11 results on '"Sas, Gabriel"'
Search Results
2. Comparison and Joint Evaluation of Importance, Redundancy and Robustness Indicators Applied to Aging Prestressed Concrete Bridges.
- Author
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Sarmiento, Silvia, Thöns, Sebastian, González-Libreros, Jaime, Björnsson, Ivar, and Sas, Gabriel
- Subjects
BRIDGE failures ,ENVIRONMENTAL management ,CONCRETE ,ROBUST statistics ,FINITE element method - Abstract
A bridge failure can result in significant social, economic, and environmental problems; therefore, its reliability and risk management are essential. Bridges' system reliability and risks are governed mainly by their redundancy and robustness, which currently are not adequately included in most design code specifications. Thus, in this study, a comprehensive comparison between relevant importance, redundancy, and robustness indicators found in the literature with different levels of complexity is carried out. The indicators under analysis have been used separately in different studies but have never been addressed together. Therefore, this study presents a joint evaluation of deterministic, reliability- and risk-based indicators to evaluate the differences in interpretation and information provided by the indicators. The approach is exemplified by analyzing a prestressed concrete bridge subjected to continuous degradation due to chloride ingress. A procedure is implemented to couple a metamodel-based reliability approach with a Nonlinear Finite Element Analysis (NLFEA). Based on the analysis performed, the comparison between indicators showed how different interpretations can be obtained depending on the implemented approach. Thus, creating more uniform formulations and agreeing on target values is necessary to help with redundancy and robustness interpretation. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
3. Effect of Confinement with FRCM Composites on Damaged Concrete Cylinders
- Author
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Gonzalez-Libreros, Jaime, Sabau, Cristian, Sneed, Lesley H., Sas, Gabriel, Pellegrino, Carlo, Mechtcherine, Viktor, editor, Slowik, Volker, editor, and Kabele, Petr, editor
- Published
- 2018
- Full Text
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4. Shear strengthening of a concrete trough bridge using embedded through‐section (ETS) FRP bars.
- Author
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Carrasco, Carlos Hermosilla, Farré, Alfredo García, Gonzalez‐Libreros, Jaime, Wang, Chao, Carolin, Anders, Kjellman, Jouko, and Sas, Gabriel
- Subjects
OPTICAL fiber detectors ,CONCRETE bridges ,REINFORCED concrete ,STEEL bars ,RAILROAD bridges - Abstract
As worldwide infrastructure is ageing, significant efforts have been paid to the development of strengthening techniques that will restore or increase the initial capacity of existing structures. Considering that it is expected that shear failure happens in a less ductile mode than that observed under bending actions, special attention has been devoted to shear strengthening methods. These methods included externally bonded fiber reinforced polymers (EB‐FRP), near‐surface mounted (NSM‐FRP) method, and the embedded trough‐section (ETS) technique, among others. In this paper, ETS method is used for the strengthening in shear of a reinforced concrete railway bridge located in Finland. The ETS method consists in the embedment of FRP or steel bars through predrilled holes into the concrete core. The bars are bonded to the concrete using adhesives. The paper includes a brief review of recent advances in the use of ETS and comparison with other available techniques, the description of the case study, instrumentation of the bars using fiber optic sensors (FOS) for strain monitoring, the procedure used for the installation of the bars in the field, and a preliminary analysis of the data collected. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
5. Strengthening Concrete Structures using Mineral Based Composites
- Author
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Blanksvärd, Thomas, Sas, Gabriel, and Täljsten, Björn
- Subjects
Mortar ,Infrastrukturteknik ,Beams ,Strengthening ,Shear ,Engineering mechanics - Construction engineering ,Teknisk mekanik - Konstruktionsteknik ,CFRP ,Grid ,Infrastructure Engineering ,Concrete - Abstract
During the last two decades, strengthening concrete structures with epoxy bonded carbon fiber reinforced polymers (CFRP) has shown excellent results in increasing bearing capacity. However, there are some limitations with epoxy coated concrete surfaces, e.g.; low permeability which may provoke freeze/thaw problems, poor thermal compatibility to the concrete substrate which makes epoxy coating more sensitive to the surrounding temperature and regulations when it comes to the security and health (allergic reactions) of applicators and third party users. In this respect, using mineral based composites (MBC) may overcome some of these challenges associated with epoxy bonded strengthening systems. MBC, in this context, refers to high strength fibers bonded to the surface using a mineral based bonding agent. This study examines the cracking behavior and strain development of shear MBC strengthened RC beams. The results show that using MBC as shear strengthening postpones the formation of macro-cracks and that a considerable strengthening effect is achieved by using MBC. Godkänd; 2013; 20131113 (gabsas)
- Published
- 2013
6. Photographic strain monitoring during full-scale failure testing of Örnsköldsvik bridge.
- Author
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Sas, Gabriel, Blanksvärd, Thomas, Enochsson, Ola, Täljsten, Björn, and Elfgren, Lennart
- Subjects
BRIDGE testing ,STRAIN gages ,BRIDGES ,PHOTOGRAMMETRY ,FINITE element method ,STRAIN sensors ,CONCRETE beams ,STRUCTURAL health monitoring - Abstract
Full-scale failure tests are rarely performed on structures, primarily due to their high costs and the lack of suitable test objects. This article reports the results of a 'test-to-failure' performed using a real bridge. The results obtained in such tests are valuable for assessing analytical models, updating finite element models and investigating the real behaviour of structures. The specific intention in these experiments was to study the shear failure of the bridge, which is a less well-understood mode of failure than is bending. To this end, it was necessary to strengthen the bridge using near-surface-mounted reinforcements made of carbon fibre–reinforced polymer bars in order to prevent bending failure. The bridge was heavily monitored during the test, using both traditional sensors such as electrical strain gauges and linear variable differential transducers alongside new monitoring systems such as fibre-optic sensors, strain rosette linear variable differential transducers and a novel photographic monitoring system. This article presents the photographic strain measurements and describes the use of the photographic tools in monitoring and characterizing the behaviour of the failure zone during the full-scale test. The strains measured using the photographic method were found to agree well with those measured using classical strain gauges. In addition, the strain contour plots generated using the photographic method provided crucial insights into the strains within the bridge's failure zone. This study was conducted under the remit of the EU 'Sustainable Bridges' Project. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
7. Biochar-Added Cementitious Materials—A Review on Mechanical, Thermal, and Environmental Properties.
- Author
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Mensah, Rhoda Afriyie, Shanmugam, Vigneshwaran, Narayanan, Sreenivasan, Razavi, Seyed Mohammad Javad, Ulfberg, Adrian, Blanksvärd, Thomas, Sayahi, Faez, Simonsson, Peter, Reinke, Benjamin, Försth, Michael, Sas, Gabriel, Sas, Daria, and Das, Oisik
- Abstract
The enhanced carbon footprint of the construction sector has created the need for CO
2 emission control and mitigation. CO2 emissions in the construction sector are influenced by a variety of factors, including raw material preparation, cement production, and, most notably, the construction process. Thus, using biobased constituents in cement could reduce CO2 emissions. However, biobased constituents can degrade and have a negative impact on cement performance. Recently, carbonised biomass known as biochar has been found to be an effective partial replacement for cement. Various studies have reported improved mechanical strength and thermal properties with the inclusion of biochar in concrete. To comprehend the properties of biochar-added cementitious materials, the properties of biochar and their effect on concrete need to be examined. This review provides a critical examination of the mechanical and thermal properties of biochar and biochar-added cementitious materials. The study also covers biochar's life cycle assessment and economic benefits. Overall, the purpose of this review article is to provide a means for researchers in the relevant field to gain a deeper understanding of the innate properties of biochar imparted into biochar-added cementitious materials for property enhancement and reduction of CO2 emissions. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
8. Freeze-thaw damage evaluation and model creation for concrete exposed to freeze–thaw cycles at early-age.
- Author
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Liu, Dongyun, Tu, Yongming, Sas, Gabriel, and Elfgren, Lennart
- Subjects
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DAMAGE models , *FREEZE-thaw cycles , *CONCRETE , *HYDROTHERAPY , *PREDICTION models - Abstract
• Frost resistance of concrete exposed to E-FTCs worsen with the decrease in pre-curing time. • Subsequent curing conditions after E-FTCs significantly affects the later-age frost resistance of the damaged concrete. • There are good correlations between the parameters of the damage model and the pre-curing strengths of damaged concrete. • Prediction models of freeze–thaw damage suitable for damaged concrete exposed to E-FTCs are created. • For concrete expected to experience E-FTCs, adequate pre-curing strength and re-curing conditions are essential. Concrete subjected to freeze–thaw cycles action at early-age will suffer serious physical damage, resulting in degradation of the concrete's performance. The subsequent curing conditions after early-age freeze–thaw cycles (E-FTCs) are critical to the development of the properties of frost-damaged concrete. Four test environments were set up for this study, based on different numbers of E-FTCs and subsequent curing conditions. The later-age resistance to freeze–thaw of concrete exposed to E-FTCs was evaluated by analysing the influence of pre-curing times and curing conditions. Results show that the earlier the FTCs occur, the worse the later-age freeze–thaw resistance is. In particular, for the frost-damaged concrete with a pre-curing time of 18 h, its freeze–thaw resistance is significantly worse than that of other concretes that have a longer pre-curing time. The increase in the number of E-FTCs exacerbates the damage to early-age concrete, which causes the reduced later-age freeze–thaw resistance. Subsequent water curing can significantly improve the freeze–thaw resistance of damaged concrete, while air curing is the least effective. Based on previous freeze–thaw damage models, prediction models for concrete exposed to E-FTCs were created by using the test data obtained in this study. The critical pre-curing strengths which can ensure that the damaged concrete has satisfactory frost resistance at later-age were thus obtained. For concrete structures expected to experience E-FTCs, adequate pre-curing strength and good re-curing conditions are essential. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
9. A nonlinear prediction model of the debonding process of an FRP-concrete interface under fatigue loading.
- Author
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Min, Xinzhe, Zhang, Jiwen, Li, Xing, Wang, Chao, Tu, Yongming, Sas, Gabriel, and Elfgren, Lennart
- Subjects
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MATERIAL fatigue , *DEBONDING , *PREDICTION models , *CRACKING of concrete , *REINFORCED concrete , *DEAD loads (Mechanics) , *ECCENTRIC loads - Abstract
• The fatigue debonding rate was determined by the amplitude and level of the load. • The proposed model explicitly took into account the noted factors. • The d a /d N and the S ¯ · Δ S show a linear relationship in double logarithmic coordinates. • The debonded FRP has a significant effect on the subsequent debonding development. Externally bonded Fiber Reinforced Polymer (FRP) strengthening has been proven to be an efficient and reliable method for structural strengthening of reinforced concrete (RC) members. However, the beneficial effects of this method can be diminished due to the debonding of the FRP laminates. The mechanism of FRP debonding still requires further research, especially for strengthened members under fatigue loading. To understand and predict the FRP fatigue debonding process better, eleven FRP-concrete joint specimens were tested under static or fatigue loading. Both the theoretical derivation and the experimental study indicated that the debonding growth rate of the FRP laminate depended not only on the mean level (S ¯), but also the amplitude (Δ S) of the applied fatigue load. In addition, the debonded portion of the FRP laminate had a significant impact on the following debonding process due to the friction and mechanical interaction between the debonded FRP and the concrete surface. Therefore, a new nonlinear prediction model is proposed in this paper. The proposed model explicitly took into account the amplitude and the mean level of the fatigue loading, which enabled the effect of both to be modelled. Meanwhile, a correction term was also introduced into the model to account for the influence of the previously debonded FRP laminate. The predicted results of the debonding growth rate and the debonding length agreed well with the experimental results. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
10. A review of concrete properties under the combined effect of fatigue and corrosion from a material perspective.
- Author
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Liu, Dongyun, Wang, Chao, Gonzalez-Libreros, Jaime, Guo, Tong, Cao, Jie, Tu, Yongming, Elfgren, Lennart, and Sas, Gabriel
- Subjects
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DETERIORATION of concrete , *CORROSION fatigue , *FATIGUE cracks , *MATERIAL fatigue , *FATIGUE life , *FREEZE-thaw cycles , *POROSITY , *CONCRETE durability , *CONCRETE fatigue - Abstract
• There are coupling effects between fatigue and environmental corrosion actions. • Transportation models of harmful substances in the concrete accounting for fatigue damage. • Physical damage of freeze–thaw cycles and sulphate attack decrease fatigue life. • Multiple alternated simulation test is a potential way to study combined effect of fatigue and corrosion. When in use, reinforced concrete bridge structures not only experience high-frequency fatigue loading caused by passing vehicles, but also suffer from the effects of a corrosive environment. In addition to fatigue damage to reinforcement, long-term fatigue loading also causes concrete cracking and deterioration of pore structures, thereby accelerating the ingress of external corrosive substances and reducing concrete durability. Long-term exposure to a corrosive environment also reduces the performance of concrete and causes corrosion of reinforcement materials, affecting the fatigue performance of the structure. Therefore, there is a combined effect between fatigue loads and corrosion on concrete. This paper is a review of the current literature from a material perspective on the performance degradation of concrete under the combined action of fatigue loading and corrosion, that is, carbonation, chloride ion attack, freeze–thaw cycles, and sulphate attack. The paper includes (1) a description of a test method for examining the combined action of fatigue loading and corrosion, (2) a summary of performance degradation of concrete under the combined effect of fatigue loading and corrosion, and (3) an introduction to durability deterioration models considering fatigue damage, and fatigue models that can account for corrosion. Finally, potential future research on concrete under the combined effect of fatigue loading and corrosion is described. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
11. Evaluation of freeze-thaw damage on concrete material and prestressed concrete specimens.
- Author
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Qin, Xiao-chuan, Meng, Shao-ping, Cao, Da-fu, Tu, Yong-ming, Sabourova, Natalia, Grip, Niklas, Ohlsson, Ulf, Blanksvärd, Thomas, Sas, Gabriel, and Elfgren, Lennart
- Subjects
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CONCRETE , *COMPRESSIVE strength , *ELASTICITY , *CEMENT , *GROUTING , *CONCRETE construction - Abstract
The pore structure of the hardened concrete and the microscopic changes of a few selected pores throughout the freeze-thaw test were investigated by a method combining RapidAir and digital metalloscope. Traditional tests were also performed to evaluate the macroscopic change caused by freeze-thaw cycles (FTCs). The investigation shows that the concrete material, of which the spacing factor is 0.405 mm and the air content is 2.38%, can still withstand more than 300 FTCs. Severe microscopic damages occurred after approximately 200 FTCs and the freeze-thaw damage were gradually aggravated afterwards. Prestress forces have a remarkable impact on the failure pattern under FTCs. It was further found that the compressive strength as an indicator is more reliable than the relative dynamic modulus of elasticity in evaluating the freeze-thaw damage on concrete material. In addition, the test and analysis show that the measured prestress losses of bonded specimen are larger than that of unbounded specimen under the attack of FTCs due to the duct grouting effect. The ultimate freeze-thaw prestress loss is about 5% of σ con for both the bonded and unbonded specimens because the grouting cement paste will eventually be completely destroyed. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
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