| Diaphragm is an important part of orthotropic steel deck.Fatigue loads lead to serious cracking problems in structural details of diaphrams It is necessary to reinforce and repair for the cracked area and comprehensively evaluate the effect of the reinforcement.The evaluation method using stress or stress intensity factor as the index ignores the multi-fatigue cracking modes of structural details,which is difficult to fully reflect the strengthening effect of the reinforcement system used on the structure.In this thesis,the linear elastic fracture mechanics are adopted to study the crack arrest effect of each reinforcement scheme,and the fatigue deterioration characteristics of diaphragm before reinforcement and the strengthening performance after reinforcement are studied.Considering multi-fatigue cracking modes of diaphragm,the reinforcement effect is evaluated based on the residual fatigue life.The main research work and conclusions are as follows:(1)Considering the multi-fatigue cracking modes,the reinforcement evaluation framework is established based on the residual fatigue life,and the reasonable value of crack surface thickness for the calculation of equivalent structural stress at diaphragm is determined.The equivalent structural stress method is applied to the calculation of base metal stress response;(2)The general analysis software ANSYS is used to simulate the three-dimension propagation of two typical fatigue cracks at the structural details of the diaphragm.The magnitude of the stress intensity factor at the point of interest at the crack front shows that the two types of cracks are mainly dominated by type Ⅰcracking when the crack do not penetrate the diaphragm,and it will turn to composite crack dominated by type Ⅰ and type Ⅱ after penetrating the diaphragm.(3)The linear elastic fracture mechanics theory is applied to analyze the restraining effect of each reinforcement method on the fatigue crack of the diaphragm structure.Several reinforcement methods were used for finite element analysis for the penetration cracks of weld toe cracking and arc opening cracking,and the influence mechanism of different reinforcement parameters on reinforcement effect is studied based on linear elastic fracture mechanics.The equivalent structural stress method is applied to calculate the stress response of the potential cracked parts after reinforcement,and it is proved that the introduction of the reinforcement system will change the mechanical properties of the original structure,thereby affecting the cumulative rate of fatigue damage at the potential cracked parts.(4)For the penetration fatigue crack of welding root cracking mode and arc-shaped opening cracking mode,both the fatigue deterioration characteristics of potential cracked parts before reinforcement and residual fatigue life of the overall structure after reinforcement are calculated.Based on the comparative analysis of residual fatigue life The strengthening effect of each reinforcement scheme on different cracking modes is analyzed,and a reasonable reinforcement scheme for through-type fatigue cracks under various typical cracking modes is obtained. |
PDF Full Text Request