# Can Any Building Survive an Earthquake?

## Seismic Solutions in Symmetry

It is difficult to imagine any house withstanding the 7.4 kind of earthquake that shook western Indonesia in February 2008. Even the much smaller 6.0 quake in Wells, Nevada that same month managed to flatten dozens of buildings.

Later, in May 2008, a 7.9 earthquake in China sent shock waves through the world. What, if anything, could have saved the children who died in the collapsed school buildings or many thousands killed throughout the Sichuan Province?

Then Haiti in 2010. Christchurch, New Zealand and Japan in 2011.

In an effort to design safer structures, architects are learning from the research of earthquake engineers who study the stresses that earthquakes cause. Square and circular buildings seem to have the design edge.

### Available Options:

"During the duration of ground shaking, seismic energy is stored in a structure," writes structural engineer Eric Elsesser. "If the structure can safely dissipate energy as rapidly as it is input to the structure, no problem occurs." (FEMA 454, p. 7-38)

So how can we design buildings that will withstand the forces all around it? With an illustration of a flagpole, architect Christopher Arnold, FAIA, suggests these options for "tuning" a structure:

• Change the position of the weight to a lower height
• Change the height
• Change the shape
• Change the material
• Alter the base anchorage

(FEMA 454, p. 4-12)

From this options list of what can be done, what should be done?

### Engineering for Earthquakes:

It should come as no surprise that the Roman architect Vitruvius had it correct about symmetry and proportion. Balanced aspects of design and construction are also what 21st century architects must consider when engineering safe structures.

"Since ground motion is essentially random in direction, the resistance system must protect against shaking in all directions. In a rectilinear plan building...the resistance elements are most effective when placed on the two major axes of the building in a symmetrical arrangement that provides balanced resistance. A square plan...provides for a near perfectly balanced system."â€”Christopher Arnold, FEMA 454, p. 5-8

What characteristics are desirable for "near optimum seismic performance"?

• Low height-to base ratio. Minimizes tendency to overturn.
• Equal floor heights. Equalizes column or wall stiffness, no stress concentrations.
• Symmetrical plan shape. Minimizes torsion.
• Identical resistance on both axes. Balanced resistance in all directions minimizes torsion.
• Identical vertical resistance. No concentrations of strength or weakness.
• Uniform section and elevations. Minimizes stress concentrations.
• Seismic resisting elements at perimeter. Maximum torsional resistance.
• Short spans. Low unit stress in members, multiple columns provide redundancy, loads can be redistributed if some columns are lost.
• No cantilevers. Reduced vulnerability to vertical accelerations.
• No openings in floors and roof. Ensures direct transfer of lateral forces to the resistant elements.

(FEMA 454, pp. 5-6 to 5-8)

If a square building plan is "a near perfectly balanced system," a circular plan might be called perfect. The dome shape is the perfect balance in the eyes of some practitioners.

### Monolithic Domes:

"In a building in which the mass is approximately evenly distributed," explains Arnold, "the ideal arrangement is that the earthquake resistant elements should be symmetrically placed, in all directions, so that no matter in which direction the floors are pushed, the structure pushes back with a balanced stiffness that prevents rotation from trying to occur.

This is the reason why it is recommended that buildings in areas of seismic risk be designed to be as symmetrical as possible." (FEMA 454, p. 4-23)

No structure can withstand the powerful force of a major quake, but for communities on fault lines, monolithic domes are becoming a prudent choice. Just as these concrete shell buildings can withstand tornadoes and hurricane force winds, they appear to provide remarkable strength during earthquakes. How?

The word monolith helps explain. The prefix mono-, of course, means "one" or "single," and the Greek word lithos means "stone." The construction of a monolithic dome is one, continuous hard shell.

The shape of the dome is significant. As an experiment, take a raw egg and squeeze it with continuous, even force using your bare hand. The egg will not break, because the force you exert onto the hard shell is evenly distributed around the curved surface.

What other common objects are likewise constructed? Think of a construction worker's hard hat or a football player's helmet. The round shape distributes any force upon it. Why not houses?

Builders say monolithic domes are strong because they are self-supporting structures. During tremors, a dome acts like an upside down bowl. It moves with the ground instead of collapsing.

### Science into Practice:

Of course it's more complicated than even what's outlined above. Site planning is crucial to building an earthquake-tolerant structure, and risk management is often a function of economics. The failure of structures in a seismic event can be frustrating for professionals.

"Why," says Elsesser, "with all our accumulated knowledge, does all this failure continue? Buildings tend to be constructed essentially in the same manner, even after an earthquake. It takes a significant effort to change habits, styles, techniques and construction." (FEMA 454, p. 7-44)