Kowal-Michalska, K., and R. Grądzki. “The Post-Buckling Behaviour of Thin-Walled Columns in the Elasto-Plastic Range”. Engineering Transactions, vol. 34, no. 4, Dec. 1986, pp. 503-15, https://et3.ippt.pan.pl/index.php/et/article/view/1825.