“…The definition of the drilling DOFs proposed by Allman [3,4] can be treated as a milestone for this topic, in which a quadratic displacement approximation was introduced to supplement the drilling DOFs at element nodes. Based on Allman's work, numerous researches on plane elements with drilling degrees of freedom have been accomplished, such as the models proposed by Bergan and Felippa [5], Cook [6,7], MacNeal and Harder [8], Yunus et al [9], Hughes and Brezzi [10], Ibrahimbegovic et al [11], Iura and Atluri [12], Cazzani and Atluri [13], Piltner and Taylor [14], Geyer and Groenwold [15], Pimpinelli [16], Groenwold et al [17], Choi et al [18], Choo et al [19], Zhang and Kuang [20], Kugler et al [21], and Cen et al [22]. Long et al [23][24][25] presented a new definition on the drilling DOFs.…”