plaxis tutorial 01

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Tutorial mengenai Plaxis

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  • The Program and its Applicationsby Ari Cohen

  • Developed at the Technical University of Delft for Dutch DPWWMInitially was intended to analyze the soft soil river embankments of the lowlands of HollandSoon 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 interfacesInputCalculationsOutputCurves

  • 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 ConditionsPrescribed DisplacementsSpecial Conditions placed on geometry lines that control the displacement of the linesDrawn over geometry linesCan be altered by double clicking on the geometry line associated with itFixitiesPrescribed displacements equal to zeroCan be of horizontal, vertical, or total (horizontal & vertical)Fixities take priority over displacements and other loadsStandard FixitiesConvenient and fast input option for many applicationsTractionsDistributed loads applied to geometry linesInput values given in the dimensions force per unit areaCan be altered by double clicking on the geometry line associated with itPoint ForcesAre actually line loads in the out-of-plane directionCan have vertical and horizontal componentsFixed RotationsFixes 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 PropertiesDatabase with material data setsSoil properties and material properties of structures are stored within the database as four types of material setsSoils & InterfacesBeamsGeotextiles &AnchorsModeling of Soil BehaviorThere exist three types of soil models that PLAXIS supports:Mohr-Coulomb modelHardening-Soil model &Soft-Soil-Creep modelMohr-Coulomb is most often used as good soil data is not always available to the engineer or scientistModeling with the Mohr-Coulomb default requires the following five variables to be input:Youngs modulus, (E)Poissons ratio, (n)cohesion, (c)friction angle, (f) anddilatancy angle, (y)

  • All clusters and structural elements in a given model must be assigned a material before a mesh can be generatedThe 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 GenerationGlobal CoarsenessDistinction 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 settingGlobal RefinementAutomatically generates a refined mesh; one step per selectionLocal CoarsenessIn 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 pointLocal RefinementInstead 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 ConditionsOnce 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 modeWater Conditions modeWater 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/m3Phreatic 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 typeGroundwater 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 conditionsWater Pressure Generation: After a phreatic line or groundwater boundary conditions are specified, the generate water pressures button is selected to complete the water conditions processGeometry Configuration modeDeactivating 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 notInitial 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 Jakys 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?

    More than half of the Netherlands is below sea level