6 Trusses, Frames, and Machines Free Online FlashCards

What assumptions define an ideal simple truss?

An ideal simple truss has straight, weightless two-force members joined by frictionless pins; loads and support reactions act only at the joints.

How do tension and compression act at a truss joint?

Tension pulls away from a joint; compression pushes toward it.

Which joint is a good starting point for the method of joints?

Begin at a joint with no more than two unknown member forces, then move to neighboring joints as forces become known.

What does a negative result mean when member forces are assumed tensile?

If an assumed tensile force is negative, the member is actually in compression.

How should a solved member force be drawn at its other joint?

At the connected joint, the member force has the same magnitude but the opposite direction.

How does the method of sections find selected truss forces?

Cut through the members of interest, isolate one side, and apply equilibrium. A useful planar truss cut generally exposes no more than three unknown member forces.

How can a moment center simplify a truss section analysis?

Take moments about the intersection of two unknown cut-force lines of action; their moments vanish, allowing the third force to be solved directly.

When should you choose joints versus sections?

Use joints when many or all member forces are needed; use sections to find selected forces efficiently.

How does a machine differ from a frame?

A frame is a stationary assembly intended to support loads; a machine has parts that move relative to one another, often to transmit or multiply force.

What distinguishes a multi-force member from an ideal truss member?

A multi-force member may carry axial force, shear, and bending moment; its force is not necessarily restricted to its axis.

What can ideal planar pin and fixed connections transmit?

A planar pin transmits two force components but no couple; a fixed connection can transmit force components and a couple.

Where do forces between connected parts appear on free-body diagrams?

For a whole-assembly free-body diagram, forces between its parts are internal and cancel in pairs. They appear when the parts are isolated separately.