Category Archives: Engineering

The Road on Two Wheels

Though I haven’t written much in the past year, I’ve been logging away thoughts (engineering, and otherwise). One in particular kept resonating with me last summer when looking over some road designs: how can you design a road for all vehicles without having driven them?

Designers rarely refer to books alone, but utilize experiences that back up the numbers. You’d be hard pressed to find a transportation engineer in the United States that has never driven a car; it’s the most prominent personal transportation method here. But you might more easily find transportation engineers that have never driven a motorcycle. Or an FHWA Class 8, four-axled truck and trailer. Yet we design roads daily, sometimes with the use of simulations, sometimes with nothing more than a reference guide and our engineering judgement. But there’s a disconnect there. Last October, I aimed to remedy one part of this problem and have some fun doing it: learn how to ride a motorcycle.

The MSF Course

I highly recommend the MSF Beginner Rider Course. In three days they have you prepped to pass the DMV rider test, without having ever ridden a motorcycle. Kim and I took the course together for fun and we had a blast. Click here to find a course near you.

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Road Design

Lets look at a standard road curve. While many characteristics of road design have remained for years, roadway curves changed drastically with the invention of the automobile. Super-elevated roads, for example, were inspired by cant railways, where the two rails are designed at different elevations to accommodate a “banked turn”. As a road designer, it’s easy to check the Green Book to find super-elevation guidelines, but they mean so much more with a bit of experience behind the wheel; anyone who has driven a vehicle faster than 30 miles an hour can recognize the importance of a banked turn. Superelevation can be even more important to motorcycle riders. Leaning on a motorcycle is a fantastic way to appreciate how banked turns work to your advantage and the turns reinforce the importance of getting your spirals, runoff, and runout lengths correct.

Road designers also immediately appreciate other successes and deficiencies of road design while riding a motorcycle. Adequate drainage for sheet flow during a storm, stopping and decision sight distances, pavement cross slopes, the condition of the pavement, and locations of road debris accumulation all become much more apparent. The affect of ANY road condition that could develop into a traffic safety hazard magnifies a hundred-fold, as do the consequences of a collision. Experiencing these road conditions on two wheels can be both humbling and horrifying.

For those more interested in the physics side there is a whole subject on the mechanics of bicycle and motorcycles which explains leaning and counter-steering at high speeds. These, along with the center of gravity of the bike, can be used to calculate the maximum degree of lean possible.

New Bike

You can probably see where this is going. Three months after I took the MSF course, I bought a bike and took a trip with my roommate from college. Here we are on the Blue Ridge Parkway:

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Credit is rarely placed on the experiences many take for granted, so designers and engineers should always be looking for new experiences that share insight into their designs. I highly recommend the experience I’ve had, and I’ll be looking into a class on semis in the future. Perhaps a bit of time behind the wheel of a semi will lead to a better understanding of maneuverability on roads designed without trucks in mind. I encourage other road designers to do the same.

Safe Riding!

Design Challenge

Challenge: Put together a preliminary design layout of a roundabout for the intersection of one-way streets being converted to two-way streets. Keep all lanes at 12′ widths, avoid right-of-way conflicts by keeping the design within the current curb-and-gutter boundaries.

Done before lunch. Who at your firm takes these challenges with this kind of excitement? Click through for full resolution graphics.

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Collision Statistics

I was passed along this article today, reporting on a sharp increase in pedestrian fatalities in Minnesota. In the StarTribune letter of the day yesterday, written by Michael D. Hoy, he questioned the conclusions of the reporter, showing that the fatalities fall in line with what is expected of normal fluctuations.

About two-thirds of the time, the statistic will lie within one standard deviation of the mean. This is what happened in the last 11 years. Two-thirds of the years had a death count between 33 and 45.

Also, about 95 percent of the time the statistic will lie within two standard deviations of the mean. Again, this is just about what happened. – Michael D. Hoy

It’s easy to look at collision fluctuations and be immediately concerned, but it’s important to remember that fluctuations can be random without any significant cause. That’s why it’s especially important to have good collision data collection methods in place when looking at collision rates and the safety of intersections. Sadly, most municipal resources are too scarce to spend a lot of time and effort on very involved collision reports.

If you’re a municipality or state agency focused on safety, you face a serious challenge everyday: with limited data, dollars, and man-hours available, how do you pick the most dangerous sites in your jurisdiction?

A background in statistics is always helpful, especially for researchers in this field. But for engineers who want to apply models everyday, there are plenty of methods already figured out for you to use. I highly recommend pursuing a graduate level course on highway safety like I did at NC State. Without delving into a statistics degree, you can pick up many effective methodologies to rank sites. Use them to your advantage and get the most efficient use out of precious tax-dollars while saving as many lives as you can!

It’s important to keep these things in mind:

Look at available data carefully. How long has the intersection been open? How much data do you have? Without enough historical data, it will be impossible to see any kind of trends.

Don’t revisit the same sites every year. Did you check the site last year? What were the findings? Unless the site has changed significantly, there’s no reason to check it again. There are tons of dangerous intersections that you haven’t investigated, get to those next.

Volume bias. Sites with the most collisions aren’t necessarily the most dangerous sites. Ranking sites by the number of collisions gives bias to the busiest intersections with the highest volumes. Similarly, sites at the bottom of the list may be dangerous, but have so few vehicles traveled on that they are skipped altogether.

An increase in collisions doesn’t imply a decrease in safety at the site. Especially in areas of high growth, increased collisions may just be because an increase in traffic. Check historical AADTs when you check historical traffic reports, and pick good comparison sites when comparing increases in collisions at one intersection with other intersections in your systems.

And try not to be overwhelmed by media.

News is always more interesting when there is a fright element, but there is no reason to believe that walking is any worse now than before.

NCSITE Technical Retreat 2012

I’ve recently become more involved in the North Carolina Section of the Institute of Transportation Engineers (NCSITE), a fantastic group of people from the industry. I attended a NCSITE lecture and meetup last month and played a lot of catch-up with professionals I know but don’t widely see on a day-to-day basis.

“So, you’re going to the technical retreat in August?”

This is the question of the hour. The thought crossed my mind, but I had such a busy month ahead, I was hesitant to make plans. NCSITE needed commitment early to reserve the facilities they planned to use, and holding off on registration for too long was going to make things difficult for the event.

With some shuffling, it was feasible to adjust my work schedule to get the time off I needed. Peer pressure is the strongest around those who’s careers you admire, so what do you say? You say “Yes.”

* * *

Monday, August 27th

11:35 PM

I carpooled with Dr. Reza Jafari of RSTS, Inc., and driving to the retreat was an experience by itself. Never having visited the Caraway Conference Center before, we almost passed it. Reza and I share a curious look turning into the driveway. “Camp Caraway” couldn’t possibly be where we were going, but the name matched the driving directions. From the road, it looks more like a boyscout summer camp.

“I didn’t pack a sleeping bag,” says Evan in the back seat, half-smiling, half-serious. Neither did I.

Following the drive through dense woods, we eventually pull up to a building that could’ve been a stand-in for the Overlook Hotel, so I make a mental note to stay clear of Room 237. After a brief check-in, we meet with other attendees in the conference room, have lunch, and sit down for the afternoon sessions.

Scott Lane, Don Kostelec, and Ram Jagannathan all had wonderful presentations covering decision-making, the design of the human environment, land use, and alternative intersections and interchanges.

6:30 PM

After dinner, we had the opportunity to listen to terrific NCSITE stories and experiences of some more prominent and senior members of NCSITE. But what made the retreat truly special were the team building and learning exercises Camp Caraway staff engaged us with afterwards. Climbing aboard some tractor-transit, we took a ride to another side of camp with fields lit for the evening’s activities. The irony of the game titles was not lost on me: transit-trains, red-light / green-light, and a game involving subway cars making roundabouts.

There was more fun, learning, and leadership coming from these activities than I knew what to do with. So I pocketed as much as I could for future reflection, and before I knew it, it was time for s’mores at the campfire.1

Tuesday, August 28th

6:00 AM

There was an optional morning jog scheduled. I briefly saw the clock out of one sleep-encrusted eyeball. I then proceeded to close said eyeball and dream about jogging instead.

7:30 AM

A light breakfast in the cafeteria and on to more sessions. I especially liked Pete Nicholas’s planned signal design activity. This session was my favorite. Complete with a design scenario, blank plans, and an answer sheet to check once completed, our groups were able to look at a proposed signal location and locate signal poles and heads around utilities and property lines. We then had an introduction to isolated timing and an overview of signal cabinet hardware.

This was followed by an introduction to ITS by Kevin Smith and coordinated signal timing by Denys Vielkanowitz. After a group discussion on the retreat as a whole, it was time for lunch and the ride back home.

Lasting Impressions and Memories

One thing that was especially neat about this retreat: it really held my attention. I rarely found myself compulsively checking my iPhone.2 Yes, Camp Caraway is in the middle of nowhere. But that’s kind of what made it special. We couldn’t just drive home for the night, or separate and go to different restaurants. We were stuck with each other for better or worse, and it allowed us to get to know one another much more than I expected.

I shouldn’t have waited so long to register. If registration was open today for a 2013 retreat, NCSITE would have my money already. Special thanks to the NCSITE members who did all the hard work planning everything, you all did a fantastic job. To students, professionals, and others who couldn’t make it this week: there’s no way around it. You truly missed out.


  1. Yes, it was a little warm to have a campfire. But after forming trains of sweaty engineers and running around in a soccer field, a seat on a log in front of a fire with marshmallows is as good as any.
  2. Of course, this could also have been affected by the complete lack of cell signal anywhere near Camp Caraway.

Roundabout Changes

I was a huge fan of the roundabout installation on Hillsborough St. near the NC State Bell Tower. It was well thought out, it reduced delay, and it was a pleasure to drive in. For a traffic engineer.

Unfortunately, everyone else had a collision in it. A little over a year ago, I personally wrote my recommendations here on my blog when numerous collisions were reported. I still stand by many of my points, especially the point on safety. No amount of fender-benders equal a fatality in my eyes, so I still say the intersection is safer than a four-way signalized intersection.

City and State engineers have done all they could to improve the design. Signage, pavement markings, flyers, flags, you name it. But downtown Raleigh drivers simply can’t afford the time to drive carefully in an unfamiliar design. With roundabouts being such an uncommon occurrence in North Carolina, I cede and will say that a two-lane roundabout of this size is too unfamiliar for uneducated drivers.

What changed my mind? I recently had lunch with Reza Jafari, President at Road Safety and Transportation Solutions, Inc. We talked at great length about driver education and the roundabout. He convinced me that the diameter is just too small for unfamiliar drivers, drivers that have never driven multi-lane roundabouts and are prone to change lanes (or disregard lane markings entirely) while navigating one. The point is fair.

We shall see how well a one-lane roundabout manages the traffic. Anything is better than a signal.

Reza Jafari is the President of Road Safety and Transportation Solutions, Inc. located in Cary, NC. He is a terrific resource on traffic safety and I would go to great lengths to recommend him and his company for a safety study.

Signal Warrants and Why We Use Them

A friend sent me a link to a recent WRAL article posted yesterday about a fatal collision in Cary on Sunday, February 12th1. Tragically, both passengers in a left-turning vehicle died when the driver crossed the path of another vehicle. This is terrible and my condolences go out to those affected by the incident. I also feel for safety engineers everywhere who feel the emptiness of failure at each reported fatality2, especially the highway safety professionals who work in this jurisdiction. However, as an engineer and scientist it is of utmost importance to step back and remember a few things about working within the confines of the real world: with limited tax funds, systems are imperfect and not every collision is preventable.

Keeping these things in mind, how do traffic engineers decide if an intersection requires a traffic signal? We use a system of “warrants”, or reasons that warrant the installation of a control device. The Manual on Uniform Traffic Control Devices (MUTCD) lists nine signal warrants for varying reasons in Chapter 4C. A pdf of this manual can be found here. These reasons range from volume to school-zone related conditions and yes, even crash experience.4 Most generally, traffic signals are never installed without first qualifying for one or more warrants.

Why? In many cases a signal can make an intersection worse than it started! Traffic signals are often viewed in the public eye as a cure-all, when in fact they can have adverse affects on safety and efficiency: increased delay, increased traffic control disobedience, increased use of other routes such as neighborhoods (just to skip the light!), and others. The increased stops can also increase the number of rear-end collisions at the site as well.4 This has led to the installation of many lights that were never needed, at sites that may now be less safe, at the cost of a six figure installation. Thats right, your average 4-way simple traffic signal costs between $150,000-200,000. Plus continued maintenance from now until forever.

The Media

One of the biggest reasons that the public is so ill informed about the affects of traffic signals is the media, and we can see it in this article.2 It’s not necessarily their fault that the public demands stories that move the heart, either in tenderness, controversy, or horror. But people get so caught up in political partisan biases, that many forget how easy it is to be biased to the heart instead of the mind, allowing an element of “controversy” to develop conspiracy, scheme, even frustration in the reader. Lets take a moment to analyze some of the diction used in this article:

“hasn’t met the criteria for a traffic light, despite pleas from drivers and neighbors that the intersection is too dangerous”

I’d be pulling my hair out if there was any left to pull. On the logic side, uninformed readers could assume two very incorrect conclusions: drivers and neighbors always know a dangerous intersection when they see one3, and that pleas from drivers and neighbors warrant a traffic signal. But theres so much on the emotional side as well. Using the word “plea” to stab the hearts of our readers, the author has clearly set the tone of the entire article to:

“People have begged on hand and knee, offering to sacrifice their first born for just one, ONE traffic signal. The site would be safer, and this wouldn’t have happened”.

No wonder people think traffic signals are a cure-all! This conjecture could be patently false. For all we know without adequate evidence, adding a traffic signal could make this site WORSE. But not now. As uninformed citizens we now know that the evil city of Cary is denying us the promise of safety and security that only a traffic signal can bring.

“she attempted to turn left from West Chatham Street onto Cary Parkway and crossed into the path of a Dodge Avenger.”

This one earns the reporter kudos. Notice how quickly and easily the blame of the incident could have been shifted: 1) “she unwittingly pulled in front of traffic”, or 2) “the Dodge Avenger smashed into the side of her vehicle”. Unfortunately for the reader, we don’t know the exact cause of the collision. We may never know for sure. It could’ve easily been texting or another form of distracted driving. The author calls this collision “correctible”, though as a reader we are left unsure as to whether or not it is she or her interviewee that thinks it’s correctible and why. But by calling this collision “correctible”, the public will be wondering why correctible collisions are happening at all. And they should! But they are missing an important piece of the puzzle: some intersections are more correctible than others and warrant more immediate attention and funding, of which there is a finite amount of both.

“In addition to traffic volume and other criteria, to warrant a light an intersection would need to have had five crashes that would have likely been corrected by a traffic light in a single year.”

But I have to draw the line here, this is a complete falsehood and is misreported. Intersections do not require crashes for a traffic signal. In fact, new roads are constantly being built in conjuction with signals before they are even opened. But the remark is so instigating and confusing, it left one commenter with a terrible impression of traffic safety methods. If anything should make an engineer feel like a failure, it is the terrible miscommunication with the public that can lead to this:

Let me see if I have this right….The criteria for installing a traffic light requires multiple occurrences of either property damage, bodily harm, or loss of life. The wisdom of our city fathers leaves much to be desired. carrydoggymom, February 13, 2012 7:55 p.m

Concerned Citizens

As much as a I try to avoid reading the comments section on a news website, it’s important from a public administration point-of-view to see how this fraction of the populace thinks. Some comments are enlightening, some are sad. This time, I was mostly surprised to see intelligent debate in the comments section. Mostly.

“I bet if it was the mayor’s family, there would be a light there tomorrow. What a load of bull!” bjandroxie88, February 13, 2012 7:42 p.m

Here is the advocation that, not only should tax dollars be spent willy-nilly by those in power when they find misfortune, but that politicians should make engineering decisions. There is a problem when the politically inclined try to mingle in the affairs of those who put safety first, a perfect reason why engineers should use MUTCD warrants instead of bending to political pressure from above.

“…If the vehicle was close enough to hit them, it was close enough to see and avoid.” pedsrndad, February 14, 2012 11:56 a.m

While my first instinct is inclined to agree, sight distance plays an important factor in intersection design, and it may need reinvestigation at this particular intersection. Though I imagine it was addressed and not seen as a big problem during the original design, factors such as reclassifying the speed-limit or increased volume year-to-year could play a part in changing the environment here.

The Intersection

I’ve driven the intersection myself, and especially during rush hour it can be difficult to turn left. The median supplies a little refuge, but not much. I glanced at the traffic volume maps, but without knowing more about peak hour data, it’s difficult to say exactly what warrants the intersection can qualify for. I’m surprised it doesn’t hit the peak-hour warrant, or even the school-crossing warrant with it’s proximity to Laurel Park Elementary. With the limited data I have on hand, I might recommend the following traffic studies to take another look at the signal warrants: sight distance study, spot speed study, and/or a volume study.5

If a light is installed in the near future, I hope it will be because it is warranted and that conditions have changed since the last inspection of the intersection. Not because of the ravings of uninformed watchers of the 6 o’clock news. We should all strive to be more cognizant of the impact media can have on the heart of the public, and how important good communication can be when working for the public sector. These efforts will make it easier to limit the affect of a tragic story in the news from opening our wallets too wide when there aren’t enough collisions to merit a new, expensive, and possibly ineffective traffic control device.

Wrap Up (Read: Important Conclusions)

By now you should have gathered the following:

  • Traffic signals are not a cure-all; sometimes, when not really needed, they cause problems.
  • We use Signal Warrants to come to justified conclusions, recommended by the MUTCD, on whether or not to add a traffic signal at an unsignalized intersection.
  • MUTCD has 9 different signal warrants for varying reasons of safety.
  • Intersections do not require collisions to warrant a traffic signal.
  • “Pleas from drivers and neighbors” is not an MUTCD signal warrant.
  • “The mayor found misfortune” is not an MUTCD signal warrant.
  • Crashes and fatalities do not necessarily merit an MUTCD signal warrant.

References and Notes:

  1. Cary intersection doesn’t meet criteria for traffic light, WRAL, Monday, February 13th, 2012
  2. Mental Note: Prevented collisions never make the news. How could they?
  3. Mental Note: Drivers and neighbors are an invaluable resource when discussing what they think of an intersection. However, everyone’s seen a collision somewhere. This does not always, a “dangerous” location, make.
  4. Manual on Uniform Traffic Control Devices 2009, published by the Federal Highway Administration.
  5. As found in the Highway Safety Engineering Studies Procedural Guide, published by USDOT and FHWA 1991, commonly referred to as “The Parker Manual”.

Engineering Trek 2012

Twin Cities, MN

I had a few spare weeks recently, and decided to go on a cross-country trek to visit some friends. I also took the opportunity to take in some civil engineering landmarks along the way. First stop was Minneapolis/St. Paul, Minnesota. Had a great time visiting my college buddy Garrett, now a grad student at U of M. We passed by the Civil Engineering building on campus, a building residing almost completely underground. For it’s unique design it was awarded with the Outstanding Civil Engineering Achievement Award by ASCE in 1983.

I visited the new 1-35W Mississippi River Bridge, the replacement bridge on the site of the disastrous 2007 bridge collapse. Improper design as well as large loads from construction equipment and extra layers of pavement caused the original bridge to collapse. Nearby, I walked across the Stone Arch Bridge of Minneapolis, overlooking the only waterfall on the Mississippi river. Built in 1883 and named a Historic Civil Engineering Landmark, the bridge served as a railway bridge but now serves as a pedestrian and bicycle path across the Mississippi. In the area are many parks that serve the historic district and showcase the history of the water-powered mills that put the Twin Cities on the map.

It’s always exciting to see public transportation improvement projects, and it was neat to see the construction of new light rail stations by the local Metro Transit in St. Paul. We also visited the Town Hall Brewery and attended the Beer Dabbler Winter Carnival 2012.

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Next stop was Colorado. Not too many civil engineering landmarks on this leg of the trip. Instead, I had the wonderful opportunity to have some family in the area expose me to some really neat experiences. I went ice-fishing, fed buffalo, visited Odell Brewing, and sat in on a volunteer-firefighting training seminar. For those most interested in the sciences, here’s a nerdy exposition: you can calculate the thickness of clear ice h (inches) that can withstand failure from a load of p (tons) with the following formula: h = 4√p

There’s all sorts of other factors you can throw in for safety, and if you plan on driving out on the ice, you should probably give these a good read:

Some more neat information:

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Los Angeles, CA

My last stop was LA, visiting another NC State friend and former roommate, Joe. Much warmer than the previous stops, I enjoyed the beautiful sunny weather of Pasadena. I visited Venice Beach, the infamous Hollywood sign, Griffith Park Observatory, El Pueblo, Hollywood Boulevard, La Brea Tarpits, IO West Improv Club, In-N-Out Burger, and Point Fermin Lighthouse.

Of course, my visit to the locale wouldn’t do my “engineering” trek justice if I didn’t review local transportation resources. I rode both the Metro Bus and the Metro Rail, visited Union Station, and found it all to be exceptional for my use as a tourist. Joe commutes to and from work daily via Metro Rail and bicycle (which he can bring on the train) and finds them more than adequate. I was impressed with the timeliness, cleanliness, and usefulness. I only wish we had this kind of rail in Raleigh.

I also noticed the use of ramp meters both here and in Twin Cities. These are not a congestion tool we currently use in North Carolina, so I sent a quick email to Dr. Hummer, professor at NC State, with some questions on use cases and statistics. He responded rather quickly and gave me great information on the topic. They can keep the mainline traffic moving better than Level of Service “F”, preventing a 100-300 vehicles per hour per lane drop in capacity. They break up “platoons” of cars, and can decrease travel time up to 10%. In North Carolina, it’s been easier to add conventional capacity in the past, but NCDOT may need to look at ramp meters more closely for use on I-77 in Charlotte and areas around RTP.

All in all, the trip was very rewarding, and I can’t wait for the next opportunity to do a similar trip in the future. Special thanks to family and friends for taking time to spend with me and making my trip possible!

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Bonus Footage


Recipes for Success in 2012

Those who know me know I like to create, and cooking is a fantastic hobby I’ve picked up. There’s always something new to learn. It’s art. It’s expression. And best of all, you can eat it.

But like all things, if you do it, do it right. Cook like you mean it. Go big or go home. And recently I’ve learned that the culinary arts, or at least the kitchen responsibilities involved therein, have a lot in common with the engineering industry. It was this wonderful article on a chef’s blog that really punched it home to me: sous chefs are engineers, but not all engineers are sous chefs.

Being a sous chef has little to do with the title and all to do with what you make of it…

Cook your ass off. Organize your station better than I would. Stop whining. Turn problems into solutions. Take challenges and ride them one handed. The bull threw you? Get up and get back on. Ask for help when you need it. Rally support that’s available to you. Work cleaner every day. Create systems and implement them. Learn stations you’ve never known.

Get out of your comfort zone.

Manager or not, if an engineering office was a kitchen, everyone should strive to be a sous chef.

Think about it as you set your goals for the new year. Be the sous chef. Leave egos at home, get your hands dirty, and get cooking.

Happy Holidays everyone!

Block quote comes from the following article. Make sure you give it a read: Shuna Fish Lydon, Eggbeater Blog

Enterprise: Time to support Mac Users

The times they are a-changing. A new survey on IT professionals and executives by Forrester Research shows that Mac users are HEROs, or “highly empowered and resourceful operatives”. Where once the research group stood by the recommendation to not support Apple devices in the enterprise arena, they now see that many of the brightest and best insist on using Macs.

“Most of the Macs today,” writes Johnson, “are being freewheeled into the office by executives, top sales reps, and other workaholics. Forrester believes this is the same demographic that we’re now calling the “power laptop user,” and according to the latest Workforce Technology And Engagement Survey, power laptop users make 44% more money, use more collaboration apps, and carry an average of three devices wherever they go.”

So much so, that these power users are willing to purchase their own Macs because the Window’s PCs supplied by their firm are slowing them down.

I know what they mean. And while I have both, I too prefer my Mac.

Via: CNN.

The Lateral Forces of Earthquakes

So it seems there were a few damages from the Virginia earthquake earlier this week. The biggest damages on the news? The National Cathedral and the Washington Monument. The Washington Monument suffered some cracking at the very top and has since been closed indefinitely to the public until damages can be assessed. As for the National Cathedral, gargoyles, spires, buttresses, and walls cracked, shifted, or fell and shattered. Other homes and businesses near the epicenter were damaged as well.

While damages under 6.0 earthquakes are rare, they do indeed occur, especially in a region less known and under-designed for quakes. In fact, the area falls in a zone of very small seismic risk (see the 2012 International Building Code Map, courtesy of USGS), which is a big part of the problem. Another part of the problem is the age of these structures. Newer buildings and building methods are much safer than they used to be in this regard, but many older buildings will suffer problems, especially since there is little desire to improve them and little funding to do so.


Figure 1: Building Motion During an Earthquake (1). Click to Enlarge

What causes these damages? The lateral forces caused by the accelerating displacement of the ground. When an earthquake occurs, the acceleration of the ground will cause the building to move sideways at the base of the building. It is, after all, firmly attached to the ground in most cases, causing a lateral load and an equivalent shear force at the base (see Figure 1). The building will then begin to swing to and fro, according to the change in direction of the ground.

Familiar with Newton’s law of force? You could very simplistically apply it here to calculate the forces on the building: F = M(A), or force equals the mass multiplied by the acceleration. What may not be immediately obvious is that the higher the mass of the building, the higher the force on the building. But we CAN control the acceleration, which gives us an advantage if we play our cards right. The acceleration can be affected by the natural period of the building, or a complete oscillation, which is dependent on the building stiffness.

Supposing we could create a building that was perfectly stiff, it would match the acceleration of the ground perfectly and it would not oscillate and not experience force. This, unfortunately, is an impossibility for any material, and the slightest deformation would cause large forces due to short natural periods. So contrary to instinct, we do not want to make the stiffest buildings possible, what we want are flexible, long natural periods in our buildings. We need them to sway.


Steel buildings have certainly come a long way, but a large part of the problem with older buildings is their dependence on stone, under-reinforced concrete, unreinforced masonry, and designs incapable of holding even the most moderate earthquake and wind loads. Many of these buildings were built at the turn of the 20th century and are still being used today.

Stone and concrete hold well under compression, but not under tension. Without an element of tension, these older stone buildings simply crumble. Newer concrete structures today are reinforced with steel, doing wonders for flexibility. When allowed to, the steel in reinforced concrete catches tension loads and transfers them. Steel is ductile, and the greater the ductility of a building, the better forces can be absorbed. When designed correctly, even after structural failure, warning signs in reinforced concrete structures are easily apparent, often allowing people to clear from the site before catastrophic failure. After all, people are more important than the buildings.

Figure 2: Deformation Components of a Reinforced Concrete Column (2). Click to Enlarge

While working on a graduate research project during my time at the Constructed Facilities Lab at NC State, I worked on a thesis by Pablo Robalino (2). We tested lightweight concrete columns for seismic lateral forces to see flexural and shear deformation. Notice in Figure 2 how the flexural damage occurs on the side of the lateral force, while the shear damage occurs throughout the column towards the ground. The combination of these effects must be considered when designing columns for the lateral loads associated with earthquakes.

Figure 3: Column Specimen From Seismic Test

Figure 3 is a chunk of a column we tested. Notice the lines drawn with permanent marker. These lines follow cracks in the concrete caused by forces on the column. As we tracked their progression, they naturally followed similar trajectories as those depicted in Figure 2.

These aren’t difficult concepts to understand, but even with the best methods of absorbing forces, costs often limit the investment we can place in a structure to prepare for the worst. While we can’t feasibly prepare for earthquakes of every magnitude, we can use physics, properties of materials, and our growing understanding of these natural disasters to build structures capable of sustaining many of the forces that seem beyond our control.


  1. Professional Publications Inc. “Lateral Forces – Earthquakes”
  2. Robalino, Pablo. “Shear Performance of Reinforced Lightweight Concrete Square Columns in Seismic Regions”. August, 2006.