Experimental Study on Influencing Factors of Fatigue Performance of Larch Plywood Beam

To investigate the fatigue performance of larch plywood beams under cyclic loading, this study systematically examined the effects of three key factors—loading frequency, loading waveform, and span-to-height ratio—on fatigue life, failure modes, and stiffness degradation through static and fatigue tests. Three plywood beams were first subjected to static tests, yielding a maximum load capacity of approximately 88 kN, with failure primarily occurring due to fiber fracture in the tension zone. Subsequent fatigue tests were conducted under varying loading frequencies (1 Hz, 3 Hz, 5 Hz), waveforms (sine, triangular, square), and span-to-height ratios (12,15,18). Results demonstrated that higher loading frequencies extended fatigue life, though the gain effect diminished beyond 3 Hz. The loading waveform significantly influenced fatigue life, with square wave loads causing maximum damage at equivalent stress levels compared to triangular wave loads. Increased span-to-height ratios reduced fatigue life, while smaller ratios exhibited more pronounced shear stress-dependent failure. A fatigue damage evolution model based on stiffness degradation theory was established, showing good agreement with experimental predictions. This research provides theoretical foundations for fatigue design of timber-structured bridges.