Summary:
Your firm has been hired to design a roof truss and supporting columns. Analyze member loads will be using Visual Analysis (or another structural analysis software with which you are already familiar). Prepare a project report that discusses the ultimate loads on the structural members as well as provides details of the design calculations. The use of Excel spreadsheets to create design templates is strongly encouraged and will earn extra credit points. This project will comprise 20% of your course grade. You may work in teams of three, one report per group.
Your report should be professionally prepared. It should read like a continuous report, with complete sentences and correct grammar and spelling. All figures and tables included in the report should be introduced in the text and clearly labeled. The final report and appendices of supporting work should be professionally bound. Include a table of contents and title page.
Before beginning work on this project, carefully read all parts of this assignment. Material plagiarized or copied between groups will receive no credit.
Geometry:
As shown in Figure 1, a long span roof truss is used to create large, open spaces without interior columns. The 60-foot frame is composed of two 30-foot columns supporting a roof truss.
The truss topology is up to you and your group to design! The height of the truss at its maximum point should be 10 feet. The truss should be connected to the columns using pinned (not moment bearing!) connections. Remember that truss members should have pinned joints (not moment bearing joints) and that loads should be applied only at the joints.
Loading:
The following loads should be applied to the structure:
- Dead load = 1 k/ft uniformly distributed dead load on roof to be transferred to top chord of roof truss via purlins (in addition to self-weight of frame).
- Roof live load = 3 k/ft uniformly distributed live load on roof to be transferred to top chord of roof truss via purlins.
- Wind load = lateral load distributed along the windward column of 1 k/ft.
Dead and live loads are acting on the structure's roof. Purlins are used to transfer this load to the truss's top chord joints in the form of point loads. Assume a purlin is placed at each truss joint, and load is shared equally between adjacent joints. (See p. 79 and following of the Segui steel text.)
Use the following load cases:
- D + Lr + W
- 1.2 D + 1.6 Lr + 0.5 W
- 1.2 D + 1.0 W + 0.5 Lr
Design Notes:
The following are a few suggestions to help your firm accomplish its design:
- Consider whether you want to use multiple grades of steel for the truss vs. the columns.
- Our work on compression members focused on I-shapes, but designing a truss with I- shapes is awkward. Consider alternate geometries. Section E3 of the code can be used to design channels, tees, and double angles, among others. You should be able to differentiate what you have already done to fit new geometries.
- Visual Analysis will show preliminary results in the "design view" window. Use this feature to consider different member shapes quickly and easily, but remember that your final design check needs to be calculated by hand.
- The columns in this frame will be pinned at one end and fixed at the other. Because they are not rigidly connect to other frame members, it is probably best to use approximate effective length factors instead of the alignment charts.
- A final design of a tension member should include connection details. While connection design is not a requirement of this report, it is suggested that you read ahead to the first part of Chapter 7 in the Segui text to create realistic approximations of connections for your tension member designs.
Report Requirements:
As stated in the Summary, the written report should be professionally prepared: typed, serif font, 12 point font size, single spacing, 1" margins. Spelling and grammar count towards the final grade. Writing should be concise and coherent. Any hand calculations should be neatly prepared, on engineering paper, and submitted in the form of an appendix. The report should be bound and include a table of contents. The report should include the following elements:
- Selected views of the computer models sufficient to illustrate geometry and loading. Be sure to label your members so they are clearly related to your output.
- A sample of a computer-generated report that includes a summary of shear, axial, and moment internal forces. Focus on the "worst case" members for tension, compression, and bending. Use a highlighter or other documentation to indicate your extreme load data for the selected members!
- Summary tables listing the values and units for the extreme member forces for the truss members and columns. This table should include extreme shears, moments, axial forces, and cases where the member is subject to combined (axial and moment) loads, as appropriate to the member type. Identify the load case creating the extreme load events for each member. An envelope analysis is not sufficient.
- Full design calculations for each member type demonstrating that the final cross-sections selected are adequate to support the applied load. The use of Excel to create design templates is strongly encouraged. If members encounter more than one type of load (eg, shear and moment, axial and combined axial/moment), then calculations must be provided showing they are adequate for all load types.
- Full details of your final design and the cross-sections selected.
- Any assumptions you made in the creation of the computer model or Excel template(s) and / or the member design.
Format and Style (5 pts each)
Paper is presented neatly and professionally (typed, 12 point serif font, at least 1" margins, new paragraphs clearly indicated).
Paper flow is clear and includes discernable sections for the introduction, main body, and conclusions.
Spelling and grammar are correct.
Writing illustrates understanding of the material.
Content
Report satisfies all required elements: assumptions, challenges, results, documentation. Sufficient details of computer models, design calculations, and final design are provided.
Report of force outputs for selected members with documentation of extreme force values.
Table(s) listing accurate member extreme values and associated load cases.
Table(s) listing final member design.
Supporting design calculations are accurate and complete.