3.1.11.3. Multisupport Excitation¶

The Multi-Support pattern allows similar or different prescribed ground motions to be input at various supports in the structure. In OpenSees, the prescribed motion is applied using single-point constraints, the single-point constraints taking their constraint value from user created ground motions.

The command to generate a multi-support excitation contains in squirrelly brackets the commands to generate all the ground motions and the single-point constraints in the pattern. The command is as follows:

Argument	Type	Description
$patternTag	integer	unique tag among load patterns
groundMotion & imposed motion commands`	commands	command to generate a ground motion & constrain nodes

As will be demonstrated in the example, the actual support conditions that are applied depend on a series of additional commands Ground Motion and Imposed Motion Command. The Ground Motion create ground motion objects, which are applied to a particular node with the Imposed Motion Command command.

Warning

The results for the responses at the nodes are the ABSOLUTE values, and not relative values as in the case of a UniformExcitation.

When using MultiSupport pattern, the ground motions are applied by specifying for each constrained node a ground motion. This is done using the Imposed Motion Command command. The ground motions at each of the supports is specified using a Ground Motion. When enforcing the constraint at the node, the imposedMotion constraint will obtain the displacement from the ground motion. If the groundMotion was built by user specifying the acceleration, the trapezoidal rule is used for integration to obtain the displacements.

Example:

The following example shows how to construct a Multi-Support Excitation pattern with a tag of 1* that will constrain the nodes **1, 4, and 7 to move in the 1 dof direction with the ground Motion supplied by the groundMotion with tag 101, whose displacement is given by timeSeries with a tag of 3.

Tcl Code

timeSeries Path 3 -filePath elCentroDisp.dat -dt 0.02
pattern MultipleSupport  1  {
     groundMotion 101 Series -disp 3

     imposedSupportMotion 1 1 101
     imposedSupportMotion 4 1 101
     imposedSupportMotion 7 1 101
}

Python Code

timeSeries('Path', 3, '-dt', 0.02, '-filePath', 'elCentroDisp.dat')
pattern('MultiSupport', 1)
groundMotion(101, 'Series', '-disp', 3)
imposedSupportMotion(1,1,101)
imposedSupportMotion(4,1,101)
imposedSupportMotion(7,1,101)

Code Developed by: fmk