Improvement Of Fatigue Performance Of U-ribbed Welds By STC Pavement

The orthotropic steel bridge deck exhibits many advantages such as strong bearing capacity,large span,and excellent stress performance in terms of structural performance,and is now widely used in various bridge types.However,there are two problems in bridge deck pavement damage and structural detail cracking when applied to actual bridge structures.The reasons can be summarized as the following: vehicle load,cyclic reciprocating action;complex structure,easy to cause stress concentration;welding connection,easy to produce defects and residual stress.Domestic and foreign researchers have experienced many years of experimental calculations and tried various structural optimizations,but they have not yet been able to fundamentally solve the above problems.The paper takes a steel cable-stayed bridge with serious pavement defects and slight cracks in the welded seam of the U-rib top plate as the prototype.The ultra-high-tenacity concrete structure is prepared as a new pavement replacement for the asphalt pavement with serious damage.To explore the effect of replacement pavement on the fatigue resistance of structural details and the control of the continued expansion of small cracks at the weld.The main research work can be divided into the following three aspects:(1)Establish two kinds of multi-scale finite element models for pavement structures respectively(set different stiffnesses for asphalt pavement to simulate different degrees of damage,and set different interlayer friction coefficients for ultra-high toughness concrete pavements to simulate Different interfacial bondability.Using the extrapolation formula to obtain the hot spot stress at the weld seam of the U-rib roof,the fatigue life of the joint was evaluated using the SN curve method.As a result,it was found that the asphalt pavement damage would greatly reduce the fatigue life of the welded details of the U-rib roof.The replacement of the structural details after STC pavement has theoretically infinite life.(2)Finite element analysis of welding residual stress of U rib top plate was performed to simulate the filling process of the weld.The temperature and stress changes during the whole welding process were observed,the temperature field results were extracted,and the distribution of residual stress was analyzed.The results show that the residual Von Mises stress near the weld seam of the bridge deck almost reaches the yield strength,and the residual stress of the vertical bridge far away from the weld seam shows a compressive stress state,which is consistent with the existing experimental and numerical analysis conclusions,and verifies the correctness of the residual stress numerical simulation.(3)Based on fracture mechanics theory,determine several initial cracklengths The equivalent stress amplitudes in the eight states of the two paving structures obtained in(1)are used as the stress boundary conditions.The two-dimensional finite element model containing cracks is established using ANSYS,the crack growth increment is defined,and the stacking is calculated multiple times.The crack propagation curve was obtained,and it was considered that the crack extended to a plate thickness of about 0.7 times reached the cut-off limit of structural instability fracture.Based on the statistical data of the daily traffic volume,the entire life span of crack propagation to failure is obtained.Find The results obtained with the method in(1)are basically the same.Considering that the length of visible cracks in the actual structure must be greater than It is considered that the fracture mechanics method is more conservative.At the same time,it also proved that the STC pavement has a good control effect on the crack propagation at the U-rib top plate weld seam.