Entwicklung eines Berechnungsmodells zur Beschreibung des Trag- und Verformungsverhaltens von Holzrahmenwänden unter Berücksichtigung lokaler Effekte

Vogt, Tobias

kassel university press, ISBN: 978-3-86219-920-4, 2015, 240 Pages
(Schriftenreihe Bauwerkserhaltung und Holzbau Heft 6)

URN: urn:nbn:de:0002-39216

DOI: 10.19211/KUP9783862199211

Zugl.: Kassel, Univ., Diss. 2014

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Content: The target of this dissertation is the development of an advanced modeling of timber-framed wall elements, using element types and material formulations which are available in common FE programs. Both the capacity and the stiffness should be described as exactly as possible without the necessity of performing experimental tests on wall elements or connection units.
In chapter 1, a description is given of why an underestimation of the load-bearing capacity and an overestimation of the stiffness does not automatically lead to calculation results which are “on the safe side”. In chapter 2, different calculation methods for timber-framed wall elements were analyzed.
The first part of a literature review gives an overview about the developments in the modeling of timber-framed wall elements and the most important approaches are presented (cf. chapter 3). If global spring elements are used to model full wall elements, experimental tests on wall elements are necessary for calibration. If local spring elements are used to model every single fastener, either the load bearing capacity will be overestimated (Carthesian spring pairs) or the element types are not available in all common FE programs (oriented spring elements).
For this reason, a new FE model was developed using beam elements to model the fasteners (cf. chapter 6). This type of element is available in all common FE programs. The input parameters for the materials are based on characteristic values and can be taken from standards and technical approaches. If test results on connection units are available, the mean values of the capacities can be taken directly, otherwise an overstrength factor has to be defined.
The second part of a literature review about experimental tests on connection units, anchoring units and timber-framed wall elements (cf. chapter 4) was conducted for the validation of the FE model developed. It becomes clear when looking at the connection units that many tests have been documented over the last few decades, however, there are many possible test configurations, materials and material parameters. In addition, differences in the wall geometries, the upload and the post-processing of the performance under earthquake loadings exist (calculation of ductility, energy dissipation, etc.) for timber-framed wall elements. Furthermore, there are considerable differences in the way of anchoring the wall elements. Interestingly, there have only been a few tests on anchoring units carried out so far. This study demonstrates that a comparison of certain test results cannot easily be done, although there are many publications regarding this topic.
Based on this background, test series on connection units, anchoring units and timber-framed wall elements were performed (cf. chapter 5), whereby the focus was on wall configurations and anchoring situations typical of the construction practice in central Europe. For the tests on the wall elements, the local deformations in the wall components were measured using optical measurement devices, so that not only the global load-displacement characteristics, but also the local effects are available for the validation of the FE model.
The results show that the newly developed FE model is suitable for describing the load-displacement behavior of timber-framed wall elements under monotonic loadings. Using an overstrength factor derived from experimental tests on connection units, the load capacities calculated are close to the test results on wall elements. Using characteristic material parameters, the results of the load capacities are considerable higher compared to the calculation method according to DIN EN 1995-1-1. Furthermore, the initial stiffness and the local deformations of the single wall components can be predicted in good accordance with experimental results.
In order to fully achieve the target of an FE model which uses only types of elements which are available in common FE programs and input data which is generally available, a database with overstrength factors for different combinations of fasteners and sheathing materials would be desirable. Further studies could be aimed at increasing the number of different test configurations and increasing the number of tests for each test configuration for an optimized statistic validation. Because the validation of the FE model showed that the local effects can be described correctly, the FE model could be used to analyze wall elements with both an asymmetric anchorage and openings with regard to critical parts of the wall elements.

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