| 1. |
- Balksten, Kristin, 1977-, et al.
(författare)
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Construction and materials of Visby medieval city wall – risk of damage
- 2014
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Ingår i: 9th IMC, Book of Abstract. - 9789728692858
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Konferensbidrag (refereegranskat)abstract
- The City Wall in Visby was built in two periods in 13th and 14th century. The first wall was made as a lower three-leaf wall with two shells built of lime stone and fat lime mortar and a soft and porous rubble core of lime stone and clay mortar. The second wall was built higher on top of the old one. It was mostly built as a solid wall in lime stone and lime mortar. Due to its construction and form, a major part of the force is carried by the outer shell of the wall. As restorations have been made during 20th century the joints of lime mortar has been partly repointed with strong cement mortar, followed by leached lime inside from the mortar in the wall. In February 2012 a part of the wall collapsed and fell down as the outer shell of the masonry collapsed. This paper presents an analysis of the wall structure and its materials as well as the increased risk of damage due to the restorations of the 20th century.
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| 2. |
- Balksten, Kristin, et al.
(författare)
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Increased use of ruins through secured masonry and comfortable climate
- 2010
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Ingår i: Proceedings of the 7th International Conference on Science and Technology in Archaeology and Conservation, Petra, Jordan.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a unique scientific research project, funded by the KK-foundation in Sweden together with several companies participating in the project. A primary goal is to find methods to examine and take care of open masonry constructions thereby enabling an increased use of them in a safe and comfortable way without diminishing their cultural values. A second goal is to establish a long-term cooperation/network of researchers, conservators, engineers, antiquarians and craftsmen that can keep and develop the knowledge. The project takes place in year 2010 and 2011. This paper presents a model of cooperation as well as the ongoing experiment and expected results. The project is divided into three major parts:1) Description and assessment of historic masonry as load bearing structures. 2) Assessment of stone and mortar in old masonry and finding the methods to secure and preserve them. 3) The climate in the ruin with respect to comfort and preservation. The goals for the different parts of this research project are to find the best possible solutions of how to: a) Evaluate the construction of complex masonry structures to enable new additions that are appropriate with respect to statics. b) Find efficient methods to evaluate and conserve the status of the materials (stone, mortar) and walls in old masonry to grant safe accessibility. c) Create a comfortable climate in an open masonry structure without closing it. These three research areas all focus on the historic masonry which at the same time forms the climate shell, the bearer of plaster and the historical setting to the activities that are to take place in the ruin.
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| 3. |
- Balksten, Kristin, 1977-, et al.
(författare)
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Visby ringmur : att återuppbygga med autenticitet
- 2015
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Ingår i: Bebyggelsehistorisk tidskrift. - 0349-2834 .- 2002-3812. ; 70, s. 43-61
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Tidskriftsartikel (refereegranskat)abstract
- In February 2012, one part of the medieval city wall and Unesco World Heritage of Visby collapsed. It is the best preserved medival city wall of nothern Europe. The wall was built in several stages in the 13th, 14th and partly even 15th centuries. The first wall was made as a lower three-leaf wall with two shells built of lime stone and fat lime mortar and a soft and porous rubble core of lime stone and clay mortar. The second wall was built higher on top of the old one. It was mostly built as a solid wall in lime stone and lime mortar.During its 700 year long history parts of the wall has collapsed and been rebuilt many times and after the collapse 2012 it was decided that also this collapsed part of the wall should be rebuilt. To determine a procedure for the rebuilding and to secure a safe work site, it was necessary to define the construction and structural behaviour of the wall. Furthermore, what caused the collapse needed to be identified, in order to assess and predict the risk of future damage to other parts of the wall. An investigation into the construction of the wall was carried out through archival research, building acheology and on-site examinations. Laser scanning made it possible to describe and study the geometry of the wall and the damage in detail, and a structural analysis was carried out.The results show that the wall was built in two stages, making its construction complicated. The structural analysis indicates that there is a concentration of forces to the outer masonry leaf of the lower part of the wall. The collapse was most likely triggered by freezing of the water contained in the masonry. The combination of high stress levels in the outer masonry leaf, due to the construction of the wall, with a loose core, thin outer masonry leaf and insufficient binding stones and weak adhesion in the bedding lime mortar in the lower part of the wall, resulted in a domino effect that explains the extent of the collapse. To secure the wall during dismantling, a temporary steel structure was constructed.The medieval types of construction and material in a two-leaf masonry wall have proven to be durable if correctly implemented, with sufficient binding stones and a core in order, and will therefore be used for the rebuilding.As restorations have been made during 20th century the joints of lime mortar has been partly repointed with strong cement mortar, followed by leached lime inside from the mortar in the wall.As the rebuilding took place it has been a desire to use as authentic materials and constructions as ever possible. On Gotland there is a unique knowledge preserved and developed since middle ages how to handle the local lime, from burning, slaking, storing to mixing mortars. This knowledge and avalibility of local traditional materials has made it possible to rebuild the wall with the perspective and wish that the wall built 2014 shall stand another 700 years. Keywords: Visby city wall, medieval wall, masonry structure, structural behaviour, lime mortar, two-leaf masonry wall
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| 4. |
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| 5. |
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| 6. |
- Nyström-Rosander, Christina, et al.
(författare)
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High incidence of Chlamydia pneumoniae in sclerotic heart valves of patients undergoing aortic valve replacement
- 1997
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Ingår i: Scandinavian Journal of Infectious Diseases. - 0036-5548 .- 1651-1980. ; 29:4, s. 361-365
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Tidskriftsartikel (refereegranskat)abstract
- Chlamydia pneumoniae has previously been demonstrated in the atherosclerotic lesions of various arteries, including the coronary arteries, and has been proposed to play a role in the pathogenesis of atherosclerosis. A prospective study of the incidence of C. pneumoniae in the sclerotic valves of patients undergoing aortic valve replacement because of aortic stenosis and in the aortic valves of cases dying of non-cardiac reasons and undergoing forensic autopsy was undertaken. The results were correlated to serological markers of past (IgG) or persistent (IgA) C. pneumoniae infection. C. pneumoniae, as determined by the polymerase chain reaction (PCR), was detected in the aortic valve in 19/39 (49%) patients and in 1/11 (9%) autopsy controls (p = 0.018) and confirmed by electron microscopy in one patient. There was no significant difference in the incidence rate of IgG or IgA antibody positivity between PCR-positive and PCR-negative cardiac patients. These results extend the hypothesis of a pathogenic role of C. pneumoniae in atherosclerosis to include also aortic valve sclerosis.
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| 7. |
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| 8. |
- Thelin, Carl, et al.
(författare)
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Analysis and assessment of Swedish vaulted masonry structures using funicular methods
- 2021
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Ingår i: 12th International Conference on Structural Analysis of Historical Constructions, SAHC 2021. - : SciPedia. ; , s. 1799-1810
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Konferensbidrag (refereegranskat)abstract
- Practising structural engineers working with historic masonry structures need access to further developed methods to analyse and assess the structural behaviour of masonry vaults. The aim of this study is to evaluate methods to analyse vaulted masonry structures and to develop a methodology for the application of suitable methods to the work of practising structural engineers. A secondary aim is to use the methods studied to analyse and assess the structural behaviour of three Swedish church buildings of different types and with vaulted structures. The churches are Gökhem church, a small parish church built in the 12th century, and the Lund cathedral, also built in the 12th century; both originally in the Romanesque style but with later alterations. The third church is St Johannes church in Stockholm, built in the neogothic style in the late 19th century. The methods used are parametric graphic statics of thrust line analysis and Thrust Network Analysis (TNA), both based on funicular analysis. The results show the strength of using such methods to assess and evaluate the structural behaviour of historic vaulted masonry structures. They provide a pedagogical description of the structural behaviour of masonry vaults and the conditions that affect their load-carrying capacity. Another result is the implementation of a method to perform the analysis in a feasible and effective way. For the analysed church buildings, the results provide an understanding of their structural behaviour and clearly show how different variables affect the magnitude and impact of the thrusting force. Thrust Network Analysis has great potential to become a very effective method to perform advanced 3d analyses of masonry vaults but needs to be developed in order to enable “best fit solutions” to map the thrust network to the shape of the existing vaults. Such methods are under development.
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| 9. |
- Thelin, Carl, 1974-, et al.
(författare)
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Collapse and Rebuilding of a Medieval City Wall – Anassessment of the Structure and Material
- 2014
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Konferensbidrag (refereegranskat)abstract
- In February 2012, a part of the medieval city wall of Visby collapsed. The wall was constructed in several stages in the 13th and 14th centuries. It was decided that the collapsed part of the wall should be rebuilt. To determine a procedure for the rebuilding and to secure a safe work site, it was necessary to define the construction and structural behaviour of the wall. Furthermore, the cause of the collapse needed to be identified, in order to assess and predict the risk of future damage to other parts of the wall. An investigation into the construction of the wall was carried out through archival research and on-site examinations. Laser scanning made it possible to describe and study the geometry of the wall and the damage in detail, and a structural analysis was carried out. The results show that the wall was built in two stages, making its construction complicated. The structural analysis indicates that there is a concentration of forces to the outer masonry leaf of the lower part of the wall. The collapse was most likely triggered by freezing of the water contained in the masonry. The combination of high stress levels in the outer masonry leaf, due to the construction of the wall, with a loose core, thin outer masonry leaf and insufficient binding stones and weak adhesion in the bedding lime mortar in the lower part of the wall, resulted in a domino effect that explains the extent of the collapse. To secure the wall during dismantling, a temporary steel structure was constructed. The medieval types of construction and material in a two-leaf masonry wall have proven to be durable if correctly implemented, with sufficient binding stones and a core in order, and will therefore be used for the rebuilding.
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| 10. |
- Thelin, Carl, 1974
(författare)
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Historiska träbärverk : Strukturmekaniska metoder och visualisering
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In designing and erecting buildings in historical times, creating the loadcarrying structure was perhaps the greatest challenge with which the architect and the builder were faced. We encounter structures in which there was a strive to reach vertical heights in the pillars and walls and to extend the horizontal span of the beams and vaults that were built. Yet the roof trusses, working structures that were often hidden in an attic behind a large assortment of decorated vaults and ceilings, was the part of the building that represented the greatest challenge of all. In discovering these, we encounter impressive structures of highly differing form reflecting a desire to increase the span and to expand the space. The aim of the thesis is to explore and develop methods of facilitating an understanding of the static behaviour of historic load carrying structures of this kind generally and more specifically of roof trusses, endeavouring to provide a sound basis for decisions concerning the maintenance and preservation of such structures. An essential element in the approach described is use of the Finite Element method (FEM) combined with visualisation. To provide an overview of different types of structures and problems to which the methods proposed are applicable, six specific examples are taken up. These highlight the importance of a conceptual understanding of the structural behaviour involved, both before and during the design process or any repair of an existing structure, as well as the advantages that visualisation can provide. Paper 1 examines the roof truss of the Swedish castle of Glimmingehus by use of FEM and visualization in order to determine the probable reasons for certain damages observed in the structure. Highly predictable causes were found and visualizations of their influence on the behaviour of this structure were presented. Paper 2 introduces a new approach, so-called static eigenvalue analysis, for investigating how effectively different truss types are able to carry both dead and wind load. The importance of different structural elements and their placing were assessed and a measure of this in terms of relative deformations was provided. The deformation modes emerging from the method and the comparison of deformation patterns in terms both of shape and of size were found to be intuitive and graspable.
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