Drop-in Cantilevered Beam System. (Gerber System)

Transcription

1 Drop-in Cantilevered Beam System (Gerber System)

2 Introduction The following example illustrates how to design a three-span glulam roof beam, using cantilever and suspended span construction, with WoodWorks SIZER A preliminary design is drawn using SIZER s Concept Mode, then checked in Beam Mode The presentation is made up of instructional slides and screen captures

3 Given Values and Assumptions Beam Spacing = 40 ft Beam Span = 33 ft Flat roof with no ceiling Dead Load = 18 psf Live Load = 32 psf Flat roof trusses provide full lateral support

4 Step 1: Settings Start a new WoodWorks Sizer project in Concept Mode Using the Settings menu, set the snap increment to 1 and the viewing area to 100 by 133 ft

5

6 Step 2: Layout Grid In Concept Mode, beams, joists, columns, and walls are positioned in relation to grid points Click Grid View button Place cursor slightly above the horizontal ruler and click left mouse button to create vertical grid lines A, B, C, D and E at X = 0, 10, 43, 76, and 109 ft respectively Similarly, create vertical grid lines F and G at X= 38 and 43 ft Place cursor slightly to right of the vertical ruler and click left mouse button to create horizontal grid lines at Y = 10, 50 and 90 feet

7 Note: Grid lines can be moved by selecting and dragging or by selecting and entering the new position in the text box labeled X or Y

8 Step 3: Draw Columns Click on Column View button Point cursor at grid intersection B-2 and click left mouse button to create a column Draw columns where vertical grid lines B, C, D and E intersect the horizontal grid lines (see next slide)

9

10 Step 4: Define Beam Groups Select Beam View button Click Material Design Groups button The Beam Design Groups form will open (see next slide) Using the form, define a design group, named Cantilever, using a Glulam Reverse material assign the group a load transfer # = 0 The load transfer # is used to define how beams are supported - beams can be supported by other beams with lower load transfer numbers (or by any column) Define a second group named Suspended, using a Glulam material assign the group a transfer # = 1

11

12 Step 5: Draw Beams From the Groups pull-down menu (to right of printer icon), select Cantilever group Draw cantilevered beam B1: Click grid point F-4, hold left mouse button, drag cursor to G-4 and release Draw beam B2 from point F-3 to G-3 and beam B3 from point F-2 to G-2 Select Suspended group from the Groups pulldown and draw the suspended beams as shown (next slide)

13

14 Step 6: Define Parallel Truss Group Select Joist View icon Click Material Design Groups button The Joist Design Group form will open Define a group named PCTrusses De-activate the checkmark beside This group to be designed by WoodWorks SIZER (top-left of form)

15

16 Step 7: Draw Trusses Select PCTrusses from the Groups pull-down Draw Joist Area J1 by clicking its four corners in sequence: B4, F4, F3 and B3 In the same way, draw Joist Bays J2 to J6 as shown (next slide)

17

18 Step 8: Define Loads Click Load View button Define the dead load: From the Load Type pull-down (beside printer icon) choose Dead Area and enter a magnitude of 18 psf in the adjacent text box In sequence click the four corners of the load area: B-4, E-4, E-2, and B-2 Define the live load: Change load Type to Live Area and enter 32 psf as its magnitude In sequence click the four corners of the load area: B-4, E-4, E-2, and B-2

19 Step 9: Preliminary Design Click Run button (calculator icon) Results by Group report is shown preliminary member section sizes are given for the Cantilever and Suspended beam groups Note that for Cantilever group of the current example, Concept mode suggests trying a 6-3/4 by 34.5 inch section of 16F- V6 VG.West DF Glulam Reverse (shear is critical

20

21 Step 10: Check Design In Concept Mode, live loads are assumed to be distributed over the entire loading area. To check the effect of patterning live loads, use Beam Mode: Click Beam View Select Cantilever Beam B2 (the center beam) Click the Switch Modes icon (top left icon) to activate Beam Mode Click Loads View (downward arrows icon) to view the loads transferred from the joists and suspended beams Activate the pattern loading check for each of the snow loads

22 Activate pattern loading for snow loads - Select load, click Pattern Loading check, then click Modify

23 Check Design (cont d) Click Beam View to view the material properties Enter the section size suggested in Concept Mode (i.e. depth = 6-3/4 in., width = 36-1/2 in. Click Run Design to view Design Check Note that the design check shows that if snow loads are patterned with full load over the center span and half loads over the cantilevers, the section barely fails due to positive bending, f b /F b = 1.04 Click View Diagrams to see the Bending Moment Diagram

24

25

26 Step 11: Modify Design Positive bending on the mid-span of the cantilevered beam can be reduced by increasing the length of the cantilevers: Close Beam Mode and Return to Concept Mode Change the Snap Setting to 1 inch Select Grid View Select Gridline F and change its position to 37 9 using the text box labeled X Select Gridline G and change its position to 81 3 The cantilevers have now been stretched to 5 3 (from the original 5 )

27

28 Step 12: Check Modified Design Select the cantlivered beam B2 and click Switch Modes to activate Beam Mode Click Loads View and activate pattern loading for live loads Click Run to show the Design Results Report Select the 6-3/4 by 36-1/2 section from the Select a Section pull-down (top right) The Design Check Calculation Sheet now shows that the section passes (with the longer cantilevers)

29

30