Could earthquakes on San Andreas Fault be stopped by driving huge steel piles deep into bedrock on either side of fault and welding huge cross beams, thereby anchoring ever north moving Pacific Plate to more stable North American Plate?

No.

Imagine you are floating a large thin cookie on a lake of milk.

When you went to move the cookie it fractured.

For some reason, you decided to mend the fracture using staples. Now remember, you’re really good at mending cookies with staples, so it is a good fix.

The problem is that when you go to move the cookie again it will likely fracture just outside the mending. And that assumes the mending was strong enough in the first place.

Compared to the forces exerted on the cookie the mend will never be strong enough because the cookie isn’t strong enough to resist the forces.

Hopefully, my analogy makes sense. I’m going for a snack!

Why do we consider the steel strength critical in finding the strength of any RCC member?

While I like the different answers let me try this a bit more simply:

Concrete is very strong in compression. Such as placing a block of it on the ground and setting a large weight on it.

Concrete is comparatively weak in tension. Treat it like a rope or chain and breaks easily.

Bending, which is just both compression and tension within an element, happens in most cases because almost nothing is in pure compression. So, we add something that is really good at tension: steel, thereby creating reinforced concrete.

The concrete deals with the compression and the steel deals with the tension. In designed members, we can tell where we are expecting to get tension forces and correspondingly place the steel along those points.

How do you mitigate autogenous shrinkage in concrete?

Depending on your use, you use separation and control joints.

There are a lot of guides available that cover this subject, but it can vary quite a bit depending on use, thickness and available friction surface. Most guides will call for roughly rectangular pieces. Slabs tend towards 1:2 to 1:4 ratios on width to length.

Slabs are based upon friction stress breaking up the slab. Walls tend towards the ability to “tilt-up” the section without cracking.

Of course, I’m making assumptions of what you are making out of concrete.

As a last note, most texts will state that concrete will shrink by about 4%. I will tell you that that is a worst case scenario, and that most cases that shrinkage on site tended more towards 1%-2%.

Theoretically, if PZT applied to an elastomer substrate (see attached) were affixed to trees, what might be the potential output of, say, a 50ft pine with approx. 10sq.ft. of PZT ribbon in average conditions?

In average conditions, I would expect near zero potential. Wind tends to be periodic, or very low.

What you need are at least two conditions: 1. regular wind. 2. flutter.

So, coastal areas or very large open areas (think great plains or ocean surface) with little height variation would work best. One problem is that the presence of a large number of trees will affect this.

Leaves will help with the flutter but really you need turbulent airflow.

If you were thinking to recover energy from the trees you need to remember that trees sway, oscillate, very slowly so not a good source without some mechanical conversion.

While I realize I didn’t give the answer you were looking for, I do hope this helps.

Theoretically, could a Mine Clearing Line Charge be used to demolish buildings?

Theoretically; yes. But, it would be far from the best option.

Mine clearing explosives give a large push at a distance so that mines in the blast area receive enough pressure to trigger.

Building demolition is about cutting (shearing) pressures that stay precisely in their intended area to reduce any unintended results.

In short, its sledgehammer when you only need a tack hammer. It will work, but the additional damage may not be worth it.

Is it true that wooden skyscrapers are ultimately stronger than steel skyscrapers?

No, wood is not stronger than steel for skyscrapers.

This point comes up from time to time resulting in analyses done with individual wood fibers. The result is that in a number of species of wood the fibers have comparable tensile strength to mild steels. A lot of people took away from this that wood is as strong, and sometimes stronger, than steel.

Wrong! First, this is one of several properties comparable to steel. The others, compression and shear, are not. Additionally, the wood fibers are held in a matrix. While this is moderately good at compression it is bad at tensile and shear. So basically, should you subject wood to steel stresses it will break apart the matrix leaving only wood fibers. These same fibers aren’t rope-like but extend only a few inches each.

And after all of that, that doesn’t go into how wood is a natural material. Meaning that every specimen has differences, variations while steel comes as a monolithic homogenous material.

So, at the end of the day steel is stronger than wood in almost every case, and definitely those leading to skyscrapers.

How are bridges and/or tunnels that go over or in water maintained?

In rare cases, they are constructed of corrosion-resistant materials. But for the most part, they are painted to limit and slow corrosion. Where corrosion does occur, the material is stripped down to the base material, cleaned of the corrosion, and repainted. The process is repeated over the life of the structure. The frequency is usually determined by inspection and the how hostile the environment turns out to be.

How much weight can a real truss bridge hold?

This would be difficult to say in most cases due to the way bridges are designed.

AASHTO has basic guidelines based on the traffic level of service and site conditions. Depending on who has jurisdiction over that bridge can further increase the amount of loads on the bridge.

The engineer(s) then determine the weight of the bridge itself along with environmental factors (soil conditions, wind loads, earthquakes,…), and the design the bridge to withstand all of these plus an additional factor of safety.

The result of all of this is that any given bridge should be able to take an 80,000lb trailer (about 8′x45′) and load the bridge with these; you should have a bridge that can take several times that under “bad” conditions.

Just as a parting thought. It is rarely the weight bearing capacity of a bridge that causes it to fail, and thusly tends to be one of the strongest capacities of a bridge.