This command is used to construct a truss experimental element object. Two nodes define this element.

To following command is to define the experimental element on the middle-tier server side and use a generic-client element in the finite element software:

expElement truss $eleTag $iNode $jNode –site $siteTag –initStif $K <–iMod> <-noRayleigh> <–rho $rho>

To following command is to define the experimental element directly in the OpenSees finite element software and therefore not using any element on the middle-tier server side:

expElement truss $eleTag $iNode $jNode –server $ipPort <ipAddr> <-ssl> <-udp> <-dataSize $size> –initStif $K <–iMod> <-noRayleigh> <–rho $rho>

$eleTag unique element tag
$iNode, $jNode
end node tags
$siteTag tag of previously defined experimental site object
$K initial stiffness of the element
-iMod error correction using Nakashima’s initial stiffness modification (optional, default = false)
-noRayleigh do not include Rayleigh damping contributions (optional, default = include Rayleigh damping)
$rho mass per unit length (optional, default = 0.0)
$ipPort IP port of middle-tier server
ipAddr IP address of middle-tier server (optional, default = “”)
-ssl secure transactions using OpenSSL (optional)
-udp use udp sockets instead of tcp sockets (optional)
$size data size being sent (optional)


The valid queries to a truss experimental element when creating an element recorder object are:

  • global forces:                     force, forces, globalForce, globalForces
  • local forces:                        localForce, localForces
  • basic forces:                       basicForce, basicForces, daqForce, daqForces
  • control displacements:    defo, deformation, deformations, basicDefo, basicDeformation,     basicDeformations, ctrlDisp, ctrlDisplacement, ctrlDisplacements
  • control velocities:              ctrlVel, ctrlVelocity, ctrlVelocities
  • control accelerations:       ctrlAccel, ctrlAcceleration, ctrlAccelerations
  • daq displacements:           daqDisp, daqDisplacement, daqDisplacements
  • daq velocities:                     daqVel, daqVelocity, daqVelocities
  • daq accelerations:              daqAccel, daqAcceleration, daqAccelerations



# Define geometry for model
# ————————-
# node $tag $xCrd $yCrd $mass
node 1 0.0 0.0
node 2 144.0 0.0
node 3 168.0 0.0
node 4 72.0 96.0# Define experimental site
# ————————
# expSite LocalSite $tag $setupTag
expSite LocalSite 2 2# Define experimental elements
# —————————-
expElement truss 1 3 4 –site 2 -initStif [expr 3000.0*5.0/135.76]

Nodes 3 and 4 connect the above 2D truss experimental element. The element is defined using a local experimental site. The initial stiffness of this element is [expr 3000.0*5.0/135.76] = 110.5.

Code Developed by: Andreas Schellenberg, University of California, Berkeley.

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