Damage Assessment of Monumental Structures in the 2011 Virginia Earthquake

  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 continues on a number of facilities more than a year 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, assessemnts and repairs of buidlings and other strutures that experienced damage of vaiours 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.

Today’s Architectural Engineering Building Failures Seminar features Eric Sohn, a 2001 Penn State AE alumnus who along with 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.  In particular, Mr. Sohn will disucss 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. 

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

 In order to fully appreciate and carry out follow up discussions on the presentation, you 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 recent quakes in New Zealand and the Mineral Virginia earthquake in particular are provided below:

     USGS One Year Anniversary – VA 5.8 Quake     2010 Canterbury, New Zealand Earthquake Summary     2011 Christchurch, New Zealand Earthquake Summary

 

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61 Responses to “Damage Assessment of Monumental Structures in the 2011 Virginia Earthquake”

  1. Ramsey N
    October 18, 2012 at 1:19 am #

    In reading about the New Zealand earthquakes, 2 contrasting ideas got my attention the most. First, the fact that pre-1970 R/C buildings sustained only minor damages, and second, the fact that even some retrofitted masonry structures collapsed (christchurch). What isn’t clarified in the article is whether or not pre-1970 construction was actually designed against EQs, or if it was simply very heavily and massively reinforced, and therefore, while not an efficient type of construction, was effective. On the other hand, the fact that retrofitted construction only achieved 10% of the prescribed strength by the code is probably an indication of poor quality control and not enough inspections and follow up by the municipality. Unreinforced masonry is counter-indicated in seismic areas anyway, and probably should have never been used.

  2. Ramsey N
    October 18, 2012 at 1:09 am #

    One point I would like to stress further on is the design aspect of the mitigation for earthquakes. While the 5.8 magnitude earthquake in Virginia was the strongest in scores of years in the area, a similar earthquake in more tectonically active regions, such as Japan, or California, might not have even made it to the news with such attention. What this tells us is that earthquakes should be designed for, as many other participants in the forum mentioned, but not just for magnitude. Among other factors to be studied with regards to earthquakes is the period of oscillation produced by the shaking of the ground. Also important to note is that designing against earthquakes doesn’t mean designing against structural damage, but rather against structural collapse. It is the responsibility of the engineer to design against earthquakes in that sense, and the magnitude and other factors usually designed is a result of a probabilistic approach (since we can only guess the EQ magnitude based on previous data); the fact that this earthquake was the strongest recorded in this region is indicative of the fact that nature got the better of probability on this occasion.
    I was very impressed however, by how minimal the extent of the damage and water ingress problems were on the washington monument.

  3. James C
    October 15, 2012 at 11:13 pm #

    After reading about the 2 New Zealand earthquakes, I found it very interesting how much damage results from soil liquefaction. I find it a bit unsettling that a very well designed and strong building can still possibly collapse from differential foundation settlement. The Christchurch Earthquake wiki states that the majority of the structural damage incurred during the earthquake was a result of soil liquefaction. It seems that much more is known about soil liquefaction now than when the New Zealand buildings were built, but there still appears to be a large level of uncertainty about it. Although soil tests and samples can predict the properties of the soil, the magnitude of the earthquake that triggers the liquefaction is unknown. So, how do you know when enough soil modification (compaction, adding structural fill, etc.) has been done? It seems like you can never tell since a larger earthquake may always hit. I’m sure this sort of work isn’t cheap either. Are there any products or special designs out there that are a cost effective alternative to coping with the threat of soil liquefaction?

    • mkev
      October 16, 2012 at 8:32 am #

      Deep foundations can be used to support the building on better material but that can be costly which is why they are always looking for alternatives. I also recall reading that the maps that were used to define areas of potential liquefaction were inaccurate relative to the recent quakes which means they may not have been expecting that problem as much as it happened.

    • Thaison N
      October 16, 2012 at 9:47 am #

      From my knowledge soil liquefaction is primarily caused by water saturation of soil. This is especially prevalent in locations where land is reclaimed from the bodies of water and/or the ground water is pressurized. I agree with professor Parfitt that deep foundations would alleviate the threat of soil liquefaction. But I also think that foundations systems which can take bending moments and prevent un-even settlement will reduce the impact of soil liquefaction. Examples include monolithically cast-in-place reinforced concrete slab or mat foundations.

  4. Jordan R
    October 15, 2012 at 4:34 pm #

    When reading about the two earthquakes in New Zealand I was very surprised at the amount of failures that were due to unreinforced masonry construction. It is mentioned that Christchurch is working on updating their code for the retrofitting of URM buildings since some failed even though they were retrofitted. I think this is something that Canterbury and all of New Zealand should do though. Canterbury has about 900 URM buildings and in a survey of approximately 600, 21% were deemed unsafe. That is a huge amount and surely a risk to so many lives. With 2 large earthquakes and the faults located so close to the populated areas it seems it is imperative to updating the code and retrofitting as soon as it is possible. I know that New Zealand is quite far away from the US, but I was curious if other countries ever seek assistance from the US in updating their codes? It’s something that has never dawned on me and would be interesting to know. Even though the region is much different, the US code associations have a broad knowledge base and many experienced engineers and could possibly provide them with help.

    • mkev
      October 22, 2012 at 10:03 pm #

      Jordan,
      Actually, the NZ earthquake codes are considered pretty good but everyone benefits from collaboration on topics like this. In fact, US representatives were in NZ for an earthquake cooperation seminar when one of the quakes hit. See the post at https://buildingfailures.com/2011/03/08/us-representatives-were-in-christchurch-when-earthquake-struck/ The good news is that the engineers who were needed were actually downtown in the middle of it all when the quake hit. The scarry part was that most of the earthquake knowledge in the region could have been wiped out in seconds if they had been in a different building.

  5. Emily W
    October 11, 2012 at 9:36 am #

    Once again big thanks to Eric Sohn for an informative presentation and insight into a less traditional career path for Penn State AE structural students. Being able to hang 500 feet in the air off of such a historically significant structure must have been an amazing experience.

    Upon reading about the 2010 Canterbury earthquake and the 2011 Christchurch earthquake from the suggested readings above, both summaries got me thinking about the potential for even worse damage to occur if a second earthquake were to hit somewhere along the east coast. As Mr. Sohn stated in his presentation, extensive repairs have not yet begun on the monument and only temporary fixes are in place. In the 2011 Christchurch earthquake the majority of the damage was to buildings weakened by the 2010 earthquake in Canterbury. Although both of these earthquakes in New Zealand were stronger in magnitude and much more devastating, is the possibility of more seismic activity in the Washington DC area still a concern? Especially while permanent repairs are not yet in place?

    • Xiao Z
      October 14, 2012 at 6:10 pm #

      From what I know, seismic activity was never a major concern in the east coast, until the 2011 Virginia Earthquake. According to this news article, Slate, http://www.slate.com/articles/news_and_politics/explainer/2011/08/is_washington_as_earthquakeproof_as_los_angeles.html, the IBC for seismic provisions apply for “a quake so strong that it should only occur once in a 500-year period.” I also remembered someone, maybe Mr. Sohn, mentioned that because of this earthquake, the seismic code may/will be rewritten.
      I think the possibility of more seismic activity will always be a concern now, but regardless, nothing can be done at a faster pace because of a tight budget. It is a major problem because buildings are designed to withstand strong earthquakes every long periods of time, like 100 to 500 years. Because of this, if another earthquake happens in a few years close to the same area, there will be a lot more damages, just like the earthquakes in New Zealand.
      According to the 2010 New Zealand Earthquake Wiki page, New Zealand’s strict earthquake code is what minimizes their damage in that earthquake. But, they never anticipate a back to back earthquake. Even if they did anticipate it, it makes me wonder will they be able to do anything about it, building wise. Can all these buildings be repaired on time? And is there really a budget that not only fixes but makes buildings stronger for the ‘anticipated’ earthquake?

      • Emily W
        October 15, 2012 at 12:07 am #

        I agree with Xiao that even with the possible threat of another earthquake hitting the east coast, repairs to damaged buildings such as the Washington Monument and National Cathedral will likely not be completed any faster. This is completely understandable considering how rare earthquakes are on the east coast compared to a high seismic zone such as the west coast. I was curious about other earthquakes that have hit the east coast in the past and discovered the following in my research:

        September 1886 – According to data from the U.S. Geological Survey, the highest magnitude earthquake to hit the east coast struck Charleston South Carolina, registering 7.3 in magnitude with an estimated $5-$6 million in property damage

        1944 – An earthquake in New York (largest recorded in this state) caused an estimated $2 million dollars in property damage, and was felt across all the New England states

        January 1994 – Two earthquakes struck southeastern Pennsylvania within the same day, the largest being 4.6 in magnitude

        September 1998 – A 5.2 magnitude earthquake occurred in northwestern Pennsylvania, which is the largest recorded in the state of Pennsylvania

        April 2002 – A 5.1 magnitude earthquake occurred in northeastern NY, damaged several highways

        All of these earthquakes were around the same intensity or less than the one that struck Virginia in August 2011. However none of them were centered around a city such as Washington D.C. with numerous important monuments and a high population density. Perhaps that is why this earthquake received much more publicity, and will probably be well remembered in the future.

        Source:
        http://earthquake.usgs.gov/earthquakes/states/state_largest.php

        • Ben B
          October 15, 2012 at 11:11 pm #

          I remember when the earthquake in Reading occurred, I live about 15 miles from the epicenter, though I didn’t feel the earthquake itself. I do recall seeing footage from surveillance cameras of items falling from shelves on the local news. I didn’t really do much damage even there but I remember everyone feeling a little uneasy about the reality that one could still occur so close to home. The DC earthquake was about 60 times greater than the largest earthquake in Reading, and about 8 times larger than the largest in Pennsylvania. The epicenter of the Virginia Earthquake was 80 miles from DC but was of such larger magnitude that it was significant there and was felt much farther away.

      • Nick L
        October 15, 2012 at 8:34 pm #

        Xiao makes strong points, and I agree with all of them. I would like to add though, also noted in the Christchurch 2011 earthquake, that particular earthquake exceeded the maximum considered earthquake. Only to happen shortly after another devastating earthquake. As engineers, we have to use our best judgement to predict the conditions of a particular site, and then design accordingly. Typically, we use case studies and history as the foundation of design, especially earthquakes. As Xiao stated, it should have been for a strong quake only in a 500-year period. Even thought the past 500 years did not result in this damaging of an earthquake, that is not to say that there could be the potential for a stronger earthquake, which was the case in Christchurch. If the owner had all the money in the world to spend, engineers could design the strongest building ever against earthquakes, but unfortunately, that is far from the truth. Though there were many casualties, I still don’t think it was the engineers fault for lack of under design. I am glad to see that New Zealand is taking the initiative to adapt to the new design provisions and make it code.

    • Gea J
      October 15, 2012 at 11:55 pm #

      There is definitely a concern that a another earthquake of similar magnitude will occur again in the Eastern United States. According to the EOS Volume 93 Journal (Source: http://www.agu.org/pubs/pdf/2012EO330001_rga.pdf, Date: 8/14/2012)
      it is estimated that an after shock with a magnitude of M=4.5 is still possible over the nest few months. According to the article, “Research is under way to better understand the geologicaland geophysical setting of the August 2011 earthquake and the severity and distribution of seismic shaking, including the geologic characteristics of seismic recording sites, the characteristics of the earthquake source, and associated
      ground deformation and failures.” The Journal further states, “Infrequent large earthquakes and sparse evidence
      of Quaternary (~2.6 million years ago to the present) earthquake history in the eastern United States point to the importance of investigating this rare earthquake to develop scientific insights necessary to improve seismic hazard assessment in the region.” Since the structures that were affected by the earthquake were not designed to resist seismic loads, the damage in Louisa County, VA is estimtated to be $80 million and the damage to the Washington Monument and Washington National Cathedral are estimated to be $40 million (Source:EOS). The 2011 Virginia Earthquake is the largest earthquake to hit the central and eastern United State since the N=5.8 earthquake near CornWall and Massena, NY in 1944, much research is currently being done to improve seismic hazard assessment in the eastern United States.

  6. Eric C
    October 11, 2012 at 9:14 am #

    I would like to thank Mr. Sohn for the interesting presentation that most people would not get to see. The thing I found the most interesting is the fact that most of the damage that was done to the Washington Monument was not a structural stability issue but rather an appearance or water issue.
    I also find it interesting that the cause of these performance issues was for the most part due to the detailing of the interaction between blocks such as the interlocking aspect, but that same detailing is what caused it to remain standing today. Design is often a give and take process where some things have to be given up in order to benefit another. I feel during the design process for the monument there were several things that were given up (whether intentionally or not is another question) such as the water tightness in order to maximize the structural component of it and that is ultimately why it is still standing today.

  7. T.J. K
    October 11, 2012 at 9:05 am #

    Thank you Mr. Sohn for coming to Penn State and presenting your experiences in the field resulting from the VA earthquake.

    I would like to talk about the Washington Monument first, which resisted the VA earthquake fairly well for as tall and slender as it is and not to forget the age of the structure. What I found the most interesting was the structure at the top of the obelisk, the ribbing used to stiffen the upper part. I enjoy looking at old structures just to see the different things they come up with to accomplish certain things such as the Washington Monument. I’m assuming the transition of stiffness form the middle part to the reinforced upper part are fairly the same even though the upper part is reinforced with those ribs, however the upper must be slightly more stiffer since it seemed to have taken most of the damage, force follows stiffness. Has there been any thought of stiffening the middle section also, trying to get a uniform stiffness going up the monument?

    The National Cathedral surprisingly took a lot of damage, I never knew that those peaks were so close to falling off in areas. You may have said this in your lecture but what was the procedure used to attach them back on? Do you epoxy a dowel rod into the rock below and have that rod epoxied into the displaced stone?

  8. Thaison N
    October 11, 2012 at 9:00 am #

    First off, I’d like to thank Mr. Sohn for taking the time to present WJE’s assessment of the Washington Monument and National Cathedral. Mr. Sohn’s presentation broadened our knowledge of the building forensics and media influences.

    I’m curious about the cracking and spalling of stone previously repaired. It is understood that environmental conditions like water infiltration and the freeze-thaw cycle will deteriorate building materials. My question is: Was there evidence that some damage to the repaired stone were compromised by environmental conditions before the earthquake?

    Though superstructure was assessed, there is no information on the condition of the foundation. I’d like to know if there were any damage, concerning the foundation; as well as the changes in soil characteristics during the earthquake?

    • Devon S
      October 12, 2012 at 4:44 pm #

      On the topic of previous damages to a structure pre-earthquake… What are the methods used to assess whether the earthquake caused a crack, or some other failure induced cracking. We have learned that cracks can form from a number of issues including water infiltration, structural integrity, earthquakes, soil properties, and many others.

      Cracks propagated from water infiltration are fairly simple to recognize, but it would seem difficult to tell the differences between other causes of cracking. This topic of differentiating failures of a similar type is transferrable to other issues, not just cracking. It would seem that experience is the only way to become an expert on this, but I would like to hear if there are other ways which could include texts or lectures that are out there that students can use to educate themselves.

    • MinGao L
      October 14, 2012 at 6:48 pm #

      I was also concerned about the weakening of the soil caused by the earthquake. However, after looking up articles about foundations damage due to earthquake, it is stated that there would be notable sights of danger if foundations are at risk. These sights includes slightly sideways shift of the structure, damaged gas pipes, burst of water mains, etc… It is also said that a soil test should be performed to test the stiffness of the soil to determine whether or not the foundation is okay.

      If you want, you can get more details from this article.
      http://www.inspectapedia.com/structure/Earthquake_Damaged_Foundations.htm

  9. Gea J
    October 11, 2012 at 8:53 am #

    The presentation Erik C. Sohn gave about Seismic assessment and repair on the Washington Monument and the Washington National Cathedral was very informative and a good crash course in what is required when restoring structures that were subjected to seismic damage. In addition, I did not know that the 2011 Virginia Earthquake causes damage to these two historical structures. Erik Sohn did a good job at explaining the damage that each structure had due the 2011 Virginia Earthquake, the survey/ documentation of the seismic damage, and the access considerations required to survey the hard to reach regions of the structures.

    First, the three methods used for surveying/ documenting the extent of the damage to these historical structures were a visual survey of the exterior elements, identifying and removing unstable elements, and to access the overall extent of the damage resulting to the earthquake. Second, for the Washington monument, I thought the access considerations were very interesting. The fact that Difficult Access Team (DAT ) had to analyze the exterior damage on the outside by use anchors and ropes and hanging over 500 feet above the ground to do so was very interesting. Third, the extent of the damage to the Washington Monument included spalls, cracks, displaced stores, loose mortar, interior spall at panel baring points, lateral offset of stone units, and damage to the lightning protection system. The damage to the Washington National Cathedral included bondline failures, step cracks, and isolated interior damage. The extent of damage to the Washington Cathedral caught my eye because the damage was relatively severe. Lastly, I enjoyed the discussion of the steps that were taken to repair both of these historic structures.

    I would like to thank Erik Sohn for a well organized and informative presentation on seismic assessment and repair.

  10. Nick L
    October 11, 2012 at 7:55 am #

    I would like to first thank Mr. Eric Sohn for providing such an interesting an informative presentation on the Washington Monument. Because of his willingness to donate his time, I was able to become even more educated in the world of forensics.

    Mr. Sohn provided an extensive explanation of the effects of the Earthquake on the Washington Monument, going into detail on seismology and the response/effects toward the structure. However, what caught my attention were the the unexpected repercussions of repairing both a national monument and located so close to the president. In my opinion, becoming an engineer is much more than crunching numbers, as shown in Mr. Sohn’s experience, he had to deal with the tourists/media poking their nose into the business of the repair of the structure, and the security measures taken, because of such close proximity to the White House.

    When it comes to dealing with the media, unless already addressed, it is important to make every word count, and the best way to do that, is (1) know your stuff, and (2) premeditate responses for any media encounter. For the second point, this is where good English/communication skills are important. The situation with the media and the Washington Monument is a prime example of that, and with that said, it is vital that engineers work to improve their English skills constantly.

    My question for Mr.Sohn, is if there were certain things he could say or couldn’t say while speaking to the media, and if there were, maybe provide and example?

    • Eric C
      October 12, 2012 at 2:54 pm #

      I agree with the point that English/Communication skills are very important in this situation since you would have to be very careful what you say and how you say it so it does not get out and twisted into something that is not true. Although this specific situation is something that most people may not experience, I believe that these skills are more widely used in the engineering environment than initially thought. Communication skills not only come into play when you have a sensitive topic such as this but in a daily setting are important in order to get your thoughts, ideas, directions and concerns across to subcontractors and workers. If you are directing work as an engineer and are not specific, the mistake could mean life or death to various people either immediately or in the future.

    • Li J
      October 14, 2012 at 5:44 pm #

      I totally agree with the point that communication skills are crucial when you are dealing with this kind of situation. You need to be sure the things you said are correct about what happened but you also need think about how to use the words to describe the situation in a smart way.

      In addition, I think risk management skills are also very important in this kind of situation. I remembered a case in our class talking about an existing residential building that showed serious structural problems but people were still inside. The moment you think about how to save the building, the more important thing is to save people’s lives. Although this situation doesn’t happen often, Mr. Sohn also mentioned they’ve been asked to provide a safe area for people to do ritual ceremonies when they are doing the repair of National Cathedral.

      • Scott M
        October 15, 2012 at 5:03 pm #

        Another aspect of the media communication issue is to not only be careful with your technical description of issues, but also be prudent with what information you are giving out. In the case of the Washington Monument, Mr. Sohn and WJE were working for their client, the National Park Service on a structure with very sensitive sercurity concerns. Mr. Sohn touched on some of that when he mentioned that only certain photos could be used in his presentation and that he couldn’t fully describ aspects of the project. This highlights an ethical responsibilty that any engineer has toward their clients. That responsibility is to respect the privacy of your client, similarly to why we need owner permission for our thesis buildings and photographs.

        I agree that the media needs to be addressed and that blatanly inaccurate statements like the 14′ long by 2′ wide crack need to be corrected, but there is definitely a limit to what can be said. Obviously WJE could not discuss the monument’s internal structure with the media. If they had, the NPS and others in the government would probably have been furious. Breaking a client’s trust by releasing information they do not wish released reflects badly on the engineer and would potentially cause them to lose their client.

        The bottom line with dealing with any media outlet is this- Know the bounds of what you can and cannot say, but always tell the truth.

  11. Ben B
    October 11, 2012 at 3:08 am #

    Thank you very much Mr. Sohn for your presentation on WJE’s involvement in the investigation of the Washington Monument and National Cathedral after the 2011 earthquake. I very much appreciated seeing the models and pictures diagramming the structures of the two buildings.

    It must have been very exciting to be able to get such a unique look at some of the nations most commemorated buildings, but it is a reminder to me of how they are vulnerable. The 2011 earthquake was also a reminder of the importance for seismic provisions even in low seismic zones.

    I was surprised in the presentation to learn that the large stones at the top of the monument are only seven inches thick, which is very thin compared the size of the stones as well as the rest of the structure. Do you think that if the stone at the top was thicker the monument would have resisted more force without cracking?

    More interesting than the structures however, was the manner in which he was able to investigate. WJE’s difficult access team may not be a common destination of AE graduates, but it is an exciting opportunity away from the norm. The idea that you can get apply structural engineering suspended hundreds of feet in the air really got me excited. Thank you again.

    • Logan G
      October 11, 2012 at 9:03 am #

      Like Ben, I was very intrigued when presented with the information about WJE’s Difficult Access Team (DAT). A building that is held in such high regard as the Washington Monument has some unique challenges that come with it, but I am curious to know if any other buildings that WJE has assessed caused similar headaches. What is the most prolific building that WJE has assessed? What was the most difficult building to assess for the DAT? What was the tallest building that the DAT has scaled? How far has WJE had to travel to perform a DAT survey?

    • Issa J.
      October 12, 2012 at 2:02 pm #

      One of the most important factor during earthquake is weight of structure, especially in tall building the weight of the head of tower is one of the most important factors of building. I think reduction of weight of the building head was the reason of selection of thin stone. Also the stone was tilt and therefore it’s strength against lateral loads is more than a vertical stone. Also at the top of building there was lots of constrain, therefore thickness of surface stone decreased. In addition replacement of small and thin stones is more practical.

      • Brandon R.
        October 15, 2012 at 4:27 pm #

        I do agree with Issa for the most part, we do want the building top to be light in earthquake design, but we do also need to think of the other factors. In this particular earthquake due to the thin stone used at the top of the Washington Monumentthe stone also had some significant cracks that may not have occurred if thicker stone was used. I feel there has to be some sort of trade off when it comes to designing monuments and building such as this. Thin stone may be great as far as keeping the weight down, but it may have issues in an earthquake as far as cracking which can also be a significant issue especially if there is a storm (i.e. the hurricane Mr. Sohn talked about) coming shortly after the earthquake. Now obviously it is unrealistic to think we can predict every little event happening and plan for all of them, but we should be finding a happy medium to alleviate all issues a structure could see.

    • mkev
      October 13, 2012 at 9:33 pm #

      A number of PSU AE alums are now participating in some form of industrial rope access inspection for WJE or one of the other major forenic firms. As you note, most students never think that they can turn their interest in staying physically fit or love of rock climbing into part of their regular job after graduation. Want to just do difficult access? Take a look at Vertical Access, a consulting firm that started the use of rope access in the US in the early 1990s. http://www.vertical-access.com/

      Looking for something unique? It doesn’t end with rope access. At least two AE students I know of went on to take jobs doing underwater inspections and forensics. Both were certified divers while they were at Penn State. My recollection was one of them went to work at McLaren engineering, which by the way also has an entertainment division where their structural engineers do the stages and rigging for the big Vegas hotels and casinos. http://www.mgmclaren.com/

  12. James C
    October 11, 2012 at 2:03 am #

    Thank you to Eric Sohn for the excellent presentation on The Washington Monument and National Cathedral. I never thought that a structural engineering degree could lead to such an awesome job. Sign me up!!

    One thing that I was curious about during the presentation was how new cracks caused by the earthquake were distinguished from old ones. I would imagine that the very old ones were clearly weathered over the years or had been previously sealed. What were some of the clues as to figuring out the difference between cracks caused by the earthquake and ones that were only, say a year or two old (something that hadn’t seen much if any weathering)?

    It was also found during the investigation that some previously repaired chunks of stone broke off again during the earthquake. I’m not sure for this case, but some repairs tend to be stronger than the original substrate (similar to a well constructed weld). The particular repair on the monument coming to mind is the corner chunk of stone that was pinned back into the surrounding stone. Could this piece having the same failure as it previously had be an indication of a larger problem internal to the structure?

    • T.J. K
      October 14, 2012 at 11:48 pm #

      If I remember correctly they had used old drawings from an assessment done in 2000 (I think?) and they used their iPads to review the drawings as they were on the monument and then they recorded the cracks that they found in red. I think information such as crack length and width was also given on the drawings, which would make sense.

      • mkev
        October 22, 2012 at 10:10 pm #

        Yes, they had pretty good records from the previous survey including photographs and sketches of damaged areas. That certainly made the job go faster. One simple way to tell if a crack is recent (assuming that you got there right after the damage event) is to look for insect activity inside the cracks. Spiders and such move in pretty quickly so if it is clean, it is likely fresh. You also can often find very small sharp edged particles still clinging at the crack edges which usually indicates a fairly recent event.

  13. Devon S
    October 11, 2012 at 12:32 am #

    Thank you Erik for the “VIP” treatment regarding the information and visuals that were shared during your presentation.

    The restoration process that was shown sparked a curiousity of what techniques can actually be done to historical buildings that won’t change their visual integrity, but will change their structural integrity. After poking around on the web I ran into seismic epoxy injection. ACI did a study on this technique along with experimentations and found that the use of epoxy for earthquake related cracking does a great job of restoring structural resiliance to a building. An abstract and ordering of the full study can be found here [http://www.concrete.org/PUBS/JOURNALS/AbstractDetails.asp?ID=1547].

    Is epoxy injection something that is common in the field and if not, what are the reasons? As a newbie to the field of forensics and repair, the only reasons I could think of would be due to color matching issues or a crack may be to big or obscure in shape to be filled.

  14. MinGao L
    October 10, 2012 at 11:32 pm #

    Thank you, mister Sohn. Your presentation on the damages caused by the 2011 Virginia earthquake is fabulous. I learned that the Washington Monument is the tallest masonry structure in the world and it has a complex interior structure construction.

    Speaking from my own experiences, when the earthquake hit state college at that time, I thought someone was playing a prank on me by shaking my chair. I did not take the signs seriously, but I am surprise that this earthquake did some damage to the monumental structures after hearing the presentation. The public tend to ignore problems until they see obvious sights of threat. When I was reading the article about liquefaction, I was thinking what if the earthquake reduces the stiffness and strength of the soil that support the monuments. Although we might not notice any settlement of the monument yet, but can we guarantee that the support of the structure will not fail as time goes by? If liquefaction does happen, how can we fortify the foundation of an old structure?

  15. Fangxiao L
    October 10, 2012 at 10:34 pm #

    Mr. Sohn gave us a deep talk about the seismic assessment work of the Washington Monument and the National Cathedral.

    It is my first time to see the structure inside the monument, and the 3D models developed by Sketchup are awesome. Was the monument designed by any seismic codes over 100 years ago? Besides, how frequent will this historic building be assessed and maintained?

    I think another interesting thing about assessing the monument is to deal with security issues and media attentions. Will the involvement of some political departments affect the schedule of the assessment? Historic buildings are of significant values, and the repair and maintenance work may need to coordinate with other departments. Are there any specific issues when dealing with them?

    The earthquake is said to be the most severe one striking the east area, and a lot of buildings in Washington have been affected. Dealing with seismic impacts would become a big problem in the construction industry. Thank you Mr. Sohn for innovate us in this field.

    • mkev
      October 10, 2012 at 11:00 pm #

      The earliest seismic design provisions in the US were introduced in the Appendix of the 1927 Uniform Building Code (UBC) which was the first edition of the UBC. Few if any structures of the era of the monument were designed for earthquakes, particularly on the east coast. That said, I don’t know the specific history of lateral loads for the monument.

      • Seth M
        October 15, 2012 at 11:32 pm #

        It’s a very interesting point that until 1927, there was no comprehensive set of seismic requirements for use in structural design. After looking a little further into the origins of these early provisions, I found that their inclusion in the first edition of the UBC was a result of the 1925 earthquake in Santa Barbara. The earthquake registered a magnitude of 6.8 and the main shock lasted for 19 seconds. It claimed 13 lives and utterly destroyed the historical center of the city.

        The 1933 earthquake in Long Beach helped to further push along provisions for seismic design, especially in public buildings. After the earthquake, about 75% of the schools in the city experienced heavy damage and many other buildings were extensively damaged to the point that they were deemed useless.

        Although the UBC was the first model code to include and kind of comprehensive seismic requirements, they remained a feature of the appendix for many years after their introduction.

        Sources:

        http://www.urban.illinois.edu/faculty/olshansky/FEMA/Appendix%20A.pdf

        http://en.wikipedia.org/wiki/1925_Santa_Barbara_earthquake

  16. Xiao Z
    October 10, 2012 at 10:18 pm #

    Thank you Mr. Sohn for a wonderful presentation. It is nice to see that there are careers out there that can be so much fun. Being five hundred feet up from the ground on the Washington Monument must be an amazing experience.
    It is an interesting fact that with technologies many things can be done easier. Mr. Sohn mentioned that the initial tour on the top of the Washington Monument, for damages, was done virtually on a computer rather than physically being up there. This made it easier for the clients, because they can actually see what had happened to the monument without having to go up to the top. Also, the model of the interior of the monument must be very accurately detailed to match the actual interior. Because of that, I am also very surprised that they allow WJE to use them, when they prohibit the use of the photos.
    Because the budget is low, the Washington Monument cannot be repaired in a timely manner. But once the contractors do make the necessary repairs, can it resist the same earthquake with minimal damage? Is the current plan to make the monument stronger or just repairs for safety issues?
    Thank you once again to Mr. Sohn for letting us experience what you had.

  17. Brandon R
    October 10, 2012 at 9:11 pm #

    First of all, I would like to thank Mr. Sohn for taking time out of his busy schedule to speak to us. The presentation was very interesting especially since we all saw the guys hanging off the side of the monument after the earthquake on the news.

    During the presentation spoke about how there is some of the stone used originally stocked around, but a big issue was the thickness of these panels. I am curious if there has ever been any talk about possibly thickening these panels or doing something to strengthen them to alleviate some of the issues in the panels as far as thermal expansion? It seems to me that with such an iconic building as the Washington Monument a lot of times we as designers are afraid to do things to improve on the original design, but is there some amount improvement that can be done to negate some of the issues a historical building such as this may have down the road. From the presentation on Tuesday it seemed as if the panels were thicker or not as wide maybe some of the cracking may not have occurred either from the earthquake or other effects on the structure.

  18. Scott M
    October 10, 2012 at 4:20 pm #

    Thank you Mr. Sohn for taking the time to relate your experiences with the aftermath of the earthquake. From what I saw you had a pretty awesome time top roping on the Washington Monument.

    My case study topic for this class is the structural assessment of historic buildings so I am very interested in the work you did with both the Washington Momument and Cathedral, two buildings that symbolize the entire nation. Obivously these are high profile buildings as evidenced by the media attention you recieved. I was wondering what specific methods you used to evaluate the structure. Did you perform any tests to determine if the structure was at any risk? And after your on site investigation, did you set up any monitoring devices to measure crack increases throughout the winter to determine if they are increasing?

    As for the Cathedral, were any load tests done on the roofs or walls to determine whether or not they had lost strength due to the earthquake? Or can you just assume with mass masonry structures that if nothing specifically collapsed or came out of alignment then they are ok?

  19. Victoria I
    October 10, 2012 at 2:53 pm #

    Mr. Sohn’s presentation was both entertaining and enlightening. One of the things that caught my attention was the media’s involvement in the earthquake’s affects on the Washington Monument. When reporters are saying things like ‘2 feet wide and 14 feet long cracks,’ it becomes so obvious that what we (as engineers) consider basic knowledge and understanding, most people do not comprehend. Unfortunately, when people want to hear the stories anyway, reporters often use sources that are inaccurate and ridiculous just to get the story out there. This goes to show that even though WJE was hired to do the analysis and recommendations for the repairs, they also ended up as public figures to help get some truth into the news reports.

    Going to the actual repairs that will need to be made, the monument is now going into its second winter without repairs while it waits for all the funds to be raised. During one of the previous guest lectures, it was brought up that the longer repairs wait, the more expensive they become. Some of that is out of context (for instance, the rebar corroding in concrete will continue to corrode and spall the concrete even more) but for freeze-thaw cycles, I think the danger of increased cost is real. With all the new cracks and spalls from the earthquake, moisture will find its way in and freeze. Mr. Sohn mentioned that they did do some “reversible” repairs for temporary moisture control, but they couldn’t have gotten everything. I hope that the monument doesn’t see any significant deterioration while it waits for the actual repair.

  20. Mike S
    October 10, 2012 at 11:01 am #

    Mr. Sohn’s presentation on the damage assessment of the Washington Monument and National Cathedral was not only very interesting but very unique as well. Being able to work on two national landmarks is an opportunity that will most likely not come up too often, and I’d like to thank Mr. Sohn for sharing his experiences and knowledge.

    As people have mentioned already, WJE’s report suggests a detailed seismic evaluation may be necessary. The report further goes on to state that considerations in this evaluation would include local soil conditions and seismicity along with seismic response and performance of the monument. As far as response and performance, what is the difference in response if seismic activity generates motion diagonally in the monument rather than orthogonally (as would be the case with the maximum wind loads)? Also, what sort of damping or strengthening techniques would be most effective or most feasible in strengthening a structure as unique as the monument?

    Thank you once again to Mr. Sohn for sharing such a unique experience with us.

    • MikeP
      October 10, 2012 at 2:50 pm #

      MikeS brings up a good point. As WJE began the assessment of the Washington Monument, was there any brainstorming on how to help support the structure if it did, in fact, need stabilized or strengthened? That is to say, hypothetically, how would you go about it? The iconic nature of the building would bring up many issues with this, as you would want to ensure that the appearance of the monument is not altered. Adding a steel lateral framing system doesn’t seem like a great idea, and dampening systems such as base isolation may be possible but very expensive. Maybe using FRP on the interior could be a solution? Did your company have any solutions at hand, or has WJE had to come up with a unique seismic solution such as this in the past?

      • mkev
        October 10, 2012 at 10:05 pm #

        How about a tuned mass damper on the interior. At least it would not impact the historic exterior fabric and appearance.

        • Sean F
          October 10, 2012 at 11:09 pm #

          Professor that raises an interesting point. Did the top of the Monument act as sort of a mass dampener? The base and middle are obviously very rigid (15′ & 7′ thick masonry). I didn’t find specific rigidity criteria for the middle of the shaft, but it’s probably safe to assume that the top 85′ or so of the monument is significantly more rigid than the area between say 275′ and 450′. The report mentions that the pyramidion is the most vulnerable to seismic action, but I’m wondering if the weight shifting above the 450′ level could have helped stabilize the shaft as a dampener (though not tuned)?

  21. Evan L
    October 10, 2012 at 10:47 am #

    Thank you Mr. Sohn for a very interesting presentation and a very unique look at the Washington Monument that most people will never see. Not only was the evaluation of the monument intriguing but also some of the history was well.
    I found it interesting that the monument only received as much damage as it did. When the monument was designed, it was probably very loosely designed for seismic loads and primarily designed for wind given its location.
    As for the cathedral, were the designers of the spires thinking that the self-weight of the material would be good enough to resist loadings conditions, or was the technology that was used the best they could do at the time?

    Poofread version, I posted the last one by mistake.

    • mkev
      October 10, 2012 at 10:08 pm #

      I magically made that old one disappear!

  22. Seth M
    October 10, 2012 at 2:48 am #

    I would first like to thank Erik Sohn for his informative and eye-opening presentation on the work that he has done with WJE assessing damage to these monumental structures in the wake of the 2011 earthquake in Virginia.

    Mr. Sohn discussed some negative effects that improper mortar can have on historic structures such as the Washington Monument, which I had not heard of before. Mortar that is too hard can cause the surrounding masonry to crack and deteriorate more quickly. With these types of structures in particular, the mortar should be more flexible and weaker than the surrounding masonry for better performance during thermal movement and motion due to lateral loading. Also, mortar that is softer and more porous than the masonry itself allows the wall to breathe and creates an opportunity for the moisture that works its way into the structure to move out and evaporate eventually. This prevents potential damage that could be incurred from freeze-thaw cycles.

    I also have a question concerning the Difficult Access Team investigation procedures. What kind of initial training time is required for those DAT members who practice industrial rope access techniques like those that were used to investigate the Washington Monument? What kind of time is required to keep up with the training/certification renewals?

    • mkev
      October 10, 2012 at 10:15 pm #

      WJE has their own training and safety requirements in addition to the number of “drops” you have to make and practice time so to speak. That said, you may recall that Mr. Sohn said they follow the SPRAT guidelines. Check them out here: http://www.klatrecenter.dk/sprat/SPRATlev1req.pdf

  23. Jordan R
    October 9, 2012 at 9:23 pm #

    Thank you to Mr. Sohn for his presentation that allowed us to see the details that went into investigating these structures after the earthquake last year. This was the first time I was able to understand the construction of the Washington Monument more in depth and it certainly is a fascinating structure standing in the middle of our Nation’s capitol. Also, it is interesting and inspiring to see a structural engineer getting to scale these monuments and buildings to make sure they are not damaged and can stay with us for a long time.

    I have a question regarding the report after the evaluation of the Washington Monument. At the end of the report it mentions that the structure is obviously subject to damage by earthquakes and that a seismic evaluation be done. Have these older structures and monuments never had an in depth seismic evaluation? Or are they left as they are until something such as the VA earthquake last year causes damage, bringing attention to the matter?

    Regarding the National Cathedral, some of the shifting in the stone was simply stunning that it did not move any further. Some pieces being on the verge of falling is a scary thought. Mr. Sohn mentioned that they worked with one of the original masons for the project. Would they work together to determine what is the best way to prevent such things from occuring again? Or are the repairs just temporary fixes to be able to reopen for the public?

    Thanks goes out to Mr. Sohn once again for enlightening us about WJE’s work in Washington D.C. following the quake.

    • Mike S
      October 14, 2012 at 5:46 pm #

      Jordan brings up a great point regarding the National Cathedral. One image in the presentation showed a pinnacle completely separated from the rest of the structure but still miraculously hanging on. When dealing with such ornate pinnacles and obscurely shaped parts of the structure, how can you guarantee these pieces will be stable if a similar event was to happen?

      As always, the first order of business should be temporary stabilization to protect the public, but are there ways to permanently stabilize these ornate structures without disturbing the exterior appearance? I would imagine that in order to ensure complete stabilization, a great deal of money and time would need to be involved.

      • Evan L
        October 15, 2012 at 9:25 am #

        I agree with mike. Will the cathedral ever raise enough money to completely restore the cathedral? It was stated by Mr. Sohn that the cathedral did not have insurance and all money would come from donations. This fix will be very expensive. From what I understand of the spire’s structure, they are stacks of stones with dowels in them. They would all have to be lifted off piece by piece, modified for stronger or larger dowels, and then lifted back into place. This would be a very long and tedious process. It would be much like the stacking rings we all played with as children where they get smaller the closer you get to the top just on a much larger scale.

  24. Logan G
    October 9, 2012 at 5:39 pm #

    The Washington Monument

    Mr. Sohn made it pretty clear that there is more than meets the eye when performing a damage assessment, especially on a structure that is held in such high regards. Evaluating the Washington Monument had numerous unique challenges but it appears that the WJE team was able to overcome them and deliver a thorough post-earthquake assessment.

    Seismic Evaluation

    It appears that the NPS has taken into consideration at least one of WJE’s recommendation’s, more specifically the seismic evaluation. A link to the webpage that has this report on it can be found at the bottom of my comment, but the following is a brief summary of the results:

    • Lateral loads produced by seismic events cause typical swaying motions in the Monument.
    • The pyramidion was found to be the most susceptible to damage.
    • The possibility of another earthquake that would cause more damage than the one that occurred on August 23, 2011 is highly unlikely.
    • An earthquake with a return period of 2,475 years is the only critical threat to severely damaging the monument and that is what occurred on Aug. 23.
    • A future 2,475 year earthquake event COULD cause detrimental damage to the stone masonry units in the shaft that have deteriorated.
    • The shaft structure and soils are sufficient enough to withstand a 2,475 year event.

    Questions

    After seeing the presentation and reading through the assessment compiled by WJE I am left wondering what happens next, specifically:

    • Did WJE recommend that the NPS close the monument or was that a decision made elsewhere?
    • Have any repair recommendations been started or slated to begin in the near future?

    A generous thanks goes out to Mr. Sohn for taking the time to come talk to our class.

    http://www.nps.gov/wamo/washington-monument-earthquake-update.htm

  25. MikeP
    October 9, 2012 at 3:05 pm #

    Thanks again to Erik Sohn for his presentation on the assessment of the Washington Monument and National Cathedral after the events of the Mineral, VA earthquake last year.

    I had several question on the assessment and rehabilitation of the two structures. First, I know you had said that pressure was on due to the hurricane and planned events at the cathedral, however did further seismic activity ever worry you? As the USGS at the time thought that the earthquake could be a foreshock to a greater magnitude earthquake, was there any worry on your team that you might get stranded 400 ft up mid-earthquake? Even aftershocks could have presented a dangerous situation. Did you happen to have seismic equipment on site or anything to monitor the seismic activity in the area during assessment?

    Additionally, after reading the WJE reports, I saw that seismic strengthening was considered in the monument during restoration. I was curious if a seismic study was also done on the cathedral and if findings showed the need for improvements to the structure or other systems. For example, your presentation showed fallen pinnacle tops and other pinnacles that had displaced to the point of leaning over the edge. As you were deconstructing the pinnacles during assessment, was there any dowels added to the pinnacles to help prevent future lateral displacement? Also, I know you talked about the different construction types that occurred during the years of construction. Were there areas that seemed weak against seismic motion that WJE feels should be strengthened?

    Lastly, I saw in the report that WJE states that the VA earthquake last year was pretty much at the 2475 year scale (and greater than design EQ), and so the structures were deemed to be strong enough overall to withstand further seismic activity. However, because of the significance of the monument and cathedral, is it really enough that they pass code requirements? Should the fear of losing such an iconic monument create the need to require that extra precaution and strength requirements be instated in the monument?

    • Victoria I
      October 10, 2012 at 3:00 pm #

      Mike P brings up a good point about monumental structures. The code is just a minimum design point for public safety. When we are looking at historical structures, the code should just be a very rough starting point. When events like the VA earthquake happen, it reminds us that these historical structures may be vulnerable because they may not be designed for such a low probability earthquake (2475 years). A lot of historical structures are mass masonry construction, which helps them withstand the lateral loads that come with time. However, (as we talked about in class) these structures do not have expansion joints and so when the loads exceed what the mass masonry can handle, it creates its own expansion joint.
      Obviously, the we have no say in what the historical structures are designed for (since they are already completed). Because of this, I think it is that much more important to analyze and consider enhancing the historical structures to withstand rare events.

    • Li J
      October 10, 2012 at 3:19 pm #

      First I would like to thank Mr. Sohn for giving us such an interesting presentation. The way of using sketchup model and tablets to document, analyze, and communicate was very impressive. I think using 3d model to analyze the problems and potential solutions and explain to other people is very effective. Especially when you need to explain to some people not having strong structural engineering background, virtual models are easy for them to understand what you are trying to do.

      As Mike posted here, I’m also curious about the assessment and rehabilitation of the two structures which have significant meanings to the nation. Is there any special code or some regulations way beyond the code requirement for those kind of structures? Since there are some excellent work done to the damaged spots/area of monument and cathedral, is there any actions being done to preserve or strengthen the survived area that might have some damages in the next earthquake….?

      • mkev
        October 10, 2012 at 10:24 pm #

        I thought the Sketchup models were great as well and really made the construction easy to understand. Some of you may know this but I feel the need to tell the rest of you. Did you know that Sketchup was invented by a Penn State AE structural student several years after graduating? Anyone know his name? Bonus triva points to the first person to get the answer…

        • Issa J.
          October 11, 2012 at 12:06 pm #

          Brad Schell

          • mkev
            October 22, 2012 at 11:08 pm #

            Close. Right company. Not the Penn State AE, however.

  26. Issa J.
    October 9, 2012 at 11:55 am #

    Thanks a lot to Mr. Sohn for his great job and presentation. I think you did great in repair of these two building.
    Washington Monument built by a great idea which is construction of a tall building with old materials (stone, mortars,…). But, I think by passing time there will be lots of problem which cannot be solve easily and by low cost. For example if we want to have this building remains for hundreds of years, we cannot built such a tall masonry building without any lock between stones. There is just mortar between stones! I think it was better to use jagged stone or lock stones to each other by steel locks. By passing time and happening of more earthquakes these stones will not remain on their location and large displacement between stones will happen. There is lots of samples in my country in which building with about 2000-2500 years old remained sound because of using Iron-locks between stones. Some part of these buildings that had not locks destroyed. I think this building (which is monumental should stay sound over centuries.
    But about Washington Cathedral, I think using lime stone was not a good material for such a building. Beside, I think it was better to use steel lock between parts to limit displacement of parts of building (which happens in earthquake). It’s interesting for me to know how Mr. Sohn locked moved part of the building in retrofit of this structure.

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