Reduction of seismic sloshing in floating roof liquid storage tanks by using a Suspended Annular Baffle (SAB)

Abstract

Sloshing in floating-roof cylindrical oil storage tanks subjected to earthquake has been known as a damaging phenomenon, resulting in devastating consequences such as sinking of the roof and/or vast destructive fires. Most of the previous studies have focused on clarifying the mechanism of the dynamic failure of floating roofs subjected to seismic loads. However, applicable remedies have been rarely suggested. In this paper, an innovative and practical method is proposed to reduce the floating roof motion during earthquakes, and an experimental study, conducted by shaking table to show the efficiency of this technique is presented. This new proposed passive control technique reduces the maximum sloshing height by using a Suspended Annular Baffle (SAB), hanging from the floating-roof by some strings with adjusted length, so that the baffle is located as much likely as possible inside the impulsive part of the fluid. The tests, conducted by using various baffle widths, included both sine sweeps and seismic excitations. The experimental results prove that using SAB reduces the maximum seismic sloshing height, in average, to almost 80% and 40% of its values of non-baffled case, respectively, for harmonic and seismic excitations, in a small model tank. Results also show that the presence of SAB reduces the swirling of the floating roof to a great extent. With regard to damping of the convective mode, the results of harmonic tests related to the highest depth of liquid in the tank show that the presence of floating roof increases the damping ratio almost 2.5 times, and the presence of SAB increases it more than 6 times comparing to the case with no floating roof. It is notable that the benefits of the SAB are not limited to only floating roof tanks, and in all cases in which sloshing may have adverse effects, such as elevated tanks, and other types of roofed and even open top tanks employing the SAB can be recommended as a sloshing reduction remedy.