Modelling of Concrete Subjected to Cyclic Loading

The infrastructure of today depends heavily on concrete structures. Most of these structuresare subjected to repeated loads, known as fatigue or cyclic loads: the loads weakenthe structure. As this phenomenon is of high cost to society, a deeper understanding ofthe deterioration process of cyclic loading would be beneficial. The aim of this thesis isto add to the knowledge of the deterioration phenomenon and to develop models that candescribe the response of concrete subjected to cyclic loading.In analyses of structures of today, finite element modelling is gaining ground and is beingused more frequently in research and structural design. The investigations here use onlythe finite element method.Many structures incorporate details that are subjected to complicated loading, which resultsin complex crack patterns. A suitable tool for describing these crack patterns isanisotropic damage material models. However, anisotropic models are difficult to implementand are often computationally inefficient. One of the investigations in this thesisaims to find out what makes the anisotropic formulation suitable for complex crack patterns.This is done by implementing a model which can control the amount of couplingbetween volumetric- and deviatoric strains. It was found that this coupling is essentialfor describing complex crack patterns.To deepen the understanding of concrete subjected to cyclic loading, the phenomenonwas investigated on the meso-scale level. An interface model was developed and appliedto a three phase representation of concrete that incorporates: aggregates, cement paste,and interfacial zones around the aggregate. The model in itself does not yield cyclicbehaviour, i.e. no hysteresis loops were generated at the constitutive level. Instead, thecyclic response was generated by the meso-structure. It was found that the interfacialtransition zones are crucial in amount and strength.Concrete subjected to cyclic loading was also investigated on the macro-level, with theambition to describe the response of concrete structures subjected to cyclic loading. Twoinvestigations were made: one aims to describe cyclic response in tension and the otheraims to cover tension and the transition to reasonable high states of compression. Theinvestigations are based on the theory of plasticity and damage mechanics, which arecombined in both a serial and a parallel fashion. In the serial configuration the nominalstress is computed by adding the damage to the effective stress; for the parallel configuration,the damage stress and the effective stress are evaluated separately for the samestrain and then added to yield the nominal stress. Furthermore, both models use twoyield surfaces to describe the hysteresis loops. The result of the analyses show an overallagreement with experimental observations

A damage-plasticity model for the dynamic failure of concrete

A constitutive model based on the combination of damage mechanics and plasticity is developed to analyse concrete structures subjected to dynamic loading. The aim is to obtain a model, which requires input parameters with clear physical meanings. The model should describe the important characteristics of concrete subjected to multiaxial and rate-depending loading. This is achieved by combining an effective stress based plasticity model with an isotropic damage model based on plastic and elastic strain measures. The model response in tension, uni-, bi- and tri-axial compression is compared to experimental results in the literature.Comment: Preprint. Submitted to Eurodyn 2011, 8th International Conference on Structural Dynamics, Leuven, Belgium, 201

Sustainability-driven structural design using artificial intelligence

The construction industry is responsible for a large share of the global environmental impact. The need for addressing sustainability and increased competition calls for the development of innovative design methods that include sustainability in a transparent way. The aim of this work is to propose a framework to use machine learning and artificial intelligence (AI) for structural design optimization based on sustainability and buildability criteria. AI opens up new possibilities to optimize and assess structures early in the planning and design stages. In that way, it is possible to decrease the negative and enhance the positive environmental, economic and social impacts and create a more time‐ and cost‐effective design process. The work is meant to serve as a first step toward the development of AI‐based methods in the construction industry, which can bring digitalization in the construction industry to a new level and create new services and business models

The interplay between corrosion and cracks in reinforced concrete beams with non-uniform reinforcement corrosion

This paper investigates the interplay between corrosion of reinforcement and corrosion-induced cracking in reinforced concrete structures with non-uniform corrosion distribution based on the experimental results of a concrete beam simultaneously subjected to sustained deflection and accelerated corrosion through impressed current. Unlike previous studies, this work encompasses various refined techniques for the measurement of surface cracks, such as digital image correlation and distributed optical fiber sensors, as well as for the assessment of reinforcement corrosion, namely 3D laser scanning, to explore previously hidden aspects of the relationship between the two parameters. The applied techniques proved very effective in providing an unprecedented level of detail of both the crack development and corrosion distribution. More specifically, the formation and propagation of corrosion-induced cracks were accurately and constantly monitored over time and subsequently compared to the distribution of corrosion. The results revealed that determining the maximum corrosion level or even the location of the section with maximum corrosion based solely on visual inspection of the surface crack width may not be possible. However, the width of corrosion-induced cracks was found to increase linearly with the local corrosion level, implying that crack width monitoring can still be used to estimate the rate of corrosion degradation

CDPM2: A damage-plasticity approach to modelling the failure of concrete

A constitutive model based on the combination of damage mechanics and plasticity is developed to analyse the failure of concrete structures. The aim is to obtain a model, which describes the important characteristics of the failure process of concrete subjected to multiaxial loading. This is achieved by combining an effective stress based plasticity model with a damage model based on plastic and elastic strain measures. The model response in tension, uni-, bi- and triaxial compression is compared to experimental results. The model describes well the increase in strength and displacement capacity for increasing confinement levels. Furthermore, the model is applied to the structural analyses of tensile and compressive failure.Comment: arXiv admin note: text overlap with arXiv:1103.128

Long-term performance of distributed optical fiber sensors embedded in reinforced concrete beams under sustained deflection and cyclic loading

This paper explores the performance of distributed optical fiber sensors based on Rayleigh backscattering for the monitoring of strains in reinforced concrete elements subjected to different types of long-term external loading. In particular, the reliability and accuracy of robust fiber optic cables with an inner steel tube and an external protective polymeric cladding were investigated through a series of laboratory experiments involving large-scale reinforced concrete beams subjected to either sustained deflection or cyclic loading for 96 days. The unmatched spatial resolution of the strain measurements provided by the sensors allows for a level of detail that leads to new insights in the understanding of the structural behavior of reinforced concrete specimens. Moreover, the accuracy and stability of the sensors enabled the monitoring of subtle strain variations, both in the short-term due to changes of the external load and in the long-term due to time-dependent effects such as creep. Moreover, a comparison with Digital Image Correlation measurements revealed that the strain measurements and the calculation of deflection and crack widths derived thereof remain accurate over time. Therefore, the study concluded that this type of fiber optic has great potential to be used in real long-term monitoring applications in reinforced concrete structures

Crack monitoring in reinforced concrete beams by distributed optical fiber sensors

This paper investigates the use of distributed optical fiber sensors (DOFS) based on Optical Frequency Domain Reflectometry of Rayleigh backscattering for Structural Health Monitoring purposes in civil engineering structures. More specifically, the results of a series of laboratory experiments aimed at assessing the suitability and accuracy of DOFS for crack monitoring in reinforced concrete members subjected to external loading are reported. The experiments consisted on three-point bending tests of concrete beams, where a polyamide-coated optical fiber sensor was bonded directly onto the surface of an unaltered reinforcement bar and protected by a layer of silicone. The strain measurements obtained by the DOFS system exhibited an accuracy equivalent to that provided by traditional electrical foil gauges. Moreover, the analysis of the high spatial resolution strain profiles provided by the DOFS enabled the effective detection of crack formation. Furthermore, the comparison of the reinforcement strain profiles with measurements from a digital image correlation system revealed that determining the location of cracks and tracking the evolution of the crack width over time were both feasible, with most errors being below +/- 3 cm and +/- 20 mu m, for the crack location and crack width, respectively

Design of impulse loaded concrete structures: a comparison of FKR 2011 with various design regulations

The Swedish Fortifications Agency has a long history in the design and maintenance of military fortifications and recently published a revised version of their design regulations; FKR 2011. These regulations can be said to represent the traditional Swedish view of the design of impulse loaded concrete structures and differs from the regulations normally used (i.e. Eurocode) for static design in Sweden today. Further, even though many parts of the content of FKR 2011 are similar to that of corresponding regulations in other countries it is not identical. The purpose of this project was to assess different regulations for the design of reinforced concrete structures subjected to impulse loading. The focus was on FKR 2011 and its applicability for some common design criteria. One aim was to compare FKR 2011 with other similar regulations in order to identify similarities and differences to these; and if necessary, recommend possible improvements. Another aim was to provide an improved basis in order to give general recommendations of further investigations that is deemed necessary. The main subjects compared were how the different regulations treated material strength, bending moment, shear and spalling/breaching. The comparisons were made based on the concept/expressions used in the respective regulations, and using several case studies of a simply supported slab strip of different geometry, concrete strength and reinforcement amount. Based on this it was concluded that the concept used for bending stiffness and moment capacity was similar in all the recommendations compared. Further, the method used in FKR for plastic deformation capacity is based on an older, today non-existing, reinforcement type and there is a need of further comparisons of the method used. The concept used in FKR for shear differs much compared with the regulations compared and it is suggested that further development of it should be made. Finally, the concept used for spalling and breaching is deemed to be okay to use

Two-dimensional strain field analysis of reinforced concrete D-regions based on distributed optical fibre sensors

The introduction of Distributed Optical Fibre Sensing in experimental testing of reinforced concrete structures has enabled the acquisition of measurements with an unparalleled level of detail, providing an accurate and ubiquitous description of cracking and deflections throughout an element. However, most of the available research using this technology has focused on the study of beam specimens and high quality data for the calibration and development of models that can describe accurately the behaviour of D-regions in service is still lacking. For that reason, the application of distributed optical fibre sensing in D-regions remains a subject of interest. In this work a method for the deployment of fibre sensors in a multilayer configuration is presented for a wall element. An interpolation approach is then proposed, which combined with the distributed nature of the sensors enabled the description of detailed heat maps for the global and principal strain fields. The results indicated that shear strains can reveal the position of shear cracks well before they are formed whereas the maximum and minimum principal strains clearly show the crack pattern and crack development as well as the load transfer mechanisms including, for the first time, the experimental identification of a secondary strut-and-tie mechanisms

Challenges in the adoption of sustainable criteria in the Swedish property development industry

The construction industry is facing an increased focus on sustainability and climate neutrality, causing property developers to implement new requirements into the procurement documents, which are also driven by the national agenda. This study explores the current state of sustainability practice among Swedish property developers and identifies the main obstacles to expand further the implementation of the sustainability criteria. How the property developers define and implement sustainability requirements has been assessed through qualitative semi-structured interviews, focusing on sustainability certification systems, Life Cycle Assessment (LCA), and social sustainability. The results show usage of sustainability certification systems for marketing purposes and high awareness and practice of LCA, even though the accuracy of LCA was questioned. This study also identified guideline gaps for circular economy and social sustainability measurements, which could relate to low initiatives from the certification systems