Experimental Study on Axial Compression Bearing Capacity of Square Steel Tube Confined UHSC Short Column
To investigate the axial compression mechanism and the accuracy of ultimate bearing capacity calculation method for ultra-high strength concrete(UHSC)short columns confined with square steel tubes,the experimental study and finite element analysis were conducted by using concrete compressive strength,steel yield strength,and steel content as parameters.The calculation method for ultimate bearing capacity of short columns under axial compression was proposed based on the constraint mechanism.The result indicates that the hoop coefficient is the main factor affecting the axial compression failure mode of UHSC short columns restrained with square steel tubes.When it is less than 0.83,exhibiting shear failure;when it is over or equal 0.83,exhibiting compression failure.Through the load-displacement curves and load-strain curves,it is found that the circumferential restraining ability of steel tube is not fully utilized before the ultimate load,and the restraining effect is mainly manifested after the ultimate load.Increasing the steel content can effectively improve the compressive ductility of specimen after failure.The specimen with the lowest steel content show the sudden drop in load.When designing the steel tube to restrain UHSC short columns,it is necessary to match the appropriate restraining force according to the compressive strength of concrete.Due to the different compression ratios between ordinary concrete and UHSC,the plastic development of UHSC is lower before the core concrete approaches the ultimate load,which reduces the interaction between UHSC and steel tubes.Therefore,the increase in ultimate load of UHSC short columns restrained by square steel tube is smaller than that of specimens filled with ordinary concrete.The calculation method based on Mander model and China's standards cannot accurately evaluate the filled UHSC specimens with the hoop coefficient over 0.3.The calculation errors with China's standards are less.Based on experimental and finite element analysis results,the introduction of constraint reduction factors can control the calculation deviation within 10%.
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