Abstract In order to investigate the stiffness and strength of the loop joints, experimental studies were conducted. Two types of loading tests were performed which are static loading tests and fatigue loading tests. The test variables are the diameter of the loop bars and the width of the loop joint. Cracking, ultimate behaviour, ductility and fatigue behaviour of the loop joints were observed and compared with the behavior of RC beams without joints. From the test results, the mechanical behaviour of the loop joints was confirmed similar to that of ordinary RC beams without joints if the joint widths were enough in terms of development length concept for the anchorage of hook reinforcement. It was investigated that the overlapping section within the loop joint has similar or rather good mechanical characteristics to the RC beam section without joints. However, it is necessary to notice that a reduction of stiffness and strength could be occurring at the casting interface region in the loop joint RC members, especially with inadequate narrow joint widths. The design concept of the development length for the anchorage of hook reinforcement for the design of details of loop joints is recommended. Consequently, details of the loop joints were suggested and based on the fatigue test results, a S–N curve for the loop joints was proposed.