Study on Grouting Defects and Their Impact on Performance of CFST Columns with “Inner Tube-Flange-Grouting” Vertical Connections

Abstract

Grouting defects in concrete-filled steel tube (CFST) columns with “inner tube-flange-grouting” vertical connections were investigated in this paper. To reveal the influence of grouting technology on grouting quality and of grouting defects on connection quality, visual grouting tests were first conducted to directly observe the flow patterns of grout and the formation of defects. The test results showed that a grout thickness of 20 mm minimized defects, while the double-sided outlet layout significantly improved grouting fullness through optimized air discharge. Then, numerical simulations of grout flow patterns were performed, and the results were in good agreement with the tests, thereby validating the correctness of the model establishment method. Furthermore, digital radiography testing was used to verify grouting integrity. The testing results of eight specimens showed that the simulated defect distribution was highly consistent with the actual, further confirming the defect distribution patterns. Based on the defect sizes derived from previous investigations, subsequent numerical simulations showed that minor grout defects had minimal impact on the stiffness and load-bearing capacity of vertical connections, demonstrating the connection's high tolerance to grout defects. These findings have laid a foundation for optimizing the construction design of “inner tube-flange-grouting” column-to-column connections, enhancing the overall mechanical performance, and guiding the practical engineering applications of prefabricated concrete-filled steel tube structures.