An effective planar triangular element with drilling rotation

A modified Allman’s triangular planar element with drilling degree of freedom is formulated. The basic formulation is similar to the original Allman’s element, but a constraint is introduced which ensures that the drilling degree of freedom is a true rotation in elasticity. The new element keeps all the advantages of Allman’s element, but has no spurious energy mode. It also shows that the drilling parameter of the present element can correctly carry over the twist moment to the other kinds of element at nodes. A few examples are given for illustration.