Experiment on Torsional Stiffness of Built-up Cold-Formed Thin-Walled Steel Cruciform Members
Torsional buckling is the dominant failure mode when built-up cold-formed thin-walled steel cruciform members are subjected to axial compression load.Its ultimate bearing capacity depends on the torsional stiffness,while there is no acknowledged method to take account of the built-up effect on torsional stiffness up-to-date.In order to study the torsional behavior and built-up effect on torsional stiffness of built-up cold-formed thin-walled cruciform members,a total of 10 specimens with different cross-section parameters and bolt distributions were designed and tested under torsion.Torque-angular displacement curves and the torsion-strain curves are fully obtained during the whole testing process.A specifically designed loading adapter was fabricated to allow the free torsion to be achieved at the first loading stage,and the free torsional stiffness of each specimen was derived accordingly.The test results indicate that the built-up effect increases while the bolt space decreases,and the influence on the built-up effect is more significant on specimens with one row of bolts than those with two rows of bolts.The built-up effect is primarily dependent on the cross-section web rather than the flange;increasement of web height leads to fewer bolts per unit area,resulting in the decrease of the proportion of torsional stiffness increased by built-up effect;compared with separate members,the enhancement in torsional stiffness of the built-up members is achieved probably due to that the relative warping of adjacent webs is to some extent restricted,and could be related to the warping stiffness of the web between bolts.
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