负载下焊接外加劲肋加固圆钢管节点轴向受力性能研究

It is necessary to retrofit an engineering structure when the structural bearing capacity is insufficient due to the change in service condition or the structural damage. However, to avoid the effect on the normal activity, the retrofitting is often carried out while the structure is under load. Circular hollow section (CHS) steel structures are applied widely in long-span and space structures and the tubular joint axial loading capacity is usually lower than that of the brace(s). Therefore, the key to retrofitting the steel tubular structures is the retrofitting of the joints. This research studies the method of welding the external stiffeners to retrofit the circular hollow section steel joints while under load. This method has the merits of easy manipulation and low cost, but the standards both in China and abroad lack specifications of the joint retrofitting while under load and the corresponding research is also limited. Therefore, this research performs the axial loading strength experiments of full scale CHS T-, Y-, K- and X-joints while under load, compares the ultimate strength and deformation capacity of the unreinforced and reinforced joints to confirm the retrofitting effect. The finite element models of the joints are established, the effect of the welding heat is simulated, the ultimate strengths are computed and the FE results are compared with the experimental results to verify the FE method. Then through the comprehensive finite element parametric analysis, the influences of the initial load, welding process, welding heat, external stiffener form, size, brace/chord diameter ratio, chord diameter to wall thickness ratio on the retrofitting effect are investigated. The failure mechanism of the joints is analyzed, the theoretical model of the joint strength is derived, the formulae of the joint retrofitting effect are established and the retrofitting theory can be applied to tubular structures projects.

工程结构因为使用条件变化或者结构损伤等原因，导致承载力不足而需要加固。但为了不影响正常活动，加固通常在负载下进行。圆钢管结构广泛应用于大跨及空间结构，其节点轴向承载力一般低于支管，因此钢管结构加固的关键是加固节点。本项目研究负载下焊接外加劲肋加固圆形钢管节点的方法，此方法操作简便、造价低，但是国内外规范对此没有具体规定，研究工作也很有限。因此，本项目拟进行负载下足尺T形、Y形、K形和X形圆管节点轴向承载力试验，比较加固与未加固节点的极限承载力、变形能力等，证明加固效果。建立节点有限元模型，模拟焊接热影响，计算极限承载力，并与试验结果对比，以验证有限元方法。然后通过大规模有限元参数分析，研究初始负载、焊接工艺、焊接热量、加劲肋形式、尺寸、支管/弦管直径比、弦管径厚比等因素对加固效果的影响。分析节点的破坏机理，推导节点承载力的理论模型，建立加固计算公式，为实际钢管结构工程提供理论依据。

伴随着国家实力持续加强，建筑科技也不断发展进步，越来越多的新颖建筑雨后春笋般不断涌现。圆钢管凭借其自身截面双轴对称的结构特点，截面惯性矩对各轴相同，作为受压受弯构件十分有优势，造型简洁、管壁平整，杆件可直接相贯焊接，风阻力系数小，建筑美学效果好的优势，广泛应用在建筑领域当中。钢管结构在近年飞速发展，不仅仅在海洋工程、桥梁工程中得到应用，而是广泛应用到几乎所有领域的建筑工程中，尤其在航站楼、体育馆等大跨度、大空间的建筑结构中异彩纷呈。钢管结构本身轻快简洁，其复杂性通常体现相交节点处。因此不论是设计阶段还是在使用期间，钢管焊接节点的静力强度都是最主要的问题之一。实际工程中，由于各种原因需要在负载期间对节点进行加固，焊接加固作为简单、容易操作、成本低的方式被广泛应用。当前对于钢管节点负载下焊接加固的研究较少，也没有相关规范对此有具体要求。. 本课题组通过进行3次试验，1.支管与主管内径比β分别为0.25、0.5、0.73的三组共6个T形节点构件，每组内分别对应0.3和0.6的负载系数，探究负载下焊接外加劲肋加固的T形圆钢管节点的轴向受压承载性能。2.支管与主管内径比β分别为0.25、0.5、0.73的三组共6个T形节点构件，每组内分别对应0.25和0.5的负载系数，探究负载下焊接外加劲肋加固的T形圆钢管节点的轴向受拉承载性能。3.支管与主管内径比β分别为0.26、0.5的两组共4个Y形节点构件，每组内分别对应0.3和0.6的负载系数，探究负载下焊接外加劲肋加固的Y形圆钢管节点的轴向受压承载性能。并建立有限元模型，将模拟结果与试验结果进行对比，验证有限元的正确性，得到可靠的模拟焊接加固的有限元方法后，进行大规模参数化分析，探究负载系数、外加劲肋形式、尺寸、支管/弦管直径比、弦管径厚比等参数对加固效果、极限承载能力和破坏模式的影响，提出负载下焊接外加劲肋的加固设计方法，便于工程上的应用，以及为后续研究提供思路和参考。