Tie-down systems are used to fasten drilling rigs to the deck of offshore structures to prevent them from moving in harsh environmental conditions such as hurricanes. During Hurricanes Ivan (2004) and Katrina (2005), there were failures in tie-down systems that allowed several rigs to move and be damaged. In the present study, the reaction force and connection capacity of tie-down systems for a TLP and a spar are investigated by analyzing the dynamics of the drilling rig and its substructure as well as hull-mooring-riser coupled dynamic analysis program in time domain. The 100-year environmental conditions are taken from the API Bulletin 2INT-MET which reflects updated conditions following major storms during 2004-2005. Based on the simulated motion and acceleration time series, the inertial and gravity loads on derrick and skid base are calculated in addition to dynamic wind forces for various wind-wave-current (W-W-C) collinear headings. Then the loads that could cause tensile/shear/slip failure at derrick and skid-base footings are computed. A new concept called instantaneously progressive slip failure is introduced and demonstrated. Copyright © 2009 by The International Society of Offshore and Polar Engineers (ISOPE).