Limit States (NTC-18)

According to NTC-18, performance requirements refer to the state of damage in the structure defined through four limit states, namely Operational Level (SLC), Damage Limitation (SLD), Life Safety (SLV) and Collapse Prevention (SLC).

Limit State of Collapse Prevention (SLC)
The limit state of Collapse Prevention (SLC) may be selected, according to NTC-18, where the structure, after the earthquake, undergoes serious cracks and collapses of the non-structural components and equipment and very serious damage of structural components. The building still retains a significant stiffness and resistance against vertical loads and a small safety margin against collapse from horizontal actions. The appropriate level of protection is achieved by choosing a seismic action with a return period of 975 years corresponding to a probability of exceedance of 5% in 50 years.

Limit State of Life Safety (SLV)
The limit state of Life Safety (SLV) may be selected, according to NTC-18, where the building after the earthquake undergoes cracks and collapses of the non-structural components and equipment and significant damage to structural components associated with a significant loss of stiffness against horizontal actions; the construction preserves part of the strength and stiffness for vertical actions and a safety margin against collapse for horizontal seismic actions. The appropriate level of protection is achieved by choosing a seismic action with a return period of 475 years corresponding to a probability of exceedance of 10% in 50 years.

Limit State of Damage Limitation (SLD)
The limit state of Damage Level (SLD) may be selected, according to NTC-18, where the building after the earthquake as a whole, including the structural and non-structural elements, as well as the equipment relevant to its function, has damage that does not compromise significantly the ability of resistance and rigidity against vertical and horizontal actions. The structure remains immediately usable despite the interruption of use of part of the equipment. The appropriate level of protection is achieved by choosing a seismic action with a return period of 50 years corresponding to a probability of exceedance of 63% in 50 years.

Limit State of Operational Level (SLO)
The limit state of Operational Level (SLO) may be selected, according to NTC-18, where the building as a whole, including the structural and non-structural components, as well as the equipment relevant to its function, should not be damaged or interrupted its function after the earthquake. The appropriate level of protection is achieved by choosing a seismic action with a return period of 30 years corresponding to a probability of exceedance of 81% in 50 years.