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Lecture 4 Introduction to Engineering Approximate Running Time - 16 minutes

Lecture 4 Introduction to Engineering Approximate Running Time - 16 minutes Distance Learning / Online Instructional Presentation Presented by Department of Mechanical Engineering Baylor University Procedures:

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Lecture 4 Introduction to Engineering Approximate Running Time - 16 minutes

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  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: • Select “Slide Show” with the menu: Slide Show|View Show (F5 key), and hit “Enter” • 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” • 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”.

  2. Introduction to Static Analysis EGR 1301 Lecture 4 Professor Dick Campbell speaking

  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

  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.

  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 1st 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.

  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

  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

  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.

  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

  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/ft3. • 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?

  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.

  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?

  13. Engineering DisastersTacoma Narrows Bridge

  14. Engineering DisastersKansas City Hyatt Hotel The importance of proper engineering analysis.

  15. This Concludes Lecture 4

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