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You have been asked by your supervisor to design a Pratt steel truss that must support three 10-kip loads as shown below. The length of the truss is to be 40 ft. The height of the truss and thus the angle ?, as well as the cross-sectional areas of the various members, is to be selected to obtain the most economical design. Specifically, the cross-sectional area of each member is to be chosen so that the stress (force divided by 2 area) in that member is equal to 20 kips/in , the allowable stress for the steel used; the total weight of the steel, and thus its cost, must be as small as possible. (a) Knowing that the specific weight of the steel used is 0.284 lb/in3, write a computer program (or create an Excel spreadsheet) that can be used to calculate the weight of the truss and the cross-sectional area of each load-bearing member located to the left of DE for values of ? from 20° to 80° using 5° increments. (b) Using appropriate smaller increments, determine the optimum value of ? and the corresponding values of the weight of the truss and of the cross-sectional areas of the various members. Ignore the weight of any zero-force member in your computations. Please submit the following: A memo, no more than 2 pages long, with either single or 1.5 spacing (memos are never to be double spaced), not counting attachments, with this format: A header indicating who the memo is to. In the case of this course, that will be me. The “from” line needs to list all the participants. In this case, include all the group members (You will be working in groups of 2-3 people). The date should be the date you create the memo, and the subject line should include a few words to indicate the subject of the memo. 1) Introduction- This first paragraph is intended to give a general statement of the intent and purpose of the memo. This paragraph should never exceed four or five lines of text. All other information should appear in the following paragraphs. 2) Results/Discussion- The body of the memo is going to describe whatever information needs to be conveyed. In the business world, these memos are used to formalize information that has been discussed, or to convey results of tests that have been requested. This could include what tests were run, what the general results were and any special information, such as problems or difficulties. You should write enough that the audience can understand what you did and how you did it in general terms. In this case, you will answer the questions given in the problem statement in this section. Graphs can be placed in the body if they are imperative to understanding the text of the memo, but should be limited. If there are a lot of graphs they are better placed in an attachment, labeled and referenced in the text. Graphs and charts should follow standards for good engineering graphs, and all attachments must be labeled and referenced in the body. As an example, you might say that you have included the raw data or summary data for the simulation. If attachments are made, they must be well labeled so the reader can easily discern each attachment. You would not, for example, want to include pages and pages of raw data in tabular form, followed by more pages of post processed data in tabular form without somehow indicating what they were. You would also not want to include data that is not needed. For instance, consider the pages of raw data. Ask yourself these questions; is the attachment required? Was it asked for specifically or is it required for understanding of the results or another attachment? Is the attachment fluff? Adding pages of attachments to make a memo look “important” will quickly lead to your memo’s getting circular filed and earn you a reputation you really don’t want to have. In general, be brief and to the point but not so stingy with your words that the sentences are difficult to read, fragmented or unclear. Use good grammar and punctuation. Many times, an engineering memo may stay in a file for years, so a poor job of writing may be seen for a long time. They are also frequently forwarded up the chain of command, so a memo you wrote to your boss may end up in the hands of a company vice president. If your work and writing looks professional and well thought out, it will aid your career. If it looks poorly written and shoddy, then you will be seen by those superiors as a shoddy engineer and your career could easily be affected. 3) Conclusion- The “Conclusions” section summarizes the design/testing work completed and assesses how well the design meets the objectives presented in the “Introduction.” Note that if the design does not meet the objectives, you should analyze why the design did not succeed and what could be modified to make the design a success. Besides summarizing the work and analyzing whether the objectives were met, the “Conclusions” section also gives a future perspective for how the design will be used in the future. 4) Appendices- Here you will attach your raw data, sample calculations, code (if using Matlab) or a screen shot of your spreadsheet with an explanation of what each cell in your spreadsheet does and the corresponding formulas (e.g A2=F1*A3*sin(A6)).