A differential elevation survey (see Figure 3) was conducted to determine the difference in elevation between the edge of the ring beam and various points near the center of the roof, including the center. The difference in the ring beam elevation and the PT at the center of the roof is the “sag” of the roof. Column deformation was determined using a laser level and a laser distance meter. These measurements of the roof sag and column deformation were made to compare to theoretical values computed from structural analyses.
Figure 3. Surveying to determine roof sag.