Click on the Next Case/Step button, , and the Previous Case/Step button, , to cycle through the seven static

load cases. Rotate, pan, and zoom as necessary to clearly see the force diagrams in the various members.

12. As you are viewing the various cases, observe the following:

• Compressive (negative) axial forces display as red and tensile (positive) axial forces display as yellow. (These colors can be changed using the Options menu > Col-ors > Output command.)

• In 3-D views, compressive (negative) axial forces plot in the negative local 2 direction for each element, and ten-sile (positive) axial forces plot in the positive local 2 di-rection. Note that these directions differ from column to column since we rotated four of the columns.

13. Note the large axial forces in the braces for cases

“QUAKEY1” and “QUAKEY2”.

14. Right click on any column object. (If necessary, turn off the snap-to-points option by clicking the Snap to Points button on the left toolbar.) This will open the Axial Force Diagram form that shows a detailed axial-force diagram for that ob-ject.

15. Click the title bar of this form, and while holding down the left mouse button, move the mouse to drag the form away from the structure for clearer viewing.

Display Frame Axial Forces 4 - 15 16. At the bottom of this form is an edit box showing the dis-tance from the bottom to be “0”, and the corresponding value of axial force at this location. This location is also indicated by the red dot in the diagram in the middle of the form, and by the red dot on the blinking column object on the structure.

17. Move the mouse cursor left and right in the picture box con-taining the diagram. As the red dot moves, the values of dis-tance and axial force at the bottom of the form will change.

18. Click in the distance edit box on this form, and enter a value of “50”. The red dot will move and the axial force value will change correspondingly, as shown in the figure above.

19. Observe that there is a region at one or both ends of the col-umn object where no axial force is displayed. These are the end offsets of the member, and correspond to the portion of the object that overlaps the depth of the connected beams.

These lengths have been automatically calculated by the program (you also have the option to manually assign these lengths.)

Note:

See the section titled “Frame Rigid Offset Assignments to Line Objects”

in Chapter 14 of the User’s Manual for additional in-formation.

Display Frame Axial Forces, Step 18 Axial force diagram for load case “DEAD”.

4 - 16 Display Frame Axial Forces

20. Right click on another line object. The Axial Force Dia-gram form will update to show the diaDia-gram for the new ob-ject. Note that the axial forces are zero for all beams because they are constrained against deformation by the floor dia-phragms.

21. Click the Close Window button, , in the upper right cor-ner of the Axial Force Diagram form to close the form, or click anywhere in the display window.

22. Click the Elevation View button, , on the top toolbar, select Elevation “1”, and click OK.

23. Note that in 2-D views, the axial force is always visible even if the local 2 axis is perpendicular to the viewing plane, as it is for column “C7” on grid line “C”.

24. Click the Perspective Toggle button, , repeatedly to change between 2-D and 3-D views and observe how the orientation of the axial force plot differs in these two types of views. Return to the 2-D view.

25. Zoom into the middle bay of the bottom story so we can look at the pier and spandrel forces.

26. Click the Set Building View Options button, , on the top toolbar. Uncheck the Column (Line) and Beam (Line) boxes under Object Present in View. Check the Pier Axes box under Piers and Spandrels. Click OK to close the form.

27. Observe the following about the piers and spandrels:

• Each pier and spandrel has a set of local axes similar to frame members; these axes are largely independent of the local axes of the wall.

• The local 1 axis of a pier connects the centroid of the bottom edge of the pier to the centroid of the top edge.

• The local 1 axis of a spandrel connects the centroid of one side of the spandrel (e.g., the left edge) to the

cen-Display Frame Axial Forces 4 - 17 troid of the other side (e.g., the right edge.) These axes are not currently being displayed.

• The local 2 axis is in the plane of the wall. The local 3 axis is normal to the wall.

• The abscissa of the force diagram for a pier or spandrel is plotted along the local 1 axis, using exact force values at the two ends and linear interpolation in between.

• The force output display conventions for piers and span-drels are identical to those for frame members.

28. To see a detailed axial force diagram, right-click on the pier or spandrel, as shown in the figure above.

29. Click the Close Window button, , in the upper right cor-ner of the Axial Force Diagram form to close the form.

30. Finally, let’s examine how we can show the force values di-rectly on the structure:

Display Frame Axial Forces, Step 28 Axial force diagram for load case “DEAD”, showing piers and spandrels.

4 - 18 Display Frame Axial Forces

• Click the 3D View button, , on the top toolbar.

• Click the Set Building View Options button, , on the top toolbar. Click the Defaults button. Click OK to close the form.

• Click the Display Member Force Diagram button, , on the top toolbar to open the Member Force Diagram for Frames form.

• Uncheck the Fill Diagram box.

• Check the Show Values on Diagram box.

• Click OK to close the form.

• Rotate, pan, and zoom as necessary to see some values.

• Click the Elevation View button, , on the top tool-bar, select Elevation “2”, and click OK.

Display Frame Axial Forces, Step 30 Axial force diagram showing values on the di-rectly on the structure for Elevation “2”.