This paper presents an experimental and numerical investigation into web crippling resistance of unfastened cold formed steel Z-sections subjected to Interior One Flange (IOF). Both Z-sections have stiffened and unstiffened flanges were studied. This paper presented the results of 12 test specimens considering the IOF loading condition. A verified finite element models were developed to simulate the experimental tests. An extended parametric study was carried out based on the verified finite element models. The parametric study included the different factors affecting the web crippling resistance such as; material yield stress, web thickness, inside bend radius, web depth and bearing load length to thickness ratios. The web crippling strength according to the Eurocode EN 1993-1-3 and the North American specification AISI S100-16 were compared to the experimental and the finite element results. The comparisons showed that the two specs; Eurocode EN 1993-1-3 and AISI S100-16 overestimated the web crippling strength of the studied range of cold formed steel Z-sections. Modifications were proposed to improve the design standard predicted resistances.