Experimental Study on Axial Compression Behavior of Phosphogypsum-Filled Thin-Walled Square Steel Tube Stub Columns

A new type of cold-formed thin-walled steel wall stud called phosphogypsum-filled thin-walled square steel tube(PFST) stud was proposed in this paper. The stud consists of a square steel tube and phosphogypsum inside, which meets the characteristics of lightweight. In this kind of stud, the supporting effect of the core phosphogypsum can delay the local buckling of the thin-walled square steel tube, and the restraint effect of the thin-walled square steel tube can improve the strength of the core phosphogypsum. Hence, the mechanical properties of the two materials can be fully developed and the axial bearing capacity of the stud can be effectively improved. To study the axial compression performance of PFST studs, 3 hollow steel tubes(HST) and 24 PFST studs were designed and fabricated with consideration of the section with or without phosphogypsum, water-solid ratio, hollow ratio and wall thickness of steel tube. Through axial loading tests, the failure mode, load-deformation curve, load-strain curve, and bearing capacity were analyzed. The test results indicated that the hollow steel tube stud presented a failure mode of local buckling. For the studs filled with phosphogypsum, the “drum shape” failure mode was observed. It is evidenced that the phosphogypsum can delay the local buckling of the steel tube, and change the failure mode of the stud. Compared with the hollow studs, the axial bearing capacity of the studs filled with phosphogypsum increased by 65.52%. The hollowness ratio has a significant impact on the bearing capacity of the stud, due to the fact that the water content of phosphogypsum varies with the hollowness ratio, which finally affects the strength of the infill material. The axial bearing capacity of the stud improved with decrease of water-solid ratio of phosphogypsum. When the water-solid ratio decreased from 0.9 to 0.8 and 0.7, the bearing capacity increased by 6.36% and 12.42%, respectively. Increasing the thickness of the steel tube can significantly improve the axial compression performance of the stud. When the thickness increased from 0.85 mm to 1.48 mm and 1.93 mm, the axial bearing capacity of the stud increased by 115.36% and 176.55%, respectively. Based on the superposition theory, the axial bearing capacity calculations of the HST and PFST studs were deduced. The results showed that the calculated formula has good accuracy, which can accurately predict the axial bearing capacity of the stud. In conclusion, the PFST stud has good mechanical properties and broad, wide application prospects. This kind of stud can also provide a feasible path for applying phosphogypsum.