The principal force experienced in transportation structures during an earthquake, a hurricane, or a vessel impact is transient horizontal loading. These loads must be transmitted to the structure’s foundation. State-of-the-practice design for lateral loading of pile and drilled shaft foundations uses beam-on-elastic-foundation analysis. In this analysis, load shedding from a pile to the soil is represented by “p-y springs” in which the soil response is modelled as a series of discrete nonlinear springs. The p-y springs currently used in these analyses were developed primarily to determine the load-shedding behaviour of single piles subjected to static loads. The use of p-y springs in the analyses of pile groups subjected to static and dynamic lateral loads had not been validated. The objective of this research was to evaluate and extend current design methods for groups of piles and groups of drilled shafts subjected to lateral loads associated with earthquakes, hurricanes, and vessel impacts. Under NCHRP Project 24-09, Auburn University conducted experimental and analytical studies of pile groups. Through a series of field tests, the researchers determined the distribution of lateral loads to the individual piles in a group and verified that the pile-group response can be predicted analytically using p-y springs. Experimentally determined multipliers are used to adjust the magnitude of load carried by each row of piles in the group. The findings from this research could significantly increase confidence in and reduce the cost of foundations subjected to dynamic loads. (A) This report may be accessed by Internet users at http://gulliver.trb.org/publications/nchrp/nchrp_rpt_461-a.pdf / http://gulliver.trb.org/publications/nchrp/nchrp_rpt_461-b.pdf / http://gulliver.trb.org/publications/nchrp/nchrp_rpt_461-c.pdf
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