Experimental study on yielding behavior of joints of I-steel with corrugated webs

It is essential to provide reliable and stable support for soft rock roadways; hence, two novel kinds of yieldable joints designed by I-steel with corrugated webs (high-strength boltr and sleeve wedge joints) are proposed in this paper. Axial compression tests were carried out against two high-strength bolted joints and one sleeve wedge joint, while three high-strength bolted joints with different eccentric distances (0.1 m, 0.2 m, and 0.3 m) were conducted in eccentric loading tests to investigate their loading behavior. The joint friction, shear bearing capacity of high-strength bolts, and the strain distribution of flanges and cover plates of yieldable joints under different stress states were obtained from experimental testing. It indicated that: 1) Before bolts slid, the displacement at both ends of the specimen did not increase significantly, and the joint could resist a large load; 2) When the external load exceeded the friction that the bolt could bear, the bolt started to slide; 3) The load applied on the specimen increased rapidly when the bolts slid to the end of the bolt holes; 4) When the bolt slid, the compressive strain of the cover plate could be released; 5) The inclination angle of the joint under eccentric compression was mainly caused by bolt sliding, which was directly related to the bolts sliding distance. It was proved that the proposed yieldable joints could not only adapt to large deformation imposed by the surrounding soft rock but also provide enough load-bearing capacity to sustain fast pressure, thereby showing great applicability for underground structures. Furthermore, this study proposed a design procedure and improved configurations of yieldable joints suitable for both small and large contractions in soft rock roadways.