section plane by finite elements in order to obtain the properties. (The term quasi-three-dimensional indicates that the axial coordinate is handled analytically.) They are far more efficient than a three-dimensional finite element model would be. Unfortunately, however, most of these methods do not treat all aspects of the problem, and some of these methods are too complex for a personal computer (PC).

Rehfield's method, the simplest of these methods, was programmed for a PC by Mark Nixon (NASA, Langley). Although Rehfield's analysis takes restrained warping into account, Nixon's code does not. Explicit treatment of in-plane warping (Poisson contraction and anticlastic deformation) is circumvented by the uniaxial stress assumption. However, Rehfield does not consider initial twist and curvature, which are important for wind turbines. Also, the shear stiffnesses obtained by this code are not sufficiently accurate because of the neglect of out-of-plane St. -Venant flexural warping.

Bauchau, Kosmatka, Lee, and Wörndle have codes that are more general than Nixon's, but they are also considerably more complex. The committee knows of no industrial users of Kosmatka's and Lee's codes in the United States. Wörndle's code was developed in Germany and, although it is used by the German helicopter company Deutsche Aerospace (previously MBB), the committee knows of no users in the United States. Bauchau's code is used in the U.S. helicopter industry. It accounts for restrained warping and initial twist and curvature. It is restricted, however, to the thin-walled case and yields results that are comparable to those of Rehfield's analysis (Bauchau et al., 1987).

The code of Giavotto et al. (1983) (called ANBA) was developed in Italy. Although it is the most powerful of all these codes, it does not account for