3.3.1.3. Element Recorder

The element recorder is used to record element-level response during an analysis. Output may go to a file, XML, or other targets depending on the arguments. Common responses include force, deformation, and (for elements with sections) section and fiber response.

recorder Element <-file $fileName> <-xml $fileName> ... <-time> <-ele $ele1 $ele2 ...> $responseArgs

The exact arguments depend on the element type and what you want to record. The following sections describe how to record fiber and section response for fiber-section and beam-column elements.

3.3.1.3.1. Recording fiber response

For elements that use fiber sections (e.g. zeroLengthSection, forceBeamColumn, dispBeamColumn, mixedBeamColumn), you can record the response of a single fiber. What can be recorded in each fiber is defined by the UniaxialMaterial’s setResponse() method. A common option is stressStrain, which gives the fiber stress-strain history. Other options (e.g. stress, strain, tangent, damage for the Fatigue material) are available when supported by the material.

You specify which fiber to record using one of three options:

Fiber index – The index in the section’s internal array of fibers (0 to N_f − 1). Use fiber followed by the index and the response type.
Fiber closest to section coordinates – Give the section y and z coordinates; the recorder uses the fiber closest to that point. Use fiber followed by y, z, and the response type. For 2D problems, bending is about the z-axis so only y matters, but you must still provide a z value (e.g. 0).
Fiber with a given material tag closest to coordinates – Same as (2), but only among fibers with the specified material tag. Use fiber followed by y, z, matTag, and the response type. This is useful for sections with overlapping fibers (e.g. steel and concrete) when you want a specific material at a location.

What comes before fiber depends on the element:

zeroLengthSection – Use section then fiber (there is only one section).
Beam-column elements (displacement-based, force-based, mixed) – Use section secNum then fiber, where secNum is the integration point number (1 to N_p from node I to node J). Alternatively, use sectionX x then fiber to select the section closest to coordinate x along the element (see Recording section response by location (sectionX)).

Tcl Code

# zeroLengthSection: fiber closest to (y,z), stress-strain
recorder Element -ele 1 -file fiber.out section fiber 0.1 0.0 stressStrain

# Beam-column: section 1, fiber at (y,z) with material tag 2 (e.g. steel)
recorder Element -ele 1 -file steelFiber.out section 1 fiber -h/2 0 2 stressStrain

Python Code

# zeroLengthSection: fiber closest to (y,z)
ops.recorder('Element', '-ele', 1, '-file', 'fiber.out', 'section', 'fiber', 0.1, 0.0, 'stressStrain')

# Beam-column: section 1, steel fiber at tension face
ops.recorder('Element', '-ele', 1, '-file', 'steelFiber.out', 'section', 1, 'fiber', -h/2, 0, 2, 'stressStrain')

3.3.1.3.2. Recording section response by location (sectionX)

For beam-column elements you can record section response (e.g. force, deformation) by section number (1 to N_p). The mapping from section number to position depends on the integration rule (e.g. Lobatto, Legendre, or plastic-hinge schemes), so it is not always obvious which number corresponds to a given location along the element.

You can avoid relying on section numbers by using sectionX: give a location x in the range [0, L] along the element (0 at node I, L at node J). The recorder will use the section closest to that x coordinate. The remaining arguments after sectionX x are the same as for the usual section secNum recorder (e.g. deformation, force, or fiber …).

Tcl Code

# Section closest to x = 25 along the element
recorder Element -ele 1 -file sec25.out sectionX 25 deformation

Python Code

ops.recorder('Element', '-ele', 1, '-file', 'sec25.out', 'sectionX', 25, 'deformation')

Note

sectionX accepts a single x value per recorder. To record at multiple locations, define multiple recorders.