For industrial storage applications, selective pallet racks are used, which are assembled from perforated slender cold-formed steel sections. The frame of pallet racks comprises braced frames in the cross-aisle direction and moment frames with semi-rigid connections in the down-aisle direction. The European code EN15512:2009 is normally used for the design of such racks. The use of linear elastic analysis for the design is a common practice, which EN15512 permits. However, the linear elastic analysis becomes inadequate for tall racks – typically over 15 m, because of second-order effects. The second-order effects may be significant in the down-aisle direction as the height of the pallet rack increases. Codes of practice, including IS:800 uses a frame stability parameter to assess whether the second-order analysis is required or not. The aim of this study is to investigate the second-order effects on the stability of such racks in the down-aisle direction and quantify the effects with respect to the height of the racks. Frames have been modelled in MASTAN2, and analytical studies have been done on frames of various heights. The results indicate that second-order analysis, including the effect of semi-rigidity of the connections, significantly amplifies the drifts and design forces and hence, cannot be ignored in the design of such racks. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.