Which method introduces load factors (gamma_i) and a strength reduction factor (phi) to overcome the drawbacks of the ASD method?

• A. Level I Earthquake Motions
• B. Load Factor Design
• C. Allowable Stress Design
• D. Load and Resistance Factor Design

Answer: (B)

The method being tested uses a reliability-based design approach by applying separate multipliers to loads and to strength. The gamma_i factors multiply each load type to reflect the uncertainty in how loads may actually occur, while the phi factor scales the material strength to account for uncertainties in strength, construction, and performance. Together, these factors aim for a consistent target reliability across different scenarios, rather than relying on a single allowable stress as in ASD.

The design approach that explicitly uses both load factors and a strength reduction factor is Load and Resistance Factor Design. It distinguishes between how much load is considered (through gamma_i) and how much strength is allowed to be relied upon (through phi), yielding a more uniform and justified safety level than ASD.

Level I Earthquake Motions are data used for seismic analysis, not a design philosophy. Allowable Stress Design relies on an allowable stress without separate strength reduction factors. The phrasing Load Factor Design can imply using factors on loads but does not inherently include a corresponding resistance factor, so it’s not the standard method that couples both components.