of bolted angle steel assemblies commonly used in braced
steel frame systems under high temperature conditions.
The primary objective of this study is to investigate the mechanical response and failure
mechanisms of these connections through advanced numerical modelling, supported by
standard design approaches under current structural codes. To achieve this, detailed finite
element models were developed using ANSYS APDL (Ansys Parametric Design Language),
which offers robust capabilities for nonlinear, temperature-dependent simulations. The FE
models account for geometric nonlinearity, contact interactions, and temperature-sensitive
material degradation, enabling accurate prediction of connection behaviour under fire loading
conditions.
A theoretical component-based model is developed to represent the mechanical behaviour of
bolted connections in a more physically interpretable way, accounting for temperaturedependent material degradation, geometry, and contact behaviour. The model decomposes the
connection into individual elements such as bolts, angle legs, and connected plates, each
represented by spring-like components with stiffness and strength calibrated through numerical
simulations.
The proposed model is validated through a comparative study against results obtained from the
Component-Based Finite Element Method (CBFEM), which has recently gained popularity in
the structural fire engineering community for its accuracy and balance between complexity and
usability. The comparison demonstrates that the theoretical model provides reliable predictions
of connection behaviour under elevated temperatures, capturing essential features such as
stiffness reduction, load redistribution, and failure mechanisms.
This research contributes to a more accurate understanding of bolted connection behaviour in
fire conditions. It proposes a simplified modelling strategy that could be implemented in design
practice. It lays the groundwork for safer and more efficient design of braced steel structures
subjected to fire. It opens up new research directions for experimental validation and extension
vi
to other types of connections and boundary conditions and above all it provides substantial data
for future analysis
Description
THESIS
Submitted to obtain the diploma of
DOCTORATE 3RD CYCLE LMD
Speciality: Civil Engineering
Option: Structure
Keywords
Angle connections, Finite element analysis, Tensile force, OUISSAM YESSAD