Softening Instead of Strengthening for Seismic Rehabilitation

Abstract

Switzerland were designed without adequate consideration of earthquakes. They possess an unknown, but presumably often insufficient, seismic safety factor. Many of these structures would collapse under a moderate earthquake. which could result in considerable damage to the environment if hazardous materials were released. Certain chemical plants belong to this group of structures. It is in the interests of the owners of these facilities and of the general public that these risks are understood and that the necessary actions are taken to prevent serious problems. A risk assessment of an existing chemical plant in Switzerland showed that several structures designed and built in the 1970s and 1980s do not comply with current seismic requirements. The seismic rehabilitation of a large tank used to store up to 1000 t liquid gas (Fig. 1) is presented here. Large Tank for Liquid Gas The steel vessel is double walled, has a diameter of 15 m and a height of 16 m. and contains equipment to cool the gas down to-30 °C. The vessel is supported by a reinforced concrete structure consisting of a 0.5-rn-thick octagonal slab with 26 columns. 2.5 m in height. The columns are supported by 13-mlong drilled piles. An additional steel structure holds a stair tower and the piping that is needed for operation.

Simple Procedure for Seismic Analysis of Liquid-Storage Tanks

“…Methods of improving the seismic performance of tanks by increasing their ability to dissipate seismic energy need to be examined. The tank could either be anchored to its foundation with energy dissipating devices [29] or seismically isolated by special bearings [30,31].…”

Seismic analysis of a LNG storage tank isolated by a multiple friction pendulum system

“…Chalhoub and Kelly (1990) determined favorable effects of base isolation of liquid storage tanks through shake table tests on isolated and non-isolated tanks. In 2000, Bachmann and Wenk (2000) applied a seismic isolation system to a liquid storage tank supported by short columns. They named this rehabilitation scheme as softening.…”