Statics:Hibbeler 1
RealReal--WorldWorld
Why do we study free-body diagrams and use equilibrium to find unknown forces?
Results of the Kansas City Hotel disaster
33rdrd Floor Walkway Floor Walkway (Independent of 2(Independent of 2ndnd and 4and 4thth Floor Floor
Walkways)Walkways)
Design of Design of WalkwayWalkway
There was a modification of the
lkwalkway design.
4th Floor Walkway Beam4th Floor Walkway Beam View of View of Hanger Hanger Rods for Rods for 44thth FloorFloor
CloseClose--up of Rod, up of Rod, Washer, and BoltWasher, and Bolt
Statics:Hibbeler 2
Free-body
diagrams of
Design of Design of WalkwayWalkway
the 2nd and 4th
floor
walkways
Notice the free-body diagram of the 4th floor
Design of Design of WalkwayWalkway
the 4 floor walkway shows that the force at B and E doubles in the modified structure.
33rdrd Floor Floor Walkway BeamWalkway Beam
EQUILIBRIUM OF A RIGID BODY & FREE-BODY DIAGRAMS
Identify the force and moment reaction components on a rigid body for a specific connection type, including (but not limited to): smooth surfaces, roller supports, link supports, cable supports, fixed supports.
Draw free body diagrams for 2D rigid bodies, labeling all external forces and moments, known or unknown
CONDITIONS FOR RIGID-BODY EQUILIBRIUM (Section 5.1)
In contrast to the forces on a particle, the forces on a rigid-body are not usually concurrent and may cause rotation of the body (due to the moments created by the forces).Forces on a particle
For a rigid body to be in equilibrium, the net force as well as the net moment about any arbitrary point O must be equal to zero.
F = 0 and MO = 0
Forces on a rigid body
p
Statics:Hibbeler 3
THE PROCESS OF SOLVING RIGID BODY EQUILIBRIUM PROBLEMS
For analyzing an actual physical system, first we need to create an idealized model.Then we need to draw a free-body diagram showing all the external (active and reactive) forces.Finally, we need to apply the equations of equilibrium to solve for any unknowns.
SUPPORT REACTIONS IN 2-D
As a general rule, if a support prevents translation of a body in a given direction, then a force is developed on the body in the opposite direction. Similarly, if rotation is prevented, a couple moment is exerted on the body.
A few examples are shown above. Other support reactions are given in your textbook (in Table 5-1).
Action vs. ReactionAction vs. Reaction
Statics:Hibbeler 4
Flexible Cord, Rope, Chain, CableFlexible Cord, Rope, Chain, Cable Rigid LinkRigid Link Ball, Roller, RockerBall, Roller, Rocker
Smooth SurfacesSmooth Surfaces Smooth PinSmooth Pin Pin in Smooth GuidePin in Smooth Guide
Statics:Hibbeler 5
Collar on Smooth ShaftCollar on Smooth Shaft Smooth Collar with Fixed Smooth Collar with Fixed ConnectionConnection Fixed SupportFixed Support
Linear Elastic SpringLinear Elastic Spring Idealized PulleyIdealized Pulley WellWell--supported Rigid Bodysupported Rigid Body