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  • 51.
    Bennitz, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Mechanical anchorage of prestressed CFRP tendons: theory and tests2008Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Fibre Reinforced Polymers (FRPs) are slowly becoming important materials to consider also for a structural engineer. They are light-weight, insensitive to corrosion and have highly modifiable mechanical properties. Strengths five times higher than that of ordinary reinforcing steel are common and that combined with the possibility to vary the modulus of elasticity makes them suitable to use in combination with concrete. Carbon fibre based polymers (CFRPs) especially serve as an excellent substitute for steel in the rehabilitation of structures. A case study on that subject is presented in this thesis while the focus lies on the use of CFRP as a material for use in prestressing tendons, and to be more precise, on the anchorage of prestressed CFRP tendons. FRPs orthotropic properties highly influence their behaviour in different directions. The best properties are reached through tension in the fibre direction, and as such CFRP is as good for prestressing tendons as any prestressing steel. It is also not sensitive to corrosion and easy to work with due to its light weight. Mechanical properties in the transverse direction are however not that advantageous and early attempts to anchor CFRP bars by traditional mechanical prestressing anchorages have consistently failed. A thorough program for the development of a successful anchorage has therefore been undertaken. In a first step a literature review was conducted to investigate CFRPs possibilities to replace steel in prestressing applications, internally and externally, as well as traditional anchorage techniques for steel tendons. From the literature study it was concluded that CFRP may very well serve as tendons but some doubts also arose concerning the environmental effect on the CFRPs long term behaviour and the materials ability to work under bent conditions in multispan applications. The traditional anchorages will however not work properly, all of them use mechanical grip to keep the steel stressed. This is possible through the steels capacity to yield but not suitable to anchor the brittle CFRP. A state-of-the-art survey on attempts made globally during the last 15 years to come up with a suitable frictional anchorage has also been performed. It can be seen that several ideas are discussed, often in one or two publications. One Canadian research team, Al-Mayah et al. (2001-2008), has taken the development further and focused on variations of the traditional wedge anchorage. Based on the knowledge gained from the literature it was decided to further concentrate on a conical anchorage with a barrel of steel and three smooth wedges in aluminium. Simple analytical approaches to the conical wedge anchorage with smooth interior surfaces prove the importance of the angle in the wedge-barrel interface. Also frictional behaviour in the rod-wedge and wedge-barrel interfaces proves to be important factors. Numerical studies of these and other geometrical and mechanical properties give further input into the development of a pilot anchorage to be tested in the laboratory. The optimum angle of the wedge towards the barrel seems to be between 2-3°. The thickness of the wedge should be kept as small as possible and it is favourable with high strength steel in the barrel. A small displacement of the wedges towards the unloaded end of the tendon in the design of the anchorage does also reduce the overall slip of the rod during tension. After overcoming initial problems not discovered in the analytical or numerical models the developed anchorage performed well during laboratory tests. In short term tests performed on an 8 mm thick circular rod 100 % of the rods ultimate capacity was reached. During the tests measurements of displacements and strains were performed. Fibre Optical Sensors (FOS - Bragg gratings) were for the first time included in the interior of the anchorage to give a complete picture of the load phase. These measurements were compared to a refined finite element model and show reasonable agreement. The largest source of error is assumed to be the complicated frictional behaviour in the material interfaces and the transverse material properties of the CFRP. Lastly a case study on the strengthening of a 50 year old trough bridge in Frövi is included. The bridge was successfully strengthened for bending in the transverse direction with 23 Near Surface Mounted Reinforcement (NSMR) bars in the lower part of the slab while 11 holes are drilled underneath the upper steel reinforcement to facilitate CFRP tubes with an outer diameter of 32 mm and a thickness of 4 mm. The lack of bending capacity was discovered by a consultant in 2005 and calculations with a new approach in this thesis show that the strengthening was necessary although on a minor scale. New calculations of the capacity show that the bridge's capacity after strengthening is well above the design load and measurements on site secure that the CFRP is utilized correctly as a load carrier.

  • 52.
    Bennitz, Anders
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Polymerbaserade kompositspännstag: litteratursammanställning2009Rapport (Annet vitenskapelig)
  • 53. Bennitz, Anders
    et al.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Olofsson, Thomas
    Kronborg, A.
    Wahlberg, A.
    Dynamic behaviour of the Vindel River railway bridge2006Inngår i: Condition Monitoring and Diagnostic Engineering Management: COMADEM 2006: proceedings / [ed] Uday Kumar; Aditya Parida; Raj B. K. N. Rao, Luleå: Luleå tekniska universitet, 2006, s. 721-729Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Swedish Railway administration has launched several projects aimed at increasing the accessibility of the railway lines in northern Sweden to meet future demands. One of these lines connects the southern and northern parts of Sweden and constitutes one of the major arteries for the transportation of heavy goods. Major investment are planned to upgrade the load bearing capacity of this railway line. The work is mainly focused on the larger structures and their dynamical properties. These properties can be used to assess existing infrastructure and to evaluate the performance. Advantages are obvious since the existing structural integrity form the base for investments in structural repair and upgrade of bridges. The Vindel River Railway Bridge situated 55 kilometers northwest of Umeå came into focus when large motion was discovered during train passages. The behaviour of the bridge crossing the river of Vindeln has been measured two times. Measurements of displacements and acceleration of the bridge during train passages has been conducted, the first measurements was done to give more experience on the motion of the bridge and to try out new sensors. The second measurement gave more information about the bridge's motion, results that could be used to calibrate a 3D FE-Model of the bridge used in the study. Based on the measurements, eigenfrequencies in the range of 0 to 8 Hz could be detected, modal shapes up to the ninth order could be extracted, deflections and transverse displacements for different sets of train and different train speeds were also found. However, new measurements are planned for this summer and will hopefully reinforce the already attained result and give answers to some of the unresolved questions.

  • 54.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Grip, Niklas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Schmidt, Jacob W.
    Technical University of Denmark.
    Thick-walled cylinder theory applied on a conical wedge anchorage2011Inngår i: Meccanica (Milano. Print), ISSN 0025-6455, E-ISSN 1572-9648, Vol. 46, nr 5, s. 959-977Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we derive and examine an analytical model for the internal stresses and strains within the anchorage for a prescribed presetting distance. This model is derived from the theory of thick walled cylinders under the assumptions regarding plane stress and axial symmetry. We simplify the resulting system of ten nonlinear equations and derive a method for solving them numerically. A comparison of plotted results for three different angles on the wedge's outer surface and six different presetting distances follows. These results are also compared to both axi-symmetric and 3D FE (Finite Element) models. Analytical and FE axi-symmetric models show good correspondence, though compared to the 3D FE model, they show a clear difference in the predicted radial stress distribution on the FRP. Thus, the derived analytical model can be a useful and faster alternative to FE modeling of axi-symmetric anchorages. However, the model is of more restricted value and should be complemented by, for example, 3D FE models for other designs.

  • 55.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Grip, Niklas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Schmidt, Jacob W.
    Department of Civil Engineering, Technical University of Denmark.
    Thick-walled cylinder theory applied on a conical wedge anchorage: Research report with Matlab implementation documentation2010Rapport (Annet vitenskapelig)
    Abstract [en]

    Conical wedge anchorages are frequently used to anchor steel tendons in prestressing applications within the construction industry. To replace the steel tendons with non-corrosive and low weight FRPs (Fiber Reinforced Polymers), the different mechanical interactions between the steel and FRPs call for further development of the anchorage.In this paper, we derive and examine an analytical model for the internal stresses and strains within the anchorage for a prescribed presetting distance. This model is derived from the theory of thick walled cylinders under the assumptions regarding plane stress and axial symmetry. We simplify the resulting system of ten nonlinear equations and derive a method for solving them numerically. A comparison of plotted results for three different angles on the wedge's outer surface and six different presetting distances follows.These results are also compared to both axi-symmetric and 3D FE (Finite Element) models. Analytical and FE axi-symmetric models show good correspondence, though compared to the 3D FE model, they show a clear difference in the predicted radial stress distribution on the FRP. Thus, the derived analytical model can be a useful and fasteralternative to FE modeling of axi-symmetric anchorages. However, the model is of more restricted value and should be complemented by, for example, 3D FE models for other designs.

  • 56.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Schmidt, Jacob W.
    Technical University of Denmark, Division of Structural Engineering.
    Nilimaa, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Goltermann, Per
    Technical University of Denmark, Division of Structural Engineering.
    Ravn, Dorthe L.
    COWI A/S.
    Reinforced concrete T-beams externally prestressed with unbonded carbon fiber-reinforced polymer tendons2012Inngår i: ACI Structural Journal, ISSN 0889-3241, E-ISSN 1944-7361, Vol. 109, nr 4, s. 521-530Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study describes a series of experiments examining the behavior of seven beams prestressed with unbonded external carbon fiber-reinforced polymer (CFRP) tendons anchored using a newly developed anchorage and post-tensioning system. The effects of varying the initial tendon depth, prestressing force, and the presence of a deviator were investigated. The results were compared to those observed with analogous beams prestressed with steel tendons, common beam theory, and predictions made using an analytical model adapted from the literature. It was found that steel and CFRP tendons had very similar effects on the structural behavior of the strengthened beams; the minor differences that were observed are attributed to the difference between the modulus of elasticity of the CFRP and the steel used in the tests. The models predicted the beams’ load-bearing behavior accurately but were less effective at predicting the stress experienced by the tendons.

  • 57.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Schmidt, Jacob W.
    Technical University of Denmark.
    Täljsten, Björn
    Failure modes of prestressed CFRP rods in a wedge anchored set-up2009Inngår i: Advanced Composites in Construction (ACIC) 2009 Conference Proceedings / [ed] Sue Halliwell; Claire Whysall; Tim Stratford, ACIC , 2009, s. 104-114Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In the process of developing a new wedge anchorage to anchor prestressed CFRP rods, five different anchorage designs were manufactured. These designs have led to a constantly increased ultimate failure load of the prestressing system and an eventual load level above 95% of the ultimate failure load of the rod was achieved. If 100% efficiency is achieved the anchorage does not reduce the capacity of the system, but failure is then governed by the capacity of the rod itself, which is considered favourable and required by several guidelines. In the process seven different failure modes were identified: soft slip, power slip, cutting of fibres, crushing of rod, bending of fibres, frontal overload and intermediate rupture. In this paper the failure modes are discussed further. The failures are documented with explanatory figures and their backgrounds are found in the theory. Suggestions are given on how these failures can be avoided in theory and practice. From the experiences gained in the project, it is concluded that it is a challenging task to create a fully mechanical anchorage for CFRP tendons and that the failure margins are small between a successful and an unsuccesful anchorage system.

  • 58.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Innovative strengthening of Swedish concrete trough bridges2008Inngår i: Proceedings, Nordic Concrete Research, Bålsta, Sweden: [ ... XXth Symposium on Nordic Concrete Research & Development ... The current proceedings contain 90 summaries of oral poster presentations] / [ed] Johan Silfwerbrand, Oslo: Norsk Betongforening , 2008, s. 92-93Konferansepaper (Fagfellevurdert)
  • 59. Bennitz, Anders
    et al.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Undersökning av skjuvförband i trä: provning av bulttyper för Vasaskeppet2008Rapport (Annet vitenskapelig)
    Abstract [sv]

    Föreliggande rapport är resultatet av laboratorieförsök vilka utförts på avdelningen för byggkonstruktion vid Luleå tekniska universitet. Försöken har genomförts under slutet av 2007 och är en direkt fortsättning av tidigare försök från 2004 och 2005. De tidigare rapporterna pekade på ett behov av fortsatt provning. Föreliggande rapport är således en fortsättning av tidigare arbete, dock med vidareutveckling av möjliga bulltyper för Vasaskeppet. De testade bulltyperna har konstruerats och tillverkats i Statens Maritima Museer regi av Anders Ahlgren. Försöken har genomförts vid Luleå tekniska universitet och Complab, av Civ. Ing. Georg Danielsson samt forskarstuderande Anders Bennitz.

  • 60.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Danielsson, Georg
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    CFRP strengthening of a railway concrete trough bridge: a case study2012Inngår i: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 8, nr 9, s. 801-816Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an upgrading and monitoring of a Swedish concrete railway bridge. The methods used for the upgrading as well as for the monitoring are innovative and new. Carbon fibre tubes are inserted in holes in the bridge deck, drilled in the transverse direction of the slab at a location ca. 40 mm from the top. Carbon fibre NSMR bars are bonded in transverse grooves in the soffit of the slab. Both methods are intended to increase the transverse bending moment capacity of the troughs' bottom slab in the ultimate limit state. Monitoring is performed to verify the effectiveness of the strengthening and to understand the behaviour of the bridge. However, for obvious reasons, monitoring is only carried out in the SLS (service limit state). Even though only marginal effects of strengthening could be recorded in the SLS, both the strengthening and monitoring were considered successful at a cost of approximately 8% of the total cost of a new bridge replacement.

  • 61. Bennitz, Anders
    et al.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Danielsson, Georg
    Strengthening of a railway bridge with NSMR and CFRP tubes2008Inngår i: FRP Composites in Civil Engineering: proceedings of the 4th International Conference on FRP Composites in Civil Engineering ; Zurich, Switzerland, 22 - 24 July 2008 / [ed] Masoud Motavalli, Dübendorf: EMPA-Akademie , 2008Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Strengthening of structures with CFRP is considered today as an accepted method in the upgrading of concrete structures. This paper presents the use of two different CFRP strengthening systems combined to extend the service life of a Swedish double-trough-doubletrack railway bridge, constructed in concrete with a 10 meter span. One system is the reliable NSMR (Near Surface Mounted Reinforcement) while the other is new. They were used with the intention to strengthen the interior of a concrete structure using integrated CFRP tubes. Both systems were used to increase the tensile flexural strength of the slab transverse to the tracks. NSMR bars were positioned in the bottom concrete cover of the trough's bottom-slabs, while the new system was inserted in holes drilled through the bridge in the cross direction and located in the upper part of the slab. In connection with the strengthening monitoring was conducted in order to obtain an understanding of the bridge behaviour before and after strengthening, and to demonstrate any effects of the extra CFRP reinforcement. Results from these measurements are presented together with how the strengthening work was carried out. Sensors on bars and tubes show evidence of utilization of the CFRP while displacement sensors and strain gauges on the steel reinforcement show minor effect due to the small loads in the service limit state.

  • 62.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Schmidt, Jacob W.
    Technical University of Denmark.
    External prestressing of RC T-beams with CFRP tendons2009Inngår i: Proceedings of the 9th International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures / [ed] D. J. Oehlers; M.C. Griffith ; R. Seracino, Adeleide: University of Adelaide , 2009Konferansepaper (Fagfellevurdert)
  • 63.
    Bennitz, Anders
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Schmidt, Jacob W.
    Technical University of Denmark, Division of Structural Engineering.
    Förankringsanordning för fiberkompositstängerPatent (Annet (populærvitenskap, debatt, mm))
  • 64.
    Bergdahl, Lars
    et al.
    Chalmers University of Technology.
    Fransson, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Waves for design of wind-power plants in shallow seas2009Inngår i: Proceedings of the 20th International Conference on Port and Ocean Engineering under Arctic Conditions: June 9-12, 2009, Luleå, Sweden, 2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Usually there is little knowledge of long-term wave conditions at prospective sites for windpower plants, while the deep-water or open sea conditions may be more known and geographically less varying. However, most wind-energy plants are intended for water depths less than 20 m. A concept for assessing design waves at a near-shore site is to transform the offshore wave spectra to the target site by a model for spectral wave-energy transfer over the actual bottom topography. The inshore spectra can be used for linear statistics of extreme waves and design wave loads can be produced. In this context it is important to know the realism of used spectral forms.Based on 58 measured wave spectra at 6 m water depth at the near-shore wind farm Bockstigen in the Baltic the most realistic spectrum was found to be the TMA spectrum, which is a JONSWAP spectrum modified for shallow water. Some few examples are given.

  • 65.
    Bergström, Markus
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Assessment of existing concrete bridges: bending stiffness as a performance indicator2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Optimizing the use of existing civil reinforced concrete (RC) structures could be interpreted in such a way as to say that the capacity should be used and taken care of in an effective manner, both from a technical and economical point of view, keeping the safety in mind. Achieving this requires thorough understanding of the structure and also of the tools used for assessing current and future capacity and needs. Monitoring together with finite element modelling could give relevant and important information about a structure's capacity. In a case where monitoring alone is used, it is beneficial if a quantity is monitored which is interpretable on material and geometrical level. It is further important that the measure is practically possible to capture, and that it reflects the behaviour in a theoretically well-known mode. One example of a quantity which fulfils these requirements is the bending stiffness. In the Serviceability Limit State (SLS), in particular, a high bending stiffness is beneficial as this reduces deflections, vibration amplitudes and crack widths.It is shown within the thesis that four phases are distinguished during loading of an RC member; Un-cracked phase (I), Crack forming phase (II), Crack stabilised phase (III) and Failure phase (IV). It is also shown that corrosion and flexural strengthening are possible to capture through the bending stiffness by monitoring the curvature. Linear elastic theory has in addition been concluded to give satisfactory results in terms of good agreement between measured and theoretical results. It is shown that it is possible to determine the highest load which the structure has been previously exposed to, presuming that the structural element has not reached phase (III). The stiffness is almost constant in phase (III) which implies that it is the same for a certain load interval. One limitation coupled to the stiffness plateau formed in phase (III) is that it is difficult to predict a possible failure by monitoring the bending stiffness, caused by the limited forewarning prior to the beginning of phase (IV). Other tools, such as reliability-based assessment, become especially important here since active degradation, for example, is difficul to verify by curvature measurements in phase (III). Estimating the safety, and also finding the probable failure mode is important since curvature measurement is not effective in the Ultimate Limit States (ULS) and only captures the behaviour in bending. In the reliability-based assessment, the agreement between analytical results and actual capacity of the particular failure mode must be treated with special attention, since it has been shown that the model uncertainty can affect both the safety level and also probable failure mode. If it can be shown from monitoring that the structure is located within phase (I) the load effect during the past time has not affected the integrity of the structure in terms of bending cracks.It is preferrable to use the global curvature when evaluating the bending stiffness, since this property gives a more robust average curvature and also additional information about the structural member. Especially changing bond properties, during e.g. corrosion, is more likely to be detected if the global curvature is monitored. Another important conclusion is that the local and global stiffness development is very similar. This implies that a crack at a certain location is not allowed to increase without redistribution of stresses, which affects the global stiffness in an comparable extent. Two criteria are suggested for the least distance over which the global curvature should be measured, LG. The first one concerns the fact that at least four macro cracks is suggested to be covered and is based on the maximum crack spacing recommended by Eurocode (2004). The other requirement is that the distance should not be that small that the estimated deflection become less than one hundred times the in-built measurement error in the displacement gauge. A measurement error above one percent is hence not allowed.Curvature assessment could be useful from three different aspects * Condition assessment. The monitored quantity is back-calculated to input data, such as material property or geometry. That is, solving the inverse bridge management problem. Decisions about the use of the structure are then based on the outcome of this assessment.* Refined calculations in serviceability and ultimate limit states. Use the results to refine the models used for SLS and ULS performance. For example, it might be possible to treat the structure in its actual condition. * Optimized LCC. Time until a major repair and/or strengthening procedure is estimated using the bending stiffness development captured by curvature measurement.The approach using bending stiffness as a performance indicator is applied in two case studies in Sweden, the Panken road bridge located east of Karlstad and the railway bridge located in Örnsköldsvik. The Panken Bridge was located within phase (III) (crack stabilised phase), while the Örnsköldsviks Bridge was located within phase (I) (un-cracked phase). It is shown in these case studies that monitoring of the bending stiffness through curvature measurements can give valuable information regarding how the structure is affected by loads and/or degradation. One challenge when evaluating the bending stiffness from curvature measurements is that time dependent mechanisms, e.g. creep, could affect the curvature but not necessarily the bending stiffness. Time dependent mechanisms will thus give rise to what is here defined as a "fictitious stiffness change". Any movement or deformation which produces a fictitious stiffness change must be given extra attention to avoid misleading results. Another challenge is that monitoring is commonly performed for additional loading, which means that the curvature caused by the dead weight of the structure itself is in most cases not captured. Further research is suggested to address the effects of these phenomena for curvature assessment applications.

  • 66.
    Bergström, Markus
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Bro över Järpströmmen: mätning av påkänningar före och efter förstärkning2004Rapport (Annet vitenskapelig)
    Abstract [sv]

    En trespannsbro över Järpströmmen förstärktes med avseende på tvärkraftskapacitet med kolfiberväv. Förstärkningen genomfördes under sommaren 2004. För att utröna effekten av förstärkning har mätning utförts såväl före som efter ingreppet. Föreliggande rapport redovisar mätprogram samt sammanställande mätresultat. Resultatet från mätningen visar att påkänningarna är mycket små och att det är svårt, med den belastningsnivå som valdes, att påvisa någon säkerställd skillnad före och efter förstärkning. Det är dock fastställt att förstärkningen är aktiv och tar last, och kan därför förutsättas bidra till en ökad kapacitet i brottgränstillstånd trots att effekterna är svåra att bestyrka i brukgränstillstånd och utförd mätning.

  • 67.
    Bergström, Markus
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Degradation of structural performance of concrete structures: literature survey2005Rapport (Annet vitenskapelig)
    Abstract [en]

    This literature survey is the start of a project with the title Degradation of structural performance of concrete structures. The project will be carried out at the Division of Structural Engineering, the Department of Civil and Environmental Engineering at Luleå University of Technology (LTU) within the research group "Innovative materials and structures".

  • 68.
    Bergström, Markus
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Life cycle behaviour of concrete bridges: laboratory test and probabilistic evaluation2006Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The structural life for a concrete structure located in an environment where corrosion is promoted by humidity or chlorides from sea or de-icing salt could in general be described in the following manner. The structure is manufactured and is at that point considered to be intact. Corrosion is assumed to attack the steel reinforcement, and at a certain corrosion level the structure has to be repaired. The cover concrete is removed and the corroded steel reinforcement is cleaned from corrosion products. A repair system consisting of primer and repair mortar is used to refill the cavity left after the removed concrete. The structure is now considered repaired in the sense that the degradation rate is decreased and the signs of corrosion are taken away. The corrosion attack and repair procedure could affect the load carrying capacity of the repaired beam in terms of decreased steel content and changed interface conditions between the steel and repair mortar. Strengthening could be applied to fulfil a possible lack of load carrying capacity. The life cycle described above has been simulated in a laboratory environment. The test program and the results provided from the monitoring of beam specimens are presented in the thesis. A probabilistic approach is employed in this thesis to calculate the change in probability of failure for the different stages of the life cycle. First, all relevant parameters were considered as stochastic and given appropriate statistical properties. With this information the increase in probability of failure is estimated for the corroded, repaired and strengthened beams compared to the intact beam. It has been found that the accelerated corrosion setup provided a steel mass content loss of 12% in the corroded region, corresponding to an average decrease in steel bar diameter by 6%. This corrosion damage was obtained after 75 days of accelerated corrosion at a corrosion current density of 0,10 mA/cm2. Both evenly distributed corrosion as well as pitting corrosion attack was observed. The concrete beam stiffness was recorded to 2980 kNm2 before the corrosion process and decreased by 15% to 2530 kNm2 after corrosion of tensile steel reinforcement. This is verified both by measuring stiffness globally using displacement gauges and locally using strain sensors. The result indicates that there is a strong relation between the deterioration process and the change in curvature and stiffness, suggesting that this is a method to measure the status of the structure. The status could for instance be defined by a performance factor, which equals 1 for the intact structure and then decrease to represent the relation between the stiffness of the deteriorated and the intact structure. If the structure is strengthened, the performance factor could be larger than 1. The ductility of the corroded steel reinforcing bars decreased with 55% due to corrosion compared to the undamaged steel reinforcing bars. The ultimate strain for the corroded bars was recorded to 10%, while the ultimate strain for the undamaged bars was 22%. This reduction is caused by pitting corrosion, which produces local stress concentrations along the bar. The failure occurs when the ultimate strain capacity is exceeded in one cross section, leading to an early failure of the steel bar specimen. The global extension of the steel specimen remains small as the failure strain acts on a small region of the total length. For the structural element this will lead to a failure at a particular corrosion level, since the local pits will dramatically decrease the load carrying capacity in one section. A failure of a structural member which is attacked by pitting corrosion could be unnoticed in terms of visual evidence, since the elongation of the steel reinforcement is be kept at a moderate level at failure of steel reinforcement because of the local damages that pitting may create. The strain at yielding is recorded to 0,39% for the intact steel bar and 0,43% for the corroded. Failure was defined as yielding of steel reinforcement for unstrengthened beams, and as debonding of CFRP plate for the strengthened beam. The load carrying capacity for the intact beam was 79,8 kN. The load carrying capacity was decreased by 15% after corrosion of steel reinforcement to 69 kN. For the beam where the cover concrete was removed the load carrying capacity was decreased another 18% down to 60 kN in comparison to the intact beam. Yielding of steel reinforcement for the repaired beam occurred at 64,8 kN, and debonding of CFRP plate for the repaired & strengthened beam occurred at 82,7 kN. These results show that a 12% reduction of steel content in the cross section occurred during the corrosion phase, at the same time as the stiffness was reduced by 15%. An analytical model indicates that the 12% reduction of steel content should decrease the stiffness by 9%. The remaining stiffness decrease may be coupled to creep. Another important fact is that the particular strengthening design upgraded the repaired & strengthened beam to reach a load carrying capacity which exceeds the intact beam. The life cycle behaviour for the concrete beams used in the study shows the same general results in comparison to an FE-analysis. It should be mentioned that the FE-analysis performed has not been done on the tested beams in this study. An analysis of these will however be conducted at a later stage. The probabilistic approach of the studied life cycle shows that the probability of failure increased two times for the corroded beam compared to the intact beam, and further up to seven times for the repaired beam. The increase in probability of failure for the corroded beam is related to steel mass loss. The repaired beam has an even higher probability of failure than the corroded beam since the effective height is reduced during removal of cover concrete of the loaded beam. By strengthening the repaired beam by bonding a CFRP plate, the probability of failure is decreased beyond the intact beam for the particular strengthening operation performed in the study.

  • 69.
    Bergström, Markus
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Mätning på järnvägsbro över Fröviån2004Rapport (Annet vitenskapelig)
    Abstract [sv]

    En bågbro för järnvägstrafik över Fröviån förstärktes under sommaren 2004 med NSMR (Near Surface Mounted Reinforcement). För att utröna effekten av förstärkning har mätning utförts såväl före som efter. Föreliggande rapport redovisar sammanställande mätresultat. Utvärdering efter liknande projekt har tidigare genomförts vid Avdelningen för Byggkonstruktion, se Täljsten & Carolin (1999) och Danielsson et al (2002). Stor spridning mellan axellaster, mellan och i tågseten, innebar att en jämförbar faktor för tågöverfarterna identifierades för utvärdering. Genom att studera lokets påverkan på bron tas ingen hänsyn till vagnarnas vikt, varvid relevant jämförelse är utförd. Förstärkning med NSMR har i uppgift att förbättra en konstruktions momentkapacitet. Vissa konstruktioners utformning ger upphov till litet moment, däribland bågkonstruktioner. Denna typ utvecklar i huvudsak tryckspänningar. Vid förstärkning av en bågkonstruktion med NSMR kan en procentuell förbättring förväntas, men förbättringens absolutvärde är relativt liten pga. liten momentbelastning i konstruktionen. Mätningar visade på låg belastning i kolfibermaterialet, med töjningar omkring 10 microstrain. Armeringstöjning vid loköverfart minskade med 20 procent i mittspann, från i snitt 12 till 10 microstrain. Mätning av en böjsprickas maximala öppnande vid loköverfart visade att den minskade från 0,0078 mm till 0,0053 mm, dvs. en minskning med 30%. Här relateras öppnandet ifrån ett jämviktsläge som motsvarar att bron endast är belastad med egentyngd, dvs. då givaren monterades. Sprickans totala vidd är inte uppmätt. I brons fjärdedelspunkt ökade armeringstöjningen från 7 till 8 microstrain. Detta beror på omfördelning av betongsprickor pga. förstärkningen, men det kan också bero på mätfel eftersom skillnaden var liten.

  • 70. Bergström, Markus
    et al.
    Danielsson, Georg
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Bro över Järpströmmen: kompletterande mätning av påkänningar vid tung överfart2005Rapport (Annet vitenskapelig)
    Abstract [sv]

    Kompletterande mätning på bron över Järpströmmen genomfördes då lasten vid föregående mätning ansågs för liten. Vid aktuell mätning bestod lasten av ett transportekipage med en totalvikt på cirka 400 ton fördelat på 20 hjulaxlar och en bit över 100 däck. Mycket låg påkänning i kolfibermaterial och stålarmering, i storleksordningen omkring 5 m/m. Den låga påkänningen härleds inte till en för låg last, då ekipagets tyngd är stor. Däremot kan mätresultaten förklaras i att tvärkraftsarmeringen och förstärkningen inte tar last förrän uppsprickning av brobetongen inträffar. Betongbrons spricklast förutsätts inte vara uppnådd vid aktuell lastnivå, vilket förklarar de små töjningarna på armering och kolfiber. Detta resonemang baseras på genomförda försök (Carolin, 2003). Erfarenhetsmässigt är tvärkraftsförstärkning med kolfiberlaminat en fungerande och effektiv metod för att uppgradera en konstruktion. Kolfiberförstärkningen har konsekvent en töjning omkring 5 με vid överfart, vilket visar att förstärkningen tar last och därmed fungerar. Ingen tendens av vidhäftningsproblem finns vid aktuell lastnivå, vilket stöds av att armeringen och kolfibermaterialet töjs lika mycket. Detta betyder att förstärkningen fortsätter ta mer last vid ökad belastning. Förstärkningen kan därför förutsättas bidra till en ökad kapacitet i brottgränstillstånd, då uppsprickning av betong inträffar, trots att effekterna är svåra att bestyrka i bruksgränstillstånd och utförd mätning.

  • 71. Bergström, Markus
    et al.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Degradation of structural performance: Experiment introduction and expected results2006Inngår i: Bridge maintenance, safety, management, life-cycle performance and cost: proceedings of the Third International Conference on Bridge Maintenance, Safety and Management, Porto, Portugal, 16 - 19 July 2006 / [ed] Paulo J. S. Cruz; Dan M. Frangopol, London: Taylor & Francis Group, 2006, s. 251-252Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Much effort has been put on investigating degradation of concrete structures, repair and upgrading separately, as can be read in numerous publications, i.e., Green et. al. (2003), Morgan (1995) and Täljsten (2004). However, an overall view has not been taken where the whole life cycle of a concrete structure is considered. In particular, no laboratory tests have been presented in the literature to the author's knowledge. A structure passes several stages during its life. Normally two major stages are discerned, the service limit state (SLS) and the ultimate limit state (ULS). Concrete structures are designed for both these stages. In the SLS normally the deformation and crack widths are controlled. Deformation due to comfort demands and crack widths due to durability demands. In the ULS the structure is designed for its ultimate capacity - which for civil and building structures almost never is reached. From a safety aspect the ULS is most important; however, for the client the SLS with regard to maintenance, repair and upgrading are most costly. If the SLS was better understood, in particular from a rehabilitation point of view, more robust and cost effective repair and upgrading system could be developed. (Figure Presented). This paper is also a part of "Sustainable bridges". "Sustainable bridges" is a European project which focus is to preserve bridges throughout Europe and create unanimous codes for all participating countries. The project presented in this paper, Degradation of Structural Performance (DOSP), will investigate the behaviour of concrete beams which will endure a simulated life cycle procedure. The test program will direct the beams from full strength of the intact beam through degradation, repair and upgrading with FRP plate bonding to its original strength again or near. The cross-sectional strain distribution will be monitored during the test using Fibre Bragg Grating (FBG) Strain Sensors as well as traditional strain gauges. This gives the possibility of comparing results in between the two monitoring techniques over proportionately long time span. An accelerated corrosion procedure is used to corrode the flexural tensile reinforcement. The cycle may be divided into seven stages, a to g, presented shortly in Figure 1, Horrigmoe (1998) and Sand 2001. This life cycle is possible in the real case scenario for bridges or other concrete structures which are subjected to chlorides, i.e. de-icing salt or sea water

  • 72. Bergström, Markus
    et al.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Reparation och förstärkning av betongkonstruktioner2007Inngår i: Bygg & Teknik, ISSN 0281-658X, Vol. 99, nr 7, s. 48-50Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [sv]

    Att utnyttja moderna metoder och material för att återställa befintliga och åldrande betongkonstruktioner till ett funktionellt skick är viktigt. Studier kring möjligheter att öka såväl den ekonomiska som fysiska livslängden är ett omfattande forskningsområde. Även de praktiska tillämpningarna ökar i antal. Trots att erfarenheten och kunskapen att bygga långsiktigt hållbara betongkonstruktioner hela tiden ökar finns det relativt nya konstruktioner som inte uppfyller ställda krav på säkerhet och funktion. Det finns dessutom otaliga betongkonstruktioner som har brukats under flera årtionden som börjar visa tecken på omfattande brister.

  • 73.
    Bergström, Markus
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Carolin, Anders
    Failure load test of a CFRP strengthened railway bridge in Örnsköldsvik, Sweden2009Inngår i: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 14, nr 5, s. 300-308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The results obtained when performing a load test to failure of an existing structure are valuable when assessing calculation models, updating finite element models, and investigating the true structural behavior. In this paper a destructive testing and monitoring of a railway bridge in Örnsköldsvik, Sweden is presented. In this particular test the shear capacity of the concrete girders was of primary interest. However, for any reasonable placement of the load (a line load placed transverse to the track direction) a bending failure would occur. This problem was solved by strengthening for flexure using carbon fiber reinforced polymer (CFRP) rectangular rods epoxy bonded in sawed up slots, e.g., near surface mounted reinforcement. The strengthening was very successful and resulted in a desired shear failure when the bridge was loaded to failure. The load-carrying capacity in bending for the unstrengthened and strengthened bridge as well as the shear capacity was predicted with Monte Carlo simulations. The particular calculation presented showed that there was a 25% probability of a bending failure instead of a shear failure. Monitoring showed that the strengthening reduced the strain in the tensile steel reinforcement by approximately 10%, and increased the height of the compressed zone by 100 mm. When the shear failure occurred, the utilization of the compression concrete and CFRP rods were 100 and 87.5%, respectively. This indicates that a bending failure indeed was about to occur, even though the final failure was in shear.

  • 74.
    Bergström, Markus
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Täljsten, Björn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Danielsson, Georg
    Bro över Pankens utlopp: mätning före och efter förstärkning2009Rapport (Annet vitenskapelig)
  • 75.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Active earth pressure build-up: a trigger mechanism in large landslides in sesitive (quick) clays1983Inngår i: Symposium on slopes on soft clays: Linköping March 8-10, 1982, Linköping: Statens geotekniska institut (SGI) , 1983, s. 55-67Konferansepaper (Fagfellevurdert)
  • 76.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Brittle Failures in Normally Consilidated Soils1978Inngår i: Väg- och Vattenbyggaren, ISSN 0042-2177, Vol. 1978, nr 8-9, s. 49-Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 77.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Dynamic response of buildings on breakwater in Monaco1993Inngår i: Proceedings of the International Colloquium on Structural Serviceability of Buildings, Zürich: International Association for Bridge and Structural Engineering, 1993, s. 291-296Konferansepaper (Fagfellevurdert)
  • 78.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Grouting in sedimentary and igneous rock with special reference to pressure induced deformations2004Rapport (Annet vitenskapelig)
    Abstract [en]

    After a short introduction in Chapter 1, typical properties of sedimentary rocks are given in Chapter 2, exemplified with limestone formations in the Malmö Region in southern Sweden. Two main grouting techniques are defined in Chapter 3, grouting by permeation (pressure not causing fracture in the rock) and grouting by hydraulic fracturing (pressure causing opening of existing fissures or tensile fracture in the rock). The deformations caused by the two methods are discussed. Permeation grouting and permeability of different rock materials are discussed in Chapter 4. The permeability of cement based grouts in soil and rock is often overestimated. In a diagram, a relationship is given between Darcy's coefficient of permeability, k [m/s]; and a crack pattern defined by the number of cracks per meter, n [1/m]; crack widths, t [mm]; and crack volume ratio [%]. Hydraulic fracturing is treated in Chapter 5. For confined conditions, equations and diagrams are given for the maximum gap deformation in the cracks and for the widths of the grouted zone. The equations and diagrams are given as functions of the injected grout volume per round and the ratio of the modulus of Elasticity and the injection pressure. Two loading cases are treated: (a) two-dimensional loading with a grouting zone length L [m] and (b) conical loading with a grouting zone diameter D [m]. For unconfined conditions the risk for spreading of the grout is discussed. The importance of the deformations is illustrated with case studies. Final remarks are given in Chapter 6. One main conclusion is that the injection pressure is not a satisfactory stop criterion. As unintended hydraulic fractures often take place, when permeation grouting is intended, an uncontrolled spread of grout may occur. Instead, the volume of grout injected per stage, or round, should be limited. It is often best to inject small amounts of grout, in several rounds, allowing the grout to stiffen between the rounds. This procedure is illustrated with two examples in an Appendix.

  • 79.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Icke-Linjär deformationsanalys vid beräkning av släntstabilitet: Är det en nödvändig eller en onödig komplikation?1981Rapport (Annet vitenskapelig)
  • 80.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    On limit criteria for plastic failure in strain rate softening soils1985Inngår i: Proceedings of the eleventh International Conference on Soil Mechanics and Foundation Engineering: San Francisco/12-16 August 1985, Rotterdam: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1985, Vol. 2, s. 397-400Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Deals with aspects of stability criteria for extensive slopes if the limiting large strain strength of the soil is strain rate dependent. The issue is exemplified by means of a mechanical model

  • 81.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    On transmission of restraint via construction joints in concrete structures1997Inngår i: Selected research studies from Scandinavia: dedicated to professor Göran Fagerlund on his 60th anniversary November 11, 1997, Lund: Lund Institute of Technology, Division of Building Materials , 1997, s. 22-27Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 82.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Practical measures for avoidance of cracking case records1994Inngår i: General reports of the International Symposium Thermal Cracking in Concrete at Early Ages: Munich, October 10-12, 1994 - technical recommendations (drafts) RILEM Technical Committee 119 TC, state of the art reports (drafts) RILEM Technical Committee 119 TCE / [ed] Rupert Springenschmid, Baustoffinstitut der TU München , 1994, Vol. 1, Session H, s. 74-86Konferansepaper (Fagfellevurdert)
  • 83.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Practical measures to avoiding early age thermal cracking in concrete structures1998Inngår i: Prevention of thermal cracking in concrete at early ages: state of the art report prepared by RILEM Technical Committee 119, Avoidance of Thermal Cracking in Concrete at Early Ages, London: Taylor and Francis Group , 1998, s. 255-314Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 84.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Progressive landslides in long natural slopes: Formation, potential extension and configuration of finished slides in strain-softening soils2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    After the large landslide in Tuve (Gothenburg, 1977), the author began developing a finite difference model for slope stability analysis taking the deformation-softening of soft sensitive clays into consideration. In the model, the mean down-slope deformation in each element caused by normal forces is maintained compatible with the deformation generated by shear stresses. He developed software for the model and presented it at international soil mechanics conferences during the 1980-ies. In 2000 he summarized his findings in a Licentiate thesis. An easy-to-use spread-sheet has also been developed. In this thesis the author conveys his experiences of slide modeling focusing on the nature of triggering agents and the different phases that a slope may undergo before its stability becomes truly critical.

  • 85.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Progressive landslides in long natural slopes: potential extension and configuration of finished slides in strain-softening soils2000Licentiatavhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    A finite difference method is presented for progressive slides in long natural slopes. The method is based on a strain softening material model. A detailed worked out example is given as well as examples using a spread sheet PC program and a PC program for Windows. Several Scandinavian slides are analysed and discussed as case studies e g Tuve (1977), Surte (1951), Bekkelaget (1953), Rollsbo (1967), Rävekärr (1971), Tre-styckevattnet (1990) and Svärtaån (1938). The nature of down-slope progressive failures in natural slopes is described and the applicability of ideal-plastic failure analysis is questioned. Principles and procedures for investigation potential landslides are presented. A short historical background to the landslide problem is given in an introductory chapter.

  • 86.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sprickbildning i betongpålar slagna i vatten eller i jordarter med hög permeabilitet1992Rapport (Annet vitenskapelig)
    Abstract [sv]

    Skador på grund av hydraulisk utmattning eller "vattensprängning" av betongpålar har samband med följande faktorer: » Närvaro av fritt vatten eller grundvatten i jord med hög permeabilitet. » Omväxlande stora tryck- och dragspänningar i pålen under slagning, vilket medför utmattning av betongmaterialet. » Utmattningsmekanismerna i betong förstärks genom insugning och utpressning av vatten under stort tryck i förekommande spricksystem. » Förekomst av genomgående sprickor, anslutande tvärsprickor och mikrosprickor. » Sprickviddens variation med hänsyn till i betongen initiellt förekommande egenspänningar av temperatur, krympning och volymändringar av hydratation. Sprickor med mot ytskikten avtagande vidd är speciellt ofördelaktiga. Ogynnsam variation hos sprickvidden ökar med tilltagande dimensioner hos pålens tvärsnitt. » Betongens tryck- och draghållfasthet jämte andra mekaniska egenskaper hos betongen i pålelementet. » Pålens konstruktiva utformning, speciellt m h t armeringens storlek och fördelning över påltvärsnittet. Bygeldelning. » Geotekniska förhållanden. » Slagningsbetingelser. Stora tryck- och dragspänningar uppkommer företrädesvis vid hård slagning av långa pålar i relativt fasta leriga eller siltiga friktionsjordarter, varvid situationen kännetecknas av att mantelmotståndet (vanligen på grund av porvattenundertryck) är stort samtidigt som spetsmotståndet är litet eller måttligt. Typiskt för dessa tillstånd är att pålskallens fjädring är stor i förhållande till dess kvarstående sjunkning. Tendenser till uppträdande av stora dragkrafter kan diagnosticeras och övervakas med hjälp av modem stötvågsmätningsteknik.

  • 87.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Sprickrisk i grova betongkonstruktioner1992Inngår i: Betong, ISSN 1101-9190, Vol. 2, nr 3, s. 22-26Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 88.
    Bernander, Stig
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    The landslide at Tuve, nov. 19771983Inngår i: Symposium on slopes on soft clays: Linköping March 8-10, 1982, Linköping: Statens geotekniska institut (SGI) , 1983, s. 69-97Konferansepaper (Fagfellevurdert)
  • 89.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Dury, Robin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Laue, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Progressive Landslide Analysis in Canadian Glacial Silty Clay in Churchill River2017Inngår i: / [ed] Vikas Thakur, Jean-Sébastien L’Heureux, Ariane Locat, 2017, s. 1-Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The poster presents the risks for a progressive landslide in a natural dam. The stability will be critical when the water level is raised after the building of a hydro power plant, Bernander (2016), Dury (2017). The analysis is based on a finite difference method developed by Stig Bernander (2011), Bernander et al.(2016)

     

    The following issues will be discussed:  

    - Material properties

    - Risk for liquefaction

    - Three possible failure surfaces: one horizontal, one inclined and one curved

    - Failure riska for different material propeties

    - The need to check the real properties of the soil

  • 90.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Dam Bank Stability in loosely layered silty sands and lean silty sandy clays: Comments on the risk of failure in the North Spur at Muskrat Falls in the Churchill River Valley, Labrador, Newfoundland2018Rapport (Annet vitenskapelig)
    Abstract [en]

    The differences in landslide analysis between the classic limit equilibrium method (LEM) and a progressive failure procedure is outlined. In LEM the soils are presumed to be fully plastic, whereas in the progressive failure approach the joint effect of strain-softening material properties and deformations in the soil mass are considered.

    The risk of failure in the North Spur ridge due to the dam impoundment at Muskrat Falls in the Churchill River Valley (Labrador/Newfoundland) is investigated. An important issue in this context is e.g. that sloping failure surfaces near the cut-off wall (COW) are bound to be much more critical than the horizontal failure planes, which have hitherto been considered according to Nalcor/SNC-Lavalin Engineering Reports.

    Results from progressive failure analyses have now been obtained, applying plausible deformation-softening material properties to the soils in the ridge. These results, which are presented at the end of this report, render unsatisfactory safety factors – i.e. lower than 0.5, thus indicating potential risks of failure when the water surface is raised to the proposed levels.

    Three reports and a summing up are appended, where Dr Bernander strongly emphasizes the need of stability evaluations based on proper progressive failure analysis – i.e. using soil properties based on tests that are not carried out under fully drained conditions.

    Measures to reducing the detrimental effects of high in-situ porosity are also proposed.

  • 91.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Riverbank stability in loose layered silty clays: Comments on the North Spur Dam at Muskrat Falls in Churchill River, Labrador, Newfoundland2017Rapport (Fagfellevurdert)
    Abstract [en]

    The differences are outlined in landslide analysis between the classic limit equilibrium method with assumed plastic properties of the soil and a progressive analysis applying softening material properties.

    The risk for failure is studied in the dam at the North Spur riverbank ridge at Muskrat Falls in Churchill River in Labrador, Newfoundland, Canada. A sloping failure surface is much more critical than the horizontal surfaces which have hitherto been studied. Results from new analyses have now been obtained applying softening material properties probable for the ridge. The results indicate safety factors lower than 0.5, i.e. there is a high risk that the ridge will fail if the water level is raised to the proposed level.

    Three reports are appended where Stig Bernander argues in detail for the need for a proper progressive failure analysis based on measured material properties. He also proposes how such properties may be obtained and gives an example of a way to stabilize the ridge if the soil properties show a softening behaviour. Finally examples of progressive failure analyses are included using probable material properties.

  • 92. Bernander, Stig
    et al.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Assessment of the risk of internal cracking in hardening concrete1990Inngår i: Proceedings: Nordic Concrete Research Meeting : Trondheim 1990 / [ed] Jens Jacob Jensen, Oslo: Norsk Betongforening , 1990, s. 302-303Konferansepaper (Fagfellevurdert)
  • 93. Bernander, Stig
    et al.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Early age thermal crack control: industrial benefits of new technology1997Inngår i: Selected research studies from Scandinavia: dedicated to professor Göran Fagerlund on his 60th anniversary November 11, 1997, Lund: Lund Institute of Technology, Division of Building Materials , 1997, s. 14-21Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 94. Bernander, Stig
    et al.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Risk of cracking in massive concrete structures: new developments and experiences1995Inngår i: Thermal cracking in concrete at early ages: proceedings of the international symposium held by RILEM at the Technical Univ. of Munich ..., Oct. 10-12, 1994 / [ed] Rupert Springenschmid, London: Spon press, 1995, s. 385-392Konferansepaper (Fagfellevurdert)
  • 95. Bernander, Stig
    et al.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Temperaturförhållanden och sprickbegränsning i grova betongkonstruktioner1992Inngår i: Betonghandbok. Arbetsutförande: projektering och byggande, Solna: Svensk byggtjänst , 1992, 2, s. 639-666Kapittel i bok, del av antologi (Annet (populærvitenskap, debatt, mm))
  • 96.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Gustås, Hasse
    Skanska.
    Consideration of in sity stresses in caly slopes with special reference tp progressive failure analysis1984Inngår i: NGM-84, Nordisk Geoteknikermöte 1984 i Linköping, Linköping: Statens geotekniska institut (SGI) , 1984, s. 417-430Konferansepaper (Fagfellevurdert)
  • 97. Bernander, Stig
    et al.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nilsson, Martin
    Inverkan av eftergivlighet hos underlaget på spänningar i nygjutna betongkonstruktioner1997Inngår i: Bygg & Teknik, ISSN 0281-658X, nr 7, s. 25-27Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 98.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Kullingsjö, Anders
    Skanska Teknik, Göteborg, Chalmers University of Technology.
    Gylland, Anders K
    Multiconsult, Norwegian University of Science and Technology (NTNU), Trondheim.
    Bengtsson, Per-Evert
    Statens Geotekniska Institut, Linköping, PEB Geoteknik.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Olofsson, Jan
    Skanska Sverige AB, Skanska Teknik, Göteborg.
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och brand.
    Downhill Progressive Landslides in Long Natural Slopes: Triggering Agents and Landslide Phases modeled with a Finite Difference Method2016Inngår i: Canadian geotechnical journal (Print), ISSN 0008-3674, E-ISSN 1208-6010, Vol. 53, nr 10, s. 1565-1582Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A large landslide in Tuve (Gothenburg, Sweden 1977) initiated the development of a model for slope stability analysis taking the deformation-softening of soft sensitive clays into consideration. The model studies triggering agents and five phases in progressive slope failure are identified: (1) in-situ, (2) disturbance, (3) unstable ‘dynamic’, (4) transitory (or permanent) equilibrium, and (5) ‘global’ failure. The clay resistance in these phases may differ widely; mostly due to different rates of loading. Two time dependent failure criteria are defined: (i) the triggering load condition in the disturbance Phase (2), and (ii) the transitory equilibrium in Phase (4), indicating whether minor downhill displacements or a veritable landslide catastrophe will occur. The analysis explains why downhill landslides tend to spread over vast areas of almost horizontal ground further down-slope. The model has been applied to landslides in Scandinavia and Canada. Three case studies are briefly discussed. The model is a finite difference approach, where local downhill deformations caused by normal forces is maintained compatible with deviatory shear deformations above the potential (or the established) failure surface. Software and an easy-to-use spreadsheet are introduced as well as recent developments. See also Video Abstract.

  • 99.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Olofsson, Ingvar
    Skanska.
    Synpunkter på orsaker till Tuveskredet1981Rapport (Annet vitenskapelig)
  • 100.
    Bernander, Stig
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Svensk, Ingemar
    Skanska, Göteborg.
    On the brittleness of soft clays1983Inngår i: Symposium on slopes on soft clays: Linköping March 8-10, 1982, Linköping: Statens geotekniska institut (SGI) , 1983, s. 99-112Konferansepaper (Fagfellevurdert)
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