Experimental Investigation of Ultimate Shear Force Capacity of Glulam Reinforced with Glued-in Threaded Rods

Glued-in threaded (GIT) rods have been considered an effective timber connection method having several advantages, such as high load-carrying capacity, great stiffness, and good fire resistance. This type of connection has widely been utilized in newly built modern timber structures and for reinforcing the existing ones.

The purpose of this experimental research is to investigate how the ultimate shear force capacity (USFC) of glulam is affected if it is reinforced with GIT rods and to study the interaction between the glulam and GIT rods. The results of this research can help researchers and engineers to select a suitable method of reinforcing the glulam with GIT rods at a superior inclination angle (IA) to the fiber direction in order to achieve higher USFCs.

A total of forty glulam samples were tested for failure. The experimental tests consisted of five different series of samples with eight samples in each series. Sample series 1 were unreinforced glulam. Sample series 2 and 4 were glulam reinforced with the GIT rods at two different IAs of 45° and 90° to the fiber direction, respectively. Sample series 3 and 5 were glulam reinforced in the same way as sample series 2 and 4, but they were split in the middle. The samples were tested for failure using a standard testing machine. The machine was connected to a computer that recorded all the values obtained from the tests.

The results of the study were obtained as force-displacement graphs. The stiffness of the samples and interaction between the glulam and GIT rods were also calculated. The results achieved from the experimental tests of different series were compared and discussed.

The experimental tests resulted in a 12.5% increase in the average USFC of sample series 2. However, the average USFC of sample series 4 was not enhanced significantly. The interaction between the glulam and GIT rods was obtained as 31.8% for the samples with reinforcing at the IA of 45° to the fiber direction and 3.8% for the samples with reinforcing at the IA of 90° to the fiber direction. Reinforcing the glulam with the GIT rods demonstrated the potential of enhancing its USFC. However, reinforcing the glulam with the GIT rods at the IA of 45° to the fiber direction was found to be superior to reinforcing the glulam with the GIT rods at the IA of 90° to the fiber direction.