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Class 3AT

Class 3AT - ENGR 111 Week 2 ~ Monday Class 3 T Pollock Fall...

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1 ENGR 111 Week 2 ~ Monday Class 3 T. Pollock Fall, 2009

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2 Is this a truss? Is it statically determinate? All joints are pinned . Fixed restraint Rolling restraint (support) (support) (nodes)
An assembly of bars with pinned ends can only transfer forces in the direction of the long axis of the bar. Truss links (bars)

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An unconstrained bar aligns itself in the direction of an applied force.
Conversely, if the ends of the bar are constrained, the force aligns with the bar. This is easiest to see if the bars are cables in tension. cables

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Statically determinate: We can write three equations describing the forces in the plane of the paper: Σ Fx = 0 Σ Fy = 0 Σ Mz = 0 Therefore we can solve for only 3 unknowns.
A sketch of a structure, or any portion thereof, that shows the forces rather than the physical details is called a Free Body Diagram .

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8 All joints are pinned . Is this a truss? Is it statically determinate?
With two fixed joints, there are four unknowns, but only 3 equations. Σ Fx = 0 Σ Fy = 0 Σ Mz = 0 Statically indeterminate.

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10 Is this a truss? Is it statically determinate?
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