Experimental Study On The "Y"–type Tubular Joints With Cross-weld

The steel tubular structure, which is brief construction and beautiful appearance, is the first choice for large-span space structures, such as gymnasium, airport terminal, subway stations, and large industrial buildings. The joints with cross welds occuring in these steel tubular structures are inevitably. Meanwhile, the welding process are carried out many times at the cross site with the weld district being heated repeatly, which will produce larger welding residual stress. Especially nearby the cross-weld, there will be three dimensional stresses which are in the same direction, and due to the plastic deformation development of the material at the joints is limited, it will increase its brittle fracture tendency, even causes the brittle failure at the joints. Usually, the welding residual stress will reach the steel yield point at the cross site and the nearby main mental where is the most sensitive areas of the formation and development of fatigue crack.It affects the ultimate capacity of the joint and reduces the structure's safety properties. There are no studies on the cross weld in the past, almost no test studies on the cross weld of tubular joints and no related reference material.Therefore, it is necessary to study the effect of welding residual stress of cross weld on the behaviors of tubular joints.In this article, we first simulate "Y"-type tubular joints by finite element software ANSYS, initially get the distribution, variation of the stress and deformation of the joint region and the ultimate bearing capacity of the joint, then we carried out the model tests of three specimens. The main research content and conclusions are as follows:①We analyze the Mise cloud stress, growth process of plastic zone and the failure mode of the joints by finite element modeling. We use arc-length method to calculate out the load - branch piple axial displacement curve of the joints and obtained the ultimate bearing capacity based on failure criterion.②Tracking detect the butt-weld at the joint region by the ultrasonic detectors in order to understand the weld defect of the development process under loading. Through testing, butt-welded is less affected under vertical static load.③Lay out the appropriate location at the joint region to measure strain in order to understand the distribution, variation of the stress at the joint region. According to the measured data and combining with the finite element analysis, abtain the residual stress distribution curve of the joint region. The results show that the transverse and circumferential residual stress distribution is relatively complex with the transformation from tension to pressure.④Lay out the appropriate location at the joint region to measure strain in order to understand the deformation process of the joint region and obtain the ultimate bearing capacity based on failure criterion. According to the measured data and combining with the finite element analysis, we can say that the cross weld has no obvious effection on the static capacity of joint.⑤Through the failure test, observing the final failure mode and residual deformation,we can predicate the weak position of the joint area with measured test data,and provide test reference for future engineering design.