| 11. |
- Berbyuk, Viktor, 1953, et al.
(författare)
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Towards early ice detection on wind turbine blades using acoustic waves
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819499899 ; 9063, s. 90630F-1 - 90630F-11-
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Konferensbidrag (refereegranskat)abstract
- The study focuses on the early detection of ice using controlled acoustic waves propagating in the wind turbine blades.An experimental set-up with a cold climate chamber, a composite test object used in turbine blades and equipment for glaze and rime ice production has been developed. Controlled acoustic waves are generated by magnetostrictiveTerfenol-D based actuator. The propagation of three orthogonally polarized acoustic waves was studied by means of 6 accelerometers positioned, 3 each, in 2 holders on the 8 m long composite test object. The results show that for the considered composite test object the formation of ice, the ice mass, icing areas and the temperature have a significant influence on controlled acoustic waves propagation w.r.t. Fourier transform, amplitude attenuation and RMS values as indicators concluding that the proposed acoustic wave technique is a promising approach for ice detection.
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| 12. |
- Dahl, Viktor, 1988, et al.
(författare)
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An example of genetically distinct HIV-1 variants in cerebrospinal fluid and plasma during suppressive therapy.
- 2014
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Ingår i: The Journal of infectious diseases. - : Oxford University Press (OUP). - 1537-6613 .- 0022-1899. ; 209:10, s. 1618-1622
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Tidskriftsartikel (refereegranskat)abstract
- We sequenced HIV-1 in 70 CSF and 29 plasma samples and the corresponding pre-therapy samples from 17 subjects on suppressive therapy. More of the CSF sequences were hypermutants than plasma sequences. We generated on-therapy sequences from both CSF and plasma from two subjects; in one we found genetically distinct sequences in CSF and plasma indicating that they came from two different compartments, one potentially the CNS, during suppressive therapy. In addition, there was little evidence of viral evolution in the CSF during therapy, suggesting that continuous virus replication is not the major cause of viral persistence in the CNS.
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| 13. |
- Johansson, Morgan, et al.
(författare)
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Explosionslast och dynamisk strukturrespons i armerade betongkonstruktioner
- 2023
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Ingår i: Bygg och Teknik. - 0281-658X .- 2002-8350. ; 115:6
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Med syfte att frigöra attraktiv markyta för ny bebyggelse finns det imånga svenska städer idag ett önskemål att förtäta den befintliga stadsmiljön. En sådan åtgärd kan dock resultera i minskade avstånd mellan byggnader och transportled, vilket kan medföra ökade krav med hänsyn till bland annat explosioner. För att skapa en optimal helhetslösning för sådana olycksscenarion behöver de tre delområdena riskhantering, explosionslast och strukturrespons samordnas på ett korrekt sätt. I dagens explosionshantering finns dock betydande brister bland både riskanalytiker och konstruktörer, något som ofta beror på otillräcklig kommunikation och kunskap.
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| 14. |
- Peterson, Viktor
(författare)
-
Assessment of shear and energy‐absorption capacity of reinforced concrete elements under impulsive loads
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Impulsive loads have been observed to cause brittle shear failure in reinforced concrete elements designed for ductile failure modes under static loads. Brittle failure modes exhibit poorer energy absorption capabilities compared to ductile flexural failure modes due to their limited deformation capacity, leading to premature failure. The discrepancy between the responses under static and extreme dynamic loads arises from inertia and wave propagation effects, which tend to increase as the load duration decreases relative to the fundamental period of the element. This thesis investigated the occurrence of shear failures in reinforced concrete elements subjected to impulsive loads, both experimentally and numerically, and evaluated to what extent current analysis methods for impulse-loaded structures can predict shear failure. Furthermore, the study examined the influence of crucial parameters on the energy absorption capacity during flexural failure modes when shear failure was inhibited. The results demonstrated that shear-plug damage, prevalent during impact loads, may lead to premature shear failure during sequential impact testing. This occurred for a statically flexure-critical beam with a significantly larger static flexural-shear capacity relative to its flexural capacity. Similar conclusions applied to the residual static capacity after an initial impact introduced shear-plug damage. These findings indicate potentially severe consequences of shear-plug damage, which should be considered when assessing structures damaged by impact loads. The energy absorption capacity of reinforced concrete elements is closely related to the plastic work capacity of the reinforcement. The experimental study showed how the plastic work capacity varied with reinforcement properties, concrete properties, and impact velocity using static and dynamic four-point flexural tests. The results revealed that the reinforcement type, specifically whether the steel is mild or stiff, governs the strain distribution during static and low-velocity impact testing. Generally, stiff steels result in strain localization before rupturing, indicating a lower plastic work capacity. Factors such as stress and strain capacity also proved significant. However, as the impact velocity increased, wave propagation effects governed strain distribution rather than reinforcement type. Numerical studies comparing results with outcomes using proposed design methods indicated agreement for support reactions used to verify the shear capacity in the later stages of the response. However, this agreement decreased in the initial stages of the response. This may be because the dynamic equilibrium method only considers a global response, while the local response due to wave propagation is influential in the initial stages of the response. Today, resources such as Biggs [8] and the Swedish Fortifications Agency [86] recommend using two stages of the response to determine the internal forces; an elastic global response and a later elastoplastic global response. From the observations in the papers, it is suggested to add a third initial stage of the response considering wave propagation effects. However, it is deemed that this response stage only has a significant effect for high-intensity blast loads with short rise times relative to the shear wave velocity.
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| 15. |
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| 16. |
- Peterson, Viktor, et al.
(författare)
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Numerical simulations of shear reinforced RC beams subjected to blast loads
- 2022
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Ingår i: <em>fib Symposium</em>. - : fib. The International Federation for Structural Concrete.
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Konferensbidrag (refereegranskat)abstract
- The numerical simulations presented in the present paper were on beam models geometrically identical to the beams previously tested in a shock tunnel but now provided with increased shear reinforcement consisting of vertical stirrups. The tested beam failed in brittle flexural shear during the blast loading in the tunnel. The results from the numerical investigation showed that brittle shear failures of beams subjected to blast loads may be prevented by dense shear reinforcement. The guideline for impulse loaded structure showed to underestimate the dynamic shear capacity as it is not dependent on the actual transverse reinforcement amount. This is however considered in the model used for determining the static shear capacity, meaning that further work developing a similar model fit to impulse loading is advised. To realize this development a new test series is proposed.
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| 17. |
- Peterson, Viktor, et al.
(författare)
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On the Residual Static and Impact Capacity of Shear-Reinforced Concrete Beams Subjected to an Initial Impact
- 2022
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 12:22, s. 11377-
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Tidskriftsartikel (refereegranskat)abstract
- Impact loads in previous research showed to induce brittle responses of statically flexure-critical reinforced concrete (RC) beams designed for ductility. The impact load may produce flexural shear damage modes similar to that observed during quasi-static loads and local shear damage under the impact zone. The occurrence of shear damage modes during impact tests has been investigated extensively, but their effect on the residual quasi-static and dynamic capacity is not fully understood. For this aim, an initial high-velocity impact test initiated severe shear damage to RC beams. The beams were then tested quasi-statically and by sequential impact testing using the same setup as the initial tests. The results indicate a flexure-dominated response during sequential impact tests for beams containing extreme shear reinforcement amounts, favouring the energy-absorption capacity. Significant shear and flexural damage occurred for beams with less shear reinforcement, indicating a hybrid response that varied throughout the tests. The tests for the residual quasi-static capacity indicated severe consequences from initial local shear damage on the capacity, as shown by the brittle response of the beam with the most shear reinforcement. However, wide initial flexural cracks instead showed a favourable effect, as there was an indication of transfer from brittle to ductile failure. For beams showing both global and local shear damage, it was concluded that global shear damage modes were critical for the residual static and dynamic shear capacity.
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| 18. |
- Peterson, Viktor, et al.
(författare)
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Static and Dynamic Four-Point Flexural Tests of Concrete Beams with Variation in Concrete Quality, Reinforcement Properties and Impact Velocity
- 2021
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Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 65:2, s. 19-38
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the results from three experimental test series previously conducted. The tests consist of quasi-static monotonic and dynamic four-point flexural tests on reinforced concrete beams. The effect of varying material and load parameters on the plastic strain distribution and energy absorbed by the reinforcement is discussed. The main findings are the significant effect of the post-elastic region of the steel reinforcement and the impact velocity during dynamic loading. The results will be used to validate and construct numerical models in future work, where the findings presented can be investigated further.
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| 19. |
- Peterson, Viktor, et al.
(författare)
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The effect of explosions in road tunnels on critical structural elements
- 2023
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Ingår i: Expanding Underground - Knowledge and Passion to Make a Positive Impact on the World. - : CRC Press/Balkema. ; , s. 3263-3271
-
Konferensbidrag (refereegranskat)abstract
- In the present paper, the walls of a concrete frame used for over-decking in a road tunnel were first designed using the relevant design provisions. The response of the wall was then analysed using non-linear finite element analysis, and the results of the finite element analysis were compared to what was predicted using the design guidelines. Additionally, simulations of the blast load resulting from gas leakage during transportation were conducted as a separate study. The results from two vapour clouds containing gases of hydrogen and propane were compared.
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| 20. |
- Sjölander, Andreas, Ph.D, 1983-, et al.
(författare)
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Experimental dataset to assess the structural performance of cracked reinforced concrete using Digital Image Correlation techniques with fixed and moving cameras
- 2023
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Ingår i: Data in Brief. - : Elsevier BV. - 2352-3409. ; 51
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Tidskriftsartikel (refereegranskat)abstract
- The infrastructure is in many countries aging and continuous maintenance is required to ensure the safety of the structures. For concrete structures, cracks are a part of the structure's life cycle. However, assessing the structural impact of cracks in reinforced concrete is a complex task. The purpose of this paper is to present a dataset that can be used to verify and compare results of the measured crack propagation in concrete with the well-known Digital Image Correlation (DIC) technique and with Crack Monitoring from Motion (CMfM), a novel photogrammetric algorithm that enables high accurate measurements with a non-fixed camera. Moreover, the data can be used to investigate how existing cracks in reinforced concrete could be implemented in a numerical model.The first potential area to use this dataset is structural engineering. The data can be used to verify non-linear material models used in a finite element (FE) software to simulate the structural response of reinforced concrete. In particular, the data can be used to investigate how existing cracks should be modelled in a FE model. The second potential area is within image processing techniques with a focus on DIC. Until recently, DIC suffered from one major disadvantage; the camera must be fixed during the entire period of data collection. Naturally, this decreases the flexibility and potential of using DIC outside the laboratory. In a recently published paper [1], an innovative photogrammetric algorithm (CMfM) that enables the use of a moving camera, i.e. a camera that is not fixed during data acquisition, was presented. The imagery of this dataset [2] was used to verify the potential of this algorithm and could be used to validate other approach for non-fixed cameras.The dataset presented in this paper includes data collected from a three-point bending test performed in a laboratory environment on uncracked and pre-cracked reinforced concrete beams. Structural testing was performed using a displacement-controlled set-up, which continuously recorded the force and the vertical displacement of a centric-placed loading piston. First, the response of three uncracked beams was recorded. Thereafter, photos of the resulting cracks were taken, and a detailed mapping was presented. Material properties for the concrete, e.g., compressive strength, are presented together with testing of the tensile capacity of the reinforcement and a compressive test of the soft fiber boards used at the support to ensure good contact between steel and concrete. Then, the structural response of the pre-cracked beams was tested. During this test, four fixed cameras were used to monitor the crack propagation at different locations on the beam. Images are presented at the start of the load sequences and at pre-defined load stops during the testing. Hence, the crack opening captured in the images can be correlated to the force-displacement data. Moreover, a non-fixed camera was used to capture additional imagery at the location of each fixed camera.
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