Analysis

Scope

The ClearCalcs Truss Analysis calculator allows users to input the geometry of some common truss types and specify the load conditions on the truss. It then determines the cumulative load applied, support reactions, bending moment, shear and axial forces, extension and displacement for each chord of the truss. Component members of the truss may then be designed by creating a new "Design Only" calculation, and linking it to the truss analysis calculation.

The sheet has 3 main input sections, plus the Summary results section:

1. Truss/Frame Geometry 2. Member Selection 3. Distributed Loads on Chords 4. Summary

This article will explain the expected input parameters in each of those sections and present a worked example of a truss analysis calculation.

1.Truss/Frame Geometry

A. Truss Type

ClearCalcs supports a variety of truss types including flat trusses, roof trusses and scissor trusses. For a full list of all the truss types available please refer to our Truss Types article.

A visual diagram of the selected truss type will appear in the summary section, which will update as you input height, width, and loading parameters.

B. Total Truss Height

The vertical distance from the highest point of the truss to the lowest point of the truss as measured in millimetres (or feet if you are using the Imperial unit system).

C. Total Truss Width

The horizontal distance from the left-most point of the truss to the right-most point of the truss as measured in millimetres (or feet if you are using the Imperial unit system).

D. Additional Property

One or more additional properties may also appear, depending upon the specific truss type you've chosen. If you are ever unsure as to what it is asking for, simply click on the property name to obtain a drop-down explanation.

2. Member Selection

A. Truss Material / Linked Cross-Sections

The material out of which your truss has been made. You will be given a drop-down menu, from which you can select the relevant material.

For Linked Cross-Sections, refer to Section 5 of this article.

B. Size and Orientation of Truss Members

Note that this Truss Analysis Wizard is for analysis purposes only. Selecting the right cross-section directly affects the results of the calculations, as they have different stiffnesses and self-weight. As previously mentioned, if you wish to design this member (i.e., pass/fail per code), you will need to create a 'Design Only' calculation and link to this truss analysis calculator (see Section 5).

Top Chord

An inclined or horizontal member that marks the upper edge of the truss.

Bottom Chord

An inclined or horizontal member that marks the bottom edge of the truss.

Web Member(s)

Member/s that join the top and bottom chords to form triangular patterns to give truss actions.

Cross-section

The size of the top chord, bottom chord and web members need to be specified from drop-down menus. The drop-down menus will automatically display relevant industry-standard sizes for the truss material you specified. You can also use the member selector function to choose a member size. Note that the section sizes and types shown do change depending upon the building standard you are using for the current project. That is, a project using the Australian building standard will show standard Australian sections, and a project using the United States building standard will show standard US sections.

Orientation

The orientation of the top chord, bottom chord and web members need to be specified as to whether they are oriented about their major axis or minor axis.

3. Distributed Loads on Chords

A. Total Distributed Loads

For the first two sections, the total vertical distributed loads for the top chord and bottom chord need to be specified in kN/m (or plf if you are using the Imperial unit system). Depending upon the type of truss selected, inputs may also be available for loads that are perpendicular to the top chord (not vertical i.e., gravity versus aligned loading conditions).

Please note that the subsequent section "Advanced Loads (by Element Number)" can be used to enter loads for individual members, point loads, and angled loads - but most analyses should not require this.

B. Self-Weight

You can choose whether or not to include the self-weight of the truss in calculations. The default has been set to include the self-weight of the truss.

4. Summary

On top of the summary section is a diagram of your truss. The display of this diagram can be changed to show loads and supports, bending moment, shear forces, axial forces, extension of members, displacement of members and reaction forces at supports. This feature is illustrated below.

The truss diagram is followed by tables that summarise the calculations and indicate the worst case maximum moments, shears, axial forces, deflections, and extensions for each member type defined. The designer will then use these values to ensure all selected members, connections, etc. are designed to withstand these worst-case loading conditions per code as well as the designer's judgement. If you would like to link to a 'Design Only' calculator to complete your truss design in ClearCalcs, see below.

5. Designing Components by Linking New Calculators

Typically, once a truss is analysed, the components will also need to be designed. This may be done in ClearCalcs by the following procedure:

1. Select "Add New Calculation" in the left sidebar
2. Add a "Design Only" calculator for the appropriate material (for example, "Timber Member (Design Only)")
3. Next to the loads table in this new calculator, click on Link

4. In the modal that pops up, select the truss analysis calculation, and then the component of the truss you wish to design (for example, "Top Chord")

5. Complete the rest of the design as normal, referring to the help documentation for the specific material. ****

Note that loads on the member will automatically update when you update the truss analysis calculation. However, at this time, the specific section used in the analysis is not linked between the analysis module and the design module and must be selected independently in both calculations. For example, if you select a 140x45 MGP10 in this 'Timber Beam (Design Only)' calculator, you will need to manually ensure that a 140x45 MGP10 is also selected in your Truss Wizard Analysis calculator. Not to worry! Two-way linking will be coming in the future for ClearCalcs - our engineering team is already hard at work on this feature.

Example

A roof truss is to be designed in Australia. The calculation details of this worked example can be found here.

• Fink Truss type with 8 metres wide, 2.5 metres height, and a 400 millimetre overhang. Please check the diagram in Summary section to confirm the dimensions.

• Timber components, with both top and bottom chords 140x45 MGP10, and web members 70x45 MGP10, all oriented about their major axes. Note that if you change the member orientation, the bending stiffness (EI) in the table Member Data is updated.

• Factored dead plus live load of 0.7 kN/m on the top chords, and a factored ceiling dead load of 0.1 kN/m on the bottom chord (vertical loads). You can check the diagram under the Summary section to confirm if the loads are correctly applied.

• Factored wind load of 0.45 kN/m on the top chords

The figure below shows the load table, don't forget to check Yes for including self-weight.

• Under Summary, you can check all results. For axial forces, for example, the results shown in the diagram are confirmed in the table Overall Results by Member Type.

• The displacements and support reactions are also shown in diagrams and tables.