# Tag Info

### Why are two wires used in railway overhead equipment?

Overhead line worker here. It's about speed. To answer your question, the purpose of the catenary wire is to get the contact wire to lay flat, so it isn't catenary itself. In your second photo, there ...
Accepted

### Why do wooden gate designs recommend a brace under compression instead of tension?

The reason is simple: the load applied on the gate is pretty trivial, and the brace (be it a 2x4 or a wire) is mostly added for rigidity. Indeed, you could put that 2x4 in tension and it would work ...
• 12.7k

### Why do wooden gate designs recommend a brace under compression instead of tension?

The frame and the brace in the first gate shown in your question seem to be joined together with simple butt joints, probably with nails to hold them together. Such joints are strong under compression ...

### Why are two wires used in railway overhead equipment?

It isn't to do with current-carrying capacity; it is to maintain good contact between the current-carrying wire and the pantograph pickup on the locomotive, as it allows the contact wire to be ...
• 341

### Why do wooden gate designs recommend a brace under compression instead of tension?

Wood expands when exposed to moist conditions. For the first case, the elongation of the diagonal will be offset by the compressive stress, resulting in a smaller geometry change. For the second case, ...
• 7,293

### Why are two wires used in railway overhead equipment?

Why two wires: A wire hanged at two points sags (it forms a "catenary curve"). The pantograph can only handle a certain sag before losing contact and arcing. The acceptable sag depends on ...
• 231

### Why do wooden gate designs recommend a brace under compression instead of tension?

Because the wood brace works in compression and the wire brace works in tension. Just make a model and see how that wire will behave in compression. Also you would need different joints for the wood ...
• 13.6k
Accepted

### Transforming the Area of a Hollow Square Section filled with concrete into the equivalent area of just steel

You can simply calculate "equivalent" cross-sectional stiffness values. Note that all non-zero terms of the stiffness matrix depend on one of these values: $EA$ or $EI$. These are the cross-...
• 12.7k

### Work done by a force in a deformable body

Work is a strange but useful mathematical concept. It is very handy because it is conservative in inertial frames. It also has an intuitive meaning most of the time, but not always. This is what gets ...
• 3,381

### Can/should you support a sagging ceiling from above?

You don't seem to have an urgent problem, as the ceiling may have stayed there for a long period of time. However, according to the modern building code for attic space without storage, the 50 mm ...
• 7,293
Accepted

• 7,293
1 vote

### Work done by a force in a deformable body

The work of a force is by definition vector multiplication of the force by displacement. $$W =F*x$$ Let's use two examples to clarify. In a pendulum, the work done on the part of the descending of ...
• 20.9k
1 vote
Accepted

### Direction confusion for shear and moment when sectioning a beam

This is the first step to simplify the analytical model by applying the equivalent load concept as depicted below: Another way to examine the direction of forces at where the cantilever is cut off.
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