| Inevitably,there are a lot of initial defects in the weld zone of high-rise steel frame beam-column welded joints due to component processing and welding construction.Local stress concentration and micro-cracks are prone to occur.Under long-term random wind load,initial defects and cracks gradually enlarge to form visible cracks.Continuous crack propagation causes high-cycle fatigue damage to the weld of joints,and short-term burst.Under the spontaneous earthquake load,the material directly undergoes large deformation,plastic damage accumulates continuously,cracks expand rapidly,and the joint often undergoes only dozens of cycles of failure.In view of this,it is of great academic and engineering significance to develop more accurate life prediction methods for welded joints of high-rise steel structures and to study the fatigue failure modes and fracture mechanism of welded joints of high-rise steel structures under wind and earthquake.In this paper,the structural strain method is applied to the fatigue life assessment of welds in high-rise steel frame beam-column joints.This method includes the Master S-N curve method(for evaluating high-cycle fatigue)and the Master E-N curve method(for evaluating low-cycle fatigue).The Master work accomplished is as follows:(1)Considering the stress state of the beam-column connections in three-dimensional frame structure are more complex than the plane frame structure,which can reflect the actual situation.This paper establishes a multi-scale model of high-rise steel frame structure and the beam-column connection sub-model with welds and process holes.And the pulsating wind speed time history is simu lated by the harmonic superposition method.The dynamic response of the steel frame structure and the connection sub-model under wind load is analyzed.(2)Residual stress and residual deformation exist in the weld zone of steel frame beam-column connections,and it is difficult to eliminate them completely in practical engineering.In this paper,the influence of residual stress on wind-induced fatigue performance is considered.The welding temperature field and residual stress field of the beam-column connection sub-model are simulated.The residual stress is considered by the initial stress field.The wind-induced stress field is superimposed on this basis.Finally,based on the Master S-N curve method,a wind-induced fatigue evaluation method for joints of high-rise steel frame beam-column joints under the influence of residual stress is proposed.The fatigue life assessment of steel frame joint welds is evaluated.(3)Three kinds of variable-amplitude displacement loading,two kinds of constant-amplitude displacement loading and one kind of random-displacement loading,six kinds of full-scale welded low-cycle fatigue tests of beam-column connections were designed and completed.The fatigue crack initiation and propagation laws of connections under different loading regimes were recorded and studied.The hysteretic dissipation energy was analyzed.The tests under constant-amplitude loading,variable-amplitude loading and random-load were compared.The fatigue damage accumulation of the connections is studied.The effects of cyclic amplitude(constant amplitude)and loading history(variable amplitude,random)on the fatigue damage of the connections are studied.(4)According to the fatigue test model,the finite element analysis under different loading regimes is carried out.The fatigue life under different loading regimes is calculated by the M aster E-N curve method,and the results are compared with the test results,and verifies the effectiveness of the method. |
PDF Full Text Request