mech dynamics 14.5 ws06 spectrum
TRANSCRIPT
8/11/2019 Mech Dynamics 14.5 WS06 Spectrum
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© 2012 ANSYS, Inc. March 28, 2013 1 Release 14.5
14.5 Release
Workshop 6
Response Spectrum(Suspension Bridge)
ANSYS MechanicalLinear and Nonlinear Dynamics
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Workshop 6 - Goals
Our goal is to determine the response of a prestressed suspension
bridge subjected to a seismic load.
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Workshop 6 – Project SchematicFrom the project schematic, insert a new Static Structural system.
Drop a Modal system onto the Solution cell of the Static Structural system.Drop a Response Spectrum system onto the Solution cell of the Modal system.
• Import the Geometry file
– simple_bridge.agdb
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Workshop 6 - Project Schematic
Edit the Model cell to open the Mechanical application.
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Workshop 6 – Units
In Mechanical, set the following units system:
• m, kg, N, s, V, A
• Degrees
• RPM
• Celcius
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Workshop 6 - Preprocessing
Set the mesh defeaturing tolerance to 0.5 m.
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Workshop 6 - Preprocessing
Insert a fixed support on the vertex of all four tower foundations.
•the Modal and Response Spectrum systems will inherit this support
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Workshop 6 - Preprocessing
Insert a zero-displacement constraint in the Y and Z directions on
the three outer edges at both ends of the bridge deck.
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Workshop 6 - Preprocessing
Finally, insert Standard Earth Gravity from the Inertial loads toolbar
button.
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Workshop 6 – Modal Solution
Change the Max Modes to Find to 10, then run the Modal solution.
•review the ratio of effective mass to total mass in Solution Information
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Workshop 6 – Modal Solution
Review the frequency table for the extracted modes.
Are the frequencies closely spaced?
• Yes
Make note of the highest extracted frequency.
• f = 0.3 Hz
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Workshop 6 – Modal Solution
Since we have closely-spaced modes, change the combination
method to something other than SRSS (e.g. ROSE).
• under Analysis Settings of the Response Spectrum branch
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Workshop 6 - PreprocessingInsert an RS Acceleration load in the Response Spectrum branch.
• change Boundary Condition to All BC Supports and Direction to Y Axis
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Workshop 6 - PreprocessingOpen the supplied seismic data from the Savannah River Earthquake,
copy the spectrum data, and paste it into the Tabular Data.
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Workshop 6 - Results
Since the seismic data were supplied in units of G acceleration,
insert a Scale Factor equal to the acceleration due to gravity ofthe working units.
• 9.81 for MKS unit system.
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Workshop 6 - Results
Note the frequency at the spectral peak for this spectrum.
• f SP = 4 Hz
How does this compare to our extracted modes?• all modes have f < fSP
• this means all modes are in the low-frequency region
• therefore, no rigid response or missing mass is needed
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Workshop 6 - Results
Finally, run the solution and insert the result item of your choice.
Note that the bridge deck may need some mesh refinement. Try changing themesh settings and re-solving.