| 1. |
- Bagge, Niklas, 1987-, et al.
(författare)
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A multi-level strategy for successively improved structural analysis of existing concrete bridges: examination using a prestressed concrete bridge tested to failure
- 2019
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Ingår i: Structure and Infrastructure Engineering. - : Informa UK Limited. - 1573-2479 .- 1744-8980. ; 15:1, s. 27-53
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a multi-level strategy with increased complexity through four levels of structural analysis of concrete bridges. The concept was developed to provide a procedure that supports enhanced assessments with better understanding of the structure and more precise predictions of the load-carrying capacity. In order to demonstrate and examine the multi-level strategy, a continuous multi-span prestressed concrete girder bridge, tested until shear failure, was investigated. Calculations of the load-carrying capacity at the initial level of the multi-level strategy consistently resulted in underestimated capacities, with the predicted load ranging from 25% to 78% of the tested failure load, depending on the local resistance model applied. The initial assessment was also associated with issues of localising the shear failure accurately and, consequently, refined structural analysis at an enhanced level was recommended. Enhanced assessment using nonlinear finite element (FE) analysis precisely reproduced the behaviour observed in the experimental test, capturing the actual failure mechanism and the load-carrying capacity with less than 4% deviation to the test. Thus, the enhanced level of assessment, using the proposed multi-level strategy, can be considered to be accurate, but the study also shows the importance of using guidelines for nonlinear FE analysis and bridge-specific information.
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| 2. |
- Saback, Vanessa, et al.
(författare)
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Adapting to climate change: snow load assessment of snow galleries on the Iron Ore Line in Northern Sweden
- 2024
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Ingår i: Frontiers in Built Environment. - : Frontiers Media S.A.. - 2297-3362. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The snow galleries along the Iron Ore railway line in northern Sweden have facedproblems in recent years due to increasingly large snow loads, and several gallerieshave been damaged. These incidents motivated an evaluation of the maximumload supported by the galleries before collapse, which is presented in this study. In2021, a monitoring system was installed in one of the main frames of two snowgalleries built in the 1950s to follow up with temperature and displacements,including a trigger that sends out a warning message when a critical load isreached. A literature review on snow loads was performed, followed bycalculations on snow distribution on the galleries based on the Eurocodes andNational Swedish Standards. Finite element 2D and 3D models were created usingAxisVM to accurately assess the efforts in the structural elements. Analysis anddiscussion are complemented by observations from site visits. It was concludedthat the critical loads supported by the galleries are lower than the requirements oftoday’s standards, but since secondary construction elements were damagedbefore the main frames reached their full capacity, no major collapse has yet takenplace. The cobweb effect (load re-distribution between the neighboring elementsin a 3D structure) influenced the behavior of the galleries in the 3D analysis and thecapacity of the main frames proved to be significantly increased compared to the2D assessment.
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| 3. |
- Saback, Vanessa, et al.
(författare)
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Crack monitoring by fibre optics and image correlation: a pilot study
- 2022
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Ingår i: IABSE Symposium Prague, 2022: Challenges for Existing and Oncoming Structures, Report. - : International Association for Bridge and Structural Engineering. ; , s. 437-444
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Konferensbidrag (refereegranskat)abstract
- As reinforced concrete structures reach the end of their design lives, technology for improving accuracy and efficiency of inspections and structural health monitoring rapidly progresses. Concrete cracking and reinforcement strains are two relevant parameters in assessing damage and safety ofthese structures. The use of Digital Image Correlation (DIC) systems and distributed Fibre Optic Sensors (FOS) to evaluate these parameters are two of the technologies that have been gaining momentum due to their advantages over other approaches. This study presents an experimental investigation of crack propagation of a reinforced concrete beam specimen through FOS and DIC.The FOS were positioned inside a groove carved in the rebar and in the concrete immediately outside the bar for comparison. The results showed a significant difference between both positions, with more reliable data coming from inside the bar. The addition of the DIC crack propagation images to the FOS analysis complemented the results, and good visual correlation was identified between both methods. This study is part of a broader research program, which aims at applying DIC and FOS for structural health monitoring of a real scale bridge structure.
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| 4. |
- Sabau, Cristian, 1989-, et al.
(författare)
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Local and global behavior of walls with cut-out openings in multi-story reinforced concrete buildings
- 2019
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 187, s. 57-72
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the finite element analysis (FEA) results of a multi-story reinforced concrete (RC) building having precast and cast-in-place load bearing walls. Door-type cut-out openings (height: 2.1 m, width: 0.9–4.4 m) were created at the first and second story of the building. Results from experimental tests on axially loaded RC panels were used to verify the modeling approach. The influence of cut-out openings on the response of individual RC panels, failure modes, and load redistribution to adjacent members was analyzed. Moreover, the wall bearing capacities obtained from FEA were compared with the values calculated from design equations. The results revealed that the robustness of multi-story buildings having RC load bearing wall systems decrease considerably with the creation of cut-out openings. However, owing to the initial robustness of the buildings, large cut-outopenings could be created under normal service conditions without strengthening of the building structure. Furthermore, design equations provided very conservative predictions of the ultimate capacity characterizing the solid walls and walls with small openings, whereas similar FEA and analytically predicted capacities were obtained for walls with large openings.
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| 5. |
- Täljsten, Björn, 1961-, et al.
(författare)
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Assessment of prestressed concrete bridges - challenges
- 2020
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Ingår i: IABSE Symposium, Wroclaw 2020. - Zürich : International Association For Bridge And Structural Engineering (IABSE). ; , s. 487-494
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Konferensbidrag (refereegranskat)abstract
- Prestressed concrete bridges are important parts of our infrastructure. They are susceptible to different kinds of deterioration processes. Examples of damages and deficiencies are cracking, corrosion, voids, bond loss, reduction of cover layer, delamination, fatigue and loss of stiffness and strength. This necessitates methods to continuously assess their condition in order to avoid problems that might lead to shorter service life or reduction of structural integrity. Many of the existing prestressed bridges in Europe are now approaching their design life length. However, with proper and continuous inspection, monitoring and assessment, we may plan proactive maintenance and the structural safety can be assured or – if necessary - increased. This will save both money and decrease the environmental impact of the structure.
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| 6. |
- Täljsten, Björn, 1961-, et al.
(författare)
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Bridges tested to failure in Sweden
- 2018
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Ingår i: IABSE Conference Copenhagen 2018. - : International Association for Bridge and Structural Engineering (IABSE). ; , s. 64-70
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Konferensbidrag (refereegranskat)abstract
- Five bridges of different types have been tested to failure and the results have been compared to analyses of the load-carrying capacity using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. There it is necessary to know the real behaviour, weak points, and to be able to model the load-carrying capacity in a correct way.The five bridges were: (1) a strengthened one span concrete road bridge - Stora Höga ; (2) a one span concrete rail trough bridge loaded in fatigue – Lautajokk; (3) a two span strengthened concrete trough railway bridge - Övik; (4) a one span railway steel truss bridge -Åby; and (5) a five span prestressed concrete road bridge - Kiruna. The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy and shortcomings/potentials of different codes and models for safety assessment of existing structures
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| 7. |
- Bagge, Niklas, 1987-, et al.
(författare)
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Failure tests on concrete bridges : Have we learnt the lessons?
- 2018
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Ingår i: Structure and Infrastructure Engineering. - : Taylor & Francis. - 1573-2479 .- 1744-8980. ; 14:3, s. 292-319
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Tidskriftsartikel (refereegranskat)abstract
- Full-scale failure tests of bridges are important for improving understanding of bridges’ behaviour and refining assessment methods. However, such experiments are challenging, often expensive, and thus rare. This paper provides a review of failure tests on concrete bridges, focusing on lessons from them. In total, 40 tests to failure of 30 bridges have been identified. These include various types of bridges, with reinforced concrete or prestressed concrete superstructures, composed of slabs, girders and combinations thereof. Generally, the tests indicated that theoretical calculations of the load-carrying capacity based on methods traditionally used for design and assessment provide conservative estimates. It can also be concluded that almost a third of the experiments resulted in unexpected types of failures, mainly shear instead of flexure. In addition, differences between theoretical and tested capacities are often apparently due to inaccurate representation of geometry, boundary conditions and materials
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| 8. |
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| 9. |
- Huang, Zheng, et al.
(författare)
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Experimental study on shear deformation of reinforced concrete beams using digital image correlation
- 2019
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 181, s. 670-698
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental program aimed at providing reliable and comprehensive experimental data for assessing the available models of predicting the shear deformation of diagonally-cracked reinforced concrete (RC) beams. The non-contact measuring technique, Digital Image Correlation (DIC), was used to monitor the full-field displacement and strain in the shear span of five RC beams with thin webs. Virtual measuring grids were created to measure the mean shear strain and other critical deformation results which reflects the mechanism of shear deformation after shear cracking (i.e. the principal compressive strain angle, the principal compressive strain, the mid-depth longitudinal strain and the mean vertical strain). The experimental mean shear strain and other critical deformation results were compared with the predictions with several available models. The comparison indicates the available models fail to reproduce the principal compressive strain angle, the mid-depth longitudinal strain and the mean vertical strain which constitute the key parameters in estimating the shear deformation after shear cracking. As a result, significant discrepancies in the shear deformation of the beams tested in this paper are observed between the experimental and calculated results. It is also found that the predicted shear deformation of a number of beam specimens tested by other researchers with the available models deviates considerably from the experimental results. In general, the existing models are not capable of providing accurate predictions of the shear deformation of RC beams and further investigation into this topic is needed.
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| 10. |
- Mirzazade, Ali, 1990-
(författare)
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An Algorithmic Framework for Intelligent Concrete Structural Defects Detection and Classification
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The primary objective of inspecting concrete civil structures is to gather information concerning the deterioration of concrete elements, including issues like concrete cover cracking, delamination, or corrosion. Typically, this data is documented through field inspection notes, hand-drawn sketches, and photographs. Unfortunately, this information is often stored in diverse formats, relying on close-range images and paper-based records. Moreover, the process heavily depends on the inspector's experience, structural knowledge, and familiarity with the material properties of the system under investigation. Traditional inspection methods have inherent limitations, as they generally focus on easily accessible areas due to time constraints, safety concerns, or the challenging terrains often encountered in the field. This is particularly relevant when inspecting large structures like bridges, where examining the entire area would be time-consuming and potentially unsafe. The transfer of knowledge from one inspection period to the next becomes problematic when different inspectors are involved. Hence, there is a compelling need to explore modern inspection and monitoring techniques for structures, with a focus on reducing disruption and enhancing the efficiency and reliability of data acquisition.In this context, the previously published licentiate thesis was aimed to contribute by developing optical alternatives that complement existing techniques. These alternatives should be cost-effective, suitable for on-site application, and easily deployable. To align with the objectives of this research project, the following research questions were addressed before in the licentiate seminar:1. How accurate is Close-Range Photogrammetry (CRP) for monitoring geometric deviations and detecting defects?2. In pursuit of maximum accuracy and minimal computation time in crack detection, which convolutional neural network (CNN) architecture performs best in classification and semantic segmentation tasks?3. Is there a correlation between surface deformations in reinforced concrete, measured through Digital Image Correlation (DIC), and strains in the embedded reinforcement?However, there are still challenges to be addressed. Concrete civil structure inspection involves more than just defect detection and measurement. In this final thesis, the objective is to discuss an algorithm for creating an intelligent machine capable of classifying concrete defects. This requires the computer, acting as the inspector, to possess substantial knowledge about the concrete structure, including protocols, standards, guidelines, and an understanding of the overall structure's status. Consequently, two additional research questions are introduced:1. Building on our previous discussion in the licentiate seminar regarding the correlation between surface deformations and strains in embedded rebars, we aim to enhance the accuracy of the strain estimation. To achieve this, we intend to train intelligent regression models using available experimental data and newly generated synthetic data. Research Question 1: How can we estimate strains on embedded rebars with the application of machine learning regression, employing a hybrid-learning approach? This question is explored in the paper "Prediction of strain in embedded rebars for RC member: application of a hybrid learning approach."2. While computer vision techniques are effective in defect detection, structural health assessment encompasses more than just identifying defects. The objective is to provide a comprehensive solution that bridges the gap between defect detection, classification, and assessment, ultimately contributing to a more accurate understanding of detected defects. Research Question 2: How can we bridge the gap between defect detection and classification to achieve effective defect classification? This question is the subject of the forthcoming manuscript, "Defect Classification and Structural Assessment of Concrete Bridges: A Data-Driven Decision-Making Approach".
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