Tensile and fatigue investigations of timber joints with glued-in FRP rods

Glued-in rods are an effective method to form timber connections that are increasingly in the focus of research. Compared to steel rods, fibre-reinforced polymer (FRP) bars provide higher resistance against corrosion, reduced weight, and lower heat conductivity. Despite excellent mechanical performance, high fire resistance, and improved aesthetics, they are, however, not yet widely used due to lack of design regulation. This is particularly true for cyclic loads, where determination of fatigue characteristics depends upon time-intensive experimental procedures. In this research, 50 glued-in FRP rod specimens with different embedment lengths were manufactured and tested in uniaxial tension: a first set under quasi-static load and a second set under cyclic load. For the fatigue tests, a new approach based on a stepwise load increase was used to estimate fatigue strength, a method that aims at reducing the experimental effort usually associated with Woehler curves. Experimental results indicated that quasi-static and fatigue strength increased with the overlap length up to an apparent maximum. The estimated fatigue strength from the load increase tests (LITs) was approx. 41% of the quasi-static strength. Additionally, constant-amplitude tests were performed and the obtained data points fit well into established Woehler curves for timber.