Structural stability and soil liquefaction during earthquakes.

Sructural stability and soil liquefaction during an earthquake. I've tested with different building structure proportions and I've also tested different ground compositions to see which building structure or soil composition get less damage
Yugam Bansal
Grade 5

Hypothesis

Structural Stability:

Based on my background research If I use a triangular building then I think it will withstand an earthquake better than a rectangular building because triangles are the strongest shape in geometry and the force will be easily exerted out of the building

Soil Liquefaction:

Based on my understanding I think that if I use a hard surface such as gravel with lesser water content then I think the building (the wooden model house) will have the least amount of chance to sink during an earthquake. On the other hand if I use a softer surface like soil/sand with more water content then there are a higher chances that the earthquake will make the building to sink because soil liquefaction will make the higher content of water rise up in the soft surface making the building to easily sink.

 

Research

Structural Stability: 

Triangles are the strongest shape in geometry because when an earthquake occurs and the ground moves one way, the force gets pushed on one of the four triangular sides (like a pyramid) of the building.

For rectangles, the force of the earthquake makes the ground move in one direction causing the force to bend the building in the opposite direction.

Soil Liquefaction:

In soil liquefaction when an earthquake occurs the ground gets loosened up and due to the large amount of water underneath the surface, it causes the building to sink.

If the ground has less water, a firm surface has a better chance of the building not sinking during an earthquake.

Variables

Structural Stability: 

Manipulated variables

  • Structure shape
  • Structure base

Responding variable 

  • Which structure withstands an earthquake for a longer period of time                                                       

Controlled variables    

  • Same shaker table
  • Same material that we place the shaker table on
  • Same bowl and ball on the building
  • Same stopwatch down to the millisecond
  • Buildings were built with same material   

 

Soil Liquefaction:

Manipulated variables

  • Material put into the container for the ground/foundation                                                               

Responding variable 

  • Which type of ground/foundation is best to withstand soil liquefaction during an earthquake                                                 

Controlled variables  

  • Same container that I tested in
  • I used the same model house 
  • I used the same shaker table
  • Same material we placed the shaker table on
  • Same amount of time on the timer

 

Procedure

Structural Stability:

  1. First I made the shaker table (representing an earthquake) by putting 2 rubber bands around both sides of 2 cardboard sheets. And I also placed 4-6 balls (harder and bigger makes the earthquake more intense) in between the center of the cardboard sheets.
  2. Then I made three buildings, one was the small base rectangular building, second was the big base rectangular building and third was the big base triangular building. These buildings were made out of plastic straws and connecter pieces.
  3. I placed the small base rectangular building on the shaker table.
  4. For the stability of the building base, I had to put the rubber bands on the shaker table over the base connectors.
  5. Then I put a bowl with a ball in it at the top of the building (representing weight of the building).
  6. After that I set a stopwatch and immediately started shaking the shaker table.
  7. Finally I stopped the stopwatch when the ball fell down from the top of the building and analyzed how long it took. 
  8. I repeated steps 3-7 for the other buildings.

Soil Liquefaction:

  1. First I took the shaker table from the structural stability experiment.
  2. Next I took a plastic box/container and filled it halfway with sand.
  3. After that I poured 1 glass of water in the plastic box and waited till the water sunk in.
  4. Then I got a small wooden model house and placed it on the sand in the box/container.
  5. Next I placed the box/container on top of the shaker table, started a timer for 30 seconds and started shaking the shaker table.
  6. Finally when the 30 second timer rung I measured how deep the model house sunk in if it sank at all and recorded it.
  7. I repeated steps 2-6 for soil and gravel. 

 

Observations

Structural Stability:

Below table represents the data collected for my structural stability experiment

                Depth (cm)

 

Material

Test # 1

Test # 2

Test # 3

Sand

0.89

0.8

0.9

Soil

5.3

5.3

5.3

Gravel

0.1

0

0

 

Soil Liquefaction:   

Below table represents the data collected for my soil liquefaction experiment

                          Time (sec)

 

Building Structure

Trial # 1

Trial # 2

Trial # 3

Big Base Triangular

44 

45

19

Big Base Rectangular

27

17

28

Small Base Rectangular

20

17

15

Analysis

Structural Stability:                                                       

Based on my experimentation the averaged results were:

  • The big base triangular building was the most stable among all the three buildings even though there was some structural damage. The average time it took for the ball to fall off was about 44 seconds.
  • The average time it took for the big base rectangular building’s ball to fall off was about 27 seconds.
  • The average time it took for the small base rectangular building’s ball to fall off was about 17 seconds.                                                                   

Soil Liquefaction:

The average results of my experimentation are as follows:

  • A hard and rocky ground surface seems to be the best option for foundation/ground with lesser water content, the model house did not sink at all.
  • Soil with more water content sank around 5.3 cm. 
  • With sand, the average depth the house sank was about 0.89 cm.     

                             

Conclusion

Based on my experimentation both of my hypothesis about Structural Stability and the Soil Liquefaction matched my experiment’s results.

Structural Stability:

My conclusion for the Structural Stability experiment was that the big base triangular building will stand up the longest because triangles are the strongest shape in geometry.

Soil Liquefaction:

And my conclusion for the Soil Liquefaction experiment was that with less water content and with a hard foundation such as gravel, the wooden house will stay up.

 

Application

Who Cares:

An Architect (a person who designs houses) can use the information from my project to apply on real life buildings. You might be thinking, people already know that triangular buildings are earthquake resistant since people have already done this experiment before but haven’t applied it on real life buildings (I was just proving the facts). The reason people don’t build triangular buildings is because of cost, cost is why people are not making triangular buildings because the triangular buildings do not have a lot of space in them.

 

Sources Of Error

Structural Stability:

  1. Sometimes the ball from the top of the building would fall down hitting another one of the buildings delaying the testing.
  2. Another source of error is that sometimes the shaking would be inconsistent, making me have to redo my testing.
  3. The balls in the shaker table would come out making the cardboard bend and scrape the bottom cardboard sheet.
  4. When the rubberbands on the shaker table would snap, replacing the rubberbands would be a tedious task to do.

Soil Liquefaction:

  1. Like the structural stability project, the balls in the shaker table would come out resulting in the cardboard to scrape the bottom cardboard sheet.
  2. The rubberbands would also snap here and make the entire container/box to make the cardboard sheet on the top to bend and make the box/container to fall in.
  3. A source of error that has happened is that when my shaking would be inconsistent, I'd have to do the testing again.
  4. Another time there was an error in my project was when the wooden model house would not sink on the 2nd or 3rd testing of the same material, I had to do it again which made the project take more time.

Citations

Max, Science. “🔬 Science Max - EARTHQUAKES - Home Experiments 🌎.” YouTube, 1 Feb. 2019, www.youtube.com/watch?v=TLsqVjtrovo.

Rafferty, John. “Soil Liquefaction | Definition, Examples, & Facts | Britannica.” Encyclopædia Britannica, 2019, www.britannica.com/science/soil-liquefaction.

De Wolfe, Evelyn. “Triangular Towers Get High Marks for Earthquake Safety.” Los Angeles Times, Los Angeles Times, 3 Apr. 1988, www.latimes.com/archives/la-xpm-1988-04-03-re-712-story.html.

 

Acknowledgement

I would like to acknowledge my dad for helping me with some minor spelling and grammer mistakes along with helping to properly format some parts of my project. Also he helped me with shooting the videos for my project.

I would also like to acknowledge Mrs. Karen Davis and Mrs. Laura Rushton for help with some parts of the project.