Assessment of Concrete Structures Including Corrosion and Cracks
Doctoral thesis, 2020
Reinforced concrete (RC) structures constitute a major proportion of the built environment and society relies continuously on their service. Many of these structures were built in the era following the Second World War and are thus approaching the end of their intended service life. The likelihood of deterioration increases with time and so damage caused by, say, corrosion is not uncommon. Also, increased demands are often laid on the load-carrying capacity of existing bridges, aimed at increasing utilisation of the road network by allowing heavier vehicles. Simply dismantling and re-constructing all bridges at the end of their designed service life, or taking needless strengthening measures, is unsustainable. Rather, improved methods of assessing the capacity of existing infrastructure are needed.
The current work has aimed to develop improved, reliable assessment methods. Its focus areas were structures with reinforcement corrosion and structures with cracks from previous loading. Both simplified and advanced methods of evaluating anchorage capacity were developed for concrete structures with corroded reinforcement. The simplified method modifies the bond stress-slip relationship and is calibrated against a large database of bond tests, with the safety margin ensured by deriving partial safety factors. The advanced method is based on finite element (FE) analysis, with tensile material properties altered for elements positioned at the splitting cracks along the reinforcement. The latter method was also investigated for RC without corrosion damage but with cracks from previous loading. Design results from advanced nonlinear FE analyses (meaning results with a proper safety margin) are obtained by applying a “safety format”. The current work investigated whether safety formats available in fib Model Code 2010 also ensured reliable design capacities for structures with somewhat complicated load application and geometry; in this case, a concrete frame subjected to vertical and horizontal loads.
The results indicate that the anchorage capacity may be reasonably well estimated by using the simplified method. The proposed partial safety factors also provided sufficient safety margin. Furthermore, in the advanced anchorage assessment, the capacity could be estimated solely from weakened tensile properties located at the position of the splitting cracks and without input concerning the corrosion level. Moreover, by including cracks from previous loading in advanced modelling, improved predictions of the failure mode, ultimate capacity and ductility were demonstrated. Lastly, in the investigation of safety formats for nonlinear FE analysis, the method of estimating a coefficient of variance of resistance (ECOV), did not reach the intended safety level. However, the global resistance factor method (GRF) and partial factor method (PSF) did. This work has the potential to improve both simplified and advanced assessment methods, providing more sustainable infrastructure management in the future.
The current work has aimed to develop improved, reliable assessment methods. Its focus areas were structures with reinforcement corrosion and structures with cracks from previous loading. Both simplified and advanced methods of evaluating anchorage capacity were developed for concrete structures with corroded reinforcement. The simplified method modifies the bond stress-slip relationship and is calibrated against a large database of bond tests, with the safety margin ensured by deriving partial safety factors. The advanced method is based on finite element (FE) analysis, with tensile material properties altered for elements positioned at the splitting cracks along the reinforcement. The latter method was also investigated for RC without corrosion damage but with cracks from previous loading. Design results from advanced nonlinear FE analyses (meaning results with a proper safety margin) are obtained by applying a “safety format”. The current work investigated whether safety formats available in fib Model Code 2010 also ensured reliable design capacities for structures with somewhat complicated load application and geometry; in this case, a concrete frame subjected to vertical and horizontal loads.
The results indicate that the anchorage capacity may be reasonably well estimated by using the simplified method. The proposed partial safety factors also provided sufficient safety margin. Furthermore, in the advanced anchorage assessment, the capacity could be estimated solely from weakened tensile properties located at the position of the splitting cracks and without input concerning the corrosion level. Moreover, by including cracks from previous loading in advanced modelling, improved predictions of the failure mode, ultimate capacity and ductility were demonstrated. Lastly, in the investigation of safety formats for nonlinear FE analysis, the method of estimating a coefficient of variance of resistance (ECOV), did not reach the intended safety level. However, the global resistance factor method (GRF) and partial factor method (PSF) did. This work has the potential to improve both simplified and advanced assessment methods, providing more sustainable infrastructure management in the future.
reinforced concrete
corrosion
nonlinear FE analysis
reinforcement bond
assessment
cracks
Author
Mattias Blomfors
Chalmers, Architecture and Civil Engineering, Structural Engineering
Evaluation of safety formats for non-linear finite element analyses of statically indeterminate concrete structures subjected to different load paths
Structural Concrete,;Vol. 17(2016)p. 44-51
Journal article
ENGINEERING BOND MODEL FOR CORRODED REINFORCEMENT
Engineering Structures,;Vol. 156C(2018)p. 394-410
Journal article
Partial safety factors for the anchorage capacity of corroded reinforcement bars in concrete
Engineering Structures,;Vol. 181(2019)p. 579-588
Journal article
Incorporation of pre-existing longitudinal cracks in finite element analyses of corroded reinforced concrete beams failing in anchorage
Structure and Infrastructure Engineering,;Vol. In press(2020)p. 1-17
Journal article
Incorporation of pre-existing cracks in finite element analyses of reinforced concrete beams without transverse reinforcement
Engineering Structures,;Vol. 229(2021)
Journal article
We need to prepare to preserve and maintain our ageing concrete infrastructure as sustainably as possible.
Bridges and other types of concrete structure are commonplace in our society. Among other things, we need their function for travelling and to transport goods. Many of these structures were built during the construction boom after the Second World War and are now getting old. With increased age, they are more likely to be damaged by, say, rust in their reinforcement bars.
Somewhat counterintuitively, decision-makers often want to allow heavier trucks onto the roads so that more goods can be transported. This is more resource-efficient but puts more stress on bridges. Obviously, tearing down and rebuilding all old bridges costs a lot of money and is bad for the environment. Indeed, in many cases, it would also be downright unnecessary. Instead, we need better methods of calculating how heavy trucks may be allowed onto older bridges. These methods also need to work in the case of damaged bridges, as they often have hidden capacities that can be uncovered.
This work develops better models for making such calculations for damaged structures. In making these models, two kinds of damage were envisaged; rust damage and cracks from previous loading. Rust may be regarded as a process whereby steel reinforcement is consumed by the environment, weakening the structure. This affects the structure in many ways, but the focus in this work has been on the reinforcement anchorage. This means how well the reinforcement bar is fastened into the concrete. Both a simplified and an advanced model were developed. The simplified one can be used when quick, rough results are needed; the advanced one can be used when more accurate results are needed, even if they take longer. Modelling methods for calculating the capacity of a cracked structure were also developed.
Structures can never be perfectly safe, in that the likelihood of collapse is zero. Rather, the risk of harm to people and property must be acceptably low; another aspect that has been studied in this thesis.
The results of this work expand the toolbox for engineers; the people who make recommendations as to whether a structure should be kept, strengthened or demolished. This will increase the chances of sufficient capacity being shown and unnecessary strengthening or demolition being avoided. Immense resources, in terms of money and the environment, may thus be saved, greatly benefitting society.
Initial applications are envisaged in bridges and harbour structures, as many of these are damaged. Indeed, the precursor of one of the models developed in this work has already been used on two bridges in Stockholm. This led to savings of the order of tens of millions of Swedish kronor. The sooner improved capacity estimation methods are put into practice, the greater the societal and environmental savings.
Bridges and other types of concrete structure are commonplace in our society. Among other things, we need their function for travelling and to transport goods. Many of these structures were built during the construction boom after the Second World War and are now getting old. With increased age, they are more likely to be damaged by, say, rust in their reinforcement bars.
Somewhat counterintuitively, decision-makers often want to allow heavier trucks onto the roads so that more goods can be transported. This is more resource-efficient but puts more stress on bridges. Obviously, tearing down and rebuilding all old bridges costs a lot of money and is bad for the environment. Indeed, in many cases, it would also be downright unnecessary. Instead, we need better methods of calculating how heavy trucks may be allowed onto older bridges. These methods also need to work in the case of damaged bridges, as they often have hidden capacities that can be uncovered.
This work develops better models for making such calculations for damaged structures. In making these models, two kinds of damage were envisaged; rust damage and cracks from previous loading. Rust may be regarded as a process whereby steel reinforcement is consumed by the environment, weakening the structure. This affects the structure in many ways, but the focus in this work has been on the reinforcement anchorage. This means how well the reinforcement bar is fastened into the concrete. Both a simplified and an advanced model were developed. The simplified one can be used when quick, rough results are needed; the advanced one can be used when more accurate results are needed, even if they take longer. Modelling methods for calculating the capacity of a cracked structure were also developed.
Structures can never be perfectly safe, in that the likelihood of collapse is zero. Rather, the risk of harm to people and property must be acceptably low; another aspect that has been studied in this thesis.
The results of this work expand the toolbox for engineers; the people who make recommendations as to whether a structure should be kept, strengthened or demolished. This will increase the chances of sufficient capacity being shown and unnecessary strengthening or demolition being avoided. Immense resources, in terms of money and the environment, may thus be saved, greatly benefitting society.
Initial applications are envisaged in bridges and harbour structures, as many of these are damaged. Indeed, the precursor of one of the models developed in this work has already been used on two bridges in Stockholm. This led to savings of the order of tens of millions of Swedish kronor. The sooner improved capacity estimation methods are put into practice, the greater the societal and environmental savings.
Digital Twin I – Comprehensive Condition Assessment for Resilient Transport Infrastructure under Normal Service Conditions and Extreme Climatic Events
Formas (2017-01668), 2018-01-01 -- 2020-12-31.
Tool for assessment and service-life evaluation of corroded bridges
Swedish Transport Administration, 2015-03-01 -- 2018-03-30.
Development Fund of the Swedish Construction Industry (SBUF), 2015-03-01 -- 2018-03-30.
Swedish Cement and Concrete Research Institute, 2015-03-01 -- 2018-03-30.
Driving Forces
Sustainable development
Areas of Advance
Transport
Subject Categories
Infrastructure Engineering
Infrastructure
C3SE (Chalmers Centre for Computational Science and Engineering)
ISBN
978-91-7905-340-6
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4807
Publisher
Chalmers
Opponent: Docent Richard Malm, Kungliga Tekniska högskolan, Sverige