Experimental investigation of the compression-bending property of the casing joints in a concrete filled steel tubular supporting arch for tunnel engineering

摘要

The concrete-filled steel tubular (CFST) arch is an effective new support form for mine/traffic tunnels in complex conditions, and the casing joints on the arch determine its global bearing capacity. Eighteen tests, including axial compression, eccentric-compression with different eccentricities, and pure bending tests, were carried out. The bearing behavior, failure mode and failure mechanism of the specimens with casing tubes were analyzed and compared with specimens without a casing tube. Failures are mainly caused by the local stress concentration on the CFST components or the casing tube at the contact positions. The compression-bending bearing capacities of the CFST casing joints were analyzed with the help of the M-u-N-u coordinate system. Each M-u-N-u relation is described by a straight line combined with a lateral parabola, and the M-u-N-u formulas were fitted. The bearing ability of a CFST casing joint is lower than that of a conventional CFST section, and the reduction rate of the square cross section is more obvious. The effects of the concrete grade, casing tube length, casing tube thickness and gap width on the compression-bending capacity were obtained through numerical simulation tests. The concrete strength is the main factor influencing the axial compression bearing capacity, while it is the casing tube length that mainly influences the bending bearing capacity. Suggestions for use in practice are finally proposed based on the above results.