Charles Seim is a bridge engineer who worked on dozens of bridges over the course of his career. But one of his early works was a contemplation of forces in a rather different structure: the strapless evening gown.

Neatorama and Improbable Research have republished Seim's 1956 essay "A Stress Analysis of a Strapless Evening Gown," which appeared in a book of essays of the same name. In 2007, Seim delivered the (apparently updated) lecture for the first time, offering a slightly cheeky but earnest look at the challenges involved in maintaining the upright position of a strapless gown:

Effective as the strapless evening gown is in attracting attention, it presents tremendous engineering problems to the structural engineer. He is faced with the problem of designing a dress which appears as if it will fall at any moment and yet actually stays up with some small factor of safety. Some of the problems faced by the engineer readily appear from the following structural analysis of strapless evening gowns.

If a small elemental strip of cloth from a strapless evening gown is isolated as a free body in the area of plane A in Figure 1, it can be seen that the tangential force F1 is balanced by the equal and opposite tangential force F2. The downward vertical force W(weight of the dress) is balanced by the force V acting vertically upward due to the stress in the cloth above plane A. Since the algebraic summation of vertical and horizontal forces is zero and no moments are acting, the elemental strip is at equilibrium.

Consider now an elemental strip of cloth isolated as a free body in the area of plane B of figure 1. The two tangible forces F1 and F2 are equal and opposite as before, but the force W(weight of dress) is not balanced by an upward force V because there is no cloth above plane B to supply this force. Thus, the algebraic summation of horizontal forces is zero, but the sum of the vertical forces is not zero. Therefore, this elemental strip is not in equilibrium; but it is imperative, for social reason, that this elemental strip be in equilibrium. If the female is naturally blessed with sufficient pectoral development, she can supply this very vital force and maintain the elemental strip at equilibrium. If she is not, the engineer has to supply this force by artificial methods.

You can read his full analysis at Neatorama. It would be interesting to see Seim's analysis applied to various wardrobe malfunctions, but it would be even better if his engineering experience could eliminate the need for the constant tugging and readjusting of a strapless dress throughout the evening.