Liquefaction Takes a Substantial Toll
An ASCE-authorized Structural Engineering Institute reconnaissance team of five engineers traveled Monday, April 4, to Christchurch, New Zealand, to explore the causes of damage to infrastructure as a result of the magnitude 6.3 earthquake on Feb. 22. The team is being led by Robert Pekelnicky, P.E., S.E., LEED AP, M.ASCE, a structural engineer who is an associate principal at Degenkolb in San Francisco and is a member of the ASCE/SEI Seismic Rehabilitation of Existing Buildings Standards Committee. In this exclusive daily diary for ASCE, Pekelnicky relays the first-person experiences that he and the SEI team are going through in the earthquake zone.
Read each day's entry:
• Day 1 | Day 2 | Day 3 | Day 4
Day 3 – Wednesday, April 6
We arrived at the Emergency Operations Center just before 8 a.m. so that we could attend the start of the day briefing with the engineers, firefighters and other life safety personnel. We were acknowledged as being in the room and henceforth known as “the Americans.” There are a number of engineers set up to do Level 2 assessments and two members of our team – Brian and Charlene – will be tagging along with two of those engineers.
New Zealand has a document similar to our ATC-20: Post-Earthquake Safety Evaluation of Buildings, which has multiple levels of investigation. Level 1 is a very cursory, walk-around-the-building type assessment. Level 2 is a more detailed assessment, but still conceptual in nature, where an engineer goes though the building and offers their judgment about the safety of the building. The building is then assigned a red, yellow or green placard. Green means the building is fine, while red means the building is highly unsafe. Yellow means the building is unsafe, but limited entry for brief periods by persons familiar with damaged buildings is permitted. Almost all the red zone within the Central Business District (CBD) has been tagged yellow or red. Even if they were fine themselves, many buildings were tagged red because they were in the fall zone of a red-tagged building.
The remainder of our team – Owen, Matthew, and myself – was allowed to walk around the red zone with one caveat. We had to have fire/life safety escorts. So we were assigned two wonderfully helpful firefighters to escort us. We were allowed unrestricted access within the cordoned area, even within the fall zone of the red-tagged buildings. There was only one caveat – we were not allowed to enter red placarded buildings, unless accompanied by a New Zealand Chartered Professional Structural Engineer.
We were permitted to enter yellow-placarded buildings. However, if we did the firefighters had to notify the EOC that we were entering a building. Also, only one of the firefighters was to follow us in the building. The other was to stand outside in case something happened, like an aftershock. Fortunately, none did!
As we walked through the CBD, we were amazed not only by the level of building damage, but also the amount of liquefaction. There was not a street or sidewalk within the CBD that did not have some sign of liquefaction. There was everything from minor cracking of the pavement to full-blown sinkholes in the street.
As we walked around, we saw the Grand Chancellor hotel. A three-block radius around this building had been closed off due to fears that the building could fall. There were some failures in the concrete shear walls which led one side of the building to drop a reported 750mm (about 30 inches). The building just stands there ominously, leaning up to 10 degrees at some points.
We came across two buildings that we had observed in October at 223 and 225 High Streets. It appeared 223 High had a minor upgrade done to it, presumably at one-third of code. On the other hand, 225 had a brand-new upgrade done to it at 100 percent of current code. The parapet in the rear of 223 High failed and there was some cracking in the unreinforced masonry along the street-side face at the upper story. The 225 High building was undamaged. February’s earthquake managed to knock down the parapet and large portions of the upper story wall in 223, while 225 again appeared undamaged. You could get up close to 223 and see how the bricks just pulled away from the adhesive anchors.
Continuing our walk, we came to a row of buildings along Manchester Street that had also previously been damaged. What appears to be a row of about six separate buildings is actually one building built in 1880, but divided into six separate shops by unreinforced masonry walls (URM). The building looks amazingly similar to what it looked like in October. It was at first a surprise, given how much more intense the shaking had been in this more recent earthquake and how all the other buildings we’d looked at in both had performed. However when we got closer we could see that the building had been stabilized by adding some out-of-plane through bolts and horizontal wood whaler beams along the façade. While this would not aesthetically qualify as a permanent upgrade, it appeared to do the trick to strengthen the building such that the walls did not fall out into the street as they did at 223 High.
We spent the rest of the morning walking through the red zone and looking at a number of very interesting buildings, too many to describe here. We then went back to the EOC for lunch, where I was fortunate to run into an engineer whom I’d spoken with in October. We had a nice lunch together and I got to get some more information on how they thought buildings performed. Following that, we headed back into the red zone, with two new firefighter escorts.
The first building we went to was the Forsythe Barr building. It is a tall building that structurally performed well. However, there was one very serious issue with this building – the exit stairs collapsed! The exit stairs were precast concrete elements, meant to span from one floor to the next. They were situated on four-inch angles. That was not enough of a seat during the severe seismic shaking, and most of the stair elements unseated. They had to break windows and lift people out of the building.
We then looked at another building where one of the exterior columns had dropped due to soil liquefaction under it. There are a number of buildings in the red zone that are tilting due to liquefaction under their foundation.
One of the last buildings we reviewed was an apartment building with a café on the first floor. The building was a concrete shear wall building with some cracking in the core wall and some diagonal cracks in the coupling beams. But what made this building so unique for me was that it was the first time I got to don a P100 respirator. One of the ancillary consequences of the earthquake occurring around lunchtime is that everyone left their food where it was and got out of the CBD. Since then the CBD has been cordoned off. The main focus was fist rescuing people and then getting important office equipment like servers out and allowing residents to get stuff out of their homes. There has not been a high emphasis placed on cleaning up anything else. So there was all the food that had been left since the people got up and ran out of the building six weeks ago! You could imagine how rank the smell was – hence the need to don a respirator.
We wrapped up the day back at the EOC where they had an engineers’ briefing on the situation inside the red zone and steps moving forward for engineers to get into the CBD to perform assessment they’ve been contracted to do for their clients. Following that there were some presentations on various aspects of the earthquake. The ASCE/TCLEE team was also there and following the briefing we dined with them, along with SEI President Roberto Leon.
• Day 1 | Day 2 | Day 3 | Day 4