A STEP-BY-STEP GUIDE FOR FAMILIARIZING WITH THIS PIECE OF SOFTWARE Time History Analysis with SAP2000 Dr.Eng. Achfas Zacoeb Dept. of Civil Engineering Brawijaya University
A STEP-BY-STEP GUIDE FOR FAMILIARIZING WITH THIS PIECE OF SOFTWARE
Time History Analysis with SAP2000
D r. E n g . A c h f a s Z a c o e b
D e p t . o f C i v i l E n g i n e e r i n g
B r a w i j a y a U n i v e r s i t y
LIST OF CONTENT
Download recorded accelerograms from the
PEER database.
Upload a selected accelerogram to SAP2000.
Run the time-history analysis and display the
results
DOWNLOAD ACCELEROGRAMS FROM THE PEER DATABASE
Step #1
PEER STRONG GROUND MOTION DATABASE
The Pacific Earthquake Engineering
Research (PEER), headquartered at
the University of California at
Berkeley, makes available online
over 10,000 strong ground motion
records from 173 different
earthquakes
http://peer.berkeley.edu/
PEER STRONG GROUND MOTION DATABASE
The database in entirely searchable
http://peer.berkeley.edu/nga/
As an example, we want to download the
accelerogram recorded during the Imperial Valley
1940 earthquake
Once the event has been selected in the top drop-
down list, we must specify to DISPLAY the
results “In Table” rather than “On Map”
Then we can SEARCH
FIND THE ACCELEROGRAM
By right-clicking on the appropriate record (NGA0006 in our case), a new page is shown with all the relevant pieces of information about this seismic event
If we scroll down, the links to the three components of the accelerogram (180°, 270° and vertical) appear
DOWNLOAD THE TIME HISTORY OF THE GROUND ACCELERATION
By right-clicking on one
of these links (e.g. the
first horizontal
component, denote with
IMPVALL/I-ELC180), a
new textual page is
opened with the
corresponding time
history of the ground
acceleration
The first four lines contain general pieces of information about the record, namely:
Location: “Imperial Valley”
Date: 19th May 1940
Time: 4:39am
Station: “El Centro Array #9”
Direction: Horizontal, 180°
Units of acceleration: g= 9.81 m/s2 (acceleration of gravity)
Number of time instants: 4,000
Sampling time: Δt= 0.01 s (f= 100 Hz)
DOWNLOAD THE TIME HISTORY OF THE GROUND ACCELERATION
The other lines list the ordinates of the record (in units of g), which must be read from left to right, row by row
DOWNLOAD THE TIME HISTORY OF THE GROUND ACCELERATION
Importantly, the web browser (Explorer, Firefox and etc.) allows to save this page as a TXT file (you may need to manually change the extension)
DOWNLOAD THE TIME HISTORY OF THE GROUND ACCELERATION
UPLOAD ACCELEROGRAMS TO SAP2000
Step #2
DEFINE THE ACCELEROGRAM IN SAP2000
An accelerogram is basically the time-history of the acceleration experienced by the ground in a given direction during a seismic event.
We need to input the accelerogram as a generic function defined in SAP2000 starting from a TXT file.
Once the mechanical model of the structural system under investigation has been created, SELECT from the menu bar: DEFINE → FUNCTIONS → TIME HISTORIES...
The accelerogram must be uploaded to SAP2000 as FUNCTION FROM FILE, an option which can be selected from the drop-down list
DEFINE THE ACCELEROGRAM IN SAP2000
We can select:
Name of the function (e.g. EL_CENTRO_1940)
Location of the file by using the button BROWSE...
Number of lines to skip (4 for the PEER database)
Number of points per line (5 for the PEER database)
DEFINE THE ACCELEROGRAM IN SAP2000
In order to be used in a seismic simulation, the
waveform previously defined must be properly
assigned to an ANALYSIS CASE
To do this, SELECT from the menu bar: DEFINE →
ANALYSIS CASES...
DEFINE THE ACCELEROGRAM IN SAP2000
The analysis case in presence of accelerogram is a TIME HISTORY, which can be selected from a drop-down list after clicking on the ADD NEW CASE... button
DEFINE THE ACCELEROGRAM IN SAP2000
The appropriate analysis in presence of accelerograms is a TIME HISTORY case, which can be selected from the drop-down list
DEFINE THE ACCELEROGRAM IN SAP2000
This leads to a more complicated windows, in which few parameters must be input
DEFINE THE ACCELEROGRAM IN SAP2000
In particular:
The load type is an ACCELeration of the ground (first drop-down list)
For a planar model, the ground shaking is generally assumed to happen in the X direction, i.e. Load name U1 (seconddrop-down list)
The records from the PEER website are given in units of g, so the scale factor would be 9.81 m/s2 or 981 cm/s2, depending on the units selected in the model of SAP2000
The number of time steps should be given by the duration of the accelerogram divided by the sampling time:
In our example: 40 s / 0.01 s = 4,000 steps
DEFINE THE ACCELEROGRAM IN SAP2000
RUN THE DYNAMIC ANALYSIS
Once the accelerogram has been defined in SAP2000, it is possible to run the time-history analysis as any other type of analysis.
RUN THE DYNAMIC ANALYSIS
Once the analyses are complete, you can read the pertinent results from tables and diagrams
DISPLAY THE RESULTS
In the next slides the results of the dynamic analysis are shown in terms of:
Axial Force N (left-had side graph)
Bending Moment M (right-hand side graph)
It is worth mentioning that these blue diagrams are the ENVELOPE of the corresponding outputs:
Indeed, in a dynamic analysis we have a value of the structural quantities of interest (e.g. N and M) for each time steps
As engineers, we are generally interested in both minimum and maximum value, i.e. by the “envelope” of these responses
We can also display the same structural quantities in a specific time instant, e.g. at t = 10 s.
In this case, for instance, the red colour in the axial-force diagram means compression, while the yellow colour stands for tension.
DISPLAY THE RESULTS
In order to show the time history of a given
structural response, e.g. The horizontal displacement
of the top floor, you must SELECT from the menu
bar: DISPLAY → SHOW PLOT FUNCTIONS…
DISPLAY THE RESULTS
In our example, we want to display the displacement along the X direction of the joint no. 23, for the time range from 0 to 40 s.
DISPLAY THE RESULTS
In the window with the graph, min and max values of the selected time history are also reported.
DISPLAY THE RESULTS