Effect of radial base-plate welds on ULCF capacity of unanchored tank connections

• Capacities of welded steel tank connections are determined experimentally.
• Shell-to-base connections containing radial welds are considered.
• Empirical fatigue–life equations are created from test data to aid in design.
• Decreased ductility within the radial weld HAZ reduces fatigue capacity.
• All connections tested reached higher fatigue capacity than current code limits.

The base of large steel liquid storage tanks can uplift during severe earthquakes, causing large inelastic rotations at the connection between the tank shell and tank base. While recent experimental studies indicate significantly higher connection rotation capacity than what is specified in the current Eurocode standard (set at 0.2 rad), additional radial base-plate welds (present in some tank connection details due to fabrication methods) have never been considered in tests. This study experimentally investigates the effects of these radial base-plate welds on the fatigue capacity of tank shell-to-base connections during uplift. Twelve tank shell-to-base connection specimens taken from existing tanks throughout Switzerland are tested at rotation ranges greater than the current Eurocode limit (eight specimens with radial welds and four specimens without radial welds). Testing indicates that tank base-plate sections containing radial welds govern the shell-to-base rotation capacity during uplift. The rotation capacity of connections containing radial welds was nearly 30% lower (on average) than equivalent connections without radial welds. This reduced capacity is directly related to the reduced base-plate ductility created by the radial weld heat affected zone. All connection capacities were far greater than the current Eurocode limit.