| 1. |
- Gottsäter, Erik, et al.
(författare)
-
Simulation of thermal load distribution in portal frame bridges
- 2017
-
Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 143, s. 219-231
-
Tidskriftsartikel (refereegranskat)abstract
- Uneven exposure to e.g. solar radiation can cause temperature differences between various structural parts of a bridge, which leads to tensile stresses if the parts cannot move freely. In this study, thermal simulations and stress calculations on a model of a portal frame bridge are performed with the aim of evaluating the temperature difference between the bridge parts. Factorial design is used in a parametric study to determine the influence of different factors on the temperature difference and the largest reasonable temperature difference obtainable for the chosen weather data. The study shows that the quasi-permanent temperature difference between parts which is proposed by Eurocode 1 is overestimated, causing tensile stresses in the transverse direction to be exaggerated significantly. Using the design method proposed by Eurocode 1 is therefore likely to overestimate the required reinforcement in crack width limit design, which in turn would lead to unnecessary costs and environmental impacts. The results also indicate that the temperature distribution within the bridge is different from what is given in Eurocode load cases, and consequently, the largest tensile stresses appear in other areas of the bridge. A simplified temperature distribution is therefore investigated and shown to give similar results as the detailed thermal simulations.
|
|
| 2. |
- Nilenius, Filip, 1982, et al.
(författare)
-
A 3D/2D comparison between heterogeneous mesoscale models of concrete
- 2013
-
Ingår i: RILEM Bookseries. - Dordrecht : Springer Netherlands. - 2211-0844 .- 2211-0852. - 9789400768772 ; 8, s. 249-259
-
Konferensbidrag (refereegranskat)abstract
- A model for 3D Statistical Volume Elements (SVEs) of mesoscale concrete is presented and employed in the context of computational homogenization. The model is based on voxelization where the SVE is subdivided into a number of voxels (cubes) which are treated as solid finite elements. The homogenized response is compared between 3D and 2D SVEs to study how the third spatial dimension influence the over-all results. The computational results show that the effective diffusivity of the 3D model is about 1.4 times that of the 2D model.
|
|
| 3. |
- Nilenius, Filip, 1982, et al.
(författare)
-
A multi-scale method for modeling of moisture and chloride ion transport in concrete
- 2011
-
Ingår i: Nordic Concrete Research. - 0800-6377. - 9788282080255 ; XXI
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modelling and simulation of moisture and chloride ion transport in concrete is carried out using a multi-scale approach due to the strongly heterogeneous structure of concrete. The macro-scale problem is solved using the finite element method (FEM) where the material response in each Gauss-point is obtained by setting up a new finite element problem on a representative volume element (RVE). The RVE, in turn, consists of the meso-scale constituents of concrete and the solution to the RVE problem is homogenized and sent back to the macro-scale domain. Hence,the RVE problem serves in this fashion as a constitutive model for the macro-scale problem.
|
|
| 4. |
- Nilenius, Filip, 1982, et al.
(författare)
-
Chloride transport in concrete modeled by the FE^2-method
- 2011
-
Ingår i: Proceedings of NSCM-24, the 24th Nordic Seminar on Computational Mechanics. - 1799-4896. - 9789526043470 ; 24, s. 107-110
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An FE^2-method is employed for modeling diffusion of chloride ions in concrete. Concrete is considered on the mesoscale, within a representative volume element (RVE), as a heterogeneous composite material consisting of the cement paste, ballast and the interfacial transition zone (ITZ). In addition, the proposed model accounts for the fact that the diffusion of chloride ions is cross-coupled to the diffusion of moisture.
|
|
| 5. |
- Nilenius, Filip, 1982, et al.
(författare)
-
Computational homogenization of diffusion in three-phase mesoscale concrete
- 2014
-
Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 54:2, s. 461-472
-
Tidskriftsartikel (refereegranskat)abstract
- A three dimensional (3D) mesoscale model of concrete is presented and employed for computational homogenization in the context of mass diffusion. The mesoscale constituents of cement paste, aggregates and Interfacial Transition Zone (ITZ) are contained within a Statistical Volume Element (SVE) on which homogenization is carried out. The model implementation accounts for ITZ anisotropy thereby the diffusivity tensor depends on the normal of the aggregate surface. The homogenized response is compared between 3D and 2D SVEs to study the influence of the third spatial dimension, and for varying mesoscale compositions to study the influence of aggregate content on concrete diffusivity. The computational results show that the effective diffusivity of 3D SVEs is about 40% greater than 2D SVEs when ITZ is excluded for the SVE, and 17% when ITZ is included. The results are in agreement with the upper Hashin-Shtrikman bound when ITZ is excluded, and close the Taylor assumption when ITZ is included.
|
|
| 6. |
- Nilenius, Filip, 1982, et al.
(författare)
-
Determining effective diffusion properties of concrete through mesoscale analysis
- 2012
-
Ingår i: Microstructural-related Durability of Cementitious Composites: Second international conference. - 9782351581230 ; :2, s. 214-
-
Konferensbidrag (refereegranskat)abstract
- Diffusivity of both moisture and chloride ions in concrete are determined here by the use of computational homogenization. Concrete is modelled on the mesoscale as a heterogeneous three-phase material within a representative volume element (RVE), consisting of the pure cement, gravel and interfacial transition zone (ITZ). By imposing moisture and chloride ion gradients over the RVE, its response is solved for and homogenized through finite element (FE) analysis and computational homogenization. By this method, the diffusivity of concrete is determined as a function of the ballast content within the RVE. The numerical results correspond well with an analytical model used for determining the influence of ballast on concrete.The model proposed here allows for the inclusion and study of the ITZ and its influence on the diffusivity. In practise, the ITZ is included in the FE model as lattice elements placed in between the cement paste and ballast. In this manner, it was possible to determine the diffusivity coefficient of ITZ by calibrating the model to experimental data of concrete diffusivity.Furthermore, a multiscale (FE2) framework, for coupled chloride ion and moisture transfer in concrete is also presented. The mass transfer problem is set up as an initial boundary value problem on the macroscale where the mesoscale heterogeneities are introduced via RVEs in the Gauss-points. The macroscale quantities in terms of mass fluxes are obtained through suitable homogenization of the RVE response in a nested fashion during the computations. In this manner, the RVE problem serves as a constitutive model for the macroscale. The overall goal is to better simulate chloride ion and moisture transfer in concrete by including the strong heterogeneities of the material in the model.
|
|
| 7. |
- Nilenius, Filip, 1982, et al.
(författare)
-
FE2 Method for Coupled Transient Diffusion Phenomena in Concrete
- 2015
-
Ingår i: Journal of Engineering Mechanics - ASCE. - 1943-7889 .- 0733-9399. ; 141:2, s. Art. no. 04014110-
-
Tidskriftsartikel (refereegranskat)abstract
- Acoupled finite-element squared (FE2)-framework is formulated and employed for simulation of a transient and coupled moisturechlorideion diffusion problem in concrete. Simulations are carried out on the macroscale, where the material response is obtained concurrentlyin the computations by introducing a representative volume element (RVE) in the macroscale quadrature points. The RVE, in turn, contains themesoscale heterogeneities of concrete in terms of cement paste, aggregates, and interfacial transition zone (ITZ). In this fashion, the RVE comesto serve as a constitutive model for the macroscale.Anumerical example is given to show how the transient macroscale diffusion is influenced bythe composition of the mesoscale constituents. Parametric studies were carried out with respect to the aggregate content within the RVE, bothincluding and excluding the ITZ, and the coupling parameters of moisture and chloride ions.
|
|
| 8. |
- Nilenius, Filip, 1982, et al.
(författare)
-
Macroscopic diffusivity in concrete determined by computationalhomogenization
- 2013
-
Ingår i: International Journal for Numerical and Analytical Methods in Geomechanics. - : Wiley. - 0363-9061 .- 1096-9853. ; 37:11, s. 1535-1551
-
Tidskriftsartikel (refereegranskat)abstract
- Effective moisture and chloride ion diffusivity coefficients for concrete are determined by computational homogenization, where concrete is modeled on the mesoscale as a heterogenous three-phase composite material. By imposing moisture and chloride ion gradients on a representative volume element, effective macroscale properties are obtained through finite element analysis. A parametric study of the effects of the ballast content was carried out. The numerical results correspond well with an estimate of the Hashin-Shtrikman type available in the literature. The computational homogenization strategy proposed here also includes the interfacial transition zone, and its influence on the effective diffusivity coefficients is assessed.
|
|
| 9. |
- Nilenius, Filip, 1982, et al.
(författare)
-
Mesoscale modelling of crack-induced diffusivity in concrete
- 2015
-
Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 55:2, s. 359-370
-
Tidskriftsartikel (refereegranskat)abstract
- Cracks have large impact on the diffusivity of concrete since they provide low-resistance pathways for moisture and chloride ions to migrate through the material. In this work, crack-induced diffusivity in concrete is modelled on the heterogeneous mesoscale and computationally homogenized to obtain macroscale diffusivity properties. Computations are carried out using the finite element method (FEM) on three-dimensional Statistical Volume Elements (SVEs) comprising the mesoscale constituents in terms of cement paste, aggregates and the Interfacial Transition Zone (ITZ). The SVEs are subjected to uni-axial tension loading and cracks are simulated by use of an isotropic damage model. In a damaged finite element, the crack plane is assumed to be perpendicular to the largest principle strain, and diffusivity properties are assigned to the element only in the in-plane direction of the crack by anisotropic constitutive modelling.The numerical results show that the macroscale diffusivity of concrete can be correlated to the applied mechanical straining of the SVE and that the macroscale diffusivity increases mainly in the transversal direction relative to the axis of imposed mechanical straining.
|
|
| 10. |
- Nilenius, Filip, 1982, et al.
(författare)
-
Modeling of mass transfer in the micro-structure of concrete: Towards computational homogenization within a FE2-strategy
- 2010
-
Ingår i: Proceedings of NSCM-23: the 23rd Nordic Seminar on Computational Mechanics. - 0348-467X. ; :Number: 23, s. 322-325
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Chloride ion ingress in concrete is of great concern for concrete structures as the ions can initiate corrosion of embedded reinforcement bars. The micro-scale constituents of concrete are the cement paste and gravel, and the porosity of the cement paste allows for transport of chloride ions. Furthermore, the transport of chloride ions within the cement paste is nonlinearly coupled to the transport of moisture. Due to this nonlinearity, and the heterogenous micro-structure of concrete, it is of interest to find a suitable homogenization tool in order to simulate mass transfer on the macro-scale level.In this paper, simulations of coupled chloride ion and moisture transfer in concrete are presented. The problem is set up as an initial boundary value problem on a representative volume element (RVE) with impermeable gravel embedded in the porous cement paste. The mass transfer is modeled as being of diffusion type, which allows for implementation of Fick's law and adsorption isotherms as constitutive models. Boundary conditions are set up for varying conditions on the macro-scale and the problem is solved numerically using the cG(1)dG(0) finite element method in space-time. Finally, homogenization over the RVE is applied in order to establish the pertinent macro-scale quantities.A discussion of the mass transfer models and their assumptions is given in relation to the physical mechanisms governing mass transfer in concrete. Simulations are presented for different setups of micro-structures and boundary conditions, showing the relation between the macro-scale response and the micro-structure. Finally, an outlook towards a concurrent computational multiscale model is given, which means that a macro-scale problem is solved concurrently with multiple micro-scale problems in a nested, so-called FE^2, fashion.
|
|
