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Figure 4-5: Illustration of force effects on bridge foundation (after Abu-Hejleh et al. 2011). 4.3 STRENGTH LIMIT STATE FOR LATERALLY LOADED FOUNDATIONS Strength Limit State failure modes are related to the strength and stability of the foundation under loads applied during the design life of abridge or structure. This Limit State includes an evaluation of typical geotechnical and structural resistances to resist the loads applied to them with an adequate margin of safety against damage or collapse. For laterally
loaded deep foundations, Strength Limit States include geotechnical strength (failure of the soil) and structural strength (failure of the foundation element) Limit States. Structural Strength Limit State is discussed further in chapter 11. Resistance factors have not been calibrated for lateral analysis
of deep foundations however, Table 4-1 provides recommended values for geotechnical strength limit state design. The values recommended in the table are suggested based on engineering judgement (Brown et al., 2010) in recognition that this recommended approach provides a check for ductility and geotechnical stability that exceeds the level of reliability provided by the AASHTO (2014) code provisions. The recommended resistance factors apply to lateral analysis of driven piles or drilled shafts for the Strength Limit State using load-displacement (p-y) analyses. These resistance factors provide a check for ductility and geotechnical stability that exceeds the level of reliability provided by the AASHTO (2014) requirements.
