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VisualAnalysis Tutorials: Timber Beam-Column Design

Project Description:

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The challenge here is to choose a section for the beam-column shown below. The section should be a standard dressed timber made from No. 1 graded Douglas Fir-Larch.

Building the Model

The member is 16 feet long. It is pinned at its base and fixed in the X-direction at its top. For a preliminary size, use a 5x5 Standard Dressed Timber. For the material, from the Visually Graded Timbers/Beams and Stringers category choose Douglas Fir-Larch for the species and No. 1 for the grade.

If you need help creating the model please consult the VisualAnalysis User's Guide (Help | Contents).

Loading

Create the following load cases:

Service Cases:

Dead loads: Apply an axial force of 10 kips as shown above.

Wind +X loads: Apply a uniform transverse load of 0.3 kips/ft in the X-direction.

Factored Combinations:

Use the Load | Load Case Manager menu to create the ASCE 7-05 ASD load combinations.

Information on applying loads and creating factored combinations is available in the VisualAnalysis User's Guide (Help | Contents).

Setup the Design Parameters

Go to the Design view and select the beam-column to make it active for editing using the Modify tab of the Project Manager. Go to the Modify tab and set up the following parameters.

Wood:

The Member Type should be set to "Other." As mentioned above, we want to design the member as a Standard Dressed Timber. Make sure the Shape Category is set up properly.

Bracing:

Select unbraced for all bracing options. Assume the member is part of a braced system in both the y and z directions.

Columns:

With unbraced in mind, leave both the Sidesway y and Sidesway z parameters set to No. Leave the k factors unchanged so they are calculated automatically.

Deflections:

Assume a deflection limit of L/240 was specified for the Wind Loading. With this in mind, choose Member Span Ratio as the Strong Deflection type and enter 240 for the "W or S' value.

No drift limits were specified so use "Member Span Ratio" for defection.

Constraints:

No size limits are given, so leave the Depth and Width limit boxes unchecked.

Configuration:

The member is not a repeat member and it does not have bolt holes.

C-Factors:

Leave the Temperature Range at T<=100 F. Also leave the High Moisture Content, Pressure Treated, Qualifies for Buckling Stiffness Factor, and Qualifies for Incise Factor boxes unchecked.

Beam:

Choose Simply Supported for the Beam Type. For the Loading Pattern, choose Uniform. Leave the Custom Length Between Inflection Points option unchecked. The member does not have notches.

Overrides:

Leave the Advanced parameters unchanged.

Designing the Member

Analyze the model and switch to a design view if you aren't already there. Select one of the members and choose Design | Design Selected Group. The Wood NDS ASD Design Selection dialog will be brought up, with a list of acceptable sizes. Choose a size and click OK.

After accepting the design, the unity value that appears in the design view should have a ~ in front of it indicating that it is a preliminary value based on the analysis results with the member in place. To get the real updated unity value you must synchronize the design changes.

Synchronizing Design Changes

To synchronize the design changes, select Design | Synchronize Design Changes. You will be prompted to re-analyze, select "Yes", and when it finishes re-analyzing go back to a Design View and review the unity check. It should no longer have the ~ in front of it, indicating that is a final unity value.

If the unity value is greater than one the member has failed and you need to reiterate the design process. The closer the unity value is to one the more efficient, but less conservative the member is.


Reporting Design Checks

To report the extreme design checks, double-click on the member in the design view. As you scroll down through the report you will eventually reach the Extreme Checks area. In this area the extreme cases for design checks such as Combined Stresses and Strong Deflections are reported.