Attic Truss: TrusCAD Square Room Input (Available for use with VIEW, VIEW-Plus and ProVIEW) 

Square rooms may be created in a truss when the Collar Tie (attic room ceiling member) frames to the Knee Walls somewhere below the location where the Knee Wall meets the top chord.  Of the 3 Attic Truss Types available (ATIC, HIP ATIC, & GAMBREL), plating of the Collar Tie to the Knee Wall is only possible when using the ATIC and HIP ATIC Truss Types.

Truss Input

1.   Start a new truss by selecting the New icon , the Truss option from the main menu toolbar, or by pressing the <Ctrl+N> keyboard buttons. 

2.   Select the Truss Type (ATIC or HIP_ATIC) using either the browse button or the drop-down toggle list (Figure-V.01).

Figure-V.01

3.     Complete the entry of information in the remaining fields, including the Bearing, Loading, Wind Load, and Overhangs tab dialog windows, and then click the OK button to continue.

4.   The Attic dialog window window is displayed (Figure-V.02), which allows you to enter the configuration for the Attic Truss.  Enter the criteria for the following fields:

Figure-V.02

  Pitches: The Pitch of the Attic Truss TC.

  Lengths: The horizontal lengths necessary to establish the size of the Attic room space based on the diagram in the dialog window (Figure-V.02).  For ATIC trusses there are two horizontal input lengths required: an L1 length, which is the BC distance from the Heel to the inside of the Knee Wall, and an L2 length, which is the BC distance between the inside of the Knee Walls.  Each of these distances entered in the Lengths field is separated by a space.

!                 Note: by entering a question mark character (?) for the L1 length, followed by a dimension entry for the room size, VIEW automatically centers the Attic room space in the truss span.  For example, a Length entry of ? 12 centers a 12-0 room space in the Attic Truss span.

For HIP-ATIC trusses there are three horizontal input lengths required: the L1 length is the TC distance from the Heel to the Hip pitch break, also referred to as the Setback distance.  L2 is the BC distance from the Heel to the inside of the Knee Wall, and L3 is the BC distance between the inside of the Knee Walls.  Each of these distances entered in the Lengths field is separated by a space.

!                 Note: by entering a question mark character (?) for the L2 length, followed by a dimension entry for the room size, VIEW automatically centers the Attic room space in the truss span.  For example, a Length entry of 15 ? 12 sets a 15-0 TC setback, then centers a 12-0 room space in the Attic Truss span.

  Heights:  This vertical dimension establishes the ceiling clearance between the top of the BC and the bottom of the Collar Tie.  This enables you to position the Collar Tie anyplace within the height of the Knee Wall.

!                 Note: If the Room BC Size field is set to be a larger size than the BC Size field, and the room height must be a specific height, the difference in BC material sizes needs to be considered for the height dimension, since the room height is based on the BC Size field setting.  For example, if the BC Size is set to 2x6, and the Room BC Size is set to 2x8, and you want a room height of 8-0-0, you must enter a height dimension of 8-1-12, since 1 is the difference in size between a 2x6 and a 2x8.

  Collar Tie Size: The size of the member used to form the ceiling of the Attic room space.

  TC Size: The size of the Attic Truss TC.

  BC Size: The size of the Attic Truss BC.

  Knee Wall Size: The size of the vertical member which forms the wall of the Attic room space.

  Room BC Size: The size of the BC in the Attic room space.

  Continuous Bottom Chord or Omit BC-Floor, L/R Bearing Pinned button:  Click this button to toggle between the two selection options.

v  Continuous Bottom Chord: This button selection causes there to be a Room BC included in your Attic Truss room space (Figure-V.03).  Refer to Figure-V.02 for the button location.

Figure-V.03

v  Omit BC-Floor, L/R Bearing Pinned: This button selection prevents the application of a Room BC in the Attic Truss room space, and automatically applies interior bearings under the BC at the Knee Walls (Figure-V.04). It also disables (read-only) the Room BC Size field setting. 

Figure-V.04

!                       Note: The dimension entered in the Heights dimension field is measured from the bottom of the BC, to the bottom of the Collar Tie when the Room BC is omitted.

Once you have made your field selections, click the OK button to continue.

5.   The Web Pattern dialog window now appears.  Select the web pattern for each of the Attic Truss web zones from the Web Patterns dialog window.  As each zone pattern is selected, VIEW automatically opens another dialog window for the next web zone pattern to be selected (Figure-V.05), until all zone web patterns are chosen.

Figure-V.05

6.   You are now ready to begin the Attic Truss analysis.  Once the analysis begins, VIEW automatically prompts you for the Attic Truss room space loading (Figure-V.06).  The default Attic loading is: Live load floor = 40 psf, Dead load floor = 10 psf, Dead load ceiling = 10 psf, and Knee wall load = 10 psf.  You may change any of these fields as necessary.  Click the OK button to continue the analysis.

Figure-V.06

7.      Save the truss to the job when satisfied with your Attic Truss design.

 

See Also: