Abstract: A new and improved two point constraint approxmiation is presented, which uses the information of the exact function valueits first order derivatives and approximate second order derivatives at the current design point, and also the first order derivatives at the previous point of design iterations. The improved approximate expressions are proposed to create the sequential approximation problems which are solved with the constrained variable metric method. This approximation is efficient and suitable for solving structural optimization problems. And it is proved by some well known examples.

Key words: structural optimization, approximation function