Experimental and numerical study on seismic performance of aluminum foam infilled steel frame-braced structural system

To investigate the seismic performance of a steel frame-braced structural system filled with aluminum foam, the static eccentric and axial compression experiments were performed respectively for square and round steel tubes filled with aluminum foam to obtain a failure deformation diagram and load–displacement curve. Based on the experimental study, a finite element model was established to analyze the seismic performance of the steel frame-braced structural system filled with aluminum foam influenced by different bracing slenderness ratios and diameter-to-thickness ratios. The results show that the failure deformation of the square and round steel tubes filled with aluminum foam was principally constrained by aluminum foam to significantly prevent premature local or whole buckling of the specimen and excellently improve the vertical bearing capacity. The vertical bearing capacity of the pure square steel tube and that filled with aluminum foam under the same loading eccentricity of 50 mm and section size was primarily provided by the steel tube in the elastic stage, and the beneficial effect of infilled aluminum foam was tiny. The ultimate loads of the aluminum foam-filled square steel tubes under the static eccentric experiment with a loading eccentricity of 30 mm, 50 mm and 150 mm were 52.2 kN, 42.1 kN and 10.1 kN respectively. The failure mode of the aluminum foam-filled round steel tubes with specimen lengths and thicknesses increasing respectively from 144 to 336 mm and 1.8 to 3 mm transformed from symmetric folding at the loading end to local buckling at the middle of the specimen under axial load, and the ultimate load of the filler was prominently increased by diminishing the specimen length and increasing the specimen thickness. The increasing rate of ultimate bearing capacity for the aluminum foam-filled steel frame-braced structural system of the bracing with a slenderness ratio of 80 and a diameter thickness ratio of 30 was increased by 73.3% compared to the pure steel frame-braced structural system, and the specimen with the slenderness ratio of 100, 120 and 150 and the diameter thickness ratio of 120 was raised respectively by 65.7%, 37.6% and 43.0%. Infilling aluminum foam remarkably reduced the maximum stress value of the bracing to improve the buckling phenomenon and stress concentration phenomenon and enhance the structure's secant stiffness and energy dissipation capacity. The slenderness ratio of the bracing was recommended to be 80–100 when mainly considering the bearing performance, and the diameter-to-thickness ratio was referred to be 30–40 and 100–120 when the slenderness ratio was 80 and 100, respectively.