This page describes how to model pile lateral support based on P-y curves.

Introduction

P-y curves describe the lateral soil resistance along the depth of a pile or drilled shaft and are typically provided by geotechnical engineer. For each layer of the soil along the depth of a pile, the P-y curve describes lateral soil reaction P per unit length along the pile mobilized by lateral pile displacement y. The relationship between P and y is nonlinear.

The modeling of lateral soil support involves the following steps:

• Define the properties of links that will represent the lateral support provided by the soil.
• Draw discrete links at the joints of the pile: one link per joint for non-gapping soil behavior; and two links per joint at each side of the piles for gapping soils:

          
            One link per joint for non-gapping soil behavior 

           
           Two links per joint at each side of the piles for gapping soils

Link Definition

Nonlinear link properties can be defined (in SAP2000) via "Define > Section Properties > Link/Support Properties" as follows:

• Add new link property of "MultiLinear Plastic" type and specify nonlinear link stiffness for U2 degree of freedom to match the stiffness described by the P-y curve"
  • For material with non-gapping behavior, define the link with stiffness in both sides of the curve, and select Kinematic as the hysteretic model

          
           Link Definition Non-Gapping Behavior

• •        For material with gapping behavior, define the link with the tension side stiffness equal to zero, and select Takeda as the hysteretic model,

                
                 Link Definition Gapping Behavior

Link Assignment

Assign the above-defined links to the links using the Assign>Link/Support>Link/Support Properties menu command.

Hysteretic

Example of the hysteretic behavior obtained from a Displacement- Based Quasi-Static Nonlinear Time History Analysis.  In this example, an increasingly cyclic displacement load was applied to a pile joint:

             The Kinematics model gives non-gapping behavior

           The Takeda model gives gapping behavior when one side of the curve is all zero

Miscellaneous

• For non-gapping material, you can assign the links to the frame elements representing the piles as line springs, instead of drawing them as discrete elements
  
  • Mesh the piles within each soil layer.
    
  •   Select the pile frame elements within a given soil layer and use the "Assign > Frames > Line Links" menu command to assign the P-y link with the properties corresponding to that layer. Repeat this for all layers.
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