http://docshare04.docshare.tips/files/17204/172048919.pdf#page=291&zoom=100,86,56
http://dl.mycivil.ir/reza/ans_thry.pdf
https://docs.plm.automation.siemens.com/data_services/resources/nxnastran/10/help/en_US/tdocExt/pdf/element.pdf
See MEC 21
https://www.code-aster.org/V2/doc/v12/en/man_r/r3/r3.08.01.pdf
pp.45-53