Earthquake Resistance of Elevated Water-Tanks

The problem of building elevated tank structures that are truly earthquake-resistant is considered in detail; and a new type of construction, embodying increased flexibility combined with snubbing action, is suggested as a practical solution. Extensive model studies, directed toward obtaining engineering data for design purposes, are described and the results summarized. The writer concludes that the commonly used statical method of design against earthquakes cannot be applied safely to elevated tank structures, and that the suggested new type of construction has a safety factor in stress of at least 2 over the standard type of tower. Experiments in which reproductions of actual earthquake motions were applied to a model of a 60000-gal, 100-ft structure show that dangerous stresses are not avoided by designing against a statical horizontal force of one-tenth the weight of the tank and contents. Rules are given for designing structures of the new type suggested, and reasonable limits of applicability are set.