轻钢结构屋顶光伏改造中应用预应力碳纤复材板增强檩条的设计方法

Design Method of Prestressed CFRP-Reinforced Purlins in Reconstruction of Photovoltaic System for Light-Gauge Steel Structure Roofs

基于大量既有工业建筑轻钢结构屋顶光伏改造的工程背景,应用普通和顶撑两类预应力碳纤复材板增强技术对其檩条进行增强。前者使用千斤顶张拉碳板施加预应力,增强后碳板紧贴檩条下翼缘;后者使用跨中顶撑张拉碳板施加预应力,增强后跨中碳板远离檩条下翼缘而呈现三角形状。为研究两种方法,首先,分析了两类增强技术的增强机理。然后,基于我国现有规范,应用直接强度法考虑了局部屈曲和强度破坏相关性,并考虑了碳板变形造成的预应力增加,从而得到了两类增强方法增强后檩条的承载力及变形计算方法,并证明了该方法的准确性,同时获得了参数影响规律:碳板刚度越大、撑出长度越大、预应力越大、增强效果越好。基于此,考虑增强阶段最大预应力、碳板强度及增强檩条变形等实际限制条件,建立了预应力碳板增强檩条的设计方法,针对光伏改造工程下檩条的强度增强或局部屈曲增强给出设计算例。通过设计算例的比较,得到了两类增强方法的不同适用条件,发现顶撑增强更容易实现承载力和刚度的大幅度提升,可供工程参考。

Based on the engineering background of reconstruction photovoltaic systems on the light-gauge steel structure roofs of many existing industrial buildings,two categories of reinforcing techniques using prestressed CFRP laminates are applied to reinforce the purlins of such structures.The former uses hydraulic jack to prestress the CFRP laminate,which is close to the lower flange of steel purlin;and the latter uses a prestressing chair at the midspan of the steel purlin to prestress the CFRP laminate,thus the CFRP laminate is far away from the lower flange of the steel purlin and forms a triangular shape.Firstly,the reinforcement mechanisms of the two reinforcing techniques were analyzed.Secondly,based on current codes in China,the direct strength method was applied to form a calculation method of the bearing capacity and the deformation of the reinforced steel purlin,which considered the correlation between the local buckling and strength failure of the reinforced steel purlin and the increase of prestress caused by the deformation of CFRP laminate.The calculation results had good accuracy and the influencing tendencies of the parameters were obtained.It was found that using a large stiffness of CFRP,a large supporting length,and a large prestress value led to a high reinforcing efficiency.Based on this,considering the practical limitations of maximum prestress in the reinforcing stage,CFRP laminate strength and maximum deformation of the reinforced steel purlin,a design method of the reinforced steel purlin was established,and design examples of such steel purlins were given for flexural strength or local buckling enhancement.Through the comparisons of design examples,different applicable conditions of the two categories of reinforcing techniques were obtained.The technique of using prestressed CFRP with prestressing chair was easier to achieve a significant increase in flexural capacity and stiffness.This paper provided references of reinforcing steel purlins with prestressed CFRPs in real engineering.