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- Broo, Helén, 1968, et al.
(författare)
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Non-linear finite-element analysis of the shear response in prestressed concrete bridges
- 2009
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Ingår i: Magazine of Concrete Research. - : Thomas Telford Ltd.. - 1751-763X .- 0024-9831. ; 61:8, s. 591 -608
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Tidskriftsartikel (refereegranskat)abstract
- For the structural assessment of concrete bridges, the non-linear finite-element method has become an important and increasingly used tool. The method has shown a great potential to reveal higher load-carrying capacity compared with conventional assessment methods. However, the modelling method used for reinforced and prestressed concrete members subjected to shear and torsion has been questioned. The aim of this study is to present an analysis method for evaluation of the load-carrying capacity of prestressed concrete bridges, when failure resulting from shear and torsion is the main problem. The modelling method used was previously worked out and verified for shear-type cracking and shear failure. Here, shell elements with embedded reinforcement were used together with non-linear material models, taking into account the fracture energy of cracking plain concrete and the reduction of the concrete compression strength owing to lateral tensile strain. Analyses with the method proposed have shown to predict the shear response and the shear capacity on the safe side. In the work presented here, the load-carrying capacity of a box-girder bridge was evaluated as a case study. The whole bridge was modelled, but only the part that was most critical to shear and torsion was modelled according to the method previously worked out and was combined with beam elements for the rest of the bridge. The case study showed a substantially higher load-carrying capacity for the bridge compared with the assessment with conventional methods. In the evaluation, several possible safety formats were used in combination with the non-linear finite-element method. It was shown that the format using partial safety factors gave unrealistic conservative results; it is more correct to use the semi-probabilistic formats for non-linear finite-element analysis. © 2009 Thomas Telford Ltd.
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| 3. |
- Broo, Helén, 1968, et al.
(författare)
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Reinforced and prestressed concrete beams subjected to shear and torsion
- 2007
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Ingår i: Fracture Mechanics of Concrete and Concrete Structures. - 9780415440660 ; 2, s. 881-888
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Konferensbidrag (refereegranskat)abstract
- Today, the nonlinear finite element method is commonly used by practicing engineers, although design and assessment for shear and torsion in reinforced concrete structures are still made using methods based on sectional forces. By modelling the shear behaviour, using 3D nonlinear FEM, higher load carrying capacity and more favourable load distribution was shown, compared to conventional analysis. A modelling method using four-node curved shell elements with embedded reinforcement was evaluated in this study. Tests of reinforced and prestressed beams loaded in bending, shear and torsion were simulated. The increase in shear capacity, in addition to the reinforcement contribution, was modelled with a relationship for concrete in tension according to the modified compression field theory and compared with the use of a relationship related to the fracture energy of plain concrete. The results show that evaluations of the load-carrying capacity or crack width will be on the safe side, if only the fracture energy is used to define the concrete in tension.
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| 4. |
- Broo, Helén, 1968, et al.
(författare)
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Shear and torsion in hollow core slabs
- 2005
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Ingår i: Proceedings Nordic Concrete Research Meeting. - 8291341915 ; , s. 305-307
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Konferensbidrag (refereegranskat)abstract
- In many applications hollow core units are subjected to combined torsion and shear. The present calculation method adds stresses from various effects linearly. Here, advanced non-linear finite element modelling methods were developed and verified against full-scale tests, both for whole floors, and for individual hollow core units. By combining these two modelling methods, it is possible to design hollow core floors with arbitrary geometries and loadings for shear and torsion. Compared to the traditional approach the modelling method for units resulted in higher capacities for most ratios of shear and torsion and the floor model showed reduced torsional moments.
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| 5. |
- Broo, Helén, 1968, et al.
(författare)
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Shear and torsion in prestressed hollow core units:finite element analyses of full-scale tests
- 2007
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Ingår i: Structural Concrete. ; 8:2, s. 87-100
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Tidskriftsartikel (refereegranskat)abstract
- The present calculation methods for shear and torsion in prestressed hollow core slabs add stresses from various influences without taking into account deformations and compatibility, the softening of cracking concrete, or restraint at the boundaries, therefore they are most likely conservative. The main purpose of this work is to establish three-dimensional finite element models, which can be used both to analyse the effect of parameters that influence the shear and torsion response and to be included in global models of complete floors. An important aspect was therefore to simplify the models to avoid time-consuming analyses. Coarse meshes with solid elements were combined with beam elements. The established models were validated by simulating a series of full-scale tests conducted on both 200 mm and 400 mm thick hollow core units subjected to various combinations of shear and torsion. In general, although very coarse meshes were used, the finite element analyses of the tests succeeded in describing the overall behaviour, crack pattern, failure mode, and maximum load, with a reasonably good agreement.
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| 6. |
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| 7. |
- Broo, Helén, 1968, et al.
(författare)
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Simulation of shear-type cracking and failure with non-linear finite element method
- 2007
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Ingår i: Magazine of Concrete Research. - : Thomas Telford Ltd.. - 1751-763X .- 0024-9831. ; 59:9, s. 673-687
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Tidskriftsartikel (refereegranskat)abstract
- Today, the non-linear finite element method is commonly used by practising engineers. Simulating the shear behaviour and shear failure of reinforced concrete structures, using three-dimensional non-linear finite element methods, has shown higher load-carrying capacity due to favourable load distribution, compared to conventional analyses. However, the modelling method for reinforced and prestressed concrete members subjected to shear and torsion has not been generally verified. Therefore, the method needs to be further investigated and confirmed to be practically reliable. The aim of this project is to develop, improve and verify a method to simulate the shear response of reinforced and prestressed concrete members. The method should be possible to use for large structures, for example box-girder bridges, subjected to various load actions. Experiments with panels loaded in shear and beams loaded in bending, shear and torsion are simulated by using non-linear FE analysis. The results showed that four-node curved shell elements with embedded reinforcement could simulate the shear response. It is well known that the shear sliding capacity is larger than what can be explained by the reinforcement contribution determined from a truss model. This increase is due to dowel action and aggregate interlock, and has been accounted for in the past by modifying the concrete tension response in models, e.g. according to the modified compression field theory. Results from the analyses show that without any modification, the capacity was underestimated and the average strains, i.e. the crack widths, were overestimated. On the other hand, if the concrete contribution to the shear capacity was considered with the expression from MCFT, the capacity was in many cases overestimated and the average strains underestimated.
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| 9. |
- Engström, Björn, 1950
(författare)
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Ductility of Tie Connections in Precast Structures
- 1992
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Precast concrete structures are normally provided with tie connections that make it possible to transfer tensile forces across the joints. The tie connections are essential for the structural integrity and can contribute to the formation of alternative load-bearing systems in case of local damages of the structure. The aim of the present research was to develop a method for prediction of the load-displacement characteristics of tie connections in the plastic stage. Tie connections between concrete elements were studied experimentally. The load-displacement relationship and the strain distribution along the tie bar were evaluated from measurements. In most of the tests it was possible to obtain large plastic deformations and the ultimate displacement was determined by the rupture of the reinforcing steel. The anchorage capacity of tie bars anchored in grouted joints between hollow core elements was studied in separate test series. A numerical approach was developed for the analysis of tie connections in the plastic stage. The local bond-slip behaviour of the steel-to-concrete interface and the strain hardening of the steel were considered in the analysis. The bond-slip relationships that are recommended today could not be used in the calculations as the yield penetration along the embedded tie bar and, as a result, the displacement was considerably underestimated. Modified bond-slip relationships are proposed which take into account the yielding of the steel. It was found that the load-displacement relationship often had the same proportions as long as ductile types of tie bars were used even when the strength of steel and concrete varied substantially. The relative strain energy was defined and was found to be a valuable parameter describing the ductile behaviour of tie connections. An approach for the analysis of alternative load-bearing system is presented and exemplified. The approach is based on a condition of energy equilibrium. It is shown how the dynamic resistance of an alternative load-bearing system is affected by the ductility and the deformability of tie connections. The theoretical approach was confirmed by dynamic tests where a collapse situation was simulated.
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| 10. |
- Engström, Tomas, 1950, et al.
(författare)
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Materialhantering i storkök. Delrapport
- 1984
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Consumer report ("avnämarrapport" in Swedish) for a research foundation (Styrelse för Teknisk Utveckling STU, Stockholm). This research project was carried out together with personnel from the Swedish Food Institute SIK, Gothenburg. A comment: Publishing consumer reports was the praxis during this (early) period of time at Chalmers University of Technology, as well as probably at some other universities. This means that frequent and vast academic publication by means of e.g. conference papers and refereed contributions to scientific journals was almost unheard of. At least so for some of the applied science disciplines (today are the situation indeed very different) (i.e. earlier was the publication in many respects focused on trying to satisfy the executive administrator the research foundation in question).
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