What is the requirement for factored demands in LRFD?

In Load and Resistance Factor Design (LRFD), the requirement that factored demands shall not exceed reduced nominal strength ensures that structural components can safely support the loads to which they will be subjected. This approach incorporates factors of safety into both the resistance (strength) of materials and the loads applied to structures.

Factored demands are derived from the application of load factors to the various loads the structure will experience, including dead loads, live loads, wind loads, and seismic loads, essentially amplifying the service loads to account for uncertainties and variabilities in those loads. The reduced nominal strength refers to the factored strength of a material or component obtained by applying resistance factors to the nominal strength determined from material properties and structural analysis.

This relationship helps ensure that safety and reliability are maintained under the extremes of loading conditions, while also minimizing the risk of structural failure. Thus, by design, factored demands must be accurately calculated to remain within the bounds of reduced nominal strength to provide a safe and effective structure.