Journal of Constructional Steel Research 67 (2011) 1174–1184 Contents lists available at ScienceDirect Journal of Constructional Steel Research journal homepage: www.elsevier.com/locate/jcsr Experimental determination of the rotational capacity of wall-to-base connections in storage tanks G. Cortés ∗ , A. Nussbaumer, C. Berger, E. Lattion Steel Structures Laboratory (ICOM), Swiss Federal Institute of Technology, 1015-Lausanne, Switzerland article info Article history: Received 22 September 2010 Accepted 10 February 2011 Keywords: Unanchored tanks Rotational capacity Uplift Earthquake resistance Fatigue Wall-to-base connection abstract Earthquakes around the world have affected many unanchored tanks used for the storage of petroleum- derived liquids. When these unanchored tanks are subjected to strong motion, the moment generated at the base, by the mass of liquid contained in the tank, will cause partial uplift of the base (i.e. rocking of the tank), inducing cycles of rotation at the wall-to-base connection. Actual codes of standard practice used in Europe and New Zealand limit the rotation that may be allowed at this connection to 0.2 rad. This limit was based on a series of assumptions since no realistic tests had been conducted. This paper presents the experimental research conducted to determine the real rotational capacity of these connections. The tests were carried out considering the bending stresses and the membrane stresses that develop at the base plate when uplift occurs. Specimens from an old existing tank (dismantled) were used. New specimens were also fabricated and used to allow for a more comprehensive study. Results from this research are presented in the form of plots of maximum rotation vs. number of cycles to failure, called RN curves. These curves revealed that the current Eurocodelimit of 0.2 rad is overly conservative. Based on the limited data, a limit of 0.4 rad would be more realistic. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction For many years thin shell tanks made from steel plates welded together have been widely used to store liquids such as water, gasoline and other petroleum-derived liquids. This type of tank is very advantageous and cost effective since thin steel sheets welded together are used. This is possible due to the effectiveness of the shell to carry the hoop stresses that arise from the hydrostatic pressure of the liquids in the walls. Moreover, very often these tanks are designed and constructed without any anchorage to the ground, further increasing the economy of these tanks. Thus, many of these steel tanks lay on ground (usually compacted soil) on their own weight. Earthquakes around the world have affected many of these tanks [1], resulting in economic losses from the loss of contents and cost of rehabilitating/replacing the structure, and environmen- tal hazards due to gasoline/petroleum spillage. The most common types of damage observed in tanks are: damage to the roof caused by the sloshing liquid near the roof, damage of the piping connec- tions, damage to the tank walls, usually in the form of buckling caused by the high compressive stresses in the walls of the tank, ∗ Corresponding author. E-mail addresses: gustavo.cortes@epfl.ch (G. Cortés), alain.nussbaumer@epfl.ch (A. Nussbaumer), christoph.berger@proteng.co.jp (C. Berger), eric.lattion@acs-partner.ch (E. Lattion). and damage of the wall-to-base connection, caused by the uplift- ing of the tank [2]. Fire and total collapse have also been observed in some cases. Many researchers have studied the behavior of these tanks under seismic loads [3,4]. From these early studies it was found that when the tank is subjected to lateral excitations, the lower portion of the liquid stored was acting along with the tank while the upper portion was displacing in a long-period sloshing mode. The part that moves along with the tank is termed the impulsive part, since it deforms rigidly with the tank. It is this part that contributes the most to the base shear and overturning moment in the tank. The sloshing portion of the liquid, also called the convective liquid, is responsible for most damage observed in the roof. Enough clearance should be provided to avoid any damage in the roof. The behavior of an unanchored tank is similar to that of an anchored tank under small magnitudes of ground displacement. However, when the shaking of the ground is strong enough, the moment generated at the base by the impulsive mass will cause partial uplift of the base (i.e. rocking of the tank). The phenomenon of rocking causes an increase in the period of the tank, and thus, an increase in the deformations experienced by the tank. Uplift of the tank is mainly affected by the height-to-radius ratio (H/R) of the tank, the thickness of the base plate, the configuration of the connection, and the stiffness of the underlying soil. While all these parameters have some influence over the rocking behavior of the tank, the H/R ratio has the greatest influence. A tall tank would 0143-974X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcsr.2011.02.010