桩是岩土工程中的基本结构构件，用于在表层土质不足的情况下将荷载从上部结构传递到更稳定的土层或岩石上。 Unlike shallow foundations, which rely on the surface soils for load-bearing capacity, piles transfer the load to deeper layers, providing greater stability in weaker or compressible soil conditions. These deep foundation systems are essential in various civil engineering projects, including high-rise buildings, bridges, and offshore platforms.
RFEM 6, the advanced structural analysis software from Dlubal Software, provides engineers with an efficient and accurate way to model piles in a structural model. It includes a specific member type called “Pile” (Image 1) which allows you to represent these foundational elements effectively. This member type is designed to both simulate the mechanical properties of the pile itself and to ensure that its interaction with the surrounding soil is taken into account in the overall design.
Choosing the "Pile" member type, as illustrated in Image 1, enables you to define the specific characteristics of the pile, starting with its cross-sectional shape and dimensions (Image 2). RFEM 6 provides the flexibility to specify the pile's geometry, whether circular, square, or a custom shape tailored to the design. You can input detailed parameters such as diameter or width, material properties (e.g., concrete, steel), and length. Moreover, materials and sections can be pre-defined in the navigator, allowing you to easily select them from a drop-down menu during this step.
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桩的截面特性
In contrast to the "Section" tab shown in Image 2, which is universally available for all member types, the "Pile" tab that follows is dedicated exclusively to piles. This is because it enables the definition of the pile's resistance (Image 3), which is essential for understanding the mechanism by which the pile transfers loads to the surrounding soil.
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桩阻力类型选择
The resistance offered by the soil to the pile is divided into two components: skin resistance (also known as shaft resistance) and base resistance. Both play a key role in determining the load-carrying capacity of a pile. This is also reflected by the input you must make in the window shown in Image 4.
The primary mechanism by which a pile transfers load to the surrounding soil is through skin friction. Skin friction arises from the frictional forces between the pile surface and the adjacent soil. This resistance is distributed along the length of the pile and varies depending on the properties of both the soil and the pile material. Hence, to start defining the pile resistance type, first you must define the shear resistance distribution along the pile; you can choose between trapezoidal and varying (Image 4).
Next, you can specify the values for shear strength and shear stiffness. Shear strength refers to the maximum shear stress the soil can withstand before failure, while shear stiffness represents the soil's resistance to shear deformation as the pile moves relative to it. Likewise, you need to define the base resistance parameters, including axial strength and axial stiffness. Initially, these parameters can be determined using the formulas provided below. Later, they can be adjusted based on a load-displacement curve from field tests or standards to achieve the desired pile behavior.
Final Words
RFEM 6 offers a powerful and efficient platform for performing geotechnical analysis and design of pile foundations. With its comprehensive tools, the software enables accurate modeling of pile behavior, simulation of soil-pile interactions, and execution of essential design checks, which will be explored further in an upcoming Knowledge Base article. By incorporating advanced geotechnical analysis into a unified structural modeling environment, RFEM 6 empowers engineers to design safer and more efficient pile foundations, ensuring structural stability and optimal performance in challenging soil conditions.
