# Effect of Wood Densification and GFRP Reinforcement on the Embedment Strength of Poplar CLT
###### Abstract  
Embedment strength is an important factor in the design and performance of connections in timber structures. This study assesses the embedment strength of lag screws in three-ply cross-laminated timber (CLT) composed of densified poplar wood with densification ratios of 25% and 50%, under both longitudinal (L) and transverse (T) loading conditions. The embedment strength was thereafter compared with that of CLT reinforced with glass-fiber-reinforced polymer (GFRP). The experimental data was compared with results obtained using different models for calculating embedment strength. The findings indicated that the embedment strength of CLT specimens made of densified wood and GFRP was significantly greater than that of control specimens. CLT samples loaded in the L direction showed higher embedment strength compared to those in the T direction. In addition, 50% densification had the best performance, followed by 25% densification and GFRP reinforcement. Modelling using the NDS formula yielded the highest accuracy (mean absolute percentage error = 10.31%), followed by the Ubel and Blub (MAPE = 21%), Kennedy (MAPE = 28.86%), CSA (MAPE = 32.68%), and Dong (MAPE = 40.07%) equations. Overall, densification can be considered as an alternative to GFRP reinforcement in order to increase the embedment strength in CLT. embedment strength; densification; cross-laminated timber Article  
Effect of Wood Densification and GFRP Reinforcement on the Embedment Strength of Poplar CLT  
1 Wool Science and Technology, Department of Natural Resources, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabili 56199-11367, Iran  
2 Centre for Infrastructure Engineering (CIE), School of Engineering, Design and Built Environment, Western Sydney University, Sydney 2145, Australia; [EMAIL_ADDRESS]  
Connections and fasteners in timber structures are subjected to numerous external loading conditions, including the lateral load. Estimating the embedment strength of CLT is essential, especially under lateral load conditions. In general, embedment strength is a system property representing the resistance of wood to laterally loaded embedment fasteners. When fasteners are inserted into the side face or the narrow face of cross-laminated timber (CLT) at different angles relative to the fastener axis and load, the resulting system property encompasses a range of inputs from the layers and laminations, which is due to the varied load-grain angles [7]. Due to considerable variations in embedment strength, deformation, ductility, and failure modes between the longitudinal and transverse layers, the orthogonal lamination complicates the connection properties of CLT [1]. Additionally, due to the orthogonal lamination, the embedment locations of dowels in CLT become more complicated. It is possible to locate dowels parallel and perpendicular to the grain within and between a single lamina in one layer as well as between layers when dowels are installed on the narrow face of CLT [1]. Similarly, when installed on the flat side of the CLT panel, the dowels may penetrate into multiple layers. Therefore, it is necessary to evaluate the embedment strength in wood structures. The embedment strength of wood is necessary for estimating the capacity of structural timber connectors using dowel-type fasteners. This strength is derived from expressions that are based on tests carried out on timber. Dowel-type connectors are the most frequent form of joint used in modern construction, and they are typically made of wood or metal [10]. Dowel-type connections provide a number of benefits, one of which is their ductile characteristic, which makes it possible for considerable relative deformations and rotations to occur between the wood pieces [11]. Therefore, the embedding strength is not a specific attribute of the material but rather a property of the system. Different empirical equations have been proposed to estimate embedment strength.