Time History Analysis With Recorded Accelerograms

41,107 views

Published on

Published in: Education, Technology
13 Comments
24 Likes
Statistics
Notes
No Downloads
Views
Total views
41,107
On SlideShare
0
From Embeds
0
Number of Embeds
3,001
Actions
Shares
0
Downloads
1,952
Comments
13
Likes
24
Embeds 0
No embeds

No notes for slide

Time History Analysis With Recorded Accelerograms

  1. 1. Time-history seismic analysis with SAP2000 A step-by-step guide for BEng/MEng/MSc students familiarizing with this piece of software
  2. 2. List of Content <ul><li>Download recorded accelerograms from the PEER database </li></ul><ul><li>Upload a selected accelerogram to SAP2000 </li></ul><ul><li>Run the time-history analysis and display the results </li></ul>
  3. 3. DOWNLOAD ACCELEROGRAMS FROM THE PEER DATABASE <ul><li>Step #1 </li></ul>
  4. 4. PEER Strong Ground Motion Database <ul><li>The P acific E arthquake E ngineering R esearch (PEER), headquartered at the University of California at Berkeley , makes available online over 10,000 strong ground motion records from 173 different earthquakes </li></ul><ul><li>http://peer.berkeley.edu/ </li></ul>
  5. 5. PEER Strong Ground Motion Database <ul><li>The database in entirely searchable </li></ul><ul><li>http://peer.berkeley.edu/nga/ </li></ul><ul><li>As an example, we want to download the accelerogram recorded during the Imperial Valley 1940 earthquake </li></ul><ul><ul><li>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” </li></ul></ul><ul><ul><li>Then we can SEARCH </li></ul></ul>
  6. 7. Find the accelerogram <ul><li>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 </li></ul><ul><ul><li>If we scroll down, the links to the three components of the accelerogram (180°, 270° and vertical) appear </li></ul></ul>
  7. 9. Download the time history of the ground acceleration <ul><li>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 </li></ul>
  8. 10. <ul><li>The first four lines contain general pieces of information about the record, namely: </li></ul><ul><ul><li>Location: “Imperial Valley” </li></ul></ul><ul><ul><li>Date: 19 th May 1940 </li></ul></ul><ul><ul><li>Time: 4:39am </li></ul></ul><ul><ul><li>Station: “El Centro Array #9” </li></ul></ul><ul><ul><li>Direction: Horizontal, 180° </li></ul></ul><ul><ul><li>Units of acceleration: g= 9.81 m/s 2 (acceleration of gravity) </li></ul></ul><ul><ul><li>Number of time instants: 4,000 </li></ul></ul><ul><ul><li>Sampling time: Δ t= 0.01 s (f= 100 Hz) </li></ul></ul>Download the time history of the ground acceleration
  9. 11. <ul><li>The other lines list the ordinates of the record (in units of g), which must be read from left to right, row by row </li></ul>Download the time history of the ground acceleration
  10. 12. <ul><li>Importantly, the web browser (Explorer, Firefox and etcetera) allows to save this page as a TXT file (you may need to manually change the extension) </li></ul>Download the time history of the ground acceleration
  11. 13. UPLOAD ACCELEROGRAMS TO SAP2000 <ul><li>Step #2 </li></ul>
  12. 14. Define the accelerogram in SAP2000 <ul><li>An accelerogram is basically the time-history of the acceleration experienced by the ground in a given direction during a seismic event </li></ul><ul><li>We need to input the accelerogram as a generic function defined in SAP2000 starting from a TXT file </li></ul><ul><li>Once the mechanical model of the structural system under investigation has been created, SELECT from the menu bar: </li></ul><ul><li>DEFINE -> FUNCTIONS -> TIME HISTORIES... </li></ul>
  13. 16. Define the accelerogram in SAP2000 <ul><li>The accelerogram must be uploaded to SAP2000 as FUNCTION FROM FILE , an option which can be selected from the drop-down list </li></ul>
  14. 17. Define the accelerogram in SAP2000 <ul><li>We can select: </li></ul><ul><ul><li>Name of the function (e.g. EL_CENTRO_1940) </li></ul></ul><ul><ul><li>Location of the file by using the button BROWSE... </li></ul></ul><ul><ul><li>Number of lines to skip (4 for the PEER database) </li></ul></ul><ul><ul><li>Number of points per line (5 for the PEER database) </li></ul></ul>
  15. 18. Define the accelerogram in SAP2000 <ul><li>By clicking on DISPLAY GRAPH we can visually check the waveform </li></ul>
  16. 19. Define the accelerogram in SAP2000 <ul><li>In order to be used in a seismic simulation, the waveform previously defined must be properly assigned to an ANALYSIS CASE </li></ul><ul><li>To do this, SELECT from the menu bar: </li></ul><ul><li>DEFINE -> ANALYSIS CASES... </li></ul>
  17. 21. Define the accelerogram in SAP2000 <ul><li>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 </li></ul>
  18. 22. Define the accelerogram in SAP2000 <ul><li>The appropriate analysis in presence of accelerograms is a TIME HISTORY case, which can be selected from the drop-down list </li></ul>
  19. 23. Define the accelerogram in SAP2000 <ul><li>This leads to a more complicated windows, in which few parameters must be input </li></ul>
  20. 24. Define the accelerogram in SAP2000 <ul><li>In particular: </li></ul><ul><ul><li>The load type is an ACCEL eration of the ground (first drop-down list) </li></ul></ul><ul><ul><li>For a planar model, the ground shaking is generally assumed to happen in the X direction, i.e. Load name U1 (seconddrop-down list) </li></ul></ul><ul><ul><li>The records from the PEER website are given in units of g, so the scale factor would be 9.81 m/s 2 or 981 cm/s 2 , depending on the units selected in the model of SAP2000 </li></ul></ul><ul><ul><li>The number of time steps should be given by the duration of the accelerogram divided by the sampling time: </li></ul></ul><ul><ul><ul><li>In our example: 40 s / 0.01 s = 4,000 steps </li></ul></ul></ul>
  21. 25. RUN THE ANALYSIS AND DISPLAY THE RESULTS <ul><li>Step #3 </li></ul>
  22. 26. Run the dynamic analysis <ul><li>Once the accelerogram has been defined in SAP2000, it is possible to run the time-history analysis as any other type of analysis </li></ul>
  23. 27. Run the dynamic analysis <ul><li>Once the analyses are complete, you can read the pertinent results from tables and diagrams </li></ul>
  24. 28. Display the results <ul><li>In the next slides the results of the dynamic analysis are shown in terms of: </li></ul><ul><ul><li>Axial Force N (left-had side graph) </li></ul></ul><ul><ul><li>Bending Moment M (right-hand side graph) </li></ul></ul><ul><li>It is worth mentioning that these blue diagrams are the ENVELOPE of the corresponding outputs: </li></ul><ul><ul><li>Indeed, in a dynamic analysis we have a value of the structural quantities of interest (e.g. N and M) for each time steps </li></ul></ul><ul><ul><li>As engineers, we are generally interested in both minimum and maximum value, i.e. by the “envelope” of these responses </li></ul></ul>
  25. 30. Display the results <ul><li>We can also display the same structural quantities in a specific time instant, e.g. at t = 10 s ... </li></ul><ul><ul><li>In this case, for instance, the red colour in the axial-force diagram means compression, while the yellow colour stands for tentions </li></ul></ul>
  26. 32. Display the results <ul><li>In order to show the time history of a given structural response, e.g. The horizontal displacement of the top floor, you mus SELECT from the menu bar: </li></ul><ul><li>DISPLAY -> SHOW PLOT FUNCTIONS... </li></ul>
  27. 34. Display the results <ul><li>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 </li></ul>
  28. 35. Display the results <ul><li>In the window with the graph, min and max values of the selected time history are also reported </li></ul>

×