David Nyarko, P.E.
Mechanical Engineer
Who Builds Big? | Career Info Index | Engineering Webography

David Nyarko is based in New York City, where he works as a lead mechanical engineer with Parsons Brinckerhoff, an international engineering and program management firm. He has extensive experience with movable bridges, including bridge inspection and rehabilitation, preventative maintenance, and machinery and component design.

Check out a project that David has worked on: George P. Coleman Bridge, Yorktown, Virginia

(click for larger image)

What kinds of things do you do as a mechanical engineer?
Well, I think a lot of people do not know that mechanical engineers work on bridges, but we work on what are called drawbridges. Technically, we call them movable bridges. And we basically design all the systems that actually move the bridge. It takes about 10 to 15 minutes for boats to go through; it could be for a railroad crossing or vehicular traffic. While the boat is coming through, the cars or trains have to wait. And this huge bridge opens slowly, because you don't want it to drift apart in any way or form. And there are different types of machines that open them up. It could be hydraulic, or it could be your normal gears and motors. You have to size them up, make sure this machinery has enough power to open up that particular bridge.

(click for larger image)

What aspects of drawbridges or movable bridges do you work on?
Well, I work on all types of movable bridges. It could be a brand-new one, where you start from scratch, and we have to do what we call a type-study, to determine the type of bridge that is adequate for that particular crossing. After the type-study, you come up with preliminary drawings of what should be there. Then you go to the final design process when you design the details of the bridge. During the construction of the bridge, we assist the client or the contractor in reviewing shop drawings and clarifying various technical issues that might come up.

Is that something that you've been involved in?
Yes, in various ways. Another major part of my job is what we call condition surveying, or inspecting the condition of existing bridges. And there's probably more work around the world in surveys than in building new bridges. We look at bridges to assess the operating condition and to evaluate whether they meet current codes and standards.

What sorts of things do you look for?
Well, first of all, we look at a bridge to make sure that nothing is falling apart. We also look at specific conditions of the machinery to make sure it will not fail or it's not deteriorated in any way. Of course, we can't fully predict failure, but we can see when something is not running right. The margin of safety in bridge design means that when components reach a dangerous amount of wear, they are still unlikely to fail immediately. On bridges with hydraulic equipment, you can do all sorts of what we call diagnostic testing of the system.

So after the inspection, do you also get involved in repair?
Of course. After the inspections, we put together reports, and out of this comes short-term and long-term recommendations -- that is, if the repair recommendation needs to be implemented immediately or if it can wait till later, when it's funded. And then, based on that, the client will ask us to do a rehabilitation, or it could be just a minor repair.

Do you use any special equipment in your work?
Yes. For power transmission equipment, we use stuff such as gears, bearings, couplings, etc. There are all sorts of tools, such as gear calipers for some gears, feeler gauges for gears, and machinist levels to check alignment. You could also use a whole computerized data-gathering system to check pressure and flow at various points, or ports, as we say, on the hydraulic system. The flow in the system represents how fast the oil is going through the piping. Or for another type of movable bridge, called a bascule bridge, we determine the balance of the bridge during operation by using strain gauges and data-gathering instrumentation.

Do you work with a team of engineers?
Yes. I normally have an electrical engineer with me, and a structural engineer. The structural engineer will be responsible for the loads and the structure itself, to make sure it doesn't fall apart when it's windy or when it's moving, just making sure that the loads are well distributed and that the bridge will be stable. There's also normally a geotechnical engineer, who looks at soil conditions and foundations, and also the alignment of the roadway. Then you have the electrical engineers, who basically make sure that all the equipment is powered well. They also work on the controls, to make sure that everything is in sequence, that something opens or something moves before something else. And then the mechanical engineer, who works on the mechanical components to make sure they're sized properly.

What does a typical day in your work look like?
Well, a typical day would be putting a report together, putting some drawings together, answering a call from a client about a problem they have out there.

What would you say is the most interesting thing about your work?
I personally enjoy what I do. My father is a mechanical engineer. He worked for Volkswagen for 25 years building cars. So that's my other passion. I always wanted to be a mechanical engineer, but I got into bridges by default. I wanted to go into the car business. But around 1987, '88, when I came out of school, they were laying off people in Detroit. So I got a job with the City of New York, and was introduced to the industry, and slowly came to enjoy it and became an expert without even knowing it.

But it's been fun. There are two things I really enjoy. You get to go to bridges all over the country. You get to work with all sorts of people out in the field -- maintenance crew, bridge operators. They're very helpful; they're very nice. There's also the new hydraulic equipment on movable bridges, what I call the high-tech end of it. The fact that there's always new equipment and new developments -- I enjoy that.

Is there something that you like least about the work?
When I started, more than 10 years ago, I wouldn't say I was scared of heights, but when I climbed up there, I sometimes looked down and said, "Boy, what if I fall in the water?" That was at the beginning. It takes a little getting used to.

Do you have to climb a lot?
Oh, yeah. On what we call vertical-lift bridges, where the middle of it lifts up like an elevator, the machinery is actually located on top of the towers or the lift span, so you need to go in there sometimes. You're just climbing around and making sure you don't fall in the river.

Is it automated? Are there lifts, or do you literally have to climb?
Some bridges have lifts. Others don't.

I'm sure that takes a little getting used to.
Definitely. Climbing into places, or crawling in there.

What's the most interesting project you've worked on?
Well, the projects have been very exciting. One of the projects that I worked on for my company, Parsons Brinckerhoff, and really enjoyed, was the construction of the Coleman Bridge in Virginia. This is probably one of the longest swing bridges in the world. The company won so many awards for it. It was interesting because it was very historic. There's quite a lot of history in that area. It was an existing bridge that was widened from a two-lane bridge to a four-lane bridge.

Do you have any advice for kids who might want to pursue a career in mechanical engineering?
There's quite a lot to do in mechanical engineering, and there are a lot of fields within mechanical engineering. My advice would be to just learn the basic concepts of mechanical engineering, go to college, and be exposed to the various fields of mechanical engineering, because we need mechanical engineers in every part of the engineering industry. You could work in buildings on building systems, which might be HVAC systems. You have engineers working in the automobile industry. Of course, I'm in transportation. There's manufacturing, of course -- that's one of the major areas; product design. The aircraft industry is also one of the biggest employers of our profession.

Finally, what kinds of things do you like to do in your free time?
I play tennis, and I do work on cars.