Sloshing Response of Floating Roofed Liquid Storage Tanks Subjected to Earthquakes of Different Types

Abstract

Using extended Hamiltonian variational principle, the governing equations for sloshing response of floating roofed storage tanks are derived. The response of the floating roofed storage tanks is evaluated for different types of ground motions, including near-source and long-period far-field records. Besides comparing the response of the roofed and unroofed tanks, the effect of different ground motions on the wave elevation, lateral forces, and overturning moments induced on the tank is investigated. It is concluded that the dimensionless sloshing heights for the roofed tanks are solely a function of their first natural period. Also it is shown that while long-period far-field ground motions control the free board height, near-source records give higher values for lateral forces and overturning moments induced on the tank. This means that same design spectrum could not be used to evaluate the free board and lateral forces in the seismic design of storage tanks. Finally, two cases are studied to reveal the stress patterns caused by different earthquakes.

Stress Analyses in Single Deck and Double Deck Floating Roofs Subjected to Earthquake Ground Motions

“…The selected value (0.005) is in accordance with the experimental ndings of Nagaya et al [8], where it was also stated that the sti ness proportional damping was appropriate for double-deck roofs. In numerical simulations, Newmark's method is employed to solve the governing equation [13].…”

“…To study the dynamic response of a seismically excited roofed tank, the following earthquakes data were used as base excitations [13] Figures 2 and 3, respectively. Kobe and Imperial Valley earthquakes have similar frequency contents with spectral peaks at low periods and are classi ed as near-source earthquakes.…”

“…(4) and (5) to limited numbers n and m, respectively, the obtained set of equations may be solved to yield the generalized coordinates and, consequently, plate de ection and liquid velocity potential. Moreover, radial and circumferential bending moments resulting in the bending stresses in roof crosssection are calculated by the following formulae [13]:…”

“…In some references [6,13], the double-deck roofs have been investigated and in other reports [7,16], the stress patterns in single-deck roofs are reported. However, the present paper compares the stress pattern of the single-and double-deck oating roofs and discusses the changes in this pattern due to change in the deck type.…”

“…Shabani et al [12] used a variational approach to evaluate the equilibrium conditions between the elastic and buoyant forces and depicted the contribution of membrane and exural constituents to the overall roof sti ness. Using extended Hamilton's principle, Golzar et al [13] introduced a set of results predicting behavior of tanks with double-deck roofs when excited by di erent types of earthquakes. Shabani and Golzar [14] extracted the governing nonlinear equation of a oating roof of a seismically excited cylindrical tank.…”