Measured and Computed Stresses in Three Castellated Beams

Three castellated beams, representative of those fabricated for the American Dental Association Building in Chicago, were tested at the Civil Engineering Structural Testing Facility of the University of Missouri at Columbia. The three beams were each approximately 37 ft in length and expanded between 40 and 50 percent from a nominal depth of 18 in. In one case rectangular plates were interposed between the chords in order to gain additional depth. The primary purpose of the testing was to obtain a comparison between the stresses measured with electrical strain gages at various points of interest and the stresses at those same locations as determined by a simplified Vierendeel truss analysis similar to an approach proposed by Toprac and his colleagues at the University of Texas. The difference lies in the assumption of the distribution of primary bending stress in the chords. A uniform distribution was assumed in the Texas approach, but a linearly varying distribution was assumed in the design of these beams. The latter approach is described in detail byBoyer in a previous article in this Journal and will not be reiterated here, except to note that for simplification inflection points are assumed at the center of each "truss member" and vertical shear on the beam is assumed to be shared equally by each of the two "chords".