Wagner, Herbert. Flat Sheet Metal Girders With Very Thin Metal Web. Part 2: Sheet Metal Girders With Spars Resistant to Bending - Oblique Uprights - Stiffness, report, February 1931; (https://digital.library.unt.edu/ark:/67531/metadc63632/m1/1/: accessed October 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .