| 1. |
- Al-Gburi, Majid, et al.
(författare)
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Simplified methods for crack risk analyses of early age concrete : Part 1: Development of Equivalent Restraint Method
- 2012
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Ingår i: Nordic Concrete Research. - 0800-6377. ; 46:2, s. 17-38
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Tidskriftsartikel (refereegranskat)abstract
- The present study deals with both the compensation plane method, CPM, and local restraint method, LRM, as alternative methods studying crack risks for early age concrete. It is shown that CPM can be used both for cooling and heating, but basic LRM cannot be applied to heating. This paper presents an improved equivalent restraint method, ERM, which easily can be applied both for usage of heating and cooling for general structures. Restraint curves are given for two different infrastructures, one founded on frictional materials and another on rock. Such curves might be directly applied in design using LRM and ERM.
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| 2. |
- Hösthagen, Anders, et al.
(författare)
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Equivalent Restraint Method Correlated to Empirical Measurements
- 2014
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Ingår i: Nordic Concrete Research. - 0800-6377. ; 50, s. 505-508
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Tidskriftsartikel (refereegranskat)abstract
- The present study deals with the correlation between numerical models and empirical observations in newly cast concrete specimens. The model used is the equivalent restraint method, ERM, which is established from several local restraint method calculations, LRM. The csating of walls in a tunnel construction is investigated. Correlation between models and empirical measurements is established in three steps.
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| 3. |
- Hösthagen, Anders, 1979-, et al.
(författare)
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Evaluation of Material Properties for Young Concrete
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Restrained volumetric changes in early age concrete may cause tensile strength failure, i.e. crack initiation and propagation. The volumetric changes are primarily induced by a change in thermal and moisture states, and it is of great importance to quantify the resulting stresses and strains that arise when the volumetric changes are restrained. Large economical and technical benefits are gained if measures to avoid cracking can be determined by calculations prior to casting. To perform such calculations, the following property areas of the concrete needs to be known; strength development, heat of hydration, basic shrinkage, thermal dilation, basic creep and stress at full restraint. This work demonstrates how the concrete can be tested in a laboratory environment and how to evaluate the numerical data, thus yielding a parameter set that may be used during stress and strain development calculations. Furthermore, a brief investigation is performed on how sensitive the evaluation for each test is, with respect to crack risk estimation. It is showed that the measured stress development from the stress development at full restraint test can be considered as a checkpoint for the total parameter set. The reason is that the calculated stress development, which is compared to the measured counterpart, is influenced by all evaluated parameters. It is discussed that out of the performed tests, three are of significant importance when it comes to provide an operational parameter set for the calculations. These tests are the ones achieving strength development, heat of hydration and stress at full restraint.
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| 4. |
- Hösthagen, Anders, 1979-
(författare)
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Thermal Crack Risk Estimation and Material Properties of Young Concrete
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents how to establish a theoretical model to predict risk of thermal cracking in young concrete when cast on ground or an arbitrary construction. The crack risk in young concrete is determined in two steps: 1) calculation of temperature distribution within newly cast concrete and adjacent structure; 2) calculation of stresses caused by thermal and moisture (due to self-desiccation, if drying shrinkage not included) changes in the analyzed structure. If the stress reaches the tensile strength of the young concrete, one or several cracks will occur.The main focus of this work is how to establish a theoretical model denoted Equivalent Restraint Method model, ERM, and the correlation between ERM models and empirical experiences. A key factor in these kind of calculations is how to model the restraint from any adjacent construction part or adjoining restraining block of any type.The building of a road tunnel and a railway tunnel has been studied to collect temperature measurements and crack patterns from the first object, and temperature and thermal dilation measurements from the second object, respectively. These measurements and observed cracks were compared to the theoretical calculations to determine the level of agreement between empirical and theoretical results.Furthermore, this work describes how to obtain a set of fully tested material parameters at CompLAB (test laboratory at Luleå University of Technology, LTU) suitable to be incorporated into the calculation software used. It is of great importance that the obtained material parameters describe the thermal and mechanical properties of the young concrete accurately, in order to perform reliable crack risk calculations. Therefore, analysis was performed that show how a variation in the evaluated laboratory tests will affect the obtained parameters and what effects it has on calculated thermal stresses.
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| 5. |
- Hösthagen, Anders, et al.
(författare)
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Thermal crack risk estimations for tunnel : equivalent restraint method correlated to empirical observations
- 2014
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Ingår i: Nordic Concrete Research. - 0800-6377. ; 49, s. 127-143
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Tidskriftsartikel (refereegranskat)abstract
- The present study deals with the correlation between numerical models and empirical observations in newly cast concrete structures. The model used is the equivalent restraint method, ERM, which is established from several local restraint method calculations, LRM. The casting of walls and roof in a tunnel construction is investigated. Correlation between models and empirical measurements is established in three steps: 1) the restraint situation is analyzed; 2) the calculated temperature developments are compared to empirical temperature measurements to calibrate the models; and 3) calculated strain ratios are compared with observed crack patterns, and in general a good correlation is achieved
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| 6. |
- Hösthagen, Anders, et al.
(författare)
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Thermal Crack Risk Estimations of Concrete Walls : Temperature and Strain Measurements Correlated to the Equivalent Restraint Method
- 2017
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Ingår i: Proceedings of the 23rd Nordic Concrete Research Symposium. - Oslo, Norway : Nordic Concrete Federation. - 9788282080569
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Konferensbidrag (refereegranskat)abstract
- Self-induced non-elastic deformations in hardening concrete, caused by restrained volume changes due to thermal dilatation and moisture deformations, often leads to cracking. In crack risk analyses, determination of the degree of restraint is vital. One model to estimate the restraint and calculate the thermal crack risk is the Equivalent Restraint Method, ERM. The method has previously been analyzed but needs to be further examined and validated. Recordings of tunnel sections were performed and compared to calculated values by ERM. Satisfying correlation between theoretically estimated and observed temperatures, strains and time of through cracking was achieve which is promising for future implementation and testing of the method.
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| 7. |
- Hösthagen, Anders, 1979-, et al.
(författare)
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Thermal Crack Risk Estimations of Concrete Walls – Temperature and Strain Measurements Correlated to the Equivalent Restraint Method
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Self-induced non-elastic deformations in hardening concrete, caused by restrained volume changes due to thermal dilatation and moisture deformations, often leads to cracking. In thermal crack risk analyses, determination of the degree of restraint is vital. One model to estimate the restraint and calculate the thermal crack risk is the Equivalent Restraint Method, ERM. This method has previously been analysed but needs to be examined and validated further. Measurements of wall castings were performed and compared to calculations with ERM in order to establish a correlation to empirical observations. A satisfying correlation between theoretically estimated and measured time of through cracking was achieved. Based on this study and other, ERM is thus considered to work satisfyingly.
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| 8. |
- Nilimaa, Jonny, et al.
(författare)
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Thermal Crack Risk of Concrete Structures : Evaluation of Theoretical Models for Tunnels and Bridges
- 2017
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Ingår i: Nordic Concrete Research. - : Nordic Concrete Federation. - 0800-6377. ; 56:1, s. 55-69
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Tidskriftsartikel (refereegranskat)abstract
- An approach for thermal crack risk estimations was introduced in the Swedish design guidelines BRO 94. The cracking occurs during the early hardening process because of the exothermic reactions between water and cement and often result in high repair costs and delayed construction. This paper studies and validates the inherent safety levels for one typical case of concrete structure. Three slab-frame structures were analysed and the original crack risk estimations were compared to the actual cracking and postcalculations were carried out, using actual parameters. This paper shows that walls with computed strain ratios over 70% were affected by thermal cracks.
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| 9. |
- Nilimaa, Jonny, 1986-, et al.
(författare)
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Validation of the Swedish Crack Risk Estimation Models
- 2017
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Ingår i: Proceedings of the 23rd Nordic Concrete Research Symposium. - Oslo : Nordic Concrete Federation. - 9788282080569 ; , s. 321-324
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Konferensbidrag (refereegranskat)abstract
- Thermal cracking may occur during the early hardening process of concrete as a result of the exothermic reactions between water and cement. An approach for thermal crack risk estimation and prevention was introduced in the Swedish design guidelines BRO 94. This paper studies and validates the current safety levels existing concrete structures. Three slab-frame structures were analysed and the preliminary crack risk estimations were compared to the actual cracking and post-estimations were carried out, using actual parameters. This paper shows that all the studied walls with a strain ratio over 70% were affected by thermal cracks.
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