Case study of the collapse of a water tank

Abstract

A 48.76m high water tank with the supporting steel lattice comprising 5 segments with uniform member configuration is conceived. Its collapse behavior is investigated through a suite of ground motion analyses. First, the tank is analyzed under 13 three-component ground motion records from the Chi-Chi and Hokkaido earthquakes. It is shown that the tank always collapses in the same manner as a result of overturning due to P-Delta instability resulting from column and brace buckling at the base. This is the consequence of the uniform member sizing in each of the five segments of the supporting lattice. Incremental dynamic analyses are performed using the Takatori near-source record from the 1995 Kobe earthquake. It is shown that the structure collapses at a ground motion scaling factor of 0.32. The FRAME3D model of the tank reveals severe buckling in the bottom mega-columns on the west face of the tower, followed almost instantaneously by compression brace buckling on the north and south faces, when the structure is hit by the Takatori near-source pulse, resulting a tilt in the structure. Subsequent shaking induces P-Delta instability resulting in complete collapse of the tank. To aid in the evaluation of the collapse-prediction capability of competing methodologies, detailed results (time-history plots as well as ordinates of crests and troughs in these histories) are provided for the analysis at 0.32 scaling.