The mechanical behaviour of timber-to-timber connections with internal panels of densified veneer wood (DVW) and fibre-reinforced polymer (FRP) dowels was experimentally assessed and a design method, based on EN 1995-1-1, was developed. Embedment tests on DVW plates and bending/shear tests on FRP dowels were performed to characterise these components, followed by full-scale tests of connections assembled with these materials. The results show that these connections exhibit a mechanical behaviour compatible with structural applications, regarding both load-carrying capacity and ductility. The proposed design model is based on EN 1995-1-1’s expressions for connections with dowel-type fasteners and gives good predictions of the experimental load-carrying capacities.
ICSI 2021 The 4th International Conference on Structural Integrity
Research Status
Complete
Series
Procedia Structural Integrity
Summary
Timber-to-timber panels (TTPs) are adhesive- and steel-free structural components formed by carpentry joints of Scots pine to be used as floors. A numerical model simulating bending tests on TTPs and considering timber as an orthotropic and bi-modulus material was validated from experimental results of deflection, and rolling shear strength. Since the serviceability and ultimate limit states of the TTPs was mainly defined by the rolling shear properties of the connectors, this paper aims to study the influence of different connector shape parameters in the structural behavior of the panels. For that, values of the connector height (hc varying between 40 and 100 mm), width (b1 varying between 40 and 100 mm) and the dove-tail angle (a varying between 45º and 75º) were introduced in the numerical models to obtain both failure load and stiffness for different span TTPs. Results showed that TTP deflection and shear stresses on the connectors decreases with the increase of the height and the width of the connectors. As the width of the connector (b1) increases, the maximum shear stress decreases up to 42%. For a same connector height, the angle of the dove-tail shows low influence in the maximum shear stress; however, it plays a greater role in the deflection of the panels. For the connectors of 40 mm of height TTP deflection was barely influenced by connector width; however, for higher connectors (hc = 60 mm), TTP deflection decreased up to 41% as width increases. So, new TTPs configurations varying the connector parameters showed an improvement on the deflection and on the shear stresses of the connectors.
A new type of interlocking timber-to-timber connection was designed to simplify the structural details and the mounting conditions between wall elements and ceilings or floor panels in timber frame constructions. An experimental test series on different connector geometries was performed due to the unclear component behaviour and failure mechanism in mode II. The connection types achieved sufficient capacity but do not reach the predicted loads according to EC5. Thus, a mixed mode failure of mode I and II obviously occurs. A design approach is provided recognising all influences on the load-bearing capacity.
Self-tapping screws (STSs) can be efficiently used in various fastening solutions for timber constructions and are notoriously able to offer high stiffness and load-carrying capacity, compared to other timber-to-timber composite (TTC) joint typologies. The geometrical and mechanical characterization of TTC joints, however, is often hard and uncertain, due to a combination of various influencing parameters and mechanical aspects. Among others, the effects of friction phenomena between the system components and their reciprocal interaction under the imposed design loads can remarkably influence the final estimates on structural capacity, in the same way of possible variations in the boundary conditions. The use of Finite Element (FE) numerical models is well-known to represent a robust tool and a valid alternative to costly and time consuming experiments and allows one to further explore the selected load-bearing components at a more refined level. Based on previous research efforts, this paper presents an extended FE investigation based on full three-dimensional (3D) brick models and surface-based cohesive zone modelling (CZM) techniques. The attention is focused on the mechanical characterization of small-scale TTC specimens with inclined STSs having variable configurations, under a standard push-out (PO) setup. Based on experimental data and analytical models of literature, an extended parametric investigation is presented and correlation formulae are proposed for the analysis of maximum resistance and stiffness variations. The attention is then focused on the load-bearing role of the steel screws, as an active component of TTC joints, based on the analysis of sustained resultant force contributions. The sensitivity of PO numerical estimates to few key input parameters of technical interest, including boundaries, friction and basic damage parameters, is thus discussed in the paper.
Fire safety has always been a major concern in the design of timber construction. Even though wood is a highly combustible material, timber members can perform adequately under elevated temperatures. The thermal response of timber connections, however, is in most cases poor and determination of their fire resistance is usually the crucial factor in evaluating the overall load-bearing capacity of wood structures exposed to fire. The analysis of timber joints under fire conditions can be challenging due to their complexity and variety. After presenting the variation of the properties of timber with temperature, this paper reviews the fire performance of various connection types, such as bolted or nailed wood-to-wood and steel-to-timber joints. Results from relevant experimental programs and numerical studies are discussed in detail and future research needs are highlighted. The effect of several factors on the fire resistance of timber connections, such as the fastener diameter, timber thickness and joint geometry, is investigated and useful conclusions are drawn. Based on these, preliminary guidelines for the efficient design of timber connections under fire exposure are presented.
Cross Laminated Timber (CLT) is a new material for midrise timber structures. CLT panels made of Japanese species like Sugi (Cryptomeria japonica D.Don) are developed in Japan. Seismic resistance of CLT structures are mainly determined by the performances of panel-to-panel connections. One of the main fasteners for CLT connections is large size self-tapping screws. It is possible to use not only CLT panels but also glulam structures. But there are few data for these joints and not used so much in Japan. In this study, shear tests of timbet-to-timber joints including CLT panels with large size self-tapping screws and several material tests were conducted. And estimating equations of single shearing properties were validated.
In this study, shear tests of timbet-to-timber joints including CLT panels with large size self-tapping screws and several material tests were conducted. And estimating equations of single shearing properties were validated. Estimation curves were fitted well with test curves. It is confirmed that estimating equations are valid for timber-to-timber connections of large size self-tapping screws.