Chapter 3: Loads

20. What are the causes of earthquakes? How are buildings equipped to resist them?

Breaks of molten rocks, magma. They can move from one location to another, and they create a lot of stresses. When stresses exceed Earth's ability to resist, they start to move and crack on Earth's crust. Destroying facilities on Earth's crust. -In foundations of the buildings, they have dampers or springs to take the vibration that sway and then dissipate. -Braces are meant to take horizontal motion or forces and keep shape of structure in tact.

3. How are dead loads calculated?

By computing the volume of elements and multiply it by the weight of a unit volume of material.

1. Define dead loads. Name some structural elements considered to be dead loads.

Dead load is the own weight of the building and includes columns, beams, floors.

8. Unlike dead and live loads, dynamic loads are considerably dangerous. Why?

Dynamic loads have large affects on the building, the suddenness that acts on the building is very dangerous.. Speed or rapidity of loads is dangerous.

14. Give two examples of failure due to dynamic effect and briefly describe the reasons suspected in the collapse. ????

"Galloping Gertie" of Tacoma Narrows Bridge, and the German infantry moved by "Goose-Stepping" that adds significant strength to the bridge. If the period and moving load are equal then the bridge will collapse. Tacoma Narrows was designed for winds of 135mph, but gained more momentum at winds of only 35mph, never occurred to engineers that at a lower wind speed could collapse.

22. What is the rationale used in predicting earthquakes?

-When a geologist notices that the velocity of the waves created by a small explosion increases know that the stress in the crust are increasing and concludes the earthquakes may be imminent. -Rats leaving, birds flying away.

23. How either correct or faulty prediction of an imminent earthquake can result in a social/societal problem? ????

A correct prediction or faulty prediction of an earthquake, can impact a lot of people.

24. Thermal effect on structures can be enormous. Why? Name two methods used to respond to this effect. ?????

A lot of thermal expansion increases on one side, a lot of stress will be generated on the members or elements of its structure. Two methods used: system of circulating chilled water, rather than having fixed connections, you have hinged connections.

12. An explosion is a type of loading that has a destructive effect. Explain this statement in light of loading on structures.

An explosion is a huge loading in a short time, and decrease so rapidly.

25. Expansion and contraction of outer columns relative to inner ones in tall structures can damage the beams in the building. Name and describe two methods to minimize such damage. ????

Expansion and contraction can damage chilled water, and moveable hinged connections.

26. Explain the reasons behind the banana shape of the Leaning Tower of Pisa.

Foundation was good, but the soil was weak, so it sank unevenly toward a lean. They built it straight after realizing it was a lean, compensate for the lean.

15. Wind effect could be costly to tall and light structures. Why?

If the building is tall, it will act as a sail, as wind effects are compounded as height increases.

5. Why is it difficult to calculate live loads? How does the building code address this issue?

It is difficult to calculate live loads b/c the loads will shift around. The building code gives recommendations and calculate for the worst case scenario.

2. The calculation of dead loads is considered to be an engineering dilemma. Why?

It's a dilemma because it's a paradox between the weight of the structure and the design. In order to know how much weight to use, you need to know the design. And in order to determine which design to use, you need to know the weight. Get around it by having experience, and basing off previously built structures.

6. Why live load reduction factors may be used in the design of buildings?

Live load reduction factors are used in the design at a factor of 60% as it's very unlikely that the building will be filled to capacity. Very conservative, and uneconomical.

4. What are live loads? Name examples of live loads acting on buildings.

Live loads include impermanent or shifted loads that can be moved around. They are not fixed, includes people, furniture, equipment, etc.

21. What does a reading on Richter scale represent?

Magnitude of Energy that the Earthquakes releases. It is measured in TNT dynamite, how much energy is compared to TNT.

28. Some structures in Mexico City seem to have settled then risen. What are the factors affecting this behavior?

Mexico city is built on a mixture of sand and water. Such soils settle when heavy buildings are erected, squeezing the water out of the sand. This floatation of water will cause the buildings to rise.

10. Define the period of a structure.

Period: The time it takes a pendulum to complete a full swing, from extreme right to extreme left and back to complete one oscillation.

13. What is resonance? Use an example to explain this phenomenon.

Resonance: Load that is increasingly progressively but not rapidly over time, and it doesn't happen so fast. An example is the yanking of a church bell.

9. What is it that determines whether the acting load on a building is static or dynamic?

Speed with which the load is applied. Acting slowly= static acting quickly=dynamic

18. What is the relationship between the stiffness of a structure and its period?

Stiffer the building (not flexible), shorter the period.

7. Live load calculations are impacted by the function and geographic location of the designed building. Explain.

The live load of a warehouse would be greater than the live load of an apartment.(function) Geography: Also, there may be natural loads such as an earthquake, snow, wind. They must be built accordingly.

16. How are wind loads used in the design of buildings determined?

They keep records of wind speed, then draw a map with wind speeds. Oklahoma and Great Lakes are good wind generators. -Tracked average, and drew maps. That's how they come up with a value, average records for 100 years for important structures.

19. Explain how a tuned dynamic damper works. What is the single most important factor that allows a damper to do its intended function?

Tuned dynamic damper works as a heavy mass(black of mass) that is tuned, so when building oscillates, the mass will oscillate in the opposite direction. -The weight of mass of damper must match the opposite oscillation of the building.

17. The shape of a building plays a significant role in how it reacts to wind pressure. Explain. ????

We learn from nature. Depending on structure, the surface gets hit by wind, and its compression wind tunnel effect acts as 4 lanes and then becomes a small river. Creates a huge draft compression on face, suction on other sides of the building and wind tunnel effect.

11. Consider the time it takes for a wind gust to grow then vanish to be T1, and consider the period of a building to be T2. State the relationship between T1 and T2 for both cases of static and dynamic loading.

Wind: T1 Period: T2 Static: If T1 > T2 Dynamic: If T1<T2

27. Thermal effect is highly pronounced in domes. Why? How is this problem overcome?

You can reinforce the dome with a ring of steel or chain of steel. Very highly pronounced b/c cracks will be significant in domes as it can create a collapse of the dome. -Since it is weak at center of the sides, it helps that there is a chain of steel around it.