Structural forces in the beam: Bending moments and axial forces.Results provided by embedded beams contain: Pile foot resistance is defined in a similar way, with a linear elastic-perfectly plastic spring in pile axial direction where the base force is limited with value Fmax also provided as a user input.įigure 4: Property definition of 3D embedded beam for pile modeling Coupling spring properties: Interface normal stresses will always remain elastic (they are not limited by any failure law), while the value of shear stress is limited by the ultimate traction value Tmax which is provided by the user along the pile shaft.Beam properties for the pile: Material stiffness and weight along with cross section shape and dimensions.The simplification of both the geometry description and the meshing process enables the consideration of hundreds of piles without any difficulty.įigure 3: The use of 3D embedded beam for modeling many pilesĮmbedded beam user input is divided into: The PLAXIS 3D calculation kernel automatically takes care of finding intersection loci between beam pile element and soil element faces, introducing at these points so-called “virtual” nodes where relative displacement between soil mesh nodes and pile nodes can be computed. Both pile lines and soil volume could be meshed independently. Another clear advantage of using PLAXIS embedded beam elements is that the generation of the coupling springs (for soil–pile interaction) does not require mesh node connectivity between the lines supporting the pile/beam elements and the surrounding soil volume. This saves a large number of elements needed in the process, compared to volume piles being filled with tetrahedra elements. The generation of linear beam elements gives the opportunity to simulate piles as structural elements with specified material properties. In this approach, the pile is represented by beam elements, while soil–pile interaction along the pile shaft and at the pile tip is described by special interface elements that are constructed based on node-to-node, non-linear coupling springs. The embedded beam is particularly useful in cases of large numbers of piles to be accounted for in a PLAXIS 3D model. This feature was developed to simulate the behavior of piles in a simplified way. The embedded beam is a special feature in PLAXIS 3D.
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Piles as embedded beams, or how to efficiently deal with many piles A large number of piles would have to be considered and the increasing number of elements (as the number of piles to be modeled increased) might become simply impractical at some point. The volume approach also requires the use of relatively small elements implicitly induced by the relatively large slenderness of the pile element itself and, as a result, large number of elements. By introducing low stiffness beam elements along the neutral axis of the volume piles, the purpose of which being to monitor the evolution of strains and change of curvature along them and easily retrieve the structural forces based on beam theory.įigure 2: Bending moment in simple pile raft model.Through direct integration of stress through the Structural Forces in Volume Piles tool, or.Piles results will be primarily provided in terms of stresses which could later be integrated into structural forces into the PLAXIS Output post-processing environment, either: With such 3D models, the piles are physically modeled, and the soil-structure interaction is accounted for by means of surface interface elements with associated Coulomb-friction behavior. This will guarantee the most accurate representation of the physical problem, especially regarding soil-structure interaction. Ideally, the piles themselves will be represented by volume elements. This could be a challenging task for the designer in the case of complex pile-soil interaction or in situations involving a consolidation process.ĭue to the 3D nature of the pile geometry and the possible lateral component of the design load, most pile foundation analyses should be set up in PLAXIS 3D. In this context, the accurate prediction of piles’ settlement and proper evaluation of pile bearing capacity is a fundamental aspect of deep foundation design. Pile foundation is a popular type of deep foundation technique used to transfer superstructure load into subsoil and bearing layers. The problem of analyzing and designing deep foundations is relevant to many civil engineering structures, because we are commonly and frequently constructing buildings on soft soils.