Performance Of Static Fatigue Crack Pipe With Concrete Nodes

Circular hollow section (CHS) tubular joint is consisted of several steel tubes.Different tubes are connected together through welding. Due to the advantages ofbeautiful configuration, simple connection and higher strength-weight ratio, this type ofstructures is widely used in many fields, such as offshore structure, high-rise tower, and soon.Moreover, if the chord is filled with concrete, then the concrete-filled circular tubularjoint (CFCTJ) is formed, which can enhance the static strength of tubular joints, becausethe filled concrete can have a restrained effect on the tube to avoid local deformation. Inaddition, concrete can be restricted by the tube, which can avoid the failure of concreteunder compression or tension within a very short period. Hence, such structures areextensively applied in bridge structure and high-rise tower. In the long-term application,however, the tiny crack will occur at the intersection between the brace and the chordunder the repeated fluctuant loads caused by wind, sea wave, earthquake and the vehiclesin a roundtrip. The crack will continue to propagate with the successive loads, and the netsectional area of the intersection between brace and chord can also decrease, which willcause higher stress concentration, and the structure will fail ultimately due to the quickercrack propagation.In a tubular joint, the stiffness of the intersection between brace and chord willdecrease because of the crack, and the static strength of the tubular joint with crack willalso reduce. Therefore, it is necessary to study the static behavior of concrete filledcircular tubular T joint with crack. In this study, experimental research and finite elementanalysis are used to carry out the following work:1) Before carrying out the fatigue test, the distribution of hot spot stress along the weldtoe of two circular tubular joints is tested, and the curves of the stress concentration factorare obtained. Therefore, the location of maximum hot spot stress of each CFCT T-joint isdetermined;2) Fatigue tests are carried out on two CFCT T-joints to prefabricate surface fatiguecrack; 3) Experimental tests on the static strength of CFCT T-joints with and without crackunder tension are carried out, from which the load-displacement and load-deformationcurves are obtained to study the residual static strength of CFCT T-joints with crack.Meanwhile, during the experimental test, data of crack depth and crack mouth openingdisplacement under different loadings are recorded to analyze the process of crackpropagation;4) Analyzing the effect of different crack depth on the static strength of CFCT T-jointsby using the experimental results;5) Finite element analysis (FEA) is studied on the CFCT T-joint without crack, and theaccuracy of the FEA is verified with the experimental test.