3.5 Limit state design Two principal types of limit state: Ultimate limit state:The whole structure or its components should not collapse,overturn or buckle when subjected to design loads. Serviceabilitiy limit state:The structure should not become unfit for use due to excessive deflection, cracking or vibration.l Two principal types of limit state: Ultimate limit state: The whole structure or its components should not collapse, overturn or buckle when subjected to design loads. Serviceabilitiy limit state: The structure should not become unfit for use due to excessive deflection, cracking or vibration