Seismic Building Codes Cost More But Save Lives.
"I THOUGHT MY HORSE WAS about to die, and would have sprung from his back ... but at that instant all the shrubs and trees began to move from their very roots, the ground rose and fell in successive furrows, like the ruffled waters of a lake, and I became bewildered in my ideas, as I too plainly discovered that all this awful commotion in nature was the result of an earthquake..."
So wrote naturalist John James Audubon in his account of an earthquake in January 1812 along the New Madrid fault in southern Missouri and northeast Arkansas.
When the New Madrid quakes, the most violent in U.S. history, occurred between December 1811 and February 1812, the area was sparsely populated and largely undeveloped. The greatest loss of was among boatmen swamped swept overboard by violent waves on the Mississippi River.
Today, the greatest threats are falling concrete and glass from tall buildings -- threats minimized in newer construction in northeast Arkansas by the state's seismic building codes.
Adopting and enforcing seismic code provisions comes at a cost, however. Construction costs to meet the seismic requirements of Act 1100, which was adopted by the Legislature in 1991, can increase the price of a building from 2 to 10 percent, depending, on the type and size of the structure, according to several architects, engineers and builders in the state. Retrofitting older buildings can increase the cost by as much as a third. "There is no earth-quakeproof building," said Tom McMillan of Garver Engineers of Little Rock. "But designing a structure to existing seismic codes will mean that it won't, fall down. It can still be heavily damaged, however. And loss of life wilt be lessened, but not entirely eliminated, if buildings are built to code."
Two recent earthquakes give quick evidence of the wisdom of adopting stricter building codes in areas near known faults. On Feb. 28, a strong quake measuring 6.8 on the Richter scale resulted in only one death in the Seattle area, where seismic building codes are in effect. An even stronger earthquake in India on Jan. 26 left thousands dead, mainly because flimsy buildings fell like sandcastles.
Over time, as new buildings replace older ones, communities in northeast Arkansas will find that more stringent building codes will be a good investment by providing a much safer working and living environment.
The Big One
But what if there isn't enough time to replace or retrofit the older structures?
"The New Madrid zone is the most active, the most dangerous zone in the country," said Dr. Haydar Al-Shukri, director of the Arkansas Center for Earthquake Education and Technology Transfer on the campus of the University of Arkansas at Little Rock.
Seismic statistics indicate there's an 80-90 percent probability of an earthquake of 6.5 magnitude or greater occurring along the fault in the next 15-20 years, he said.
"Typically, a damaging earthquake in this area -- of magnitude of 6.0 or greater -- occurs about every 80 years," he said. "The last one occurred at Charleston, Mo., in 1895."
The New Madrid fault, although not visible like some faults in California, is the greatest earthquake risk east of the Rocky Mountains. It stretches 150 miles from Cairo, Ill., through New Madrid and Caruthersville, Mo., and on down to Blytheville and Marked Tree.
Damaging earthquakes along the New Madrid fault are less frequent than along the West Coast, but when they do occur, the damage can be far greater because of the underlying geology.
The New Madrid seismic zone is actually a series of faults beneath the continental crust in a weak spot known as the Reelfoot Rift. It crosses five state lines and the Mississippi River in at least three places.
While a strong quake is not unlikely, the possibility that a catastrophic event like the quakes of 1811-12 will happen soon in the New Madrid seismic zone is small, according to a study by the Center for Earthquake Research and Information at the University of Memphis.
Scientists believe that catastrophic quakes -- those with magnitude of 8.0 or higher on the Richter scale -- occur in the New Madrid region every 550-1,200 years. A major earthquake, magnitude 7.0 or greater, happens every 254-500 years or so.
An earthquake of 7.0 would be felt throughout much of the central and eastern United States. Damage could amount to several billion dollars, the study said. A quake in the 6.0 range would cause damage to older structures, especially those of masonry construction. There could be serious damage to many schools in the region.
"The issue is not an earthquake of the scale of the 1811 New Madrid event," Al-Shukri said, but one of 6.0-6.5 magnitude that could collapse buildings.
The New Madrid fault system averages more than 200 earthquakes per year. Of these, only eight to 10 are strong enough to be felt.
A magnitude of 2.5 on the Richter scale is the smallest usually felt by humans. Every increase of a whole number means the ground motion is 10 times greater. For instance, an earthquake with a magnitude of 3.0-3.9 could cause minimal damage -- possibly cracks in old buildings. One of 4.0-4.9 magnitude could damage older buildings and cause cracks in most buildings.
Making Buildings Safer
"It seemed as if the surface of the earth was afloat and set in motion by a slight application of immense power, but when this regularity is broken by a sudden cross shove, all order is destroyed, and a boiling action is produced, during the continuance of which the degree of violence is greatest...; houses and other objects oscillate largely, irregularly and in different directions. ... The damage done was considerable; gable ends, parapets, and chimnies of many houses were thrown down."
Jared Brooks, an engineer and surveyor, recorded the effect of the 1811-12 quakes on his home in Louisville, Ky., nearly 300 miles from the epicenter. His anecdotal observations support what seismologists now say about New Madrid earthquakes: They aren't like West Coasts quakes.
While West Coast high-rises are built on shock absorbers that allow the buildings to flex and sway as earthquake waves roll by, those building techniques aren't useful in the New Madrid area, where the soil essentially turns to quicksand during massive quakes.
The New Madrid fault area is composed of thick water deposits of soaked, unconsolidated sands and muds left by the Mississippi River. Such loose and sandy materials, intensify the shaking of the earthquakes.
Also, the New Madrid region is made up of rigid basement rocks estimated to be more than 1 billion years old, so seismic energy is transmitted farther and more efficiently.
The fact that waves travel farther and with more efficiency is a reason that earthquakes with the same magnitude as those in other regions have more intensity and cause more damage. A strong New Madrid earthquake could be felt from Canada to the Gulf of Mexico, and from the Rocky Mountains to the Atlantic Coast.
Some Western states have had quake-resistant structural requirements since the early 1930s. Greater understanding of earthquakes has improved construction designs. Among the features now demanded are:
* Specific configurations of steel-reinforced concrete.
* Foundations extending down to bedrock.
* Stiffer building frames.
* Facades that fasten on to the building's steel frame.
* Shatter-proof windows to prevent glass shards from causing lethal injuries.
Danny McDaniel of Ramsons Inc., a Jonesboro construction company that works in the state's most severe quake zone, said increased costs depend on function and size.
"The heavier and taller a building is, the greater the cost to make it earthquake-resistant. Lighter and lower buildings won't see much of an increase in cost," he said.
Builders in northeast Arkansas try to make buildings stiff and more rigid by laterally bracing the walls and using earthquake ties and reinforced bars ("rebars") to tie it all to the foundation.
"When a earthquake hits in northeast Arkansas, it's going to create a wave that's like cracking a whip. We, have to build a structure rigid enough so it won't crack when the backlash comes," McDaniel said.
In addition to foundational and structural elements, gas pipes, water lines, wiring, equipment, lighting fixtures and anything else that can come apart have to be tied down, according to Bill Hannah, president of Nabholz Construction of Conway.
George Krennerich of the Jonesboro architectural firm of Brackett-Krennerich & Associates said the state building code is designed to make a building solid from the ground up by adding more steel and bolting it all together so that it shakes as one piece.
Krennerich's firm designed the Arkansas State University Library, which is eight stories tall and has a bell tower on top of that, making it one of the tallest structures in northeast Arkansas. He estimates that building it to meet seismic code requirements added 10 percent to the project's cost.
"Triangles are the strongest designs," Krennerich said. His buildings make extensive use of triangular bracing to form X-bracing.
What scares Al-Shukri and Garver's McMillan are old concrete block schools throughout the area.
"They will collapse and kill a bunch of kids," McMillan said. "It's a travesty, the danger those folks are putting their kids in."
Al-Shukri said northeast Arkansas is not prepared for a major quake at all.
"An earthquake the size of the expected 6.5 magnitude would demolish Blytheville," he said. It's easy to see what happens when structures are built of unsupported concrete block, he said. "They're coming down."
Al-Shukri and McMillan agreed that the seismic requirements, if properly enforced, would save lives. But Arkansas' seismic code applies only to public structures. Single-family residential, duplexes, triplexes, fourplexes and agricultural structures are exempted. And authorities can grant waivers.
Some buildings have been constructed outside of city limits where there is no effective enforcement of the code. And that bothers McMillan. Some were built with little concern for the safety of people working there, he said. Building regulations were often ignored to get a building in place to begin production.
Mayor Hubert Brodell of Jonesboro, one of the fastest-growing cities in the state, says the city has annexed 45 square miles as the city has expanded. In the process, some of the buildings in the land annexed were not built to city specifications. He said the city is trying to work the owners in bringing them up to standard.
On the other hand, he notes that most of the growth and new construction has taken place in the past 20 years, so Jonesboro may be better off than some other towns in the area.
The key to safety is designing by the code, McMillan said.
Al-Shukri reflects that, in time, many of the old buildings will be replaced by new buildings that follow the seismic building codes. But that's a slow process.
And no one knows how much time there is until a big quake hits.
"It's not a question of if, but when," McMillan said.
How Often, How Strong? Magnitude Expected Rate (yr) 4.0 14 months 5.0 10-12 yr 6.0 70-90 yr 7.0 254-500 yr 8.0 550-1200 yr
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|Comment:||Seismic Building Codes Cost More But Save Lives.|
|Article Type:||Brief Article|
|Date:||Mar 12, 2001|
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