time history analysis with sap2000 · upload accelerograms to sap2000 step #2 define the...

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)


The other lines list the ordinates of the record (in units of g), which must be read from left to right, row by row


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)


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


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)


By clicking on DISPLAY GRAPH we can visually check the waveform


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...


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


The appropriate analysis in presence of accelerograms is a TIME HISTORY case, which can be selected from the drop-down list


This leads to a more complicated windows, in which few parameters must be input


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


RUN THE ANALYSIS AND DISPLAY THE RESULTS

Step #3

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

DISPLAY THE RESULTS

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

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

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

Thanks for Your Attention

and

Success for Your Study!

time history analysis with sap2000 · upload accelerograms to sap2000 step #2 define the...

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