Based on the previous finite element analysis, the experiment took the position of the middle column on the lower shoulder beam as the main variable, and three specimens were designed to study the mechanical properties of double-layer shoulder beams with double-limb side columns. The monotonic loading test was conducted on the specimens. According to the test results, the yield mechanism, failure mode, bearing capacity and the force of the specimen's main parts were analyzed. The results showed that the yield of the specimen was triggered by the shear yield of inner limb side webs of lower shoulder beams, and the failure was caused by the large convex curvature deformation of inner limb side webs of the lower shoulder beams. In accordance with the yield of the measure points at the corners of inner limb webs of lower shoulder beams and load displacement curves, the yield load values of the members were determined. When the position of the middle column was shifted to the outside, the shear force of inner limbs of the lower shoulder beams decreased, and the bearing capacity of specimens improved.