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© 2006 Baylor University EGR 1301 Slide 1 Lecture 4 Introduction to Engineering Approximate Running Time - 16 minutes Distance Learning / Online Instructional Presentation Presented by Department of Mechanical Engineering Baylor University Procedures: 1.Select “Slide Show” with the menu: Slide Show|View Show (F5 key), and hit “Enter” 2.You will hear “CHIMES” at the completion of the audio portion of each slide; hit the “Enter” key, or the “Page Down” key, or “Left Click” 3.You may exit the slide show at any time with the “Esc” key; and you may select and replay any slide, by navigating with the “Page Up/Down” keys, and then hitting “Shift+F5”.

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© 2006 Baylor University EGR 1301 Slide 2 Introduction to Static Analysis EGR 1301 Lecture 4 Professor Dick Campbell speaking

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© 2006 Baylor University EGR 1301 Slide 3 Learning Objectives Understand the definition of Mechanics Understand the difference between static and dynamic analysis Understand the importance of engineering analysis in structural design Apply these concepts to a foot bridge and discuss the design tradeoffs

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© 2006 Baylor University EGR 1301 Slide 4 Mechanics Mechanics - the study of objects at rest or in motion, the effects of forces on a body, and the prediction motion. The fundamentals of Mechanics was formulated by Isaac Newton, using his three Laws: 1. A body at rest or in constant motion remains in that state until acted upon by an external unopposed force. 2. An unopposed force causes a mass to accelerate. 3. Every force action has an equal and opposite reaction. Mechanics is divided into the study of Statics and Dynamics.

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© 2006 Baylor University EGR 1301 Slide 5 Statics vs. Dynamics Newton’s 2nd Law is expressed as: Static analysis – F = 0; therefore... – a = 0 – In statics, nothing is accelerating (Newton’s 1 st Law)! –Statics is the study of forces acting on a (non-accelerating) body, and the reaction of that body. Dynamic Analysis – If an unopposed force acts: –Acceleration is proportional to the mass of the body –Dynamics is the study of the motion of a body, both in translation and rotation.

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© 2006 Baylor University EGR 1301 Slide 6 An Example of Engineering Analysis Baylor Engineers in Africa –3 professors, 6 students –Kenya, Africa –Engineering services to Kenya’s poor Foot Bridge Project –130 ft. wide river –Analyze for safety and possible design improvements

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© 2006 Baylor University EGR 1301 Slide 7 Need for Bridge Village was divided, far side had trouble: –Taking their farm produce to market –Attending school –Getting medical care Current Situation –5 miles to nearest bridge (20 mile round trip) –Several drownings per year

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© 2006 Baylor University EGR 1301 Slide 8 Need for Bridge Estimates of ~400 crossings per day –Saving 1,460,000 miles of walking per year Approximate cost: $5000 –1/3 of ¢1 per mile per year –What a deal! –Great impact at minimal cost.

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© 2006 Baylor University EGR 1301 Slide 9 How Does Engineering Analysis Help? Cable used is rated to withstand a maximum load (i.e., tension) of 16,000 lbs. –How much can the bridge support? –How is cable failure considered in the design? If six people (est. 1000 lbs.) stand in the center, what is the cable tension? What is the “safety factor”? –Definition of safety factor = cable rating / cable load

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© 2006 Baylor University EGR 1301 Slide 10 What about the weight of the bridge? The wood decking was built using 3-1”x 6” planks laid side by side. –The width of the river is 130 feet. –The density of the wood is 30 lbs/ft 3. –Can you calculate the weight of the decking to be 950 lbs? –The cable and hanger weight is ~112 lbs. What does this do to our safety factor?

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© 2006 Baylor University EGR 1301 Slide 11 Engineering is an Exercise in Trade-Offs! If we allow the bridge to have larger sag, what will happen to the tension in the cables? What will happen to the required anchors for the cables at the two ends of the bridge? What is the disadvantage of having larger sag in the bridge? We will use the Principles of Statics Analysis to answer all of these questions.

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© 2006 Baylor University EGR 1301 Slide 12 Suspension Bridges How does a suspension bridge like the Golden Gate provide a way to achieve the goals of lower cost and convenience of use? What are the disadvantages in the suspension bridge design?

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© 2006 Baylor University EGR 1301 Slide 13 Engineering Disasters Tacoma Narrows Bridge

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© 2006 Baylor University EGR 1301 Slide 14 Engineering Disasters Kansas City Hyatt Hotel The importance of proper engineering analysis.

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© 2006 Baylor University EGR 1301 Slide 15 This Concludes Lecture 4

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