consideration of fluid structure interaction in time history seismic analysis
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Consideration of fluid structure interaction in time history seismic analysis
ANSYS Conference & 6. CADFEM Austria Users' MeetingVienna 7 04 2011Vienna, 7.04.2011
Mag. Ing. Maciej Kwapisz
Outline
Introduction
FE model
Fluid structure interaction Fluid – structure interaction
Model updating
Seismic analysis (spectrum and transient)
Safety of the building
Conclusions
Introduction
The building was build in 1963 No design for earthquake impact Six water tanks with capacity of
80m³ each Masses (with life load):
tank building: 2060 t higher building: 2304 t Water: up to 400 t (5x 80t)
FE model
3D FEM Model – Ansys Elements used:
Shell63 – walls, fundaments Fluid80(solid) for water in tanks Beam4 – beams, columns
bi 14 d combin14 – ground link8 - elastic dilatation
Earthquake loadq
Fluid structure interaction Mesh of solid elements(water) Copy the mesh to shell elements(walls) Coupling of nodes – fixing direction p g g
perpendicular to the wall Problems on the funnel
Fluid structure interaction
Assures proper dynamic properties of the whole structure Changes the pressure on the walls
Vibration measurement of the building and model - updating
Connecting the mass exciter with the building by axial chain
Sweep excitation p Obtaining eigenfrequencies Comparing with FE results
Vibration measurement of the building
Water levels during measurement
2% 62%
0,4% 0,3%, ,
0,3% 0,3%, ,
Model updating – comparison with FE results
Vergleich mit der Messung
Natural frequency [Hz]Mode Natural frequency [Hz] DeviationMeasurementFE model
1 x 5.2 x2 6 3 6 2 1 6%2 6,3 6,2 1,6%3 8,7 7,6 12,6%4 11,5 11,9 3.50%
Average 5,9%
Seismic assessment
Both spectrum and transient analysis were used
Spectrum of the time- history analysis
Not enough signals were found in Strong Motion Database
Artificially created signals were used, based on spectrum from EC8
Results from both analysis were similar Results from both analysis were similar
Results of Seismic analysis Water tank building treated as alone standing Columns were determined to be the weakest part of the structure 2 Types: 40x40 cm und 100x40 cm. yp
Post processing of transient analysis - columns
Bending moments (red and violet) and Safety factoraxial force (blue)
Post processing of transient analysis - columns
Simultaneity of bending moments and normal force. Equation written to Ansys:
is the design moment around the respective axisis the moment resistance in the respective direction
a is the exponent, which depends on the axial force
The result is the highest safety factor from all columns
Conclusions
By means of experimental modal analysis and finite element calculation a very realistic computer model can be created
Fluid elements make the consideration of water motion possible, which is important for improvement of accuracy and reliability of the computations
Post- processing of transient analysis provides information about simultaneity of bending, shear and axial forces.
Similar results of time – history and spectrum analysis proved that fluid elements worked good in both of them
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