Effect of thermal induced flexural strain cycles on the low cycle fatigue performance of integral bridge steel H-piles

• Thermal strain in steel H piles of integral bridges are defined.
• A cycle counting method is developed for thermal strain in piles.
• An equation for low cycle fatigue life estimation of steel H piles is developed.
• Full scale experimental test results on low cycle fatigue life of steel H-piles are presented.
• Effect of small amplitude flexural strain cycles on steel H piles are explored.

Close examination of the field measurement data for integral bridges revealed that the measured cyclic flexural strains in steel H-piles at the abutments due to thermal fluctuations consist of large amplitude, primary small amplitude and secondary small amplitude cycles. The effect of the small amplitude strain cycles on the low cycle fatigue life of these steel H-piles has not been extensively studied yet. Accordingly, to investigate the effect of the small amplitude strain cycles on the low cycle fatigue life of steel H piles at the abutments, first a new cycle counting method is developed specifically to facilitate the counting of thermal induced strain cycles in the steel H-piles. Then, using the field measurement data of several integral bridges in North America, and the developed cycle counting method, an equation is formulated to estimate the fatigue life of integral bridge steel H-piles. It is observed that secondary small amplitude flexural strain cycles do not have a significant effect on the low cycle fatigue life of steel H-piles. Experimental studies on full scale compact steel H-pile specimens are conducted to verify the analytical results and a close match between the experimental and analytical results is observed.