Which has higher factors of safety, live load (LL) or dead load (DL)?

The factor of safety is a measure used in engineering to provide a safety margin beyond the expected loads and stresses a structure will experience. When comparing live loads (LL) and dead loads (DL), live loads typically have higher factors of safety.

Live loads are variable and dynamic loads that change over time, such as people, furniture, vehicles, and environmental factors like snow or wind. Because these loads can fluctuate significantly, including factors such as peak usage and impact from temporary conditions, engineers apply higher factors of safety to account for the uncertainty in live load behavior and to ensure the structure can accommodate worst-case scenarios without failure.

In contrast, dead loads are static and generally well-defined, consisting of the weight of the structural elements themselves and any permanent fixtures. These loads do not vary significantly over time; therefore, they are usually subjected to lower factors of safety since there is less uncertainty involved in their estimation.

This distinction emphasizes the need for an increased factor of safety for live loads to cope with their variability and to enhance the resilience of a structure under changing conditions. Therefore, live loads are associated with higher factors of safety in structural engineering design to account for the unpredictable nature of how those loads are applied.