This year marks 25 years since four airplanes leaving U.S. airports were hijacked by terrorists. Two of the planes were flown into the Twin Towers of the World Trade Center, one crashed into the Pentagon building. The fourth plowed into a field in Pennsylvania after passengers valiantly attempted to regain control of the aircraft. Including first responders, 2,977 victims perished from the attacks, an historic event known simply by the date the tragedy unfolded — September 11.

After the attacks, one New York City-based alumnus of The Grainger College of Engineering played a key role in studying the impact on buildings and rebuilding both the World Trade Center site and the Pentagon. Robert “Bob” Smilowitz (’73, M.S.; ’77, Ph.D., Civil Engineering) is an authority on protective design and security and has worked to create terrorism-resistant designs for U.S. embassies, federal buildings, airports and renovations to the U.N. buildings in New York, to name a few.

In 2025, Smilowitz was elected by his peers into the National Academy of Engineering for “protecting lives from acts of terrorism through vulnerability assessment, threat mitigation and building standards development.” The American Society of Civil Engineers honored him with the 2024 Ernest E. Howard Award for “international leadership in protecting lives from acts of terrorism through structural design and public policy and for teaching protective design to the next generation of engineers.”

When talking about his career and achievements, Smilowitz is quick to credit his colleagues, focus on the importance of teamwork and acknowledge the role of luck.

After completing your undergraduate degree at The Cooper Union for the Advancement of Science and Art in New York, you came to the Midwest for your master’s degree and Ph.D. What attracted you to the University of Illinois Urbana-Champaign?

The U. of I. was rated either #1 or #2 in the country for civil engineering and compared to the limited courses offered at Cooper Union, the course catalog was overwhelming. I spent two years at the U. of I. and went to work in California with a master’s degree. After a year, I returned to Illinois to pursue a Ph.D.

I was very lucky to have been assigned Nathan Newmark (’32, M.S., ’34 Ph.D., Civil Engineering; ’78, honorary doctorate) to be my advisor. Dr. Newmark was a phenomenal person, and he guided me through my thesis. [Newmark is considered a founding father of earthquake engineering and is the former head of Grainger Engineering’s Department of Civil and Environmental Engineering.]

When it came to getting a job, he asked me, “Where do you want to work?” And I said, “Well, I'd like to go back to New York.” So, he got on the phone in front of me, and he called Dr. Melvin Baron at the applied science division of Weidlinger Associates (now a part of Thornton Tomasetti) and said, “I have a young student who's graduating with a Ph.D. Will you hire him?” And they arranged at that time for me to have an interview. I’m forever grateful to Dr. Newmark for putting me into my future.

You had a significant role as a consultant in the rebuilding of the World Trade Center site and the Pentagon after September 11. As we commemorate the 25^th anniversary, walk us through that day from your perspective. 

I was at my desk when a young colleague came running in and announced, “I just saw a plane fly into the World Trade Center.” Because our building was about 25 blocks north of the World Trade Center, the site was visible from the street. We looked out the window, and you could see smoke billowing in the skyline. We couldn't see the building itself. We just saw the smoke. Eventually, word spread around the office; people turned on the television we had in the conference room, and we heard the reports, and then came the second plane impact. At that point we realized that it wasn't just an accident. Then people made plans to walk home.

As a structural engineer, was there a moment when you thought, “Those buildings are coming down”? 

The building survived the impact. We had no idea what was going on inside the building, and we had no real understanding of the intensity of the heat. Ultimately, the heat [from the fires] brought the buildings down. There were a lot of factors that played into it. Usually, a fire moves from one location to another, so the entire floor plate isn’t engulfed simultaneously. However, all the jet fuel that was dispersed uniformly throughout the floor plate burned simultaneously. Also, the impact scraped off the fireproofing. The intense heat caused the floors to sag and weakened the damaged steel core, and the buildings failed from reduced strength.

When the first building survived for over an hour, and not knowing the extent of damage due to the heat, I thought that there was a good chance that the buildings would stand. The buildings withstood the initial impact, and were still structurally viable at that point, which is amazing in itself. If you look at pictures of the gash, the size of the openings took out significant support of one face of each building. And yet, the buildings were able to redistribute loads and remain stable.

You were a key expert on the American Society of Civil Engineers and the Federal Emergency Management Agency Building Performance Assessment Team that studied the structural impacts and responses following the terrorist attacks. Tell me about that work.

I was just a member of a remarkable team of renowned engineers with diverse backgrounds and specialties. I chose to study the Banker’s Trust Building, also known as 130 Liberty or the Deutsche Bank Building, which was struck by debris from the south tower. The building lost a column for about a dozen floors, yet the resulting collapse was largely confined to the bays directly connected to that column, while adjacent and upper floor slabs were barely affected. By studying a building that exhibited partial structural failure, we gained a clearer understanding of why the structure responded the way it did and why the damage was so limited. 

What did your work in redeveloping the World Trade Center site entail?

My colleagues and I provided protective design services for most of the redeveloped structures, including all four towers, the memorial, the memorial museum, the visitor center, the Oculus and Transportation Hub, and the Perelman Performing Arts Center. It occupied most of my time.

I was a specialty consultant to several design teams. There was no fanfare. We came, and we did our work. One of the pleasant things about being a specialty consultant is working on a lot of projects simultaneously. The structural engineer of record is on a project for a year or two, through construction. A specialty consultant can come and go and interact as necessary at different phases.

Let’s talk about your work on the Pentagon prior to the terrorist attacks. 

Prior to September 11, we were retained by a facade manufacturer to help analyze and design hardened windows — windows that could resist blast loading — for Wedge 1 of the Pentagon.

As fate would have it, a plane penetrated the western face of the building, where Wedge 1 is located. I had no idea what to expect; however, people beyond the collapsed structure behind the renovated windows were protected. That was a remarkable achievement in my mind. Although the windows were not designed for that loading, you hope your design provides enough of an umbrella that it will protect in response to whatever may present itself. In this case, it was an airplane impact.

We then worked with the reconstruction of the damaged structure and the subsequent renovation of the entire building’s facade. Project Phoenix, in which the damaged portion of the Pentagon was designed and rebuilt, took about a year. My colleagues and I designed the exterior hardened walls to the specified protective design criteria, and we worked with the window manufacturer with whom we had previously designed the windows for Wedge 1 to design the windows for all the remaining wedges.

How did protective design and security become your specialty?

At the time [of my hire], Weidlinger was developing state-of-the-art finite element software to evaluate the damage to buried structures in response to underground explosions.

After several years working on ground-based structures, I developed software to evaluate the decoupled hydrocode and finite element analysis response of surface ships subjected to underwater explosions. Because of the limited capacity of computers at that time, we were very careful to write the most efficient software that we could — the software that required the least amount of information to be stored and yet produce accurate results. We performed pre-test analyses of the shock trials of half a dozen Navy ships.

Following the 1993 explosion in the World Trade Center parking garage, I switched my focus to help determine the size of the explosion that produced the observed damage. After the 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City, my colleagues and I were asked to help the U.S. General Services Administration implement their new guidelines to the protective design of domestic government buildings. We eventually provided protective design services for the replacement of the Murrah Building.

There are a wide range of potential terrorist events considered in protective design, and the list is ever changing. I specialized in the hazards that resulted from explosives and vehicle ramming. Most injuries result from structural collapse, from failed facade or vehicle impact. The protective design, therefore, determines the required structural members and their connection details to allow damage and deformation without precipitating collapse. Protective design also determines the required glazing materials, framing and connections that limit the extent of hazardous debris. Protective design also includes the design of anti-ram bollards at the curb to prevent vehicles from driving up onto the sidewalk.

What do you think are the most significant challenges structural engineers will face in the future to protect lives from terrorism?

Threats are constantly evolving, yet structures are built to last decades. Explosive and ramming threats will always be a concern because the components of improvised explosives are so easily obtained and ramming only requires a vehicle. I suspect drones will become the next major concern. Nevertheless, there’s constant tension between the desire to design the most economical building versus the need to protect against an unknown threat.

We therefore perform risk analyses to prioritize the levels of protection. However, protection against terrorism has to be addressed through close coordination between operational, technical and physical security. We can never let our guard down at the airports; we have to implement the smartest technologies to detect and deter threats through screening or access control, and should all else fail, structural hardening, debris mitigation measures and bollards are built into the building’s fabric to protect the people and property.

You are an adjunct professor at your undergraduate alma mater, Cooper Union. When you talk to early-career engineers and students, what do you tell them?  

They have to enjoy what they do and get invested in every project they work on; this way it doesn’t feel like work. They have to be open to new opportunities, especially if it requires them to learn something new; challenge themselves outside their comfort zone; and seek guidance from colleagues when needed. Finally, they need to understand every analysis before developing a computer model; they need to think of simple hand calculations to “ballpark” the results to know what to expect.

It all starts with Newton. Dynamic analyses solve the same equation, F = ma [Newton’s Second Law of Motion], again and again and again. I spent my whole career solving one equation.

“Threats are constantly evolving, yet structures are built to last decades. … There’s constant tension between the desire to design the most economical building versus the need to protect against an unknown threat.” - Robert Smilowitz

What advice do you have for Civil Engineering students at The Grainger College of Engineering?

This is the $64,000 question. Back in the 1960s and 1970s, students adapted to computer-based analyses (I remember waiting in a line to submit a calculation to an IBM 1620 at Cooper Union). Tools evolved as computer capabilities improved.

Artificial Intelligence is the new frontier. Thornton Tomasetti is developing AI-based design tools to help engineers in their daily activities and improve productivity, and I assume other engineering firms are doing the same. This is a double-edged sword because each engineer will become more effective, but fewer engineers may be required.

Is there anything else you’d like to add?

Luck played a significant role in what I was able to achieve. I was fortunate to be accepted into the graduate program at U. of I. and to choose to attend. I was fortunate to have Dr. Newmark as my thesis advisor. I was fortunate to begin my career alongside brilliant colleagues at Weidlinger Associates to guide me. And I was especially fortunate to meet my wife at U. of I., with whom I have two wonderful sons and two wonderful grandsons. I know how easily things might have turned out otherwise.

Photo Credit: Bess Adler, Thornton Tomesetti, July 2026