Ch 3. Beam Shear/Moment Diagrams Multimedia Engineering Mechanics Shear andMoment Shear/MomentDiagrams MovingLoads
 Chapter 1. Stress/Strain 2. Torsion 3. Beam Shr/Moment 4. Beam Stresses 5. Beam Deflections 6. Beam-Advanced 7. Stress Analysis 8. Strain Analysis 9. Columns Appendix Basic Math Units Basic Equations Sections Material Properties Structural Shapes Beam Equations Search eBooks Dynamics Fluids Math Mechanics Statics Thermodynamics Author(s): Kurt Gramoll ©Kurt Gramoll

 MECHANICS - CASE STUDY Introduction Truck Bed Failure due to Loading (© 2003, Kurt Gramoll) "Well, this is a new one for me" said the highway patrolman when he was called to investigate the accident. "I have never seen a semi snap in two due to the load. I wonder why it failed near the front and not in the middle?" His partner added, "I am sure the investigation team will let us know. I wonder if the truck was overloaded?" What is known: The trailer is 53 feet long (does not include the tractor). The trailer gross weight (total including both load and trailer) is 79,500 lb. Assume weight is evenly distributed. The truck bed is designed to withstand a bending moment of 200 ft-kip (= 200,000 ft-lb). Assume the truck bed can be modeled as a simple supported beam with supports at the left edge and at the center of the back wheels. Question Assumed Location of Trailer Supports Does the failure location agree with a basic beam analysis? What is the value of the maximum bending moment and does it exceed the design moment of 200 kip-ft? Approach Construct a free body diagram. Using static equilibrium equations, determine the assumed support reactions. Determine how many sections are needed and make a cut in each section. Sum forces and moments at each cut in terms of position. Plot the resulting moment and shear equations.

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