8/13/2019 ETABS.- Fuerzas Internas en Vigas y Columnas

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Output Convention for Frame Element Internal Forces

The frame element internal forces are:

P, the axial force

V2, the shear force in the 1-2 plane

V3, the shear force in the 1-3 plane

T, the axial torque (about the 1-axis)

M2, the bending moment in the 1-3 plane (about the 2-axis)

M3, the bending moment in the 1-2 plane (about the 3-axis)

These internal forces and moments are present at every cross section along the length of the frame element.

For each load case and load combination, the frame element internal forces and moments are computed and reported at each frame element output station.

In frame element output displayed in a tabular form, either on the computer screen, printed to a printer or printed to a file, the locations of the output stations are

identified by the absolute distance to the station measured from the i-end of the element.

The sign convention for frame element internal forces is illustrated in the figure below. This sign convention can be described by defining the concept of positive and

negative faces of an element. Consider a section cut through the element in the 2-3 plane. At this section, the positive 1 face is the face whose outward normal (arrow

that is perpendicular to the section and pointing away from the section) is in the positive local 1 direction. At this same section, the negative one face is one whose

outward normal is in the negative local 1 direction. The positive 2 and 3 faces are those faces with outward normals in the positive local 2 and 3 directions,

respectively, from the neutral axis. Note the following about the frame element internal forces:

Positive internal forces (P, V2 and V3) and positive axial torque (T) acting on a positive 1 face are o riented in the positive direction of the corresponding element

local coordinate axis. For example, when V2 acting on a positive 1 face is positive, it is oriented in the direction of the positive local 2-axis.

Positive internal forces (P, V2 and V3) and positive axial torque (T) acting on a negative 1 face are oriented in the negative direction of the corresponding element

local coordinate axis. For example, when V2 acting on a negative 1 face is positive, it is oriented in the direction of the negative local 2-axis.

Positive M2 bending moments cause compression on the positive 3 face and tension on the negative 3 face.

Positive M3 bending moments cause compression on the positive 2 face and tension on the negative 2 face.

When end offsets along the length of the frame element are present, the internal forces and moments are output at the faces of the supports rather than the ends

of the element. No output is produced within the end offset length.

The right hand rule applies in the figure for determining the sense of the moments shown by the double arrows.

Pgina 1 de 1Output Convention for Frame Element Internal Force

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