The influence of a cracking mode on fatigue crack propagation in steel girders in military bridges

This article is presented a way of taking into account mixed mode cracking in fatigue analyses of steel girders in military bridges. The influence of the angle size of the direction crack propagation phi on the evaluation of fatigue life of steel girders is also described. The conducted analyses showed that taking into account mixed mode cracking and the value of the direction of crack propagation phi has a positive influence on the accuracy of calculations related to the determination of fatigue life of steel structural elements due to decreasing a value of the equivalent stress intensity factor K-eq. The work is also presented the results of calculations of fatigue cracks propagating in the main steel girders developing in the direction away from assembly openings. The analysis was conducted using the FRANC2D software for two adopted models of physical material. The calculation results of fatigue crack propagation in the case of material models which are either ideally elastic or ideally elastic with linear plastic strain hardening are also described. The conducted analyses showed that adoption of particular material properties has a significant influence on the value of the obtained calculation results.