| 1. |
- Andersson, Patrik, 1974, et al.
(författare)
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Framtidsbilder för samhällsbyggnad
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Framtidsbilder för samhällsbyggnad 2020De kommande 15 åren står institutionen för Bygg- och miljöteknik inför stora förändringar. Därför har institutionen initierat projektet Framtidsbilder 2020 där man engagerat en framtidspanel bestående av elva yngre disputerade forskare. Arbetet inleddes med ett breddgruppsmöte där 110 personer representerande institutionens personal och studenter deltog. Vid mötet identifierades ett antal trender och osäkra utvecklingar som påverkar framtiden inom samhällsbyggnadsområdet. Deltagarna bidrog också med idéer till en önskvärd utveckling, vilket har sammanställts och utgör grunden till en gemensam önskvärd framtid/vision för institutionen. Materialet från breddgruppsmötet har bearbetats av Framtidspanelen och resulterat i fyra scenarier som beskriver hur samhällsbyggnadsområdet kan se ut år 2020. Syftet med framtidsbilderna är att de ska vara vägledande för institutionens beslut och förhållningssätt under de kommande åren.Fyra scenarierTurning TorsoSamhället präglas av en ekonomi som är på uppgång, och av ett nytänkande och öppet samhälle. Materiell status och individualism är viktigt. Detta leder till en hög arbetsbelastning samt krav på exklusiva varor av hög kvali-tet. Det finns en stor medvetenhet om miljöpåverkan och klimatförändringar och lösningarna för att klara energiförsörjningen är innovativa.Eco-metropolenDet sveper en grön våg genom dagens samhälle. Under de senaste 15 åren har vi insett att jorden skall vara en bebolig plats även åt dem som kommer efter oss. Vi söker ständigt efter nya, mer förfinade metoder att tillvarata de resurser vi har. Samhället och individen är i balans. Ekonomin är god och vi är miljömedvetna, trygga och integrerade. Nytänkande premieras och icke- materialistiska värderingar står högt i kurs. Vi tänker individuellt, men agerar mer än gärna för kollektivets bästa. Utbildning är gratis TrädgårdsstadenEtt samhälle där vi lärt oss hantera stress, men känner oss otrygga och helst umgås i slutna sociala sammanhang. Vi bor enkelt inne i stan, eller gärna på landsbygden nära storstäderna. Minskade behov av högutbildade i samhället gör att vi har svårt att rekrytera studenter till teknikutbildningar. Det traditionella tankesättet leder till kulturkrockar med företag och personer från andra länder.Gated communitiesFörsämrad ekonomi och ökad egoism har lett fram till ett stressat, otryggt och segregerat samhälle. Accelererande klimatförändringar och ökad miljö-påverkan skrämmer oss, men trots det åtgärdar vi inte problemen, utan koncentrerar oss på konsekvenserna. Arbetslöshet i samhällsbyggnadssek-torn leder till sänkt status för samhällsbyggaren. Vi har därför svårt att rekrytera studenter, och även forskningen har låg status.
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| 2. |
- Broo, Helén, 1968, et al.
(författare)
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A guide to non-linear finite element modelling of shear and torsion in concrete bridges
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Non-linear finite element (FE) analysis has become an important tool for structural design and assessment of reinforced concrete structures. When shear and torsion are limiting the capacity of a structure, three dimensional non-linear finite element methods often show higher load-carrying capacity compared to conventional analyses; therefore there is much to gain by using these methods, especially at assessment of existing structures. The reason for the higher capacities evaluated are mainly a more favourable load distribution when the structure is analysed in three dimensions and that the fracture energy associated with concrete cracking is included. In order to be able to use these higher capacities in reality, it is important that the modelling method is verified and to be aware of possible limitations. Recommendations are given concerning analysis methods and how a verification can be done, both concerning the capability of the program and concerning the actual FE model. Most important comments and recommendations are:•It is important to note that in FE programs commercially available today, beam elements cannot describe shear cracking and shear failure or reduced torsional stiffness due to cracking. The same applies for the out-of-plane shear in shell elements.•Most often in analysis of bridges, it is enough to assume full interaction between the reinforcement and the concrete. One exception is if the slip is important for the global response or the final failure, as if a shear failure takes place in a region where prestressing is anchored. Then the modelling should include slip between the steel and the concrete.•It is recommended that only the fracture energy of plain concrete is taken into account when defining the softening response of concrete, i.e. when the stress-strain relationship of the concrete is defined. This will yield results on the safe side; i.e. underestimation of the capacity and overestimation of deformations and crack widths.•It is often more stable to perform analyses using deformation control than load control. A method to enable deformation-controlled loading for several point loads by using a separate statically determined arrangement of stiff beams is described.Comments and recommendations are also given concerning how to model important details such as supports and connections, how different loading types can be considered, how to perform the analyses, how to evaluate the results through post-processing, and how to use the results in a safety format context.
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| 3. |
- Broo, Helén, 1968, et al.
(författare)
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Finite Element Analyses of Hollow Core Units Subjected to Shear and Torsion
- 2002
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Precast prestressed hollow core units are among the most advanced and widely spread products in the precast industry. The present calculation method for shear and torsion in hollow core slabs adds stresses from various influences without considering deformations and compatibility, the softening of cracking concrete, or restraint at the boundaries, and is therefore most likely conservative. The aim of this work is to improve the current knowledge and understanding of shear and torsion interaction in hollow core floors.This report deals with finite element analyses of individual hollow core units, subjected to different combinations of shear and torsion. Most of these analyses concern full-scale tests on hollow core units that were planned in cooperation with VTT and Strängbetong, and conducted at VTT during June and August 2002. Prestressed hollow core units of two thicknesses, 200 mm and 400 mm, were tested both with and without eccentric loading. The analyses were made with various levels of detailing, using the finite element program DIANA 7.2.The aim was to use a modelling technique that does not result in too time consuming analyses, but still gives a reasonable good agreement. In the final analyses presented here, only the part of the slab closest to the load and the active support was modelled with solid elements. The rest of the slab was modelled with beam elements. The concrete was modelled using non-linear fracture mechanics in a smeared rotating crack model.In general the finite element analyses of the tests were able to capture the overall behaviour, failure mode, crack pattern, and maximum obtained load, with a reasonably good agreement, though a very coarse mesh were used in the analyses. Especially for the centrically loaded specimens, the agreement was good. However, for the eccentrically loaded hollow core units the maximum load was overestimated. The reason for this is most likely that the torsional stiffness of the beam elements used in the model was too high.
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| 4. |
- 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.. - 0024-9831 .- 1751-763X. ; 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
- 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.. - 0024-9831 .- 1751-763X. ; 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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| 10. |
- Lundgren, Anna, 1974, et al.
(författare)
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Mucosal FOXP3-expressing CD4+ CD25high regulatory T cells in Helicobacter pylori-infected patients
- 2005
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Ingår i: Infect Immun. ; 73:1, s. 523-31
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Tidskriftsartikel (refereegranskat)abstract
- Helicobacter pylori chronically colonizes the stomach and duodenum and causes peptic ulcers or gastric adenocarcinoma in 10 to 20% of infected individuals. We hypothesize that the inability of patients to clear H. pylori infections is a consequence of active suppression of the immune response. Here we show that H. pylori-infected individuals have increased frequencies of CD4(+) CD25(high) T cells in both the stomach and duodenal mucosa compared to uninfected controls. These cells have the phenotype of regulatory T cells, as they express FOXP3, a key gene for the development and function of regulatory T cells, as well as high levels of the cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) protein. In contrast, mucosal CD4(+) CD25(low) and CD4(+) CD25(-) cells express little FOXP3 mRNA and low levels of the CTLA-4 protein. Mucosal CD4(+) CD25(high) T cells are present in individuals with asymptomatic H. pylori infections as well as in duodenal ulcer patients. The frequencies of CD4(+) CD25(high) cells are also increased in the stomachs of H. pylori-infected patients with gastric adenocarcinoma, particularly in cancer-affected tissues. These findings suggest that regulatory T cells may suppress mucosal immune responses and thereby contribute to the persistence of H. pylori infections.
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