A Review of FPL Studies on Stressed-Skin and Sandwich Units

Thirty years of research on experimental structural units are reviewed, and additional data to be published in Research Paper FPL-12 is previewed. Glued-laminated arches and beams exposed for 12 years showed only minor loss in shear strength, loss in strength from 1 to 8 percent, and no more than 2 percent delamination. Glued gusset-plate trusses were exposed for 3 and 4 years. Adhesive-bonded panel systems–including stressed-cover and sandwich panels– were tested after exposure for 15 years. In sandwich panels removed from the test unit and examined, it was found that of the panels which increased in stiffness, those panels facing south showed a greater increase than those facing north, perhaps due to the higher moisture content of the panels on the north side. The difference in moisture content apparently did not affect the strength of the panels. The aluminum-faced panels had the greatest loss in strength of the various combinations, almost 30 percent after 15 years. Details of tests on a stressed-cover panels after 25 years of service will soon be published.

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