Norway spruce glulam beams with artificial horizontal slits of different length and depth were reinforced using self-tapping screws and threaded steel rods in order to restore their load-carrying capacity and stiffness. The study aimed at evaluating the effects of strength and stiffness of the applied reinforcing elements on the load-carrying capacity and stiffness of glulam beams after retrofitting. Self-tapping screws and threaded steel rods of different diameter have been evaluated in the study and different numbers of reinforcing elements have been applied. Shear failure of the beams with artificial slits of different depth was provoked in loading cycles with stepwise installation of the reinforcing elements in the beam parts failed in the preceding test. The reinforcing effect of the tested self-tapping screws and threaded steel rods reached and partly exceeded the estimated level calculated with selected analytical models. Unfavourable structural behaviour arose in some cases from crack opening during installation of the rods causing a very low initial stiffness. Comparison of test results to calculations of stiffness and load-carrying capacity of the reinforced beams applying the -method, the shear analogy method and a truss model revealed that the -method and the shear analogy method provided the best estimates of strength / stiffness of the reinforced beams.
In this thesis the reliability of the design of unreinforced notched beams is evaluated and recommendations for the design of reinforced notched beams are given. The review of design approaches for reinforced notched beams shows, that so far the reinforcement is designed only with regard to the perpendicular to grain force acting in the notch corner. The evaluation of test results from literature shows that a stiff reinforcement has the best reinforcing effect but initial cracking cannot be prevented. The failure behaviour of the reinforced notch is studied in more detail by means of experiments and a FE model. Initial cracking of the reinforced notch comes along with crack opening, whereas ultimate failure with excessive crack growth is accompanied by shearing of the crack. An analytical model is presented for the description of the structural behaviour of reinforced notched beams. The parallel and perpendicular to the grain stiffness of the reinforcement is accounted for in the model. A high stiffness of the reinforcement parallel to the grain is required in order to reduce the mode 1 loading of the notch corner and to prevent initial cracking. The mode 2 loading of the crack increases with increasing crack length. In order to achieve higher load-carrying capacities for notched beams with longer cracks, reinforcement with high stiffness parallel to the grain is required. Recommendations are given for the required reinforcement of notched beams in order to restore the shear capacity of the reduced cross-section.
