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Distributed surface loads

*Dsload, <option>
<surface name>, <load label>, <Load magnitude>

This option defines a distributed surface load acting on the surface with the name <surface name> with a defined load magnitude.

  • <option>

    Specify how the load should be applied. The load can either be applied:

    • instantaneously (without any temporal delay) using
      <option> = instant

    • linearly increasing with step time (0% of the prescribed magnitude are applied at the beginning of the step and 100% at the end of the step time) using
      <option> = ramp

    • using a user defined amplitude defined prior to the step definition using
      <option> = Amplitude = <amplitude name>

    • using a user defined amplitude defined prior to the step definition using
      <option> = Amplitude = <amplitude name>

  • <surface name>

    Surface name to which the load should be applied.

  • <Load label>

    Load label defining the type of load and the direction of action of the external distributed load. Currently available are:

    Load type
    Uniform pressure
    Water weight
    Springs
    Compliant base boundary condition
    Drainage condition (seepage)

Uniform pressure

*Dsload, <option>
<surface name>, P, <Magnitude>

Distributed load acting perpendicular to the surface face.

Water weight

*Dsload, <option>
<surface name>, SWP
Distributed load acting perpendicular to the surface face compensating(positive) pore-water pressure by its deadweight (e.g. to simulate the flooding of slopes). The magnitude of the load is calculated such that the (only positive) more water pressure acting on the surface is compensated.

Spring

*Dsload, <option>
<surface name>, <spring type>, <magnitude>
Distributed surface load which corresponds to a support of the surface <surface name> by a plurality of spring elements. Two types of springs are implemented, which can be chosen by setting <spring type> to:

  • spring-n for springs acting perpendicular (in normal direction) to the surface.

  • spring-t for springs acting in tangential direction of the surface

The <magnitude> corresponds to the normalized spring stiffness \(k/L\), where \(k\) is the spring stiffness and \(L\) is the (virtual) length of the spring.

Compliant base boundary condition

*Dsload, <option>
<surface name>, <compliant type>, <dir>, <magnitude>

The compliant base boundary condition is used to impose a seismic signal at the bottom of the FE model and at the same time damping downwards propagating waves by applying equivalent viscous forces. The distributed force acts in global direction Dir to the element faces of surface <surface name> to which the force is applied. The <Magnitude> is defined as \(\rho \cdot c_{p,s}\) of the underlying material, where \(\rho\) is the density and \(c_{p,s}\) is the wave speed (\(c_s\) for shear waves and \(c_p\) for compression waves) The subsequent line then reads:

Two types of springs are implemented, which can be chosen by setting <compliant type> to:

  • compliant: This corresponds to the "implicit" implementation, where the current velocity \(v\) is used to calculate the viscous stress

  • compliant0: This corresponds to the "explicit" implementation, where the velocity \(v_0\) from the previous (converged) time step is used to calculate the viscous stress.

Drainage condition

*Dsload, <option>
<surface name>, drainage-w, <magnitude>

A special boundary condition is needed if the phreatic surface reaches an open, freely draining surface. In such a case the pore fluid can drain freely down the face of the dam, so at all points on this surface below its intersection with the phreatic surface. Above this point negative pore water pressures occur, with their particular value depending on the solution. This drainage-only flow condition consists of prescribing the flow velocity on the freely draining surface in a way that approximately satisfies the requirement of on the completely saturated portion of this surface.

The <magnitude> can be approximated as \(f \dfrac{k^{sat}c}{\gamma_w}\)

Where \(f\) is a scaling factor usually in the range of \(10^3 \leq f \leq 10^5\), \(k^{sat}\) is the saturated hydraulic conductivity, \(\gamma_w\) is the unit weight of water and \(c\) the characteristic element size of the underlying finite element.