Finite element modeling for validation of structural damage identification experimentation. Page: 3 of 6
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The 20th International Modal Analysis Conference, Los Angeles, CA, USA, February 4-7, 2002.
2.1 Components of the Structure
Each of the three floor plates is a rectangular aluminum
plate with squares cut out of each corner for the vertical
beams. The dimensions of the aluminum plate are
24.188" x 18.188" x 0.5" thick. The floor plates were
modeled with shell elements with material properties of
aluminum and the same thickness as the physical floor
The base plate is a 1.5-in.-thick rectangular aluminum
plate, 24-in. wide by 30-in. long. The base plate was also
modeled with shell elements with aluminum material
The base plate was mounted on four air bearings to
isolate the structure from incident vibrations. To model
the air bearings, springs were attached from nodes on
the base plate to ground. The nodes were chosen at
locations corresponding to where the air bearings were
attached in the physical model. Values for the spring
constants were obtained from data from the
manufacturer of the air bearings. These values were
updated during modal analysis validation to achieve
proper rigid body mode frequencies.
The vertical beams are 60-in.-long B-line brand stainless
steel channels. Figure 2 shows the cross section shape
and major dimensions of the vertical beams. Beam
elements with the same geometric cross section as the
physical beams were used in the model.
Figure 2: Cross section of vertical beam
Vertical beam brackets
To attach the vertical beams to the base plate, B-line
brackets were used. These brackets are referred to as
vertical beam brackets throughout this report. Each
bracket is comprised of a flat plate that is bolted to the
base plate and a U-shaped channel that extends
perpendicular to the base plate and encompasses the
bottom 3-1/2" of the vertical beam. The vertical beam is
bolted to the U-shaped channel of the bracket. The plate
portion of each bracket was modeled with shell elements.
To model the U-shaped channel, the cross section of the
vertical beam was adjusted in that length to include the
geometry of the bracket. The cross section of the vertical
beam including the bracket is shown in Figure 3.
Figure 3: Cross section of vertical beam with vertical
Floor plate brackets
Brackets are used to attach each floor plate to the four
vertical beams. Each bracket, referred to as a floor plate
bracket, has two flat plates to attach to the floor plate and
an L-shaped channel to attach to the vertical beam.
Each of the flat plates is rectangular with dimensions of
1.5" x 1.875". The L-shaped channel is 3.625" tall, and
fits with the vertical beam as shown in Figure 4. As was
done with the vertical beam brackets, the cross section of
the vertical beam is adjusted in the regions where the
floor plate brackets are attached to include the cross
section geometry of the brackets. The plates of each
bracket are rigidly connected to the vertical beams with
Figure 4: Cross section of vertical beam with floor plate
2.2 Contact Surfaces
The original intent of the project was to create a linear
finite element model of the structure, therefore contact
between the floor plates and the floor plate brackets was
simulated by connecting linear spring elements from
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Stinemates, D. W. (Daniel W.) & Bennett, J. G. (Joel G.). Finite element modeling for validation of structural damage identification experimentation., article, January 1, 2001; United States. (https://digital.library.unt.edu/ark:/67531/metadc934310/m1/3/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.