Timber structures are strongly depending on the design of connections, which are mostly constructed from steel components. However, these joints have a number of limitations such as the tendency to be heavy, proneness to corrosion and often poor aesthetic appearances. Therefore, this study aims to replace metallic joints by non-metallic materials. An experimental testing program was performed to investigate the use of glass fiber reinforced plastics (GFRP), densified veneer wood (DVW) and laminated veneer lumber (LVL) in the form of plates and dowels in different test configurations. Analytical and numerical models were developed to better understand the load-bearing behaviour and to perform static verifications. The models were validated based on the experimental results. The results demonstrate that the use of GFRP dowels in combination with GFRP plates can provide a robust connection system for contemporary applications.
Forest Service/USDA Wood Innovations Grants
Recipient Point of Contact: Matthew D. Aro
Location: Duluth, Minnesota
The University of Minnesota Duluth Natural Resources Research Institute (NRRI), Washington
State University (WSU), and industry partners propose to improve forest health, reduce wildfires, and improve the competitiveness of the forest products industry in MN and the USFS Eastern Region by demonstrating value-added thermally modified composite laminated strand-veneer lumber (TM-CLSVL) mass timber panels from small-diameter balsam fir.
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.
Recent studies showed the need for timber connections with high fire performance. Connections of members in timber structures commonly comprise steel connectors, such as dowels, screws, nails and toothed plates. However, multiple studies have shown that the presence of exposed metal in timber connections leads to a poor performance under fire conditions. Replacing metallic fasteners with non-metallic fasteners potentially enhances the fire performance of timber connections. Previous studies showed that Glass Fibre Reinforced Polymer (GFRP) dowels can be a viable replacement for steel dowels and that Densified Veneer Wood functions well as a flitch plate material. However, as the resin matrix of GFRP dowels is viscoelastic, connection creep, which is not studied before, can be of concern. Also no research has been carried out on the fire performance of these connections. Therefore, a study of the creep behaviour and the fire performance of non-metallic timber connections comprising GFRP dowels and a Densified Veneer Wood flitch plate was performed, as is discussed in this thesis. Predictive models were proposed to determine the connection slip and load bearing capacity at ambient and elevated temperatures and in a fire. The material properties and heat transfer properties required for these models were determined experimentally and predictions of these models were experimentally validated. Furthermore, an adjustment of the predictive model of connection slip at ambient temperature allowed approximating the creep of the connection. The material properties, required for the creep model, were determined experimentally and predictions of the model were compared to results of longterm connection tests. The study confirmed that timber members jointed with non-metallic connectors have a significantly improved fire performance to timber joints using metallic connections. Models developed and proposed to predict fire performance gave accurate predictions of time to failure. It was concluded that non-metallic connections showed more creep per load per connector, than metallic connections. However, the ratio between initial deflection and creep (relative creep) and the ratio between load level and creep were shown to be similar for metallic and non-metallic connections.
Project contact is Henry Quesada at Virginia Polytechnic Institute and State University
The goal of this project is to create a new market for hardwood use in the manufacturing of cross-laminated timber (CLT) panels. Currently, the CLT code PRG-320, only accepts selected softwood species for the manufacturing of CLT panels and all work conducted on increasing hardwood use in CLT’s has focused on producing and using them as structural components. In this project, we will focus on creating an opportunity to increase hardwood use in CLT by adding hardwood to the outer layers of CLT’s, primarily for its visual appearance. Many CLT panels are used as wall and flooring components and other materials are added for decorative walls and flooring. By using hardwood on the outer layers of softwood CLT’s, we can increase hardwood use. Hardwood veneer and lumber will be added to the outer layers of CLT panel cores made from southern yellow pine in compliance with PRG-320. This project will partner with Danzer Veneer America, Allegheny Wood Products (AWP), and Texas CLT to manufacture and evaluate the performance and potential market acceptance of CLT panels made with hardwood veneer and lumber on the outer layers. We will evaluate for delamination of the hardwood veneer and lumber from the softwood core and determine what influence the hardwood layers have on the strength properties of CLT. We will conduct a market perception test of the hardwood veneer laminated CLT panels among architects and structural designers in the U.S. We believe that the results of this work could increase the market for hardwood veneers and lumber by 10% of the current consumption.
Wood-based mass-panels (WBMP) are emerging as an attractive construction product for large-scale residential and commercial construction. Australia is following the lead of Europe and North America with several recent projects being completed using predominately cross-laminated timber panels (CLT). These sawn timber-based panels offer some key advantages to the construction and sawmilling industry. However, veneer-based mass-panel (VBMP) systems could offer additional benefits including the more efficient use of the available forest resources to produce WBMPs that have equivalent to superior performance to CLT. Research to confirm the expected technical viability of veneer-based systems is required. VBMPs could provide a valuable contribution, alongside CLT, to the Australian timber products market.