<div class="htmlview paragraph">Automobile panels are stiffened in a variety of ways to meet engineering design criteria. Current example panels are numerous and include the roof, deck lid, hood, floor pan, etc. If lightweight, low modulus materials (e.g., aluminum, sheet molding compound) are to be considered for automobile panels, it can be anticipated that some form of stiffening will be necessary.</div> <div class="htmlview paragraph">In this paper, one particular type of stiffened panel, a two-layer panel consisting of a trapezoidally corrugated plate and a flat plate fastened together, is examined analytically and experimentally. A technique for modeling the panel with finite elements is developed. Rather than assigning “smeared-out” properties to the stiffeners, the fidelity of the panel is retained by modeling it as a double-layer structure (instead of as a plate) so that local deformations are also allowed. Because the method of joining significantly affects the structural properties of a stiffened panel, the two common fastening methods considered -- spot-welding and epoxy-bonding, require special modeling treatment. It is shown that for a spot-welded panel, a finite element model which accounts for the effect of different spot-weld spacings can be constructed. This is achieved through the application of constraint relations between the component plates. For epoxy-bonded panels, different constraints are used.</div> <div class="htmlview paragraph">To verify these modeling procedures, both models are used in computing frequencies and mode shapes for free panel vibration, and the results are compared with experimental values. Excellent agreement was achieved with errors ranging from 2 to 8 percent for most of the modes. This investigation emphasizes the need for adequately representing the local deformations even when evaluating relatively simple built-up panels.</div>