Stability Investigation of a Novel Composite Parking Beam with Built-Up Section During Construction Stage

This dissertation addresses the stability of a novel built-up composite
beam system developed for long-span parking structures. The system combines
a castellated IPEo section welded onto an HEAA section with profiled
trapezoidal sheeting, aiming to reduce material use and temporary propping
during construction while achieving large spans. Owing to its
unconventional geometry and fabrication, the beam is vulnerable to global
and local failure modes, including lateral–torsional buckling (LTB),
lateral–distortional buckling (LDB), and local instabilities of the
castellated web. To ensure safe design, a stabilisation method was
developed and progressively refined through the design of the
sheeting-to-beam connection configuration.
A multi-level experimental and numerical programme was carried out. At the
component level, dedicated tests investigated the shear behaviour of
fasteners. At the structural level, large-scale rotational stiffness tests,
shear diaphragm tests, and lateral spring stiffness tests quantified the
restraint mechanisms provided by the sheeting and its connections. These
experiments were complemented by detailed finite element (FE) simulations
that incorporated nonlinear material models and calibrated fastener
behaviour.
The investigation led to the development of simplified mechanical models
for rotational stiffness, shear diaphragm action, and lateral spring
behaviour. These models were validated against experimental results and
used to interpret the governing restraint mechanisms. Parametric studies
were primarily conducted through FE simulations, extending beyond the
tested configurations to examine the influence of geometric and mechanical
parameters, including sheeting arrangement and fastening layout. The
results show that the restraint provided by the sheeting is governed mainly
by fastener behaviour and can substantially enhance construction-stage
stability by preventing or delaying LTB and LDB.
Building upon these findings, a design methodology consistent with Eurocode
principles is proposed. The methodology integrates conventional resistance
checks with additional verifications for stiffness-based restraint effects,
providing a transparent framework for the safe and economical design of
such built-up beams. In addition, advanced numerical and data-driven
approaches for predicting the elastic critical moment were explored,
including an in-house FEM program, symbolic regression, and artificial
neural networks, highlighting promising pathways for future simplification
and automation of stability checks.
Overall, the dissertation bridges experiments, numerical modelling, and
analytical formulation to support the reliable adoption of efficient
composite built-up beam solutions for parking structures and related
applications.