Designing Houses to Withstand Earthquakes

During an earthquake, an average of 22 of 1,000 people experience life-threatening injuries. This is mainly due to houses not having high-quality and easily implementable structural designs. Walls give out letting roofs slide and foundations crack. In California, earthquakes occur every 3 minutes on average. Every year there are also 2 to 3 earthquakes of 5.5 or higher magnitude on the Richter Scale. This common occurrence causes strains to the walls and foundation making it even more important to have good-quality structural designs. Unfortunately, the cost of building an earthquake-proof home is a major factor in why many people aren’t able to have the high-quality structure that they require. To address this issue, I created a scale model house with walls that can withstand earthquakes measuring up to 7 on the Richter Scale and is affordable and easy to implement. This is a guide to building an earthquake-resistant house following the engineering design process.

Designed with Fusion 360 2024

Prototype Supplies:

• 16 1 cm by 120 cm wood dowels          
• 1 Shake Table
• 15 kg Clay
• 1 Micro:bit
• 2 0.3175 cm thick 16x33.475 pieces of wood
• 2 0.3175 cm thick 16x34.875 pieces of wood
• 1 0.3175 cm thick 36.875x35.475 piece of wood
• 200 10cm by 10cm nonwoven sponges

To begin this project, I asked myself what was an issue that people struggled with in housing. I live in the bay area, and realized that many earthquakes occur in our region. I wanted to create something that can help houses be more sturdy during earthquakes and can help save people's lives.

My engineering goal is to develop a model of a building/house for the majority population so that they can be less affected during an earthquake, in a convenient, comfortable, affordable, and easily implementable way. The house is developed to help everyone, no matter their income, live their daily lives safer and less stressful. It is also developed in a way that lets people build the frames off-site and then transport them on-site so that it is easier to implement them.

• Earthquakes usually affect the foundation of the house which can cause the walls to become unstable and fall in. Usually, houses aren't able to survive a 7 on the Richter scale. The building has to be light because the smaller the reactive masses, the smaller the earthquake forces because that’s how inertia works.
• Necessary to reduce the connections of foundations with the soil – the source of seismic effects
• side faces of the foundations in contact with the soils accumulate (contribute to an increase the value) horizontal seismic effects on the foundation, leading to its displacement. In this connection, it is advisable leave an air gap to reduce these effects
• Reducing friction between the base of the foundation and the soils reduces the transmission of horizontal seismic effects on the foundation and at exceeding of the friction resistance contributes to the slippage of the seismic wave under the foundation
• Protection of the foundation by a trench is effective and depends on the depth, size and location of the trench closer to the building, from wavelength, type of foundation.

When brainstorming, I had many different ideas. I had the idea to focus on the entire house and create a foundation, walls, and roof that are sturdy. I decided to focus on one part of the house instead, as I wasn't sure if I could research, build, and test all of this in the time we had. I chose to focus on my walls and find architecture that can make it more sturdy.

While researching, I learned about inertia. For this project, I need the building to be lightweight because the smaller the reactive masses, the smaller the earthquake forces. I also found out that shear walls, cross braces, diaphragms, and moment-resisting frames are the keys to reinforcing a building. Shear walls consist of vertical and horizontal beams that create a square/rectangular shape. A cross brace is when two rods cross over each other in an X-shape inside of the shear walls. Together they help transfer movement away from the foundation and up towards the atmosphere. A diaphragm is a type of foundation that consists of a horizontal frame and floor slab. The diaphragm distributes forces to the columns and walls. It transmits lateral loads to the vertical resisting elements of a structure which in my case would be the shear walls and cross braces.

For the final design, the dimensions were 32 x 31 cm for the outer walls. For the interior pieces of wood, the dimensions are 29 x 26 cm for the inner walls. I also had 2 cm thick shear walls and cross braces made of 1 cm thick wood dowels. For the shorter, 31 cm wide side, 5 shear walls were going across and 4 shear walls going downwards. For our longer side, the 32 cm side, I had 6 shear walls going across and 4 shear walls going downwards for the longer 32 cm side. On either side of that, I had 10x10 cm cotton pads to represent insulation. For the insulation, I didn’t put cotton pads on the outer edges of the shear walls and cross braces. This allowed us to easily glue the ½ cm thick wood onto the wood dowels. Our walls are 3.2 cm thick. Our foundation is 3.75 cm tall which makes the total structure 23.75 cm tall. All of these dimensions met my criteria. To attach the walls to the foundation, I had to push the wood dowels 1 cm into our clay foundation. The roof was 32x31 cm and made out of a ½ cm thick wooden board. In total, the house cost $160 and our walls cost $130. The price also met our criteria. My plan is to test this design against a modern-day house replica on a shake table, to see which holds up better.

To start on the project, I created a scale replica of a modern-day house. I started with a foundation that is made of clay. It is 35x40 cm and 3.75 cm tall. For the walls, I used 2 1/2 cm 15.5x35cm pieces of wood and 2 1/2 cm 15.5x40 cm pieces of wood and wedged them into the clay. For the roof, I had a 1/2 cm thick 35x40 cm piece of wood.

To begin working on the design, I started with the foundation. The foundation/structure design had a design of Diaphragm Slab Foundation 7.5 cm tall. The bottom 3.75 cm is a horizontal frame. The horizontal frame is a 35 cm by 40 cm rectangle made out of clay with four 10 cm by 12.5 cm rectangles each 5 cm away from the other and the edge of the slab.

In this layer of the foundation in the top 0.5 cm, there are 6 16 cm wooden dowels with a diameter of 1 cm starting and ending 2 cm away from the edge and 6 cm apart on each of the 40 cm sides. In the top layer of the foundation, there are also be 6 16 cm wooden dowels with a diameter of 1 cm starting and ending 2 cm away from the edge and 5 cm apart on each of the 35 cm sides. These wooden dowels are coming up from the foundation to join into the shear walls and cross braces. The cross braces start 0.5 cm above the foundation. The cross braces are t-shaped structures that help even out/transfer the acceleration/force of the earthquake away from the foundation and house. There are 4 cross braces in between each of the 6 steel rods made out of totaling 20 cross braces on each wall. The cross braces on the 40 cm sides are 2.5 cm tall, 6 cm wide, and the diagonal lines are each 8.7 cm long. The number of centimeters total for the cross braces on each 40 cm side is 348 cm. The cross braces on the 35 cm sides are 2.5 cm tall, 5 cm wide, and the diagonal lines are each 8.5 cm long. The number of centimeters total for the cross braces on the 35 cm side is 340 cm. For the shear walls, there will be 5 38 cm long and 1 cm wide pieces of wood for the horizontal frames on each of the 40 cm sides and 5 33 cm long and 1 cm wide pieces of wood for the horizontal frames on each of the 35 cm sides.

After creating the sheer walls and cross braces, I wanted to insulate the walls with cotton pads that are 10x10 cm. I hot-glued them to ensure that they would stay on.

For the final design, the dimensions were 32 x 31 cm for the outer walls. For the interior pieces of wood, the dimensions are 29 x 26 cm for the inner walls. I added these on the inside and outside of the sheer walls and cross braces and nailed them in. I then added the root, which was 35cmx40cm.

I tested and analyzed the design criteria and constraints of the model house and will be primarily focused on testing the design on the shake table when it is at a speed of 1.0 g or 7.0 Richter Scale magnitude. First, I coded our micro:bit to chart the strength of the acceleration. I will code the seismograph and then look at the results to see when the strength is 1000 mg. The micro: bit measures in mg, so I will see when our strength on our chart reaches 1000 mg because that’s equal to 1.0 g. I then used the same speed on the shake motor each time I tested our model. I will compare the results of both houses to see which one had worse damage.

The first part of my data was recording the different speeds of our shake table. In order to do this I placed our house on our shake table and recorded the number of milligravities it shook for 5 seconds using a Micro:bit seismograph. Based on our data we concluded that mode 3 was equivalent to 1000 milligravities or 6 to 7 on the Richter Scale.

When we tested the modern-day house(House 1) on the shake table at mode 3 it had at least one wall collapse which resulted in the roof falling in throughout every test trial. The walls would also shake violently due to not having enough support. When we tested our house(House 2) on the shake table at mode 3 without its roof, the walls didn’t even shake due to its strong structural design throughout every single test trial. 

When I tested House 2 with its roof, none of the walls fell. Unlike the test trial without the roof, the walls did shake slightly. This was because the energy from the earthquake that was being spread out and brought up through our wall structure had nowhere to escape. If I were to further improve we would fix this problem by exploring houses and buildings with openings in the roof. (ex. Apple Campus, Traditional Japanese Houses)

The average size for a house is 50 ft by 50 ft (1524 cm by 1524). My house's size is 32 cm, so to scale the house up to an average size for an actual home is around 47 times. My price for our walls is $130. Scale that up for a regular house goes to $6110. The average house price for earthquake-proof interior wall frames is around $7,500. This is based on average interior wall framing being $3 per square foot according to Angie's list. Using this data my house is $1390 cheaper.

I set out to create a scale model of a house that can withstand earthquakes better than modern-day houses. I researched the best designs and soon came up with a design for the walls. I constructed shear walls and cross braces with insulation(cotton pads) and wood. I compared our house to a modern-day house and concluded that my house is more likely to withstand earthquakes. The cross braces and shear walls helped absorb the shaking from the shake table. Nothing collapsed which shows that this house is safer than the modern-day house, which collapses easily. In the modern-day house, the walls for an earthquake-proof house cost around $7,500, but in my house, they cost around $6,110. According to our findings, I was able to conclude that our house met all of the criteria and would be easy to implement, affordable, and cost-effective.

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