| 1. |
- Binder, Eva, 1990-, et al.
(författare)
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Temperature-Dependent Behavior of Mature Cement Paste : Creep Testing and Multiscale Modeling
- 2023
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Ingår i: International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures. SynerCrete 2023. - : Springer. - 9783031332104 - 9783031332111 ; , s. 171-180
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Konferensbidrag (refereegranskat)abstract
- The elastic compliance of cementitious materials increases slightly, and their time-dependent “creep” compliance increases significantly with increasing temperature. The present contribution provides quantitative insight into this topic. Thereby, the focus rests on mature cement paste made from Ordinary Portland cement and distilled water. Macroscopic creep experiments were performed, in order to quantify both elastic and creep moduli in the range of temperatures from 20 ℃ to 45 ℃. The experimental results regarding temperature-dependent values of the modulus of elasticity are validated herein using original results from ultrasonics testing. Finally, a multiscale model was used to establish a link to well-known stiffness constants of unhydrated cement clinker, as well as to temperature-dependent elastic and creep stiffness properties of nanoscopic hydrate-gel needles.
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| 2. |
- Binder, Eva, 1990-, et al.
(författare)
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Thermally activated viscoelasticity of cement paste : Minute-long creep tests and micromechanical link to molecular properties
- 2023
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Ingår i: Cement and Concrete Research. - : Elsevier. - 0008-8846 .- 1873-3948. ; 163
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Tidskriftsartikel (refereegranskat)abstract
- The stiffness of cementitious materials decreases with increasing temperature. Herein, macroscopic samples of mature cement pastes are subjected at 20, 30, and 45 degrees C, respectively, to three-minutes-long creep compression experiments. The test evaluation is based on the linear theory of viscoelasticity and Boltzmann's superposition principle. This yields macroscopic elastic and creep moduli as a function of temperature. A state-of-the-art multiscale model for creep homogenization of cement paste is extended to account for temperature-dependent elastic and creep moduli of the hydrate gel. This extension is based on results from published molecular simulations. Temperature-independent stiffness is assumed for cement clinker. Upscaling to the macroscale of cement paste yields elastic and creep moduli which agree well with the aforementioned experimental results. The Arrhenius-type activation energy of the creep modulus is found to be independent of scale, composition, and maturity, because of ineffective stress redistributions from creeping to non-creeping constituents.
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| 3. |
- Mang, Herbert A., et al.
(författare)
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Quantification of structural and material failure mechanisms across different length scales : from instability to brittle-ductile transitions
- 2012
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Ingår i: Acta Mechanica. - : Springer Science and Business Media LLC. - 0001-5970 .- 1619-6937. ; 223:9, s. 1937-1957
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Tidskriftsartikel (refereegranskat)abstract
- Structures may fail due to a myriad of different causes. Often, distinction is made between structural and material failure, that means a structure can fail, while the material is still intact (this is the case in so-called stability loss), or the material fails, which, as consequence, may lead to structural failure. The material behavior may turn out difficult to be mathematically guessed at the macro-level. On the other hand, a lot may be known about the chemistry or the microstructure of the material of interest. Herein, we aim at categorizing different scenarios which in the end provoke structural failure, discussing various cases investigated during the last five years, at the Institute for Mechanics of Materials and Structures of Vienna University of Technology: A well-chosen eigenvalue problem shows considerable potential for categorizing stability loss. We then turn to complex composite materials with a hierarchical organization, where a single constituent dominates the overall quasi-brittle failure of the material, such as lignin in wood and wood products, or the cement–water reaction products (shortly called hydrates) in cement-based materials. The picture changes if the first inelastically behaving constituent is related to ductile load carrying, then the loads within the microstructure are re-distributed before the overall material fails: this turns out to be the case in bone. Finally, due to highly confined multiaxial stress states, the elastic portion of the overall energy invested into the material may become negligible—and then yield design analysis employed on material volumes gives an idea of the highly ductile behavior of complex confined materials, such as asphalt. What integrates all the reported cases is the high capacity of mature mathematical and mechanical formulations to reveal the intricate, yet decipherable nature of the (continuum) mechanics of materials and structures.
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| 4. |
- Murin, Justin, et al.
(författare)
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Torsional warping eigenmodes of FGM beams with longitudinally varying material properties
- 2018
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 175, s. 912-925
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the influence of torsional warping of thin-walled cross-sections of twisted Functionally Graded Material (FGM) beams with a longitudinal polynomial variation of the material properties on their eigenvibrations is investigated, considering the secondary deformations due to the angle of twist. The transfer relations needed for the transfer matrix method are derived. Based on them, the local finite element equations of the twisted FGM beam are established. The warping part of the first derivative of the twist angle, caused by the bimoment, is considered as an additional degree of freedom at the beam nodes. The focus of the numerical investigation, with and without consideration of the Deformation due to the Secondary Torsional Moment (STMDE), is on modal analysis of straight cantilever FGM beams with doubly symmetric open and closed cross sections. The influence of the longitudinal variation of the material properties and the secondary torsion moment on the eigenfrequencies is investigated. The obtained results are compared with the ones calculated by a very fine mesh of standard solid and warping beam finite elements.
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| 5. |
- Zhang, Jiao-Long, et al.
(författare)
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Assessment of the Added Value of Multiscale Modeling of Concrete for Structural Analysis of Segmental Tunnel Rings
- 2021
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Ingår i: Encyclopedia of Materials. - : Elsevier. - 9780128197318 - 9780128197240 ; , s. 69-78
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Bokkapitel (refereegranskat)abstract
- This contribution deals with an assessment of the added value resulting from the use of a multiscale model of concrete as the basis for structural analysis of a segmental tunnel ring. The assessment rests on the comparison of a triad of results. They are obtained from a real-scale test of a segmental tunnel ring, from conventional structural analysis based on the concrete model of the fib Model Code, and from multiscale structural analysis based on a more recently developed multiscale model of concrete. In the experiment, a segmental tunnel ring was subjected to point loads simulating ground pressure. For both modes of structural analysis, a nonlinear hybrid method was used. It is termed hybrid, because not only the external loading was part of the input, but also the displacements at the joints were measured during testing. The method is nonlinear, because bending-induced cracking of concrete is accounted for. The analyzed segmental tunnel ring was subdivided into elements that are either intact or contain one central crack band. Structural analysis was based on transfer relations, representing analytical solutions of the linear theory of circular arches. As for the convergences, it is shown that conventional and multiscale structural analysis are equally reliable. Concerning cracking of concrete, it is demonstrated that multiscale structural analysis allows for a correct prediction of the initiation of cracking, while the results from conventional structural analysis overestimate the external loading at initiation of cracking by 86%. This underlines the added value of multiscale structural analysis for durability analysis of segmental tunnel linings with a designed service life of 100 years and more. © 2021 Elsevier Ltd. All rights reserved.
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| 6. |
- Zhang, Jiaolong, et al.
(författare)
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On the added value of multi-scale modeling of concrete
- 2022
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Ingår i: Frontiers of Structural and Civil Engineering. - : Springer. - 2095-2430 .- 2095-2449. ; 16:1, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- This review of the added value of multi-scale modeling of concrete is based on three representative examples. The first one is concerned with the analysis of experimental data, taken from four high-dynamic tests. The structural nature of the high-dynamic strength increase can be explained by using a multi-scale model. It accounts for the microstructure of the specimens. The second example refers to multi-scale thermoelastic analysis of concrete pavements, subjected to solar heating. A sensitivity analysis with respect to the internal relative humidity (RH) of concrete has underlined the great importance of the RH for an assessment of the risk of microcracking of concrete. The third example deals with multi-scale structural analysis of a real-scale test of a segmental tunnel ring. It has turned out that multi-scale modeling of concrete enables more reliable predictions of crack opening displacements in tunnel segments than macroscopic models taken from codes of practice. Overall, it is concluded that multi-scale models have indeed a significant added value. However, its degree varies with these examples. In any case, it can be assessed by means of a comparison of the results from three sources, namely, multi-scale structural analysis, conventional structural analysis, and experiments.
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