Abstract: Through the orthogonal experiment of a scale model for the wrap-underpinning joints under frame columns in moving engineering, the influence of the shear-span ratio of an underpinning beam to the fracture morphology and bearing capacity were studied. According to different shear-span ratios, the failure modes arranged rollers normally were classified to two forms: the flexure failure and the flexure-shear failure of the walking beams. The junction surface between a connecting beam and a column was noticed as a weak link, and the crack development and final joint destruction rule were obtained corresponding to different shear-span ratios. Based on the orthogonal analysis and regression analysis of test data, it was known that the joint bearing capacity was influenced most significantly by the shear-span ratio of all the factors. The linear relation was separately good between the shear-span ratio and the crack load, and the failing load in a range of shear-span ratio. The formula to calculate bearing capacity of the joint had been introduced, and the influence of the shear-span ratio to the uniformity of the roller stress was analyzed. Underpinning joints with different roller arrangement were studied through the contrast experiments.