Discussion on Shape Coefficient in Wind-Induced Fatigue Analysis of Rectangle High-Rise Steel Structures
摘要: 高层钢结构梁柱焊接节点在风作用下可能发生疲劳破坏。目前结构风致疲劳的分析方法是,采用体型系数整体上替代结构表面不同部位的风压系数,对风压系数分布进行平面上的平均处理,进而结合准定常假设计算风压并进行疲劳分析。然而高层结构表面风压分布较为复杂,关键节点应力的分布将有可能受到该平均化处理的影响,且GB 50009—2012《建筑结构荷载规范》中体型系数的规定值主要针对基于位移的风振计算,能否满足基于局部应力的风致疲劳计算,目前尚未有相关文献对该问题进行研究或验证,因此需验证采用体型系数计算结构风致疲劳的准确性。选取了位于风灾频发区域的某矩形截面高层钢框架支撑结构,首先考虑空间相关性,利用谐波叠加法模拟了该结构具有代表性的梁柱节点位置的脉动风速时程,通过逆傅立叶变换将模拟的风速时程转换为功率谱密度曲线,并与目标谱进行对比验证,随后通过计算流体动力学(CFD)软件FLUENT建立了结构1∶300缩尺比的数值风洞计算模型,利用雷诺平均模拟(RANS)计算了结构表面的风压系数分布,并与日本东京工艺大学风洞试验数据库中类似体型的结构模型风洞试验数据进行了对比和验证;最后,利用有限元软件ANSYS对该结构建立了多尺度有限元模型,并分别基于风压系数和体型系数,结合准定常假设计算风压时程,将风压时程转化为各梁柱节点的风荷载时程并最终施加在结构多尺度有限元模型上,采用等效结构应力法对结构梁柱焊接节点进行了疲劳评估,并将基于风压系数的分析结果与基于体型系数的分析结果进行了对比。结果表明:利用谐波叠加法模拟的脉动风速时程的功率谱与目标谱在大部分频段吻合较好;结构表面风压系数分布结果和东京工艺大学风洞试验结果较为接近且变化趋势相同,因此,该结构风压系数的数值风洞模拟结果较为合理;基于体型系数的风致疲劳计算结果与基于结构表面不同部位风压系数的风致疲劳计算结果较为接近,可满足工程需要,并且更加偏于安全;GB 50009—2012中关于体型系数规定值能够较好地适用于矩形平面高层钢结构梁柱焊接节点风致疲劳的计算。Abstract: 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.
- welded beam-column connections /
- wind-induced fatigue /
- shape coefficient /
- CFD /
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