Over the last decade, one new seismic design technology has been rapidly adopted in the US. The Buckling Restrained Braced Frame (BRBF) system is one of those rare innovations that radically improves the ability of structures to resist earthquakes, while at the same time is completely backwards compatible with previous technology. (See MSC articles from Sabelli & Lopez and Robinson for more information)
The ability of this system to resist earthquakes comes from a dramatically simple idea: decouple bending and compression. To show how easy this concept is, let us review how the inventor came up with it. An engineer, Benne Narasimhamurthy Sridhara from Bangalore, wanted to get more strength out of his braces (see my earlier post on braces for more info). He created a simple physical model using a small rod and a plastic pipe. He put the rod inside of the pipe and applied force on each end of the rod. Instead of the rod buckling out of shape and failing, the pipe held it in place. Brilliant!
A typical column buckling under applied load
Because the pipe (or sleeve) is not participating in resisting compression, it is “decoupled” from the rod. This means that the rod is continuously braced and will develop full material capacity. The implications of this small change are huge. It allows engineers to specify braces that:
- Will fit easily into existing designs, allowing retrofits and new construction
- Will act similarly in tension and compression, eliminating the need for paired braces at every location
- Help dissipate destructive seismic energy by steel yielding (like a car’s crumple zone)
- Remain stiff and strong even after the initial event
- Cost much less than comparable technologies
It’s a really awesome invention (patent info). The rapid uptake of this technology shows how important it is to the future of seismic resistant buildings. A recent article from India uncovered a little more of the interesting story behind its creation. It makes me wonder what structural engineering inventions will be discovered in the coming years. It goes to show that the simplest solutions are sometimes the best, and they are hiding in plain sight.
This technology can be applied in even more interesting applications as engineers grow familiar with its use. I am anxiously awaiting the first use of this in a bridge application. Congratulations to Mr. Sridhara for figuring out how to do more with less.
On January 12, a 7.0 seismic event centered close to Haiti’s capital, Port Au Prince, caused massive devastation. The collapsed structures and untreated injuries may cause up to 200,000 deaths.
The past few days have been a nightmare for people on the ground. The EQ knocked out much of the country’s fragile infrastructure. Haiti was a nation that was already in need of major assistance, having experienced 4 full-scale hurricanes last year and decades of political instability. A 7.0 EQ is absolutely a major event, and coming so close on the heels of last years problems is just horrible.
To put it in perspective, California’s Northridge EQ in 1994 was one of the USA’s worst disasters causing $20B worth of damage and it only registered a 6.7 magnitude. Haiti’s EQ caused strong lateral movements, and judging from the USGS map the accelerations were almost as strong as gravity. This is the structural equivalent of taking a building and turning it on its side, again and again.
Very few buildings can survive this type of movement undamaged. Haiti was even worse off because of their building materials. Many of the buildings were built from unreinforced, hand-mixed concrete blends. The images on TV show the results well enough, the TV crews probably don’t even need to look very hard to find examples.
As a structural engineer, it is always difficult to see the problems caused by improper construction and to know that many of the problems could have been avoided. Of course once an earthquake hits, engineers are powerless.
Using a list of simple rules engineers can easily design buildings that, for the most part, will preserve life safety. Designers of critical structures such as police buildings, hospitals, and bridges know in advance that they must make sure the structure will be operational in even the worst of events. The hospitals, bridges, and government buildings in Haiti appear to be worse off than other buildings, even.
So why do events like this happen? Engineers understand earthquakes, but that is only one step in the chain of safe construction. Simply stated, it is a political failure. Building codes are rolled back by politicians, with the excuse that they are too expensive. Contractors pay bribes to inspectors to pass suspect materials and shoddy workmanship. Engineers are asked to turn a blind eye in the name of patriotism. The problem with this “build quickly” theory is that the buildings remain and the legacy of poor construction becomes a ticking time bomb.
I am not trying to lay this problem at the feet of Haitians. I doubt many of them knew they were sitting on a fault line. They probably didn’t understand that reinforcing is required in columns for earthquake resistance. The engineering community needs to make a greater effort to encourage seismic resistant buildings in developing nations.
The engineer’s sole weapon against natural disasters is good design. If engineers aren’t proactive in the political realm or if engineers cede their responsibilities, then they will fail in their duty to protect the public welfare.
Anyone interesting in helping the efforts in Haiti should donate to the American Red Cross disaster relief foundation. Engineers wanting to donate specific skills should go to the ASCE Disaster Assistance page.
Last Monday, April 6th, a 6.3 Magnitude earthquake struck central Italy. Centered near L’Aquila, Italy, the seismic event was not particularly strong nor intense, but it has caused a large amount of damage.
Here is the USGS Quakemap for the event. Check out my related posts (label = seismic) if you need help reading it.
A week later, it appears that there will be about 300 casualties due to the earthquake and the aftershocks. Central Italy is famous for its Medieval, Renaissance, and Roman structures, so there is a huge stock of buildings that are susceptible to seismic events. Unfortunately, it turns out that some of the worst performing structures have been built in modern times under the jurisdiction of codes requiring seismic resistance.
The post-quake analysis seems to indicate poor construction quality and lax oversight from building inspectors set this seismic time-bomb in motion. The general public of central Italy has been told (just like the rest of us) for several decades that modern structures are different, they will be safer when disaster strikes. However, something in the system broke down and the reality of the situation did not meet the promises.
This could happen anywhere in the world. Political corruption, designer negligence, or ignorance of builders are commonplace. Each one alone is a huge problem, so faced with three issues beyond their control individuals often feel that they can do nothing to help.
I don’t think we can ever remove risk from our structures entirely, but the three problems discussed above can be addressed by the general public. It all comes down to accountability. We must hold our politicians accountable in the following ways:
- Only elect politicians who have proven themselves capable of understanding technical and scientific issues. Do not vote for someone who has an anti-scientific or anti-intellectual agenda. Someone who makes up their mind before they understand the issue will not be able to solve any problems.
- Enforce transparency and freedom of information rights. This will prevent graft and corruption in the securing of construction contracts and inspection of projects.
- Do not allow politicians to pardon or protect engineers, architects, builders, or contractors after a major disaster, beyond what is allowed by the laws currently in place. Statements like “we need to look to the future, not the past” or other broad statements absolving those responsible of criminal misconduct will only perpetuate the problem.
Italy is beginning the process of holding people accountable. People there are angry and looking for answers. A NY Times article discusses an Italian official who claimed that such a light seismic event would not have caused any deaths in California. Another story by BBC discusses the strange case of the San Salvatore hospital, built in 2000, which suffered a partial collapse during the earthquake. This is unthinkable in a place like California, or most of the countries where earthquakes are a way of life. And finally, a BBC story about beginning the process of investigation.
I’m not saying we should be on a witchhunt whenever a building collapses, but when hundreds of people die due to an expected event then we need to investigate why this is happening. If there is no clear way to attribute accountability then we need to figure out a better system. Engineers and architects are signing off on their designs, I am sure those will be reviewed. Someone needs to be signing off on the finished building, someone who will be damn sure the designs are followed through.
Heads up for all the building designers out there… Bracing is Beautiful!
There are very few building systems as cheap and efficient as braced frames. Allowing your engineers to put just a few braces in the building will make them a very happy person. You’ll see a lower cost per sq. ft of building, use less material, and make a green statement. Moment frames open up the floor areas, but you sacrifice a lot of room for the deeper beams, bigger columns, and tricky connections.
The most important reason to consider bracing is that people love seeing structure expressed in their buildings. It worked for the Hancock Center in Chicago, and it can work for you! There are buildings and architectural styles that it won’t work for, but you can hide the braces pretty easily.
There are many flavors of bracing. Concentric, eccentric, chevron, knee, buckling restrained braces, multi-story bracing, etc. Just put those terms into an image search and you’ll see a world of options waiting for you.
If you are concerned about exposed steel members (fire resistance, corrosion, vandalism) then you may want to coordinate with a specialist during your initial design. If appearance is a concern, then I strongly recommend you consider some of the newer imported components available. For smaller loads, a pin-connected rod from StaLok will work, whereas for a Cast Connex bracing component can handle even large bracing forces seen in high seismic areas.
We all want to do our part to help the owners get the building they want – at a reasonable cost with great performance. I think recommending a bracing system is a great way for engineers to add value to the project, without the high initial cost of shearwalls or moment frames.
Hopefully you guys remember the EQ in china (7.9M) from a few months earlier. The Chinese gov’t has now posted some expected costs for rebuilding efforts. Total expected costs are $147B, which is an almost unimaginably large cost. For comparison sake, the Northridge EQ (6.7M) in California cost a total of $12.5B and was one of the costliest disasters in US History.
One of the larger costs will undoubtedly be the rebuilding of 3400 schools and strengthening a further 2600 schools. How did so many schools collapse? It’s hard to pinpoint blame in a situation like this. Was it the engineers fault – a faulty design? Or maybe construction crews built it wrong? Or maybe the building inspectors who signed off on the building? Or perhaps the national government for not providing financial support or motivation to meet the applicable building code?
It should be noted that China has a modern building code, and that any of their new modern skyscrapers will probably compare pretty well to US skyscrapers. But the lower profile of rural schools and other buildings probably made them easy targets for low quality construction in return for bribes to local officials. While I haven’t personally investigated any of those sites, it seems a likely probability because students were so disproportionately affected by the earthquake.
Certainly, any developing nation has a hard choice to make between investing money and resources in EQ resistant buildings vs. building cheap and quick and hoping the big event never comes. Poor choices create a legacy of risk that future generations must live with. We all have a different personal tolerance for risk, let yours be known.
A case in point – one of the heroes of the EQ in China was a school principal in the area, Ye Zhiping, who led efforts to strengthen his school against seismic events. All 2323 students in the school were saved. The total cost for the work was about $60k, or about $25/student. I’d say that was a pretty large return on the investment.
For owners/engineers/architects looking to estimate how much it would cost to do an actual seismic renovation or upgrade to an existing building, see this online calculator.
You have a few options to get an answer, but I recommend using the detailed option and form entry. When I go through the exercise using my own building, I get ~$82 per sq. ft. which works out to a total cost of $500k for a complete seismic retrofit. I promise to get around to that as soon as I can…
Note that the choices you make can have large consequences on the overall cost. When I choose a lower the lowest goal of “risk reduction” and limit other anticipated work then the cost drops to half of the original $82/sq.ft.
The methodology is based on a database of retrofit projects. It knows how much those projects ended up costing, so it can compare the variables chosen for your project against the database and come up with an accurate market driven answer. Pretty nifty. Now you can tell your clients that you have a pretty good idea how much the work will cost. Of course, you might want to really investigate the options and help menus before you submit any numbers from it. And don’t forget to convert the answer to today’s values, because the cost it gives you is in terms of 2002 dollar values.
There was an earthquake in China on Monday. A 7.9 Magnitude earthquake in Sichuan province, to be more specific. Unlike my comments on the midwest earthquake earlier this year, this was not a good event. It was horrendous. We get earthquakes like this a few times a year throughout the world, but a lot of times they won’t hit near a populated area. This one really hurt a lot of people. Here
is a BBC website showing the affected area in detail.
There are a lot of photos and videos available on the web or youtube dealing with people who had video rolling during the event. Probably the most dramatic was this series
of still images on the BBC website taken by a wedding photographer. First one here shows the lovely church in the background. The next one shows the church after the earthquake.
A large earthquake can cause absolute devastation. Destroying the infrastructure of an entire region. Hospitals are closed, no power or communications, no gasoline, no passable roadways, and nowhere to sleep with a roof overhead. Shakemap below from USGS
shows a very high shaking intensity.
The human impact from the earthquake included 50,000-80,000 expected casualties, 5 Million people homeless, and a complete breakdown of infrastructure. China is well positioned to absorb the collateral costs, but there will be a lot of questions to answer. The first is why so many schools collapsed. You usually expect a public building funded by the government will meet very high safety standards. That did not appear to be the case, and it may be a result of regional construction methods, improper design, or outright fraud by construction officials.
The larger public policy issues will also need to be addressed:
- whether existing buildings in China are safe at all – this is especially important for the olympics
- whether China’s current building codes correctly address the safety requirements for public buildings and schools
- whether China’s enforced low-pay rates have encouraged third-world construction methods and outright corruption in a modern country
- once buildings are verified to be safe, what about the infrastructure
One of the main problems with the relief effort was gauging what response is needed. China appears to be taking the kitchen sink approach, and I think that is wise. They are center place on the world stage right now, no time to ignore a major disaster like the Myanmar cyclone response. They are limiting free access to the affected area, but there seems to be enough information getting out to the other cities so that it’s not really an issue. I think that by this point people have a good idea of how many people have been affected, now it is just an issue of getting relief efforts there.
The roadways have been destroyed by earth movements, landslides, and similar problems. You can’t just drive in and deliver supplies, especially to the remote villages. Now there is a concern that the earthquake and aftershocks have weakened the reservoir dams in the area. I’m sure a massive flood would add a lot of misery to the region, so let us hope that the dams hold. The worst hit city also has a landslide blocking a river, so flooding is now an issue for the epicenter.
Temporary housing is a huge concern for any major disaster. How would any regional government accomodate 5,000,000 homeless citizens? The challenge is monumental. Any permanent or even short-term structures must be built to the highest standards because of the risk that after-shocks present. To underscore this fact, the Chinese government is rejecting all offers of assistance from foreign countries, except tents. Most of the towns in the area have now become tent-cities. The larger cities have increased in size as refugees from smaller cities come looking for food and shelter.
These issues of temporary housing, disease/death, and collapse of economic activity are common to most disasters. The 2008 7.9M EQ in China was similar to the 1906 San Francisco 8.0M EQ. Compare the historic photos of San Francisco with those coming from the earthquake in China.
San Francisco, 1906
Here are photos of some of the rescue efforts. Here is a powerpoint presentation written for the Katrina recovery effort based on previous earthquake disasters. It’s well done and has some great information regarding disaster preparedness and relief efforts.
Governmental response can’t save everyone after an emergency. But the government response can rescue a lot of people and facilitate a return to normal life. Successful disaster response must be planned well ahead of time. If you are concerned about disaster response in your community you should be doing two things – first make sure you have a short-term and long-term plan for your family, and second write all your local politicians and let them know how you feel, as that will help them allocate resources to what people think is important.
For those who have more than a passing interest in Earthquake research happening in the Eastern US (i.e. not California) we have plenty of resources.
First off is the USGS – US Geological Survey. They are the clearinghouse for all things dealing with rock, soil, faults, etc. You will still need a qualified soils engineer to determine site classification, but their soil explorer program can sometimes provide you with some interesting advance information. If a previous soil boring was reported to the USGS, and it showed bedrock at 5 feet, you can make an assumption that soil classification will be favorable.
Next up is the Mid-America Earthquake Center. This is a group of researchers dedicated to mitigating the possible problems that a large earthquake in the Central US might cause. They especially focus on the many historic buildings (unreinforced masonry) and even modern buildings that were built before awareness of the seismic risk in the area. The worst historic earthquake (magnitude, not damage) was in this area, so there is a good reason to be concerned. A good source for graduate funding, too.
Then there is the Central US Earthquake Consortium. This was started by FEMA to handle the human aspects of Earthquakes. So this doesn’t deal so much with research, but is all about the government response and disaster preparedness/awareness. It’s all about coordination. A good resource nonetheless.
CERI is another great resource. They have a lot of independent information, as well as links for teachers and students. Was able to find a waveform taken from a Missouri station of the earthquake here. These people also have graduate funding programs available for students.
More general information about midwest earthquake risks:
New Madrid Seismic Zone
Wabash Valley Seismic Zone
I believe the most important thing when anyone asks an engineer about these topics, or related disaster topics such as building collapses, hurricanes, etc. is to refer them to the appropriate spokespersons for our industry. Alternatively, read up or interview someone from one the groups in advance if you know that a newspaper or media outlet will be contacting you for a response. It is essential that the public knows the most recent information and that we present the consensus opinion to the media. Don’t take the fools way out and use the publicity to invent your own conspiracy theory.
update – 5/30/08
How could I forget about NEHRP? The National Earthquake Hazards Reduction Program is another government entity dedicated to reducing earthquake losses in the US. This is a great resource for any structural engineer dealing with seismic design. It is especially relevant for older buildings that are being updated or going through seismic hazard mitigation. The methodologies used are somewhat different from the IBC and UBC code provisions for new buildings and you won’t always get a “yes/no” answer on a design. They have also posted a recent newsletter describing the efforts to develop a consensus based document for performance based design of seismic resistant structures. See the interim FEMA 461 document here.
Everyone by now has probably already heard of the earthquake that took place on Friday. See USGS data for information on our little friend. It was centered about 150 miles away from Indianapolis, but still quite powerful when it arrived. The attached map from USGS shows the event intensity and peak ground motion.
This earthquake did a lot of good things from my perspective, and didn’t really cause any harm to properties or people. Those are the kind of earthquakes that save lives, in my opinion.
First, it brings earthquake and emergency preparedness back to the forefront of media attention, and that is always good. Next, it reminds building owners that they have an obligation to build and maintain safe structures. But most importantly (from my point of view), harmless earthquakes give structural engineers a great opportunity.
I think going through an earthquake can give just about any engineer a better understanding of how the ground moves. Looking at seismic data for historic events, it just doesn’t affect you the same way as experiencing an actual event. What I learned was this – the ground (and building by extension) does indeed move. I can imagine that a bad earthquake would be truly terrifying. I also learned that earthquakes make noise. It was a low rumbling noise, not loud at all. I also learned that nothing I had experienced in my life so far resembled what happened, but I have to say the Modified Mercalli Intensity measurements are pretty accurate if you need a comparison. See Wikipedia Intensity article for a good explanation.
Now for a little science lesson… Earthquake magnitude is measured by the “Richter Scale” typically. This represents the energy released during an event, and is related to the waveform of movement radiating from the epicenter. It is a mathematical measurement, and completely free from objective interference by people. A 5.2 magnitude earthquake somewhere else in the world releases the same amount of energy as the one in Illinois did. One note about the Richter scale is that is a logarithmic measurement. Thus, a 6.2 EQ would indicate of release of 32 times more energy than the 5.2, while a 7.2 EQ would be 1000 times more energy. In other words, if you thought the 5.2 was scary you ain’t seen nothing yet. See Wikipedia Richter Scale article for more info.
Now, the effect of the earthquake has a lot to do with the specific area it occurs in. Here in the midwest, we have a wonderful rock layer that transfers and amplifies the waveform quite easily. So it’s not surprising that people all over the Eastern US felt this. The Modified Mercalli intensity scale includes the actions of the soil and rock, so it’s more useful for discussion when talking about structural engineering. We experienced a III-IV level intensity here in Indianapolis. Which is pretty amazing considering how far away the epicenter was. If a large earthquake were to hit the New Madrid fault in Northeast Arkansas, like many geologists say could happen, it is likely that many places in the Eastern US will be affected. It may not happen for 2500 years, it may happen tomorrow.
Back to the post at hand – This EQ gives structural engineers an opportunity to discuss seismic events with clients, business owners, and the public. It is essential that they understand the real dangers of earthquakes in the Midwest. We should not misrepresent the danger or try to scare people, but do let them know that they have choices when it comes to EQ design. Any building can be made more robust. Masonry parapets can be secured against toppling, gas and water pipelines can installed with flexible connections, and hospitals and important bridges can be designed such that only an atomic bomb will close them down. It’s a lot of work, it’s expensive, and construction proceeds slowly. However, they say the best time to patch a roof is when the sun is shining.