Insufficient bearing capacity of compression bars in space grid structures can significantly reduce the collapse resistance of structures and cause immeasurable losses. Reactive powder concrete (RPC) with high strength, micro-expansion, and good ductility is used to reinforce the compression members of grid structures by infilling steel tubes. Axial compression tests on five types of high-frequency welded pipes with different section sizes and initial stresses were carried out. The results showed that compared to steel tubes alone, the bearing capacity of steel tubes reinforced by RPC could be increased by 75.77 to 218.34%. With a decrease of either the initial stress or confinement coefficient, the contribution of the material reinforcement increased. The failure mode of the specimen after RPC grouting was the same as that of the non-reinforced steel pipe, which was dominated by elastic-plastic buckling. The grouting hole after reinforcement did not fail prior to the instability of the member, which suggests that necessary measures to repair the hole should be taken. Based on the design method of axial compression bearing capacity of concrete-filled steel tubular members in six codes in China and abroad, the test results of this paper and 242 RPC-filled steel tubes were compared and analyzed. Finally, an equation of nominal bearing capacity, which estimates the ultimate bearing capacity of compressive members strengthened by filled RPC in grid structures, was proposed.

Solid steel tubular concrete members have excellent axial compression capacity. In terms of the calculation method of their axial compression bearing capacity, the current ten domestic standards all provide specific provisions. On the basis of main structure provisions such as diameter-thickness ratio and confinement factor, the formula differences in axial-force compression capability of domestic and international standards are compared and analyzed. First, the difference value of bearing capacities reach up to 62.79% according to current standards when diameter-thickness ratio range from 4 to 30. Second, concrete-filled steel tube members with diameter-thickness ratio greater than 20 and diameter less than 200, the current specifications cannot calculate the axial compressive bearing capacity.