考虑塔与抱杆耦合的超大型输电高塔抗风分析

Wind Resistance Analysis of Transmission Tower Considering Interaction Between Tower and Crane Structure

采用风洞试验和有限元分析对考虑塔与抱杆耦合的超大型输电高塔施工过程的抗风性能进行研究,计算和验证了危险强风工况下输电塔及抱杆抗风措施的有效性。对江苏凤城—梅里500 kV输电线路385 m高跨长江输电铁塔施工装备双平臂抱杆进行风洞试验,完成了抱杆标准节节段模型及抱杆整体模型的风洞高频天平测力试验,得到了抱杆风力系数,并与GB 50009—2012《建筑结构荷载规范》进行了比较。分别建立了抱杆软连接有限元模型、抱杆与铁塔耦合有限元模型,对比分析了两种抱杆模型在不同工况风荷载作用下的结构力学性能差异。通过有限元计算得到了平衡、不平衡起吊和不同风向角等多种组合工况下抱杆最大位移及腰环主拉索最大拉力计算结果,分析了抱杆施工过程中的不利因素。针对非工作工况强风条件,计算和分析了平臂可自由转动和降低抱杆悬臂高度等主要抱杆抗风措施对抱杆与塔耦合系统整体力学性能的影响,为超大型输电高塔施工期抗风安全提供参考。结果表明:抱杆整体风力系数试验结果与规范取值存在一定差异,规范取值偏于风险,风洞试验得到的x向和y向风力系数最大值分别为2.40和2.51;不平衡起吊和45°风向角均为抱杆结构的抗风不利工况,施工过程中应尽量避免不平衡起吊并且避免平臂与来流风向成45°角时吊装重物;抱杆与铁塔耦合模型的最大风致位移计算结果大于抱杆独立模型,而腰环主拉索最大拉力计算结果小于抱杆独立模型。此外,抱杆与铁塔耦合有限元模型的计算结果显示:在主塔施工后期,由于高空铁塔截面减小、刚度降低,不能给予抱杆足够的抗侧刚度,导致腰环主拉索最大拉力急剧增大,且拉力最大值出现位置下移;非工作工况强风条件下平臂自由转动可有效降低抱杆腰环主拉索最大拉力,降幅可达30%~40%。建议在强风条件下采取平臂可自由转动和降低抱杆悬臂高度相结合的抗风措施,确保输电高铁和抱杆耦合系统的施工期抗风安全。

Wind-resistance performance of super high transmission tower during construction has been studied by wind tunnel tests and finite element methods(FEM).The effectiveness of measures against strong wind for the tower and crane has been analyzed and validated.Wind tunnel tests for the 385 m height tower and its construction facility had been conducted.Wind force coefficients of the crane structure were obtained by sectional model tests for the standard crane structure and high-frequency force balance tests for the scaled crane model,and compared with the code values of Load Code for the Design of Building Structures(GB 50009—2012).Two FEM models were established respectively for the crane structure with soft connection to the tower and the tower-crane coupled system to investigate the different wind-resistant performance between two models.FEM analysis had been performed to calculate the maximum crane displacement and the maximum tension of main cables for different cases of balance or unbalance lifting with varying wind angles,and the unfavorable factors in the process of crane construction were analysed.In strong wind conditions,detail evaluations of the proposed wind-resistance measures,i.e.,free rotations of double flat arms and lowering the cantilever height of crane,were carried out,which could provide a reference for super high transmission tower during construction.It was found there exist noticeable difference between wind tunnel results and the code values for wind force coefficients of the crane structure.While the code values may underestimate wind force,wind tunnel tests yield the maximum x or y directional wind force coefficients up to 2.40 and 2.51,respectively.The unfavorable conditions of unbalance lifting and the critical wind angle of 45°have been identified and should be avoided during the construction if possible.The maximum displacement from the tower-crane coupled model is greater than that of a single crane model.On the other hand,the maximum tension of main cables of the coupled model is smaller than the single crane model.The analysis result of the coupled model shows the decreasing of tower lateral stiffness to support the crane due to the smaller tower section at a high altitude during the later stage of tower construction.Correspondingly,a sharp increase of the maximum cable tension was observed from the coupled model at a lower position.In strong wind conditions,the maximum tension of the main cable could be reduced by 30%~40%by free rotations of flat double arms.Therefore,it is suggested to take effective wind-resistance measures,i.e.,free rotations of double flat arms or lowering the cantilever height of crane structure to ensure the construction safety of the super high transmission tower under strong wind conditions.