Medieval Timber Roof Structures: Conceptual methods for investigation and evaluation of structural behaviour, with the horizontal thrust problem as an application

The medieval timber roof structures hidden in the attics of many Swedish churches represent the advanced building technology of the time. They are an important cultural heritage, their being bearers of information from a period regarding which other direct sources of information are scarce. Understanding their structural action is necessary in order to be able to preserve them prop\uacerly and also helps one better interpret their place in history. Timber roofs can be complex to analyse since they often possess a high degree of static inde\uacterminacy, having several possible load paths. In analysing such a structure, the stiffness of its separate parts needs to be taken into account. Computa\uactional modelling by means of the finite element method (FEM) together with visualisation tools proposed for use here were found to be effective in analys\uacing their behaviour and in diagnosing damages that can occur. Many such damages can be attributed to weakness in the horizontal support of the roof structures involved. A mechanical model consisting of connected springs rep\uacresenting the horizontal supportive stiffness of different parts of a building was developed. In addition, an approach that involves classifying the exten\uacsion of horizontal supports for a roof structure in space was proposed. Both were used to analyse how the horizontal thrust is carried in existing buildings and to help develop new designs for horizontal support. Having access to the tools and methodologies proposed makes it possible to gain a better under\uacstanding of the structural behaviour of medieval roof struc\uactures, to compare different designs, to conceptualize new solutions, and facili\uactates collaboration between different professions in restoration work

Medieval Timber Roof Structures: Conceptual methods for investigation and evaluation of structural behaviour, with the horizontal thrust problem as an application

The medieval timber roof structures hidden in the attics of many Swedish churches represent the advanced building technology of the time. They are an important cultural heritage, their being bearers of information from a period regarding which other direct sources of information are scarce. Understanding their structural action is necessary in order to be able to preserve them prop\uacerly and also helps one better interpret their place in history. Timber roofs can be complex to analyse since they often possess a high degree of static inde\uacterminacy, having several possible load paths. In analysing such a structure, the stiffness of its separate parts needs to be taken into account. Computa\uactional modelling by means of the finite element method (FEM) together with visualisation tools proposed for use here were found to be effective in analys\uacing their behaviour and in diagnosing damages that can occur. Many such damages can be attributed to weakness in the horizontal support of the roof structures involved. A mechanical model consisting of connected springs rep\uacresenting the horizontal supportive stiffness of different parts of a building was developed. In addition, an approach that involves classifying the exten\uacsion of horizontal supports for a roof structure in space was proposed. Both were used to analyse how the horizontal thrust is carried in existing buildings and to help develop new designs for horizontal support. Having access to the tools and methodologies proposed makes it possible to gain a better under\uacstanding of the structural behaviour of medieval roof struc\uactures, to compare different designs, to conceptualize new solutions, and facili\uactates collaboration between different professions in restoration work

Medieval Roof Structures in Sweden

Churches in Sweden began to be built when Christianity was introduced at about the end of the first millennium. The churches gradually became important buildings generally located in the centre of a community. These early churches are now virtually the only buildings preserved in Sweden from medieval times. In the attics of the churches, a unique collection of timber roof trusses from the twelfth century and onward can be found. The church buildings usually have gabled roofs with gables of masonry. They can either have a nave, choir and apse, only a nave and choir, or be hall churches. The roof structures carry their load from wall to wall, crosswise to the longitudinal direction of the building, without use of a separate longitudinal bracing system. Longitudinal stability is achieved by the board covering and sometimes by diagonal beams between the rafters. The roof structure of the early Romanesque churches was clearly visible. Later, roof structures were concealed by ceilings. With the entry of Gothic architecture, many churches became vaulted. The structural load-carrying principles used evolved during medieval times. The early structures had tie beams connecting opposite sides of the roof at the base of them. When churches became vaulted, other approaches to supporting the horizontal thrust were developed

Medieval Roof Structures in Sweden

Churches in Sweden began to be built when Christianity was introduced at about the end of the first millennium. The churches gradually became important buildings generally located in the centre of a community. These early churches are now virtually the only buildings preserved in Sweden from medieval times. In the attics of the churches, a unique collection of timber roof trusses from the twelfth century and onward can be found. The church buildings usually have gabled roofs with gables of masonry. They can either have a nave, choir and apse, only a nave and choir, or be hall churches. The roof structures carry their load from wall to wall, crosswise to the longitudinal direction of the building, without use of a separate longitudinal bracing system. Longitudinal stability is achieved by the board covering and sometimes by diagonal beams between the rafters. The roof structure of the early Romanesque churches was clearly visible. Later, roof structures were concealed by ceilings. With the entry of Gothic architecture, many churches became vaulted. The structural load-carrying principles used evolved during medieval times. The early structures had tie beams connecting opposite sides of the roof at the base of them. When churches became vaulted, other approaches to supporting the horizontal thrust were developed

Historiska tr\ue4b\ue4rverk : Strukturmekaniska metoder och visualisering

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

Analysis and assessment of Swedish vaulted masonry structures using funicular methods

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.

Structural Definition and Comparison of Early Medieval Roof Structures

Few roof structures remain unscathed from the 12th and early 13th centuries. The relatively large amount of well-preserved early roof structures in churches in Sweden is used as a point of departure to structurally define medieval Romanesque roof structures and to make comparisons within North-Western Europe. Investigations of actual roof structures along with study of written sources provide the basis for the study. The structures are defined and compared according to load-carrying system, included parts, centre distances, slope of roof, connection with wall, joints, outer roofing and decorations. We found many structural similarities and the structures seemingly belong to the same building historical context while also showing regional differences. The early medieval roof structures of North-Western Europe can generally and concisely be described as common rafter roofs with tie beams, without longitudinal bracing systems and having strut beams and collar beams in different combinations to support the rafters