4Habibullah A. User's Manual of ETABS. VetsioN 6.1. Comaputes & Structures Inc., Berkeley, California,1995.
5Yann M W and Sun S L, The Application of Drilling Degree of Freedom in Analysis of Building Structures, Proceedings of the Sixth International Conference on Edacatiun and Practice of Computational Methods in Engineering end Science, Gnangzhou, China, 1997:283-288.
6Sun S L, Yuan M W and Chun P. A Practical Quadrilatcral Membrane Element ruth Drilling Degrees of Freedom. Acta Meeharfica Solidi Sinica, 1997, 10(2): 179-155.
7Saleeb A F and Chang T Y. An Efficient Quadrilateral Element for Plate Bending Analysis. Int. J. Hem.Meth. Engng, 1987, 24:1123-1155.