title: Reliability assessment and seismic vulnerability analysis of ageing reinforced concrete structures with plain rebars
Creators: name: Pugliese, Francesco
Publisher: name: University of Liverpool Repository
Year: 2022

description: This thesis introduces innovative numerical and analytical methodologies for seismic 
vulnerability assessments and reliability analyses of Reinforced Concrete (RC) 
structures and infrastructures with plain rebars exposed to ageing effects.
A methodology is introduced to evaluate the nonlinear stress-strain response of 
concrete for partially exposed RC cross-sections. This approach is then utilised to 
develop advanced models for assessing the residual capacity of corroded RC sections 
under ductile and brittle failure mechanisms.
Ductile failure mechanisms are analysed by introducing a numerical model to calculate 
the interaction domain of coupled axial and bending moment effects. Conversely, a 
response surface method is introduced to estimate the shear capacity of aged RC cross sections for brittle failure mechanisms.
A comprehensive threefold probabilistic approach is developed to accurately assess 
the occurrence time of corrosion initiation, propagation, and deterioration. This 
framework relies on climatological data (e.g., minimum and maximum temperature) 
to evaluate the onset of corrosion initiation. Additionally, it utilises existing 
experimental results to establish probabilistic distributions for concrete cracking 
(initiation, severe cracking, and spalling of the concrete cover) and pitting in plain steel 
reinforcement. The methodology further provides a means to integrate this 
probabilistic framework into Finite Element (FE) models of RC structures.
The inelastic buckling of plain bars is numerically investigated by incorporating a 
refined nonlinear FE model into a novel multi-optimisation strategy based on the 
Genetic Algorithm (GA) and Bayesian updating. This strategy calibrates the 
parameters of existing constitutive models designed for ribbed rebars based on 
experimental data from plain rebars. A comprehensive database is generated through 
a parametric study to consider the effects of corrosion on plain steel reinforcement, 
enabling the development of an analytical model for the inelastic buckling of corroded 
plain rebars.
A seismic intensity measure is introduced for precise seismic vulnerability 
assessments of structural systems with corroded plain rebars. Additionally, time dependent performance criteria are introduced to assess the impact of corrosion on the 
structural capacity over time.
The proposed methodologies and procedures are applied to two case studies: (1) an 
existing multi-storey RC building and (2) a continuous thirteen-bay RC bridge.
A seismic vulnerability assessment is conducted on the RC building under different 
seismic scenarios, including nonlinear time-history analyses considering both near field and far-field ground motions, as well as considering the effects of mainshock aftershock earthquake sequences. Fragility curves are developed based on the results 
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of Incremental Dynamic Analysis (IDA) and Cloud methodologies to explore the 
influence of various corrosion levels on the seismic vulnerability of the case-study 
building over its lifetime.
A reliability analysis is performed for the RC bridge exposed to spatially-variable 
corrosion, increased traffic flow, and climatological effects. Monte Carlo simulations 
are executed at 10-year intervals to establish time-dependent reliability profiles, which 
are compared against predefined standards to determine when the bridge no longer 
complies with current regulations and requires maintenance.
Finally, an experimental campaign is conducted to investigate the impact of corrosion 
on the nonlinear stress-strain response of plain steel bars under tensile loading. Tensile 
tests are employed to study the effects of ageing on the mechanical and geometrical 
properties of plain steel rebars. Degradation relationships are established based on 
experimental data. Additionally, the effects of corrosion on the nonlinear stress-strain 
response of corroded plain steel reinforcement are provided by calibrating an existing 
constitutive model using the Genetic Algorithm (GA).
Overall, results highlighted that RC structures exhibited deficient structural 
performance over time, depending on environmental exposure. In some cases, the 
structural response could not reach the targets imposed by the enforced technical 
standards. This last observation points out the importance of introducing time dependent structural design approaches, lifetime seismic vulnerability and reliability
assessments for proper and adequate risk mitigation strategies.
Nonetheless, all the proposed methods have improved the capability to evaluate the 
performance of RC structures with corroded plain rebars. This improved knowledge 
will support structures and infrastructure decision-makers to establish proper 
maintenance schemes and cost-efficient repair solutions.