STEM

Welcome to STEM! This class is taught by Dr.C. During the majority of A term, STEM class was used to introduce us to the basic concepts of brainstorming and research. Transitioning to the B term, we focused more on developing our projects and planning testing strategies. Along with the progression of my project, I also learn about the technical writing of different parts of a scientific paper such as the Introduction, Results, and etc.

Earthquake and Tsunami Resistant Structural System Design for a Risk Category IV Hospital

This project focuses on designing an earthquake and a tsunami resistant structure. There are two main parts to this project: facade testing and structural testing. The facade testing was conducted in a real life simulation of a tsunami while the structural testing is conducted in a CAD program called Risa3D. The facade testing shows that a round facade would withstand less hydraulic pressure than a traditional rectangular facade. The structural testing achieved a structure that can withstand 32,421 kips in earthquake load and 62.79 kips in hydrostatic load and 60 kips in hydrodynamic load.

Abstract

Tsunamis are rarely studied due to their infrequent occurrence. However, during and after each tsunami event, the affected areas suffered immense social and economic losses. For example, the Tohoku tsunami in Japan in 2011 cost 200 billion USD for Japan alone and a total of 131 million USD for the United States. Despite these tragic consequences of not being prepared for a tsunami, there is not enough research regarding tsunami-resistant structures, which would reduce the major causes of deaths during a tsunami such as drowning, getting trapped in failing structures, and getting crushed by the debris in the water (Tsunamis, n.d.). The objective of this project is to design a structural system for a hospital that can effectively resist or withstand the force of an earthquake and a tsunami. This project designed and analyzed a structural system consisting of rectangular beams, round columns, and other load-supporting members in Risa3D, and tested a curvy cylindrical facade that helps to reduce the hydrostatic pressure on the structure. The designed structure in Risa3D is composed of 36in. diameter round concrete columns with 28x20in. rectangular concrete beams and W14x550 hot rolled steel braces. The structure can withstand a total earthquake load of 14,430.405 kips in the X direction and the same magnitude in the Z direction. The structure could also withstand 62.79 kips in hydrostatic pressure and 60 kips in hydrodynamic pressure. The maximum drift ratio percent of the structure is 0.093%. The result of the facade testing shows that the round structure design experiences 48.9% less pressure on average compared to a rectangular design. The facade testing shows that a circular structure is more ideal in tsunami-prone environments compared to a rectangular structure.

A graphical abstract

Click here to view the Research Proposal!
Click here to view the Literature Review!

Engineering Need

Earthquakes and tsunamis often cause structures to collapse due to seismic shaking and hydraulic load.

Project Objective

The goal of this project is to design a structural system that can effectively resist or withstand the force of a 9Mw earthquake and a tsunami with an inundation height of at least 10m.

Background

A graphical abstract

Earthquakes are caused by the interaction between tectonic plates. The sudden relief of stress between two tectonic plates generates a large amount of energy in the form of seismic waves. There are three common types of tectonic plate interactions: divergent, convergent, and strike-slip faults. The type of tectonic plate interaction that is focused on in this project is the convergence of two tectonic plates underwater, also known as a subduction zone. Subduction zones are mostly present around the edge of the Pacific Ocean tectonic plate. If an earthquake in the subduction zone is strong enough, it can cause the displacement of a large volume of water in a ripple effect. This series of waves of water can travel as fast as 800km/h in the deep ocean (How Does Tsunami Energy Travel across the Ocean and How Far Can Tsunamis Waves Reach? - International Tsunami Information Center, n.d.). As the series of tsunami waves approach a shoreline, the slope of the shoreline causes the shoaling of the waves, in which the slope of the shoreline slows the waves down and causes an increase in the height of the waves. The height and velocity of the waves depend on the shoreline profile of a given sight (Chock, 2016).

The 2011 Tohoku earthquake in Japan, with a magnitude of 9Mw, generated an unexpected tsunami on the East Coast of Japan (Suppasri et al., 2013). The Tohoku earthquake and tsunami resulted in about 18,000 deaths and 6,157 injuries in Japan. The tsunami alone caused the collapse of 123,000 houses and damaged millions more (On This Day, 2021). The Tohoku tsunami not only affected the East Coast of Japan but also countries like Russia, Taiwan, and China. Tsunamis not only impact Japan but also areas in America. There are 46 reported tsunamis in America that exceeded the inundation limit of 3m. Out of the 46 reported cases, 16 occurred in Alaska and 18 occurred in Hawaii (Dunbar & Weaver, n.d.). The number of cases in which the inundation limit exceeded 3m shows the vulnerability of the American Pacific coast and territory to the detrimental impact of tsunamis.

Structures often fail during an earthquake due to seismic shaking. Seismic shaking of earthquakes is composed of P waves, S waves, Raleigh, and Love waves. P waves push and pull the ground parallel to the direction of propagation, while S waves affect the ground perpendicularly to the direction of propagation. Raleigh waves roll the ground, and Love waves horizontally shear the surface of the ground (Seismic Waves, n.d.). The shaking of the ground causes lateral displacement and interstory-drift that could cause a building to systematically collapse.

The effect of a tsunami on a structure includes hydrostatic, and hydrodynamic forces, debris impact, and scour effect (Chock, 2016). Hydrostatic load is the lateral load placed on the structure, for example, buoyant uplift force, or water surcharge load. Hydrodynamic forces include drag force, the impulsive force of tsunami bores, and water pressure. Debris impact factor in how debris carried by the flooding of the tsunami will affect the performance of the structure. Scour effect is caused by the washing of soil around a structure’s foundation (Chock, 2016). The force of a tsunami focuses on the lower stories of the structure compared to an earthquake.

Method

2 2

Two 3D printed models were designed in SolidWorks (Figure 1 and 2). The dimensions of the models were scaled down 555 times from the actual structural design. The two models were printed and tested in a tank of water. A BME280 pressure sensor is attached to a straw system. The straw system consists of two large straws connected in an L shape. The horizontal straw passes through the structure and the vertical straw allows the pressure sensor to be connected without putting the pressure sensor underwater.

Figures

2 3
2 3

Analysis

Across the testing of the 4 models: MidRect, MidRound, SideRect, and SideRound, the result shows a peak change in pressure 4 seconds from the time the test starts. The average peak change in pressure at t4 for MidRect, MidRound, SideRect, and SideRound are 1.354, 0.692, 0.511,1.293hPa respectively. After 4 seconds, the pressure drops below the original pressure and then comes back up to be relatively equal to the original pressure. The table below shows the change in pressure value for each trial within each test.

ddf

The t-test performed on MidRound and MidSquare has the ***p-value less than 0.001. The t-test performed on SideRound and SideSquare has the **p-value of 0.01. The p-values of both of the t-tests suggest that the null hypothesis should be rejected and that there is a difference in the change in pressure between the square model and the round model.

The building designed in Risa3D was analyzed using the Finite Element Method. The results were presented in an enveloped solution which shows the maximum and minimum as well as the governing loads that determined the maximum and minimum. The maximum deflection of a member in the local X direction is 1.236in. in M1853. The maximum deflection in the local Y direction is -1.236in. in the member M1850. The maximum defection in the local Z axis is -0.011in. in the member M2067.

The maximum drift ratio among all 7 rigid diaphragms in the X and Z direction is in diaphragm 6, 0.093% and 0.085% respectively. The Drift% refers to the percent ratio of the horizontal displacement of a story to the height of the story, which is 20ft high. The magnitude of drift in each story in the X Direction is shown in Table 5. According to the Design Guide for Improving Hospital Safety in Earthquakes, Floods, and High Winds by FEMA in 2007, the drift limit for essential buildings is 1% of the floor height. Therefore, the model designed in this project satisfies the drift limit.

Discussion and Conclusion

In future research, for the facade testing, the sizing of the straw could be altered on the round model to ensure equal opening area which would lead to a more accurate measurement of the change in pressure. For structural testing, more affordable solutions should be developed and analyzed as well as more considerations in regard to the foundation of the structure.

In future research, for the facade testing, the sizing of the straw could be altered on the round model to ensure equal opening area which would lead to a more accurate measurement of the change in pressure. For structural testing, more affordable solutions should be developed and analyzed as well as more considerations in regard to the foundation of the structure.

This project designed and analyzed a structural system consisting of rectangular beams, round columns, and other load-supporting members in Risa3D, and tested a curvy cylindrical facade that helps to reduce the hydrostatic pressure on the structure. The designed structure in Risa3D is composed of 36in. diameter round concrete columns with 28x20in. rectangular concrete beams and W14x550 hot rolled steel braces. The structure can withstand a total earthquake load of 14,430.405 kips in the X direction and the same magnitude in the Z direction. The structure could also withstand 62.79 kips in hydrostatic pressure and 60 kips in hydrodynamic pressure. The maximum drift ratio percent of the structure is 0.093%. The result of the facade testing shows that the round structure design experiences 48.9% less pressure on average compared to a rectangular design (**p less than 0.001). The facade testing shows that a circular structure is more ideal in tsunami-prone environments compared to a rectangular structure.

References

1
2
3
4

Poster