Study On Mechnical Behavior Of Square Hollow Section (SHS)Brace-H Section Chord Joints

Square hollow section steel has equal strength in all directions, a large flexuralrigidity and capacity, and can be cut by a line to make construction easy. H sectionsteel has a large lateral rigidity and its flanges parallel to each other so that it waseasy to construct and flexible to design. Square hollow section (SHS) brace-Hsection chord joints simplify the line of intersection. SHS brace-H section chordstiffened and unstiffened joints are widely applied to engineering, but researches onthis type of joint are much less.Based on the tests on SHS brace-H section chord stiffened and unstiffenedX-joints and T-joints, nonlinear finite element analysis on the joints is made in orderto study mechanical behavior, failure mode, ultimate capacities and influence ofstiffener on the ultimate capacities on this type of X-joint and T-joint.Firstly, experimental research on SHS brace-H section chord stiffened andunstiffened X-joints and T-joints is conducted. Experimental program is proposedand mechanical behavior, failure mode, ultimate capacity and influence of stiffeneron the ultimate capacity are studied. For X-joint, stiffener makes an influence onultimate capacity of joint.90°stiffener can improve capacity of joint, while45°stiffener cannot improve capacity of joint. However45°stiffener can improveductility of joint. For T-joint,45°stiffener cannot improve capacity of joint whateverthe value of β (define as the ratio of brace’s side length to width of H section chord’sflange) is.90°stiffener can improve capacity of joint with larger β while90°stiffenerreduces capacity of joint with the smaller β. It shows that90°stiffener can improverigidity of joint because displacements of brace to chord are all small, no matterwhat the joint’s size is. While45°stiffener cannot improve rigidity of joint becausedisplacements of brace to chord are larger. Calculated values based on Eurocode3are lower than experimental values mainly.Secondly, Finite Element (FE) validation research on capacity of eight SHSbrace-H section chord stiffened and unstiffened X-joints and eight T-joints are performed. Effective and exact FE models are set. Comparison between FE andexperimental results proves validation of FE method available based on the FEmodels. Afterwards, FE parameter analysis on64SHS brace-H section chordunstiffened X-joints and64T-joints is performed in order to study mechanicalbehavior, distribution regularities of failure mode and influence of geometricparameters to capacity of joint. For X-joint, results indicate that the geometryparameters which make a influence on capacity of joint are β (define as the ratio ofbrace’s side length to width of H section chord’s flange), γ (define as the ratio ofwidth of H section chord’s flange to double thickness of H section chord’s flange)and τ (define as the ratio of thickness of brace to thickness of H section chord’sflange). Among the three parameters, β and τ make a greater difference than γ. ForT-joint, results indicate that the geometry parameters which make a influence oncapacity of joint are also β, γ, τ while β and γ make a greater difference than τ. Thepaper suggests that when β changes from0.4to0.5, τ should be0.8~1.0, while whenβ changes from0.5to0.8, τ should be0.4~0.8for X joint, and β≥0.6, γ=10~15,τ=0.4~0.6for T joint in engineering projects.Then, on the basis of the formulas for calculating the capacity of SHS brace-Hsection chord unstiffened X-joints and T-joints in Eurocode3, a new strengthequation is developed for SHS brace-H section chord unstiffened X-joints andT-joints through simple linear regression analyses. The new formulas are proved tobe more accurate and reliable.Finally, problems which require further studies are discussed.