Abstract: To address the problems of small reinforcement spacing and poor concrete pouring in the sidewallfloor joints of underground structures, two optimization schemes for modular reinforced joints in the form of steel trusses are proposed. In this paper, three scaleddown members with a geometrically similar ratio of 1∶3 are designed to perform static unidirectional loading test to study the differences in mechanical properties and crack development between the modular reinforced joints and the reinforced binding joints. The test results show the following: (1) Under the same load, the tensile stress of the main reinforcement at the variable crosssection of the reinforced modular joints and the traditional joints is basically the same, or even smaller. The reinforced modular joints can achieve the same mechanical properties as the traditional joints. (2) As the external load increases, the initial crack location and crack width of the modular reinforced joints and the reinforced binding joints are roughly the same, which means that the initial cracks appear on the outside of the sidewall(all cracks), and the width sizes are approximately 0.05 mm. (3) Eventually, the joints crack expansion paths are basically the same, and the maximum crack widths on the sidewalls and the outside of the floor are at approximately 0.25 mm.

Key words: reinforced concrete structure, underground sidewallfloor, reinforced modular joint, experimental research