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Roof Rafter Design Module Walk-through

Starting Out

To start a roof rafter design first click on the roof rafter design module icon located in the design module dropdown in the upper right of the screen next to your username.

This will load the roof rafter design module, which loads with a preset template.


The following steps do not have to be completed in this order and are designed to work dynamically with each other, so don't worry if you realized later you clicked the wrong thing or made a mistake, just change that item and the rest will follow suit accordingly.

Set the Properties

On the left side of the screen is the Properties tab, work progressively from top to bottom to specify the desired properties. The template is used to set predetermined properties. As you move down the properties new selection dropdowns will appear based on previous dropdown selections. Examples of this can seen for any of the material selections. When Steel is selected as the material, a different set of properties selections are available.

At the top of the properties tab is the LRFD/ASD design options, as well as the dry or wet factors button. The pictures above shows LRFD and Dry. The picture below shows ASD and wet. Click the icons to toggle back and forth between the two options for each.

Below is a list of the properties selections based on the material type. Use each of these to guide you through the selection process.

Solid Sawn & MSR/MEL Selection

  • (Species) Select the species of wood
  • (Grade) Select the grade of lumber *can be skipped for autosize
  • (Include Self Weight) Check for including the self weight of the member
  • (Check Unbalanced Live Load) (ASCE 7.16 Section 4.3.3) Check to cycle through the live loads being placed on each span in every combination of spans
  • (Concentrated Live Load) (ASCE 7-16 Section 4.4)  A concentrated load is placed along the roof rafter (interval spacing can be set in settings) and the worst case placement of the concentrated live load is chosen for each load combination.

Size

  • Input or select the number of laminations, width, depth of the roof rafter *can be skipped for autosize
  • Input or select the on-center spacing of the rafters
  • Input the roof pitch

Options

  1. (Flitch Plate) Check to add a flitch plate to the roof rafter, if selected a new section will appear below the selection where you can complete the the thickness and number of flitch plates, see image below.
  2. (Round) Select if the roof rafter is round, if selected the size option will revert to a radius only instead of width and depth, see image below.
  3. (Flat Use) Select if the roof rafter will be used in the flat orientation

Factors

  • (Temperature Factor) Select the temperature range of the design
  • (Repetitive Use) Select to apply the repetitive use factor
  • (Apply the Incising Factor) Select to include the incising factor
  • (Include Creep Factor) Apply to include the creep factor

Deflections

  • (Live load deflection) Set the live load deflection limit which is in the form of (Span Length) / (Deflection Limit)
  • (Total load deflection) Set the total load deflection limit which is in the form of (Span Length) / (Deflection Limit)

Elevation

  • (Left) Input the Left elevation
  • (Right) Input the Right elevation

Glulam Selection

  • (Stress Class) Select the stress class
  • (Grade) Select the grade
  • (Include Self Weight) Check for including the self weight of the roof rafter
  • (Check Unbalanced Live Load) (ASCE 7.16 Section 4.3.3) Check to cycle through the live loads being placed on each span in every combination of spans
  • (Concentrated Live Load) (ASCE 7-16 Section 4.4)  A concentrated load is placed along the roof rafter (interval spacing can be set in settings) and the worst case placement of the concentrated live load is chosen for each load combination.
  • (Curved Glulam) Select for a curved glulam analysis, which includes radial stress checks.  Input the curvature radius

Size

  • Input or select the number of laminations, width, depth of the roof rafter *can be skipped for autosize
  • Input or select the on-center spacing of the rafters
  • Input the roof pitch

Factors

  • (Temperature Factor) Select the temperature range of the design
  • (Include Creep Factor) Apply to include the creep factor

Deflections

  • (Live load deflection) Set the live load deflection limit which is in the form of (Span Length) / (Deflection Limit)
  • (Total load deflection) Set the total load deflection limit which is in the form of (Span Length) / (Deflection Limit)

Elevation

  • (Left) Input the Left elevation
  • (Right) Input the Right elevation

Structural Composite Lumber (SCL) Selection

  • (Species) Select the SCL manufacturer
  • (Grade) Select the SCL product/size

Size

  • Input or select the number of laminations, width, depth of the beam *can be skipped for autosize
  • Input or select the on-center spacing of the rafters
  • Input the roof pitch

Steel Selection

  • (Shape) Select the shape
  • (Size) Select the size of the shape
  • (Grade) Select the grade of steel

Below is an image of the entire properties tab if Steel is selected as the material.

Adding and Deleting Spans

After the material and properties of the roof rafter are chosen move to the middle panel of the screen to edit the roof rafter span, reactions, and start the loading process.

To add or remove a span use the + and X icons shown by the image below to add or delete a span on either side.

When the plus button is selected, it will bring up the New Span input box. Type in the span distance you would like to add, specify the top and bottom unbraced lengths, and click save to add the new span. Clicking exit will not add a span and will return to the exact spot before the add span was selected.

To delete a span simply click the X icon below the plus. Additionally spans can be edited and deleted using the span cards on the lower toolbar across the bottom of the screen.

Edit Reactions 

In the middle panel of the screen, the reactions of the roof rafter are buttons therefore clicking the reaction itself will bring up the edit reactions input box. Here the available reactions can be selected to be changed based on the desired design. Each reaction icon will update the boundary conditions to correspond with the reaction type.

Adding Loads

After the materials, properties, spans, and reactions of the roof rafter are chosen move to the middle panel of the screen to start the loading process. 

Here you can add any type of load listed on the left hand side of the middle panel as shown in the image below (Distributed, Trapezoidal, Point, Axial, Moment, and Linked). 

Once a load icon is selected an input box will appear where you can enter the loading data. As shown in the example "Add Uniform Load" input box, the load end will automatically populate with the span length, the end can be edited to be any distance shorter than the total length.

After load input click "Add" and the load will be added to the roof rafter.


Once the load is added it can be manipulated in two different ways.  You can change the load by clicking on it which will bring back the load input box or you can change the load by locating the loads tab on the bottom of the screen.   

To add an out of plane load simply change the axis on the load input box or in the load cards. Select the axis icon in the upper left corner of the load screen to switch the view and see the out of plane loads.

Another useful tool is the toolbar located between the location name and the loading screen.

Each icon corresponds to a load type, the furthest left icon shows all load types. Clicking any of the others will only show loads of that specific type.

Calculators

The toolbar on the right side of the loading screen is where the calculators are located. These are some handy tools used to facilitate a faster design process, and save you time!

From top to bottom the calculators are as follows:

Dead Load Calculator

Coming Soon!

Tributary Width Calculator

Use the input boxes to enter the load type, load axis, and load psf value for each side of the roof rafter. In the tributary width section enter the distance from each side of the roof rafter. The location section is the same as the load start and load end. The resulting distributed load will be added to the roof rafter accordingly.

Roof Rafter Calculator

The roof rafter calculator is used for quick and easy loading of a typical roof rafter design.

Roof Rafter Wizard

The roof rafter wizard allows for quick, easy, and dynamic design information input for typical rafter framing.


Calculate

Once the roof rafter is loaded you can hit enter to calculate or click the calculate icon located above the properties tab on the right hand side.

From left to right the buttons are Calculate, Autosize, and Save. After calculating the Print Preview icon will appear.


Auto Size

Using the autosize function can be done dynamically, but following this order is good for first time users.

  1. These two buttons are check all and uncheck all respectively, use these to select or deselect all the grades.
  2. Check to ensure the sizing properties are okay and make any changes based on your desired design. Input any restrictions to limit the results.
  3. Use the button below the grades run the autosizer and select the size and grade which best suits your design.

Results

After calculation the adequacy cards will appear in the lower toolbar across the bottom of the screen.

If any of the calculations fail, the percentages will turn red. The controlling load combination is shown directly under the adequacy percentage. Clicking the load combo will result in showing the corresponding diagrams on the right side of the screen. The dropdown showing the load combo can be switched to any of the load combinations used in the calculations. The quick view can be switched to any of the loaded axis as well.

After successfully calculating, the print preview icon will appear in the top toolbar and clicking it will bring up the pdf report generated for the design.




B
Brian is the author of this solution article.

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