| 1. |
- Lundgren, Karin, 1968, et al.
(författare)
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Effects on bond of reinforcement corrosion
- 2007
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Ingår i: International RILEM workshop on Integral Service Life Modeling of Concrete Structures. ; , s. 231-238
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Konferensbidrag (refereegranskat)abstract
- There is a growing need for reliable methods of assessing the load-carrying capacity and remaining service life of deteriorated structures. One of the most common causes of deterioration is corrosion of steel reinforcement. In earlier work by Lundgren [1], a model describing the effects of corrosion and bond was developed and implemented in the finite element program Diana, and verified by comparisons to test results. In the work presented here, a parameter study to quantify the effect of corrosion penetration on the bond behaviour was carried out. A typical section of a reinforced concrete slab was modelled. The following parameters were varied: concrete strength and cover, main reinforcement diameter and spacing, amount of transversal reinforcement, and corrosion penetration. The bond behaviour was significantly affected when corrosion led to cover cracking. From the results, it was noted that it was possible to obtain the bond-slip response of corroded reinforcement by shifting the bond-slip curve of uncorroded reinforcement along the slip axis. The shift along the slip axis is determined by the degree of corrosion. Thus, a level of corrosion is assumed to correspond to a certain amount of slip. Good agreement was found for all the analysed cases.
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| 2. |
- Zandi, Kamyab, 1981, et al.
(författare)
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Evaluation of load-carrying capacity of damaged reinforced concrete structures
- 2008
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Ingår i: Nordic Concrete Research & Development. ; , s. 60-
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Konferensbidrag (refereegranskat)abstract
- The growing need for reliable methods to evaluate the load-carrying capacity and remaining service life of deteriorated concrete structures has exposed the request for improved understanding of damage effects upon structural integrity. The presented research deals with the two most common causes of deterioration due to environmental impacts which are corrosion of reinforcement and freezing. Corrosion process leads to reduction of the reinforcement area and volume expansion of the steel which generates splitting stresses in the concrete and spall the concrete cover and affect the bond-slip between reinforcement and concrete. Through frost process, the volume expansion of frozen water initiates tensile stresses and micro/macro cracks into the concrete body leading to change of concrete behaviour in tension and compression as well as bond properties.In earlier work by K. Zandi Hanjari et al. a methodology to analyse the mechanical behaviour and remaining load-carrying capacity of corroded reinforced concrete structures has been developed and implemented in the finite element program DIANA. A method to quantify the frost damage has been explained in K. Zandi Hanjari et al (2007), where the effect of internal frost damage was proposed to be modelled as change of material properties; such as compressive/tensile strength, Young’s modulus and bond properties. In the study presented here, change of material and bond properties for different damage situation is described quantitatively which provides a guideline for assessment of damaged structures, due to freezing and corrosion, from field measurement to analysing the mechanical behaviour of the deteriorated structure and evaluating the remaining load-carrying capacity of the structure.The effect of corrosion as a change in geometry and properties, i.e. reduction of steel area, removal of spalled concrete and modification of bond-slip properties is evaluated based on previous research where a detailed finite element model has been developed and used to determine the bond-slip response for corroded reinforcement, Lundgren (2004). The effect of freezing on material properties of concrete and bond properties for different level of frost damage is established through extensive experimental program which includes six different test types: fundamental transverse frequency test, compressive strength, modulus of elasticity, splitting tensile strength, wedge splitting test and pull-out test
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| 3. |
- Zandi, Kamyab, 1981, et al.
(författare)
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Fatigue performance evaluation of plain and fiber-reinforced concrete using wedge splitting test
- 2009
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Ingår i: 4th International Conference on Construction Materials: Performance, Innovations and Structural Implications. ; , s. 1489-1496
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Konferensbidrag (refereegranskat)abstract
- The presented study focuses on the possibility of using wedge splitting test method to study the fatigue behavior of concrete. Moreover, the application of existing material models for fatigue performance of fiber reinforced concrete is further investigated. Fatigue behavior of three types of concrete, i.e. (1) plain concrete, (2) steel fiber-reinforced concrete, and (3) synthetic fiber-reinforced concrete, were studied experimentally and numerically. First, experiments were carried out using wedge splitting specimens subjected to monotonic and cyclic loading. Next, using inverse analyses and numerical analyses, bi-linear stress-crack opening relationships were estimated.
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| 4. |
- Zandi, Kamyab, 1981, et al.
(författare)
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Frost-damaged concrete: Part 1. Material properties
- 2009
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Ingår i: 4th International Conference on Construction Materials: Performance, Innovations and Structural Implications. ; , s. 753-760
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Konferensbidrag (refereegranskat)abstract
- In an extensive experimental investigation, several tests were performed on a reference and frost-damaged concrete. The test results showed significant influence of freeze-thaw cycles not only on the compressive strength but, to a larger extent, on the modulus of elasticity and the compressive strain at peak stress. Reduced tensile strength and increased fracture energy were measured. From inverse analysis, significant effect of frost on the shape of the tensile stress-crack opening relationship was observed; i.e. tensile strength was decreased while the post-peak behavior was more ductile for the frost-damaged concrete than for the reference concrete.
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| 5. |
- Zandi, Kamyab, 1981, et al.
(författare)
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Frost-damaged concrete: Part 2. Bond properties
- 2009
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Ingår i: 4th International Conference on Construction Materials: Performance, Innovations and Structural Implications. ; , s. 761-766
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Konferensbidrag (refereegranskat)abstract
- In an experimental investigation, pull-out tests were carried out on a reference and frost-damaged concrete. The level of frost damage was quantified by relative dynamic modulus of elasticity calculated from ultrasonic measurements. The test results showed significant influence of freeze-thaw cycles not only on the bond strength but also on the slip at the maximum bond. However, similar residual bond strength was observed for the reference and frost-damaged concrete. Finally, the results were compared with pull-out tests of frost-damaged concrete available in literature and the bond capacity and slip at maximum bond were discussed.
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| 6. |
- Zandi, Kamyab, 1981
(författare)
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Load-Carrying Capacity of Damaged Concrete Structures
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AbstractA growing need for better assessment of existing structures has revealed the need for improved understanding of structural effects of deterioration. The two most common causes of deterioration in concrete structures are corrosion of reinforcement and freezing of concrete. Previous research has been concerned primarily with the causes and mechanisms of corrosion and frost deterioration; relatively little attention has been given to the important practical problem of assessing the residual load-carrying capacity of damaged structures. This study offers a methodology to analyze the mechanical behaviour of reinforced concrete structures damaged by frost or the corrosion of reinforcement. It is proposed that the effect of damage be modelled by reducing material properties, such as compressive strength, tensile strength, elastic modulus, as well as by modifying the bond properties and geometry.For frost-damaged concrete, the effect of freezing on material properties was gathered from the literature. It was proposed that the effects of internal frost damage and surface scaling can be modelled as changes of material properties and geometry, respectively. The methodology was used in analyses of concrete beams affected by internal frost damage, by using non-linear finite element analysis at component and structural levels. Comparing the results with available experimental data indicated that the change in failure mode and the decrease of load-carrying capacity due to frost damage can be predicted by using the proposed methodology.For corroded structures, the decrease in ductility and area of the corroded reinforcement and the behaviour of cracked concrete around corroded reinforcement were extracted from previous publications. The one-dimensional bond-slip model given in the CEB-FIP Model Code 1990 was extended to include corroded reinforcement. Furthermore, a method to calculate the anchorage length from the bond-slip relation was developed. The proposed methodology was used in analyses of beams, using both non-linear finite element analyses and analytical methods. Comparisons with results, taken from the literature, showed that the methodology could reasonably well estimate the load-carrying capacity and failure mode of corroded beams.The thesis provides a guideline, for the assessment of concrete structures damaged by freezing or corrosion, which can be applied in engineering practice. The change of material properties for the types of damage is quantitatively described. However, some uncertainties exist: the main ones for frost-damaged concrete are the elastic modulus and bond properties; for corroded bars they are the ductility and the bond properties when the cover has spalled off.
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| 7. |
- Zandi, Kamyab, 1981
(författare)
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Material and Bond Properties of Frost-Damaged Concrete
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Material and bond properties of frost-damaged concrete were studied experimentally. Tests were performed on a reference concrete of grade C35/45 and frost-damaged concrete of two damage levels I and II, corresponding to 25 and 50% reduction in compressive strength caused by freeze-thaw cycles. The level of frost damage was monitored and quantified by ultrasonic measurements, fundamental frequency test and number of freeze-thaw cycles. It was observed that the results from ultrasonic measurements on frost-damaged concrete were more stable and reliable compared to the results from fundamental frequency test; therefore, ultrasonic measurements together with number of freeze-thaw cycles were the basis for frost damage quantification in this study.The behavior of frost-damaged concrete was evaluated in compression by compression and elastic modulus tests, and in tension by splitting tensile and wedge splitting tests. The effect of frost on bond properties between concrete and reinforcement was assessed using pull-out test. Finally, the resistance of the reference concrete to freeze-thaw attack was evaluated using frost resistance test. The test results showed significant influence of freeze-thaw cycles not only on the compressive strength but, to a larger extent, on the modulus of elasticity and the compressive strain at peak stress. Thus, the shape of the stress-strain curve of frost-damaged concrete in compression was influenced. Regarding the behavior in tension, reduced tensile strength and increased fracture energy were measured. The latter can be explained as the effect of several micro-cracks introduced to concrete due to freeze-thaw cycles prior to mechanical loading. Therefore, the fracture energy measured included not only opening of one crack, but several micro-cracks. This explains the higher dissipated energy. Pull-out tests also showed significant effect of freeze-thaw cycles on the bond capacity of frost-damaged concrete. However, the slip at maximum bond was not considerably influenced by frost.
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| 8. |
- Zandi, Kamyab, 1981, et al.
(författare)
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Mechanical behaviour of Frost-damaged Reinforced Concrete Structures
- 2007
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Ingår i: The 6th International Conference on Fracture mechanics of Concrete and Concrete Structures. - 9780415446174 ; 3, s. 1761-1766
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Konferensbidrag (refereegranskat)abstract
- The paper presents a methodology to analyze the mechanical behavior of reinforced concrete structures with an observed amount of freezing-damage at a given time. It is proposed that the effect of internal freezing damage can be modeled as change of material properties, and that surface scaling can be modeled as change in geometry. The change in material properties was examined, and it was found that relations between compressive and tensile strength commonly used for undamaged concrete could not be directly applied to freezing damaged concrete. A modified relation was suggested. The proposed methodology was tested on concrete beams affected by internal freezing damage, using non-linear finite element analyses based on frac-ture mechanics in the program Diana, and the results were compared with available experimental results. The results indicated that an uncertainty in the analyses was the Young’s modulus for damaged concrete, and that this influenced the results to a rather large extent.
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| 9. |
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| 10. |
- Zandi, Kamyab, 1981, et al.
(författare)
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Structural behavior of corroded reinforced concrete structures
- 2008
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Ingår i: The Fourth International Conference on Bridge Maintenance, Safety, Management, Health Monitoring and Informatics. - 9780415468442 ; , s. 481-
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Konferensbidrag (refereegranskat)abstract
- This paper presents a methodology to analyze the mechanical behavior and remaining load-carrying capacity of corroded reinforced concrete structures. The effect of corrosion is modeled as a change in geometry and properties, i.e. reduction of steel area, removal of spalled concrete and modification of bond-slip properties. The methodology is tested on concrete beams affected by corrosion using finite element analysis and the results were compared with experiments.
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