Push-out tests and plastic analysis of group stud connectors

To investigate the bearing capacity of the welded group stud connectors and the force transmitting process of the group studs, the load-displacement curves and failure modes of the specimens were measured through the push-out tests and the ultimate bearing capacity and shear stiffness of the studs were hence obtained. The finite element model for the push-out specimens was built up as well and the non-uniformity of the local forces of the group studs and concrete was analyzed. The results of the tests and analysis demonstrate that with the increase of loading, the stress distribution in the roots of the group studs changes from the saddle shape to the gradual decrease of the studs row by row form the top to the bottom. The stress in the edges of the studs in the same row is greater than that of the studs inside and the non-uniform forces differ within a range of 5%. The local forces of the concrete in contact with the studs present the law that the forces of the concrete at the top and bottom two rows of the studs are great, at the middle two rows are the minimum and the maximum force difference is greater than 50%. The effect of the group studs makes the bearing capacity of the studs reduced about 5%. The average force of a single stud is greater than the shear ultimate bearing capacity of the welded studs calculated according to the codes of several countries. In the design of the studs for normal application, the design should be controlled in conformity to the ultimate strength of the local concrete and the shear bearing capacity of the welded studs should be about 30% of the ultimate bearing capacity.