Discussion on Shape Coefficient in Wind-Induced Fatigue Analysis of Rectangle High-Rise Steel Structures

Welded beam-to-column connections in high-rise buildings may be subjected to fatigue failure under wind. At present, the analysis method of wind-induced fatigue is to replace wind pressure coefficients on different parts of the structural surface with the shape coefficient as a whole to average the distribution of wind pressure coefficients, and then to calculate the wind pressure and to conduct fatigue analysis in combination with the quasi steady assumption. However, the distribution of wind pressure on the surface of high-rise structures is complex, and the distribution of stress at key connections may be affected by this average treatment. Moreover, the specified shape coefficient in "Load Code for the Design of Building Structures(GB 50009-2012)" is mainly for displacement-based wind vibration calculation. Whether it can meet the calculation need of wind induced fatigue based on local stress has not been studied or verified by relevant literature so far, so it is necessary to verify the accuracy of calculating wind induced fatigue of structures using shape coefficient.A rectangular-plane high-rise steel frame supporting structure located in the wind disaster prone area was selected. First, considering the spatial correlation, the fluctuating wind speed time history at the representative beam-to-column connection of the structure was simulated by using the harmonic superposition method. The simulated wind speed time history was converted into a power spectral density curve through inverse Fourier transform, and was compared with the target spectrum. Then a numerical wind tunnel calculation model with 1:300 scale ratio of the structure was established in the CFD software FLUENT. The wind pressure coefficient distribution on the structure surface was calculated using Reynolds average simulation(RANS), and was compared with the wind tunnel test data of similar structure models in the wind tunnel test database of Tokyo Polytechnic University, Japan; Finally, the multi-scale finite element model of the structure was established using the finite element software ANSYS, and the wind pressure time history is calculated based on the wind pressure coefficient and the shape coefficient respectively, combined with the quasi steady assumption. The wind pressure time history is transformed into the wind load time history of each beam-to-column connection and finally applied to the multi-scale finite element model. The fatigue assessment of the structural welded beam-to-column connections is carried out using the equivalent structural stress method.The analysis results based on wind pressure coefficient are compared with those based on shape coefficient. The results show that the power spectrum of fluctuating wind speed time history simulated by harmonic superposition method is in good agreement with the target spectrum in most frequency bands; The wind pressure coefficient results on the structural surfaces are close to the wind tunnel test results of Tokyo Polytechnic University with the same change trend. Therefore, in general, the numerical wind tunnel simulation results of the wind pressure coefficient of this structure are reasonable; The wind-induced fatigue calculation results based on the shape coefficient are close to those based on the wind pressure coefficient of different parts of the structural surface, which can meet engineering demands and are safer; The specified value of shape coefficient in Load Code for the Design of Building Structures GB 50009-2012 can be well applied to the calculation of wind-induced fatigue of welded joints of rectangular plane high-rise steel structures.