Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Block 9.3 – Analyze Service Limit State
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- Block 9.4 – Analyze Extreme Event Limit State
| Block 9.3 – Analyze Service Limit State Service load combinations, with applicable load and resistance factors as discussed in Chapter 4, are evaluated to check that deflections are within tolerable limits. Although for preliminary assessments, a rule of thumb deflection maybe acceptable, the final design should include evaluation of the actual tolerable deformation for the serviceability of the structure. Service Limit State deflections should include potential for amplification of or additional deflection above the top of the foundation element, such as for pier columns or at the top of a cantilevered retaining wall. In some cases, the Service Limit State deflections maybe set based more on aesthetics than on actual serviceability of the structure, such as noise walls, signposts, or cantilevered retaining walls. The Service Limit State deflections will be a function of both the ground response as well as the structural stiffness of the foundation element. Therefore, an analysis method that accounts for soil-structure interaction, such as the p-y method, must be used in this step. This analysis can often be performed using the same software and the same models that were used for the Strength Limit State analyses, however, the inputs must be adjusted to use the applicable load and resistance factors for the Service Limit States, and the criteria for evaluating the results must be based on Service Limit States. If the same models are used for both Limit States, the analyses results should clearly distinguish the service limit analyses from the strength limit analyses to avoid confusion in the project reporting. 56 Block 9.4 – Analyze Extreme Event Limit State Extreme Event Limit State loading, discussed in Chapter 8, should also be analyzed as applicable. A resistance factor of 0.80, as discussed in Chapter 4, will apply. Extreme Event Limit States involve events with a low probability of occurrence. Such events are considered to be unique and their return period maybe significantly greater than the design life of the structure (AASHTO 2014). The Extreme Event Limit State is intended to ensure the survivability of the structure during such an event. This Limit State is to protect against collapse of the structure and loss of life some damage or loss of functionality maybe acceptable in such a case. Extreme Event Limit States for design of deep foundations include the following 1. The check flood for scour 2. Earthquakes/seismic events 3. Loading from ice 4. Vessel collision 5. Vehicle collision Download 6.03 Mb. Share with your friends:
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