Improving the stiffness of the corner connections in wooden door frames

Research was carried out to determine the strength and stiffness of corner joints in interior door
frames, depending on their construction and on modifications made to their design. Initially, two
models were compared: model 1, with two connectors using a clamping screw at an angle of 45°,
and model 0, with a single connector using a cam joint at an angle of 90°. In all tests, model 1
exhibited significantly better mechanical properties. To improve the performance of model 0,
three alternative construction models (A, B, and C) were proposed by changing the position of
the door frame mounting holes. In the compression test, model A achieved an increased bending moment compared to model 0, while models B and C showed no such improvement. In the
tension test, the bending moment values remained at a similar level across all construction variants,
including model 0. In terms of bending moment, the best result in compression was achieved by
model A (48.26 Nm), and in tension by model B (48.72 Nm). The highest stiffness was demonstrated
by model 1 (up to 42.38 kNm/rad), while among the alternative models, model C achieved the
best result in tension (33.98 kNm/rad). Due to the favourable increase in bending moment under
compression in model A and the insignificant changes under tension across all variants, model A is
considered the optimal solution. To enhance the strength of the door frame, offset holes can be
applied as proposed in this model.