The client wanted to determine allowable lineset and grid loads for an existing theater gridiron built in 1931. Dozens of existing lineset loads had to be accounted for in the analysis. The age of the structure required that the analysis consider the lower strength steel, ASTM A9, available at the time of construction.
Original structural drawings were used to develop an analysis model in a commercially available structural modeling computer program. Dead loads were calculated by hand using the structural drawings and observations noted during the site visit. Existing lineset loads were determined by recording the amount of counterweight used for each lineset. Using appropriate dynamic factors, an analysis was performed and the allowable load ratings were determined.