The Washington Monument Earthquake Assessment and Damage Assessment of Monumental Structures in the 2011 Virginia Earthquake – Looking Back

(Article originally published on Oct. 8, 2012.  Revised and Updated on July 22, 2017)

On August 23, 2011, the Mid-Atlantic region experienced its strongest earthquake since 1897. The epicenter of the earth-quake was located near Mineral, VA which is approximately 80 miles southwest of Washington, D.C. and 45 miles northwest of Richmond, VA. Although the ground shook for only about 30 seconds, structural engineers in the region were very busy for several days after the 5.8 magnitude quake performing immediate damage and safety checks.  Upgrades and repair work continued for several years after the event.

On the day of the quake, the population of the eastern U.S. and southeastern Canada were surprised to experience a fairly large east coast earthquake with a magnitude of 5.8.  According to the USGS,  several small earthquakes occur every month in the eastern U.S., but this earthquake was among the largest to occur in this region in the last century.

USGS estimates that approximately one third of the U.S. population could have felt this earthquake, more than any other earthquake in U.S. history. Around 148,000 people reported their ground-shaking experiences caused by the earthquake on the USGS “Did You Feel It?” website. Shaking reports came from southeastern Canada to Florida and westward to locations near the Mississippi River.   Classified as a rare event  for the east coast, USGS also indicated that the earthquake was not a surprise in that it occurred within the Central Virginia seismic zone. This zone has been identified on USGS seismic hazard maps for decades as an area of elevated earthquake risk.  However, it is the largest known earthquake to have occurred in that zone.

Immediately after the earthquake, a number of Penn State AE alumni experienced and/or were involved in inspections, assessments and repairs of buildings and other structures that experienced damage of various degrees.  One group of AEs in a construction site in downtown DC were on a conference call with a colleague in Boston when they exclaimed there was an earthquake.  The person on the phone in Boston thought they were making it up only to yell 12 seconds later something to the effect of : “It’s here!” (That exchange was courtesy of the east coast geology).   A feature story on Penn State AE alumni involvement with the earthquake can be found in the Spring 2012 AE Newsletter. (to be distributed in class).

One of the Architectural Engineering Building Failures Visiting Practitioner Seminar features scheduled for October 2018 is a visiting lecture by Eric Sohn, P.E., a 2001 Penn State AE alum (formerly of WJE ) currently working as a structural engineer with the Penn State Facilities Engineering Institute.      Mr. Sohn and others from Wiss Janney Elstner (WJE) had the task of assessing damage to a number of monumental structures in the Washington DC area including the Washington Monument and the National Cathedral (See Cathedral Earthquake Repairs Pages).  In particular, Mr. Sohn will discuss the role of the WJE Difficult Access Team (DAT) in gaining access to these types of facilities for close up inspection to obtain information for recommendations and repairs.

Currently, The Washington Monument is closed until spring 2019 while the National Park Service is modernizing the elevator to increase long-term reliability and safety.

There are a number of suggested readings and links available to learn more about the earthquake and the recommendations made by WJE on the project.  They include:

The Washington Monument Earthquake Update Page which includes the reports noted below in addition to links to photos, videos and the Incident reports from the National Park Service (NPS).

Summary of Initial Findings for the Washington Monument (WJE) Washington Monument Post Earthquake Assessment (WJE Full Report) Washington Monument Seismic Study

 

The National Cathedral was also heavily damaged in this earthquake.  An excellent source documenting the damage and repair process can be found on the earthquake repairs Cathedral website.

It is interesting to note that an eastern earthquake of similar magnitude occurred in Oklahoma in 2016.  Wikipedia notes:  The 2016 Oklahoma earthquake occurred on September 3, 2016 near Pawnee, Oklahoma. Measuring 5.8 on the moment magnitude scale, it is the strongest in state history. It is tied with the 2011 Virginia earthquake as the strongest in the central and eastern United States in the preceding 70 years.  This particular Oklahoma earthquake was a part of the 2009 – 2017 Oklahoma Swarm which has been attributed to the disposal of oil drilling wastewater back into the earth.

In order to fully appreciate and carry out follow up discussions on the presentation, you may need to know more about the basics of the earthquake and the corresponding performance of buildings and related structures.  Suggested readings on the topic of building earthquake performance such as the quakes in New Zealand that occurred around the same time as the one that struck the DC area and the followup one year later discussion of the Mineral Virginia earthquake in particular can be found on the internal PSU AE Failures Wiki site.

 

 

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21 Responses to “The Washington Monument Earthquake Assessment and Damage Assessment of Monumental Structures in the 2011 Virginia Earthquake – Looking Back”

  1. Ryan L
    October 15, 2018 at 9:00 am #

    The Getty Conservation Institute has some great video on modeling and retrofitting historic structures while introducing the model to certain seismic conditions. I couldn’t find how reliable some of this modeling and testing is, as I am sure soil conditions, weathering, and other conditions would be difficult to model accurately.

  2. Jordan O
    October 11, 2018 at 1:58 am #

    Mr. Sohn’s presentation showed us a side of structural/facade restoration that a lot of people don’t typically get to learn. Once scaffolding goes up it is often assumed that there is being work done, but not many people outside of the industry care to know about all of the intricate, and sometimes physically demanding tasks that go into restoring a historical structure back to its original condition. WJE got into the physically demanding side on the Washington Monument and Washington National Cathedral projects, scaling facades and using a rope access system to carefully inspect many of the pieces of the facade that could potentially come loose. It is a difficult but necessary process, especially after events such as earthquakes that knock a lot of these materials lose. As difficult as the repair and inspection process is, it is equally as impressive the quality of the repairs that are done. WJE finds very similar materials and in this case of masonry, was able to install the repairs with minimal steel reinforcing. Maintaining the historical accuracy and original composition of the structure is equally as important as the end result of a successful repair, and WJE has found a way to accomplish excel in each of those areas.

  3. Jackson H
    October 10, 2018 at 11:06 pm #

    I remember the earthquake that occurred in 2011. I remember that I was sitting on my couch and thought that the quarry near my house had done some blasting and thought nothing of it. It wasn’t until later when I saw on the news and social media that I realized that it was actually an earthquake that was felt throughout the entire mid-Atlantic region. Mr. Sohn’s lecture about WJE’s analysis and restoration of the various structures impacted by the earthquake was actually my first real exposure to the real extent of the damage caused by the quake. The Washington monument and National Cathedral both experienced extensive damage. It is interesting how one of the largest challenges to repairing these structures is doing it in a way that preserves the original architecture. The fixes themselves in most cases could be done fairly easily, but it takes a higher level of expertise to preserve as much of the original structure as possible and make a minimally invasive yet long lasting repair. I thought it was great that the repair of the Washington Monument was designed in a way where it utilized the minimum amount of steel necessary to keep in line with the all masonry structure. I also had no idea that the National Cathedral has dedicated stone masons that do all of the masonry and stone carving for the entire cathedral

  4. rgstanza
    October 10, 2018 at 8:41 pm #

    The subject I found most interesting from Mr. Sohn’s presentation was the intricacy involved in the construction of the Washington Monument’s pyramidion. I never thought about how the top of the monument would actually be constructed using masonry. The interaction between the corner stones, ribs, and tie beams to allow the tapering of the monument was really fascinating.

    After reading the seismic assessment, I find it even more interesting that the reason that the pyramidion had the most substantial damage was because the period of vibration was close to that of the soils that support the monument. From my understanding, since the natural frequency of the pyramidion was similar to the soil ground motion, a mild effect of resonance in the pyramidion caused the deformations to be larger, and thus the pyramidion received the most damage.

    Fortunately, the assessment reports that the likelihood of another earthquake of similar intensity is very low. However, if this was not the case, I wonder what non-invasive design strategies could be implemented so that the pyramidion does not experience a similar fate. How could we change the mass or stiffness of the pyramidion without compromising it’s historical integrity and turning it into a “Frankenstein monster”?

    • mkev
      October 11, 2018 at 9:48 am #

      Interesting point. Something like a mini tuned mass damper at the top?

    • Jordan O
      October 16, 2018 at 2:35 am #

      Ryan,

      Similar to what MKev said, when I was studying abroad in China, we were lucky enough to take a tour of a very tall building with a huge mass damper at the top. China, and many parts of Asia near the Pacific, are at great risk of major earthquakes and designers and engineers are starting to come up with innovative methods to resist events like this. In this case, they were able to use a massive damper some 20 stories above grade to counter act the swaying of the building. I know other buildings have done some things like this, although not as extreme or as visible to the public, but it would be interesting to see if it could even be implemented into retrofits for buildings potentially susceptible to a seismic event. As Josiah mentioned, and MKev confirmed, companies are starting to examine existing structures to see if they would be at risk if an earthquake were to occur. This mass damper is one method that could be employed to help keep existing buildings from large amounts of damage in an earthquake.

    • Jackson H
      October 18, 2018 at 9:44 am #

      I too never realized how intricate the construction of the Washington Monument is. Especially when you consider the means and methods of construction that were available back then. To accurately carve and set the four-sided keystone in the top and interlock all of the panel edges and corners must have been a difficult task. And although the interlocking corners have failed in some places, I still think the level of complexity that was created through empirical masonry design is impressive.

      As Jordan said, there are many examples of mass dampeners hung from the tops of buildings. And although the implementation of such systems, especially post completion, is invasive. I think that realistically the only way to significantly improve the Monument’s resistance to earthquakes is to use something a little more noticeable. You would have to add significant structure to the building that’s wasn’t originally there. The monument isn’t getting any stronger as time moves forward, so at what point do we decide that saving the historical landmark with more invasive and noticeable systems is worth it over attempting to keep everything original.

  5. Katie W.
    October 9, 2018 at 8:51 am #

    The session on WJE’s restoration of these historic landmarks was very interesting to me. With historic restoration there is an added layer of challenge because you have to stay true to the original building and architecture. Not to mention the additional challenge of the difficult access. For example, I had no idea that the Washington monument is tallest mass masonry structure in the United States. The National Cathedral is also a mass masonry structure which presents some interesting design challenges. When repairing these two buildings, Mr. Sohn mentioned how they wanted to reduce the amount of steel they added to the project because of their intentions to preserve the original design. Over the summer, I had the chance to work on a historic silo project from the 1800s. It would have been much simpler and easier to tear down completely and rebuild the silo but then the historical significance would have been lost.

    • Sierra S
      October 9, 2018 at 8:51 pm #

      I agree with you Katie. Many historical landmarks require certain preservation requirements for aesthetics. This doesn’t only apply to large landmarks but also historical residential areas. I find that these regulations only focus on the exterior presentation of the structure and not the interior renovations. I was shocked when I found out that it was decided that it was acceptable to allow steel to show on the Washington Monument. I understand that it is part of the history but with my experience of how strict other preservation societies have been I didn’t think it would be allowed.

      How do you think these preservation requirements are regulated? Is there a different guidelines based on region, construction type or both?

      Also, you mentioned the difficult access to assess the Washington Monument and National Cathedral. With this, regular inspections seem unlikely due to its difficult nature. However, due to the age of these structures it seems that higher maintenance is required in order to maintain its structural integrity. This makes me wonder if any protocols are being considered for the regular maintenance of the historical structures.

      • Katie W.
        October 11, 2018 at 8:20 am #

        Hey Sierra,
        I was intrigued by your questions and so I looked more into regulations surrounding historic structures. I looked at the “Standards for Rehabilitation” from the National Park Service, who runs the National Preservation Society. These are the national guidelines, but I also found some state and local government historic preservation program so this could vary. From what I could understand, the most important part of making repairs is saving the original character or the important historical aspects to the building that it was preserved for in the first place. For example, one company at the career fair told me about a project where they had to fix a historic house that was built using a special type of stone that was only available in the area. As that was a defining characteristic of the house, they had to scavenge more of that stone to replace it. However, in the standards it said any alterations or changes should be “avoided” so I assume there is some leeway there if there is no other alternative.

  6. Josiah M
    October 9, 2018 at 8:05 am #

    The main takeaway that I got from this article is that, as structural engineers, we should thoroughly consider every form of loading. The presentation of the damage on both the Washington Monument and the Washington National Cathedral made it clear that some loads were not considered during design. Even though they were built before earthquake loadings were considered, the possibility for earthquake related damage exists and when it did occur, it was well documented by WJE. That leads me to wonder if it would be fruitful to start investigating historic buildings to determine how they would perform under different loading conditions that may not have been considered. I’m aware that facade inspections are done to insure that pieces don’t become dislodged. But, is there ever any investigation into the lateral resisting systems of the building or how facade elements will react in a seismic event?

    • mkev
      October 11, 2018 at 9:55 am #

      Josiah,
      They are in fact starting to do what you suggest. Here is a link to an article concerning identifying San Francisco buildings that might be susceptible to a big quake. They are looking into retrofits for various types of buildings. As was implied in some of the other posts, the historic buildings present special challenges.
      https://www.nytimes.com/2018/06/14/us/california-earthquakes-high-rises.html

  7. Steven B
    October 9, 2018 at 3:03 am #

    When working with historical structures, the original plans are rarely available and even when they are available, renovation or repairs done to the structure are not always documented. With the development of a variety of inspection tools recently, it was surprising that the team from WJE relied more on hands on and visual inspection for their initial assessment. Perhaps it might not have been possible to send a drone up the side of Washington Monument due to the sensitive buildings that are in the area. The two structures are high profile and as with most failure inspections, time is limited as the owner would like to resume use of their structure as soon as possible. Sometime, the use of the latest technology is not best inspection practices. The Engineer has to be able to understand the environment around him and be able to adapt to the situations that presents themselves. Only with the Difficult Access Team would it be possible to identify and remove the defect at the same time.

    • Josiah M
      October 11, 2018 at 8:03 am #

      Steven,

      You make a good point when talking about the hands-on inspections that WJE performs, instead of using more technological methods. I think that, in the cases presented, it is easier to conduct hands-on/visual inspections. Because the investigated structures are mass masonry damage is normally visible or easily detected using the methods like hammer tapping. These methods are a lot more thorough for buildings of this type, and I believe that WJE wanted to give as much attention to these structures as possible, given their significance.

  8. Eric I
    October 8, 2018 at 11:05 pm #

    The damage assessment and restoration of the Washington Monument and National Cathedral are two of the most interesting projects I’ve learned about while at Penn State. As we all know from the presentation, an unusually strong earthquake struck the Washington, D.C. area and as a result, a lot of National historic structures were damaged from the event. This posed a huge challenge for the National Parks Service because they had to basically verify the public was safe to enter these structures. To do this, WJE was called in to conduct a survey of the damages as well as to provide repair designs.

    These structures in particular have obvious national importance but their age and historical construction proved to create a lot of challenges. With the National Cathedral especially, a lot of the components were hand crafted from stone. With that, special care and attention was required both during the assessment and during the repairs. Also, a lot of this craft work is a dying art today so simply finding a way to replace the failed components was a tall task.

    One thing of particular interest to me is the process of actually analyzing these old buildings. Different codes were used to determine force magnitudes. Older methods were used in the analysis and design of the structure itself. Understanding current design standards is hard enough, but having to flip back in time to understand why a design is a certain way is one of the most interesting parts of forensics work to me. After understanding the initial design, the engineer must then quantify what is already there to see if it is sufficient for today’s standards and if not, they must devise a way to meet that standard. I believe this will become a huge segment of the construction industry in older cities like Washington, D.C. As these buildings continue to age and more events like this earthquake happen, verifying the structural integrity of historic structures will be vital from both a life safety standpoint and from the standpoint of wanting to keep these national monuments around for years to come.

  9. Abby S
    October 8, 2018 at 6:57 pm #

    When I think of the Difficult Access Team (DAT) conducting their investigations, I typically imagine the most critical issue to be the most obvious one – falling. Mr. Sohn, however, mentioned many other hazards they face, which are often unique to the situation. For example, he mentioned that one member of their team was cut by a spike on the exterior of the monument used for lightning purposes. Mr. Sohn also said that they had to be careful to avoid the lights on the monument so they would not burn their ropes. With a strong emphasis on fall protection and safety and having backup ropes, I found it very interesting to learn that there were so many extra precautions that had to be taken. I was also surprised about the necessary repair considerations since this is such a historic structure. Trying to find a way to use little to no steel for the repair of the all masonry structure seemed to be an incredible challenge. There are so many unique challenges in this field. Additionally, on the 2016 Oklahoma earthquake Wikipedia page, it is noted that the earthquake occurred along a previously unmapped fault. After typically hearing about earthquakes that occur repeatedly in certain areas or along the coast, I was surprised that such a strong earthquake had recently occurred in this location. This all goes to show that earthquakes and the related damage repair can be very unexpected and pose unique challenges.

  10. Smithr
    October 8, 2018 at 4:13 pm #

    In class we are often reminded that “thermal expansion/contraction is a load” and in this case we have another environmental load in seismic loading. As in every investigation, there appears to be a number reasons that led to the cracking at the pyramidion. It appears that the crack path has a pattern of following the middle of the panel where the rib support is. Obviously neither is preferred at all, but I wonder if it is preferred to have a pattern of cracking or to have random spot cracking.

  11. Ryan L
    October 5, 2018 at 12:26 pm #

    As Sierra noted, preservation of historic buildings is very interesting, particularly during seismic and other unpredictable events. As new construction standards continue to try and address these events (hurricane force winds in the Southeast/ tornadoes in the midwest/seismic events), balancing historic building construction repairs for durability and authenticity seems to be a very interesting niche.

    Specifically to the Washington Monument, The full WJE damage assessment report recommends utilization of multiple steel alternatives for structural reinforcement. The report specifically calls out conversations with conservators to find alternatives to steel. I am assuming this directly relates to the “tallest masonry structure without steel structural components” label. Which must drive the question of when does structural integrity trump certain building material considerations for historic purposes.

    • Eric I
      October 10, 2018 at 8:15 pm #

      Ryan,

      I think you’ve asked a very difficult question here. When the public hears of a historic building renovation, the first concern is usually that it must look and function the same way as before. While this is the obviously preferred option for all of us, there is a point where safety becomes a concern. As structural engineers, we may be the only ones diving deep enough into the details to understand if a building is safe or not. If it is deemed to be unsafe, it can create a difficult conversation with those who are in charge of the building. With the Washington Monument specifically, it does have the label of the world’s tallest mass masonry structure as you said. While that is a nice title to have, it dos not trump concerns over the structural integrity of the monument. Had there been stability issues, introducing steel or other materials to the monument would have been necessary. While this is not the preferred option for buildings like this, it is a conversation we must be prepared to have.

      I believe your comment on the need to balance durability and authenticity is a great way to think about it. As engineers, we are tasked with designing creative solutions for complex problems on a daily basis. With historic structures in particular, our problem solving skills are stretched because we cannot infringe on what is already there. Most of the solutions need either hidden or disguised which was the case with the Washington Monument and the National Cathedral. I believe the need to find ways to ensure that durability while keeping the building in its original form will become a huge market in DC as we enter the workforce.

  12. Sierra S
    October 4, 2018 at 5:24 pm #

    Throughout my studies at Penn State I have heard a lot about the restorations done on the the Washington Monument and National Cathedral. These national landmarks signify important parts of our history and it is a once in a life time experience to have worked on them. They are not like your typical building, those pose challenges that force you to think outside the box.

    Even though the lecture was focused on assessing the damage after the earthquake and the challenges of repairs and access I was intrigued by the construction of the National Monument. The fact that it is one of the tallest structures made purely of masonry is just the start of its’ story. Its construction was interrupted by the Civil War which effected the structures design and look. From the outside, the stone changes in color part of the way up signifying the construction before and after the war. The stone was quarried from a different batch which produced the color change. I knew this for years, however, what I wasn’t aware of until today was the change in the structural composition at that same point. The thickness of the walls at the base are significantly thicker. The thickness had to change due to the settlement that was occurring. Another component to the structure were the interior ribs. The panels transferred the load to the ribs. The load path through the ribs on the interior reminded me of the dome of the Florence Cathedral, another significant landmark that has produce a lot of attention from the structural community.

    Once again, both the National Cathedral and Washington Monument are incredible projects to hear about time and time again. There is always something new to learn about them.

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