Important Note - Please Read:

Transcription

1 Important Note - Please Read: This tutorial requires version 6.01 or later of SAFE to run successfully. You can determine what version of SAFE you have by starting the program and then clicking the Help menu and selecting About SAFE... If your version of SAFE is not at least version 6.01 and you want to run this tutorial, then you should call Computers and Structures at (510) for information on upgrading SAFE. 1

2 SAFE Problem 3 One-Way Beam-Slab System With Opening Design Information E = 3600 ksi, Poissons Ratio = 0.2, Unit Weight = 150 pcf f c = 4 ksi, fy = 60 ksi X direction top rebar cover = 2.5 (to rebar centroid) Y direction top rebar cover = 1.5 (to rebar centroid) X direction bottom rebar cover = 1.5 (to rebar centroid) Y direction bottom rebar cover = 2.5 (to rebar centroid) All columns are 12 by 12. Column height below is 10 feet. All beams are 12 wide by 18 deep (12 deep below slab). Design beams as rectanglar beams (not T-beams). Slab is 6 thick. Dead load in addition to self-weight is 35 psf. Live load is 100 psf. To Do Use the ACI code. Review the factored beam moments. Review the calculated beam flexural reinforcing. Note: Dimensions are to column and beam centerlines A B Opening Note: Our intent is that you try this problem on your own first. After you have solved it on your own, you can step through our solution if desired. If you have problems trying to create the model, then follow the steps in our solution. 2

3 SAFE Problem 3 Solution 1. Click the drop down box in the status bar to change the units to kip-ft. 2. From the File menu select New Model From Template. This displays the Slab Templates dialog box. 3. In this dialog box: Click on the Ribbed Slab button to display the Ribbed Slab dialog box. In this dialog box: À In the Along X Direction area verify that 0.5 is entered in the Left Edge Distance and Right Edge Distance edit boxes. À In the Along X Direction area type 1 in the Number of Spans edit box. À In the Along X Direction area verify that 24 is entered in the Spacing edit box. À In the Along Y Direction area verify that 0.5 is entered in the Left Edge Distance and Right Edge Distance edit boxes. À In the Along Y Direction area type 1 in the Number of Spans edit box. À In the Along Y Direction area verify that 24 is entered in the Spacing edit box. À Type.5 in the Slab Thickness edit box. À Verify that 1 is entered in the Column Size (square) edit box. À Type 10 in the Column Height Below edit box. À In the Load area type.035 in the Dead Load (Additional) edit box. Since the units are kips and feet,.035 is equivalent to 35 psf. À In the Load area type.1 in the Live Load edit box. Since the units are kips and feet,.1 is equivalent to 100 psf. À Leave the Create Live Load Patterns check box unchecked. Note: Checking the Create Live Load Patterns check box causes the program to create all sorts of automatically generated skip loading patterns for the live load. These patterns are automatically added to the defined static load cases and are identified with a Load Type called Pattern Live. In addition, these live load patterns are included in the load combinations automatically created for design. 3

4 À In the Joist area type 6 in the Spacing edit box. À In the Joist area verify that the Y Direction option is selected This means that the joists will be defined parallel to the Y- axis.. Note: We will define and assign actual beam/ joist sizes later. À Click the OK button. 4. From the Edit menu select Edit Grid... to display the Define X Grid dialog box. 5. In this dialog box: In the Display area select the Y Grid option. In the Display Grid As area verify that the Ordinates option is selected. Click in the 3rd row of the spreadsheet. In the Grid Line #3 area select the Secondary Line option. Note: Secondary grid lines do not have Grid ID bubbles. We will not specify a Grid ID for these secondary lines. Type 4 in the Coordinate column of the 3rd row of the spreadsheet. Type 20 in the Coordinate column of the 4th row of the spreadsheet. Click the OK button. The model now appears as shown in Figure Delete the center joist (beam) by clicking on it to select it and then pressing the Delete key on the keyboard. 7. Verify that the Snap to Points button on the side toolbar is depressed. Alternatively, you could click on the Draw menu, select Snap To and verify there is a check mark next to Points on the submenu. 8. Click the Snap to Intersections button on the side toolbar. After you click on the button it will remain depressed indicating that this snap option is active. Alternatively, you could click on the Draw menu, select Snap To and click on Intersections in the submenu to activate this snap option. Note: The snap options buttons act like toggle switches. You can use them to turn snap options on or off. If a snap option button appears depressed then that snap option is active. Clicking any snap option button toggles it between active(depressed) and inactive (not depressed). Similarly, the snap option items on the Draw menu act like toggle switches. If a snap option on the Snap To submenu has a check mark next to it 4

5 then that snap option is active. Clicking a snap option on the Snap To submenu toggles the state of that option. J K L M Delete this joist Figure 3-1: Model After Step 5 9. Click the Draw Line Object button on the side toolbar (or select Draw Line Object from the Draw menu). 10. Draw a line object by clicking on the point labeled J in Figure 3-1 and then double clicking on the point labeled K to complete the line object. Note: With the Intersection snap option activated the mouse cursor will snap to the intersection of the beam and grid line at points J and K. Note: We could also single click on the point labeled K and then press the Enter key on the keyboard to complete the line object. 11. Draw a line object by clicking on the point labeled L in Figure 3-1 and then double clicking on the point labeled M to complete the line object. The model now appears as shown in Figure

6 P O Q R Figure 3-2: Model After Step Click the Snap to Intersections button on the side toolbar to deactivate this snap option. 13. Click the Snap to Middle and Ends button on the side toolbar to activate this snap option. 14. Run the mouse cursor along the beam near the point labeled O in Figure 3-2 until the cursor snaps to the midpoint of the beam and a text box which says Mid Point appears. Left click the mouse to start drawing a new beam from this midpoint location. 15. Move the mouse up to the point labeled P in Figure 3-2. Again the mouse cursor will snap to the midpoint of the beam. Double click at point P to finish drawing this beam. 16. Similarly, click on the point labeled Q in Figure 3-2 and then double click on the point labeled R to draw another beam. Note that both points Q and R are at the midpoints of beams. The model now appears as shown in Figure Now we will draw the area object that will define the slab opening. Click the Draw Rectangular Area Object button on the side toolbar (or select Draw Rectangular Object from the Draw menu). 6

7 S U T Figure 3-3: Model After Step Single click on the point labeled S in Figure 3-3 and then double click on the point labeled T to draw the area object. 19. Click the Pointer/Select button to switch from Draw mode to Select mode. 20. Right click near the point labeled U in Figure 3-3 to display the Rectangular Slab Information dialog box for the just drawn area object. 21. In this dialog box: In the Locate Slab area select the By Center option. In the Identification and Location area verify that Center X and Center Y are both 12. These are the X and Y coordinates of the center of the area object. In the Identification and Location area type 11 in the X Dimension and type 15 in the Y Dimension edit boxes. Click the OK button. 7

8 22. Left click near the point labeled U in Figure 3-3 to select the just dimensioned area object. 23. From the Assign menu select Opening. This area is now designated as an opening. 24. Click the drop down box in the status bar to change the units to kip-in. 25. From the Define menu select Slab Properties... to display the Slab Properties dialog box. 26. In this dialog box: In the Slab Property area highlight the property named SLAB and then click the Modify/Show Property button to display the Slab Property Data dialog box. In this dialog box: À In the Analysis Property Data area: ä Verify that the Modulus of Elasticity is ä Verify Poisson s ratio is 0.2. Note: We will verify the unit weight later. ä Verify that the Bending Thickness (X), Bending Thickness (Y) and Twisting Thickness are all 6. Note: These values will all be 6 because we entered the footing thickness in the Ribbed Slab dialog box in Step 3. ä Verify that the Slab Type option is selected. ä Verify that the Thick Plate check box is checked. Note: Checking the Thick Plate check box tells the program to consider slab shear deformations in the analysis. If this box is not checked then slab shear deformations are not included in the analysis. À In the Design Property Data area: ä Verify that the Thickness is 6. ä Type 2.5 in the X Cover Top (to Centroid) edit box. ä Type 1.5 in the Y Cover Top (to Centroid) edit box. ä Type 1.5 in the X Cover Bottom (to Centroid) edit box. ä Type 2.5 in the Y Cover Bottom (to Centroid) edit box. 8

9 ä Verify the Concrete Strength, fc is 4. ä Verify the Reinforcing Yield Stress, fy is 60. ä Verify that the No Design check box is not checked. À Click the OK button twice. 27. From the Define menu select Beam Properties... to display the Beam Properties dialog box. 28. In this dialog box: Click the drop-down box in the Click To area and click on Add Rectangular Beam to display the Property Data For Rectangular Beam dialog box. In this dialog box: À Type XBEAM in the Beam Property name edit box. À In the Analysis Property Data area: ä Verify that the Modulus of Elasticity is ä Verify Poisson s ratio is 0.2. Note: We will verify the unit weight later. ä Verify the width is 12. ä Type 18 in the Depth edit box. À In the Design Property Data area: ä Verify the width is 12. ä Type 18 in the Depth edit box. ä Type 2.5 in the Cover Top (to Centroid) edit box. ä Type 1.5 in the Cover Bottom (to Centroid) edit box. ä Verify the Concrete Strength, fc is 4. ä Verify the Reinforcing Yield Stress, fy is 60. ä Verify the Shear Steel Yield Stress, fys is 60. ä Verify the Concrete Shear Strength, fcs is 4. 9

10 ä Verify that the No Design check box is not checked. À Click the OK button. Click the drop-down box in the Click To area and click on Add Rectangular Beam to display the Property Data For Rectangular Beam dialog box. In this dialog box: À Type YBEAM in the Beam Property name edit box. À In the Analysis Property Data area: ä Verify that the Modulus of Elasticity is ä Verify Poisson s ratio is 0.2. Note: We will verify the unit weight later. ä Verify the width is 12. ä Type 18 in the Depth edit box. À In the Design Property Data area: ä Verify the width is 12. ä Type 18 in the Depth edit box. ä Type 1.5 in the Cover Top (to Centroid) edit box. ä Type 2.5 in the Cover Bottom (to Centroid) edit box. ä Verify the Concrete Strength, fc is 4. ä Verify the Reinforcing Yield Stress, fy is 60. ä Verify the Shear Steel Yield Stress, fys is 60. ä Verify the Concrete Shear Strength, fcs is 4. ä Verify that the No Design check box is not checked. À Click the OK button twice. 29. Click the drop down box in the status bar to change the units to kip-ft. 30. From the Define menu select Slab Properties... to display the Slab Properties dialog box. 10

11 31. In this dialog box: In the Slab Property area highlight the property named SLAB and then click the Modify/Show Property button to display the Slab Property Data dialog box. In this dialog box: À Verify that the unit weight is À Click the OK button twice to exit all dialog boxes. 32. From the Define menu select Beam Properties... to display the Beam Properties dialog box. 33. In this dialog box: In the Beam Property area highlight the property named XBEAM and then click the Modify/Show Property button to display the Property Data For Rectangular Beam dialog box. In this dialog box: À Verify that the unit weight is À Click the OK button. In the Beam Property area highlight the property named YBEAM and then click the Modify/Show Property button to display the Property Data For Rectangular Beam dialog box. In this dialog box: À Verify that the unit weight is À Click the OK button twice to exit all dialog boxes. 34. Click in the plan view window titled Slab Properties to make sure it is active. When the window is active its title bar is highlighted. 35. Click the Select All button on the main toolbar to select all elements. 36. From the Assign menu select Beam Properties... to display the Beam Properties dialog box. 37. In this dialog box: In the Beam Property list box click on YBEAM to highlight it. Click the OK button. The model now appears as shown in Figure

12 V Figure 3-4: Model After Step Select the four X-direction beams that are circled in Figure 3-4 by clicking on them. 39. From the Assign menu select Beam Properties... to display the Beam Properties dialog box. 40. In this dialog box: In the Beam Property list box click on XBEAM to highlight it. Click the OK button. 41. Right click somewhere on the slab area object not in the opening, for example at the point labeled V in Figure 3-4 to display the Rectangular Slab Information dialog box. 42. In this dialog box: Note that the Slab Property is SLAB and recall that we have already defined these properties. 12

13 Note that the Load Case drop-down box says DEAD and that the associated w/area edit box says This is the dead load we initially input (see step 3). Select LIVE from the Load Case drop-down box and note that the associated w/area edit box says 0.1. This is the live load we initially input (see step 3). Click the OK button. 43. From the Options menu select Preferences... and then select the Concrete Tab. 44. In this dialog box: Verify that ACI is selected in the Concrete Design Code drop-down box. Verify that in the Reinforcement Results Units area the Sq-in and Sq-in/ft option is selected. Click the OK button. 45. On the Design menu choose Select Design Combos to display the Design Load Combinations Selection dialog box. 46. In this dialog box: In the Design Combos list box click on DCON2 to highlight it and then click the Show button. Note that this load combination is defined as 1.4DL + 1.7LL. Also note that the Use For Design check box is checked. Note: SAFE automatically creates design load combinations based on the selected design code and on the static load types. In this case where the defined static load types are DEAD and LIVE (see Static Load Cases on the Define menu) and the design code is ACI , the program automatically creates two load cases. They are 1.4DL (DCON1) and 1.4DL + 1.7LL (DCON2). If we wanted to add an additional design load combination we could define it by selecting Load Combinations... from the Define menu and then clicking the Add New Combo button, to display the Load Combination data dialog box. In this dialog box we can define the load combination and we can check the Use For Design check box if we want the load combination to be used in design. Click the OK button twice to exit all dialog boxes. 47. From the Analyze menu select Set Options to display the Analysis Options dialog box. 48. In this dialog box: 13

14 In the Analysis Type area verify that the Normal option is selected. Accept the default maximum mesh dimension of 4 feet. Note: To automatically mesh the model the program first develops a mesh that is broken at each grid line, at the edge of any area objects, at the ends of each line object and at each point object. If the dimension of any elements meshed in this manner exceeds the specified maximum mesh dimension then those elements are subdivided such that the maximum mesh dimension is no longer exceeded. Note: In general, the maximum mesh size should be based on the span length. It is good practice to have at least four elements in a span, and generally it is not necessary to have more than eight elements in a span. Thus if the typical span length is less than sixteen feet, it may be advisable to reduce the default maximum mesh size to something less than 4 feet. In this example we are accepting the default maximum mesh of four feet. This means that the slab spanning between beams will be modeled using two elements which is less than the four elements recommended in the previous paragraph. If the accuracy of the slab results (moments, etc.) were important to us then we might want to reduce the maximum mesh size to 1.5 feet. Note: The mesh automatically generated by the program can be viewed by clicking the Set Objects button on the main toolbar (or selecting Set Object Options... from the View menu) to display the Set Objects dialog box, checking the Show Mesh check box in the Options area, and clicking the OK button. You can turn off the display of the mesh by unchecking this box. Click the OK button. 49. Click the Run Analysis button on the main toolbar (or select Run Analysis from the Analyze menu). 50. When the initial analysis is complete check the messages in the Analysis window (there should be no warnings or errors) and then click the OK button to close the Analysis window. 51. Click the Show Beam Forces button on the main toolbar (or select Show Beam Forces... from the Display menu) to display the Beam Forces dialog box. 52. In this dialog box: Select DCON2 Combo from the Load drop-down box. In the Component area select the Moment option. 14

15 In the Display options area check the Show Values check box. Note that if the Fill Diagram check box is checked you will have to uncheck it before you can check the Show Values box. Click the OK button to display the moment diagrams. 53. Run the mouse cursor over the beams and read the moment values from the left-hand side of the status bar at the bottom of the SAFE window. 54. If you want to view beam force results for other force components then repeat steps 51 through On the Design menu select Start Design. When the design is complete the calculated X- strip reinforcement is displayed in square inches. 56. From the Design menu select Display Beam Design Info... to display the Beam Reinforcing dialog box. 57. In this dialog box: In the Type of Reinforcing area verify that the Flexural option is chosen. In the Reinforcing Values area verify that the Show Rebar Values at Controlling Station check box is checked. In the Reinforcing Values area verify that the Show Rebar Values at Every Station check box is not checked. Accept the other default values in this dialog box. Click the OK button. 58. Run the mouse cursor over the beams and read the flexural steel values from the left-hand side of the status bar at the bottom of the SAFE window. 15