Plaxis实例教程01.ppt

The Program and its Applicationsby Ari Cohen•Developed at the Technical University of Delft for Dutch DPWWM•Initially was intended to analyze the soft soil river embankments of the lowlands of Holland•Soon after, the company Plaxis BV was formed, and the program was expanded to cover a broader range of geotechnical issues The NetherlandsBackgroundGetting StartedPLAXIS is comprised of four interconnected but separate interfaces•Input•Calculations•Output•CurvesTutorial 1: The Modeling the Settlement of a Circular Footing on Sand1. Choose new or existing project2. General Settings3. Plane Strain or Axisymmetry / 15-Node or 6-Node4. Plane Strain or Axisymmetryxy4. Plane Strain or Axisymmetry Cont.5. 15-Node or 6-Node5. 15-Node or 6-Node Cont.6. Dimensions7. Geometry Contour8. Loads & Boundary Conditions•Prescribed Displacements1.Special Conditions placed on geometry lines that control the displacement of the lines2.Drawn over geometry lines3.Can be altered by double clicking on the geometry line associated with it•Fixities1.Prescribed displacements equal to zero2.Can be of horizontal, vertical, or total (horizontal & vertical)3.Fixities take priority over displacements and other loads•Standard Fixities1.Convenient and fast input option for many applications•Tractions1.Distributed loads applied to geometry lines2.Input values given in the dimensions force per unit area3.Can be altered by double clicking on the geometry line associated with it•Point Forces1.Are actually line loads in the out-of-plane direction2.Can have vertical and horizontal components•Fixed Rotations1.Fixes the rotational degree of freedom of a beam8. Loads & Boundary Conditions cont.Select Standard fixities button8. Loads & Boundary Conditions cont.Select Prescribed displacement button9. Material Properties•Database with material data sets1.Soil properties and material properties of structures are stored within the database as four types of material sets1.Soils & Interfaces2.Beams3.Geotextiles &4.Anchors•Modeling of Soil Behavior1.There exist three types of soil models that PLAXIS supports:1.Mohr-Coulomb model2.Hardening-Soil model &3.Soft-Soil-Creep model2.Mohr-Coulomb is most often used as good soil data is not always available to the engineer or scientist3.Modeling with the Mohr-Coulomb default requires the following five variables to be input:1.Young’s modulus, (E)2.Poisson’s ratio, (n)3.cohesion, (c)4.friction angle, (f) and5.dilatancy angle, (y)•All clusters and structural elements in a given model must be assigned a material before a mesh can be generated•The following soil parameters will be used for the footing settlement example:9. Material Properties cont.9. Material Properties cont.Click Materialsbutton 9. Material Properties cont.Select “New” material 9. Material Properties cont.Type “sand” and leave the other default inputsSelect “New” material Enter given data9. Material Properties cont.Select “New” material Enter given data and click OkDrag & Drop the “Sand” material into the cluster9. Material Properties cont.10. Mesh Generation•Global Coarseness§Distinction is made between five levels of global coarseness: Very coarse, Coarse, Medium, Fine, and Very fine. Number of mesh elements generated ranges from about 50 elements for the coarse setting to about 1000 elements for the very fine setting•Global Refinement§Automatically generates a refined mesh; one step per selection•Local Coarseness§In areas where it may not be necessary to have a very refined mesh, the mesh may be made more coarse by adjusting the “Local element size” factor for a particular geometry point. This can be accessed by double clicking on any geometry point•Local Refinement§Instead of adjusting the “Local element size” factor, clusters, lines, or points can be selected and the local refinement option can be used10. Mesh Generation cont.Select “Generate mesh” Once the mesh window appears select “Update”11. Initial Conditions•Once the geometry model has been created and the mesh has been generated, the “Initial conditions” must be inputted. There are two different modes within the initial conditions tab: Water conditions mode and the Geometry configuration mode•Water Conditions mode1.Water Weight: In projects that involve pore pressures, the input of water weight in necessary to distinguish between effective stresses and pore pressures. PLAXIS default water weight is set to 10kN/m32.Phreatic Lines: Pore pressures and external water pressures can be generated on the basis of phreatic lines. With a phreatic line it is understood that water pressures above the line are zero and increase linearly with depth below the line. The phreatic line can be a general or user defined type3.Groundwater Flow: In addition to generating water pressures using a phreatic line, water pressures can also be generated using groundwater flow calculations. This requires the input of groundwater head boundary conditions4.Water Pressure Generation: After a phreatic line or groundwater boundary conditions are specified, the generate water pressures button is selected to complete the water conditions process•Geometry Configuration mode1.Deactivating Geometry Components: In projects where embankments and structures are to be constructed the geometry model will have some elements that are initially not active. These elements must be deactivated in this mode. By default PLAXIS activates all elements of the model outlined in the previous geometry setup stage. Clicking on a particular element in this mode determines if it will be on or not2.Initial Stress Generation (K0-Procedure): Initial stresses in a body are influenced by the weight of the material and the history of its formation. The stress state is generally characterized by an initial vertical stress, sn,0 which is related by the coefficient of lateral earth pressure K0. A default value is given based on Jaky’s formula (1-sinf).1.Select “Initial conditions” button and accept default water weight 11. Initial Conditions cont.2. Water levels will not be generated in this example so proceed to generate initial stressesAccept default K0 parameters11. Initial Conditions cont.Length of lines note relative magnitude of principal stresses11. Initial Conditions cont.Orientation of lines note principal direction11. Initial Conditions cont.Finally it is time to proceed to the Calculation phase of the programQuestions?。