Study On Mechanical Behavior Of Circular Hollow Section (CHS) Brace-H Section Chord Joints

Circular hollow section (CHS) brace-H section chord joint is a new steel tubestructure. Its intersecting line is a plane curve. Because it’s easy to design andconstruct than the space curve of circular steel tube, so we can greatly reduce theworkload and speed up the construction schedule. Due to the above advantage, CHSbrace-H section chord joint is widely applied to engineering, but its application inengineering will be limited by that the research on the joint is much less, so we needcarry out the research on the mechanical behavior of the joint as soon as possible.Based on the tests T-joints and X-joints, nonlinear finite element analysis on thejoints is made in order to study mechanical behavior, failure mode, ultimatecapacities and influence of internal stiffener on the ultimate capacities on the type ofT-joint and X-joint.Firstly, experimental research on CHS brace-H section chord T-joints underaxial force and X-joints under in-plane moment is conducted. Experimental programis proposed and mechanical behavior, failure mode, ultimate capacity and influenceof internal stiffeners in H section chord on the ultimate capacity are studied. For T-joint, results of these tests show that calculation ultimate capacity of joints adoptingEurocode3can’t be well used to calculate the ultimate of the T-joints under axialforce; As value of β(define as the ratio of brace’s diameter to width of H sectionchord’s flange) increase, accordingly axial resistance of joints increase remarkable;internal stiffeners in H section chord makes ultimate capacity of the joints a degreeof improvement; the ultimate capacity of joints with small value of β increase moreobviously than the joints with small value of β after welding internal stiffeners in Hsection chord. For X-joint, results of these tests show that calculation ultimatecapacity of joints adopting Eurocode3can’t be well used to calculate the ultimate ofthe X-joints under in-plane moment; When the value of β is0.3~0.6，as value of βincrease, accordingly in-plane flexural capacity and initial flexural rigidity of jointsincrease remarkable, when the value of β is greater than0.6, the value of β is of littleconsequence to in-plane flexural capacity and initial flexural rigidity of the joints; welding internal stiffeners in H section chord makes in-plane flexural capacity of thejoints improvement with small value of β.Secondly, Finite Element (FE) validation research on capacity of CHS brace-Hsection chord T-joints and X-joints are performed. Effective and exact FE models areset for parameter analysis with all kinds of factors taken into consideration.Comparison between FE and experimental results proves validation of FE methodavailable based on the FE models.Afterwards, FE parameter analysis on64CHS brace-H section chord T-jointsunder axial force and64X-joints under in-plane moment is performed in order tostudy mechanical behavior, failure mode and influence of geometric parameters tocapacity of the joints. Results indicate that the geometry parameters which make ainfluence on capacity of the joints are β, γ (define as the ratio of width of H sectionchord’s flange to double thickness of H section chord’s flange) and τ (define as theratio of thickness of brace to thickness of H section chord’s flange). A simple designmethod in engineering is given by the results of FE parameter analysis.Then, based on calculation ultimate capacity of CHS brace-H section chord T-joints and X-joints joints adopting Eurocode3, a modified equation is developed forthe joints through one-variable nonlinear regression analyses. The modifiedequations are proved to be more accurate and reliable by comparing with the resultsof parameter analysis.Finally, the defects of the article are summarized and the direction for future ispointed out.