Structural analysis and design of Timber Light-Frame shear walls

The thesis aims at investigating the seismic performances of timber light-frame shear walls with focus on the contribution offered by the sheathing-to-framing connections in terms of energy dissipation and ductility. Numerical non-linear analyses under displacement-controlled loading conditions are carried out using an original parametric finite element (FE) model developed within the open-source software OpenSees (McKenna and Fenves, 2007) in order to allow the easy variation of some basic design variables affecting the overall racking capacity of the wall, namely: i) aspect ratio, ii) nails spacing, iii) number of vertical studs and iv) cross-section size of the framing elements. In fact, although many researches dealt with the in-plane behavior of a fully-anchored timber shear wall, few efforts have been spent so far to analyze the mechanical behavior and the energy dissipation attributable to the sheathing-to-framing connections that, with hold-down connections, represent the highest contribution in terms of a wall deformation. There are few parametric analyses that consider different wall configurations (Salenikovich, 2000; Salenikovich and Dolan, 2003; Dhonju et al., 2017) of a fully-anchored timber shear wall. Several experimental tests have demonstrated that the dissipative behavior of a shear wall is mainly influenced by its connections. Timber has, in general, a poor dissipative capacity and is a brittle material in bending and in tension, unless it is properly reinforced (Jorissen and Fragiacomo, 2011). Conversely, the steel connections ensure a good amount of energy dissipation and cyclic ductility notwithstanding their significant pinching, strength degradation and softening. This evidence is well reflected into many numerical models proposed in literature, where the non-linear wall response is related to the load-deformation relationships of the connections (Tuomi and McCutcheon, 1978; Gupta and Kuo, 1985; Gupta and Kuo, 1987). Observing the results of the sensitivity analyses and starting from the study by Casagrande et al. (2016) - who model the timber shear wall considering rigid framing elements - an analytical procedure is here proposed to predict the capacity curve of a timber light-frame shear wall. Considering the characteristic non-linear softening-type behavior of timber structures, an analytical expression of the equivalent viscous damping is provided, which allows to assess the ductility of a common timber shear wall configuration. Finally, optimal configurations of a timber light-frame shear wall, considering two values of aspect ratio (2 and 1), are provided to show how the design variables affect the variation of racking capacity and costs

Slip modeling in timber-framed walls with wood-based or fibre-plaster sheathing boards

The paper provides mathematical modelling for prefabricated timber-framed walls composed of a timber frame and two different types of sheathing boards. Since by wood-based boards (WBB) the tensile strength is similar to the compressive one, there are practically no cracks appearing in the boards. On the other hand, in case of fibre-plaster sheathing boards (FPB) the tensile strength is approximately 10-times lower than the compressive one and therefore cracks in the tensile diagonal boardćs direction usually appear. Based on analysis of experimental research results [1] special approximate mathematical models have been developed. The models enable simultaneously to consider the flexibility of mechanical fasteners in the connecting areas, as well as possible cracks appearing in the tensile area of the sheathing boards

Identification of main problem areas and lacks in design principles for stability design of multi-storey timber frame buildings.

The objective of this study is to describe the main problem areas in the current stability design of multi-storey timber frame buildings, to identify lacks in current design principles and to recommend in which areas the future development of design principles and guidelines should be focused in order to facilitate the design work and make stabilising systems more effective

Optimisation of timber frame closed panel systems for low energy buildings.

The United Kingdom published a legally binding document to reduce national greenhouse gas emissions by year 2020 up to 34% against the 1990 levels. This target also fulfils the Europe 2020 strategy of 20% carbon emission reductions by year 2020 (EC, 2010). Emissions due to space heating count for around 60% of the total domestic emissions (DCLG, 2012). The report “Rethinking Construction” published in 1998 emphasised the opportunities to improve the quality and efficiency of the UK construction sector (Egan, 1998). More recently, a framework has been published by the Government to tackle fuel poverty by building more energy efficient homes (DECC, 2015). In terms of energy performance, Passivhaus is recognised as one of the most energy efficient and researched construction standards which requires an exceptionally high-level of insulation and airtightness.Closed-panel timber frames are a relatively new system in UK with an opportunity for growth. These advanced panels are pre-fitted in the factory, reducing the on-site work. However, closed-panel systems present a more complex sole plate fixing detail which can have an undesirable long-term impact on the structural and thermal performance of the building. The work presented in this thesis investigates the structural considerations, racking performance, of timber frame closed panel systems for future building regulations. The thesis underlines the significance of structural stability, serviceability and detailing in relationship with long-term thermal efficiency and airtightness, according to Passivhaus standard.An experimental study was carried out to investigate the structural racking performance of advanced closed panel systems. A comparison was made between the behaviour of the timber frame panels and the analytical PD 6693-1. A set of different wall panel built-ups is presented for optimised Passivhaus design, including thermal bridge-free sole plate details. A timber frame racking software application was developed to optimise the structural design of shear walls. A parametric study was carried out with this tool to generate efficient timber frame wall design tables for different applied racking loads and U-values. The software application also allows for direct specification of robust sole plate base fixings and thermal bridge free details

Experimental in-plane evaluation of light timber walls panels

In general, the satisfactory seismic performance of timber buildings can be partially attributed to the material characteristics of the wood itself and to the lightness of its own structure. The aim of this paper is to analyze the in-plane behavior of light timber walls panels through a series of monotonic and cyclic tests, and to evaluate how the sheathing material and the fixation to the base influence the overall response of the wall. Five tests are presented and discussed while the reliability of an analytical method to predict the response of the walls is studied. The sheathing material revealed to be important in the overall response of the wall. Moreover, the type of fixation to the base also revealed to be important in the in-plane response of timber walls. In-plane stiffnesses, static ductility, energy dissipation and damping ratio have been quantified.info:eu-repo/semantics/publishedVersio

Racking performance of platform timber frame walls

Platform timber frame construction is considered an efficient building method for multistorey dwellings where timber walls and diaphragms provide the overall stability for the structure to resist lateral forces such as those generated by wind action. Although, so far, many research studies have been conducted on the racking performance of platform timber frame walls, there remain some gaps in knowledge in a number of key areas which this research has aimed to address.A quantitative assessment of the racking performance of partially anchored timber framed walls has been carried out via experimental test campaign. Timber framed walls, sheathed with oriented strand board (OSB) panels and/or British gypsum plasterboards (PB) were constructed from a combination of material types under different loading configurations and tested according to standardized procedure. The experimental study was designed to examine the influence of a range of geometrical parameters, such as (panel-to-frame) fastener size and spacing, wall length, arrangement of studs and horizontal members, and the effect of vertical loading on the racking strength and stiffness of the walls.When subjected to a vertical load, the wall’s racking strength has been found to be more sensitive to variations in the fastener spacings, compared to the racking strength of similar walls without applied vertical loads. Conversely, it is racking stiffness to be more sensitive to variations in fastener spacings when no vertical load is applied to the wall. In such a case, the stiffness increase was up to three folds when the fastener spacing was reduced from 150 to 50 mm. However, such gain in stiffness did not occur in similar walls when they were subjected to a vertical loading of 25 kN, with stiffness increasing by only 24%.The comparison of experimental results, with the results from the UK design code formulae, showed that, on average, the design code underestimated the racking strength by 25% for walls under vertical loading of 25 kN and by 54% for walls without any vertical loading.The influence of test procedure on the racking performance of timber framed walls was also examined in an extensive experimental and analytical programme which investigated the compatibility and suitability of the test method in BS EN 594:2011 with the racking design method of BS 5268-6.1:1996. The research findings led to appropriate recommendations for determination of the design racking values from the test results.The effects of openings/discontinuities caused by windows and doors on racking performance of OSB walls with and without the use of trimmers, as well as spreaders were also examined. The results led to determination of a relationship between the size of the opening for a window or a door and the percentage reduction in the racking performance of the wall.Finally, this research examined the racking strength and stiffness of a recently developed shear wall referred to as “Mid-ply wall”. Comparing the performance characteristics of the Mid-ply walls with the “standard walls”, the Mid-ply walls performed significant ly better in both strength and stiffness terms, therefore providing a considerable potential for use in the UK and European timber frame construction

Parametric Evaluation of Racking Performance of Platform Timber Framed Walls

This paper provides a quantitative assessment of the racking performance of partially anchored timber framed walls, based on experimental tests. A total of 17 timber framed wall specimens, constructed from a combination of materials under different load configurations, were tested. The experimental study was designed toexamine the influence of a range of geometrical parameters, such as fastener size and spacings, wall length, arrangement of studs and horizontal members, as well as the effect of vertical loading on the racking strength and stiffness of the walls. The experimental results were then compared with results obtained from design rules,as given in the relevant European standards, to determine the racking performance of the walls, and are discussed in the paper

Tests on full-scale and static analysis models of the wood-framed building stucture horizontaly loaded

This paper focuses on development of the high energy saving timber building and ecological technology protecting environment in civil engineering. Wood framed with sheathing, large panel structures became more popular building constructions in Poland last decade. Experimental tests and numerical analysis of panels and complete wood framed building have been taken into account. Typical two-story residential building was selected for test. Test of three dimensional (3D) whole building was conducted on the base of experimental investigations results of large panel similar to those used in building structure. Also adequate tests of materials and connections were accompanying of the whole structure investigations. Obtained results were adopted in numerical models elaborated for wall and floor panels and in 3D model of whole building. Load -displacements characteristics were acquired from tests and numerical models. The displacements computed from 3D numerical model were 10–20% higher than from experiment. Experimentally ob-tained lower displacements than those from analytical analysis are resulted from higher stiffness of wall system due to diaphragms interconnections, their common interaction and three-dimensional character of building structure. Presented research analyzed method of computation of internal forces in building as well in the range of engineering methods in the form of rigid beam scheme up to the advanced methods using 3D spatial model adopting FEM