Experimental Study On Statical Behavior Of Bird-beak Square Hollow Section Joints

The side view of the SHS joints with the chord rotated by45degrees along itslongitudinal axial which are called bird-beak joints is similar to the shape of head andbeak of bird. The bird-beak joints contain square bird-beak joints and diamondbird-beak joints. Bird-beak joints are able to meet the demand of structural aestheticsfor their specious structural modeling. In addition, rotating the angle of chord andbrace is good for the connection of joints and improve the property of joints if theamount of brace is large or the structure is complex. Base on the advantages mentionbefore, the new type bird-beak joints are widely used in the construction. The delay ofthe research on these type of joints has limited the application in engineering,so we need carry out the research on the mechanical behavior of the joint as soon aspossible.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, statical ultimatecapacities and influence of geometric parameters and different connection types onthe ultimate capacity on the type of T-joints and X-joints.Firstly, experimental research on T-joints under axial force, X-joints underin-plane bending and X-joints under out-plane bending is conducted. Experimentalprogram is proposed and mechanical behavior, failure mode, ultimate capacity andinfluence of both different β (define as the ratio of width of chord to width of brace)of and different connection type on the ultimate capacity are studied. The test resultsshow that, for T-joints, the ultimate capacity and ductility of square bird-beak jointsand diamond bird-beak joints are larger than conventional joints; as β increase, theultimate capacity, initial compressive stiffness, ductility of joints increase. ForX-joints under in-plane bending, the ultimate capacity and ductility of squarebird-beak joints and diamond bird-beak joints are larger than conventional joints. ForX-joints under out-plane bending, the ultimate capacity and ductility of squarebird-beak joints and diamond bird-beak joints are larger than conventional joints; as βincrease, the ultimate capacity of joints increase.Secondly, Finite Element (FE) validation research on capacity of new typebird-beak T-joints and X-joints are performed. Effective and exact FE models are setfor parameter analysis with all kinds of factors taken into consideration. Comparison between FE and experimental results proves validation of FE method available basedon the FE models.Afterwards, FE parameter analysis on64square bird-beak T-joints and64diamond bird-beak T-joints under axial force,27square bird-beak X-joints and27diamond bird-beak X-joints under in-plane bending,27square bird-beak X-joints and27diamond bird-beak X-joints under out-plane bending,236joints in total areperformed in order to study mechanical behavior, failure mode and influence ofgeometric parameters to capacity of the joints. Results indicate that the geometryparameters which make a influence on ultimate capacity of the joints are β, γ (defineas the ratio of width of chord to double thickness of chord) and τ (define as the ratioof thickness of brace to thickness of chord). As the β and τ increase, the ultimatecapacity of bird-beak joints increase; as the γ increases, the ultimate capacity ofbird-beak joints decrease. A simple design method in engineering is given by theresults of FE parameter analysis based on the principle that the insection part of chordand brace are yield.Then, based on calculation ultimate capacity of conventional T-joints andX-joints joints adopting Eurocode3, the equation of square bird-beak joints anddiamond bird-beak joints are developed through one-variable nonlinear regressionanalyses. The modified equations are proved to be accurate and reliable by comparingwith the results of parameter analysis.Finally, the defects of the article are summarized and the direction for future ispointed out.