Buildings So Unsteady It Was 'Unnerving'
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 4 – Thursday, April 7
Today was the team’s last full day in Christchurch. We all depart to Auckland tomorrow at varying times and then head from Auckland to San Francisco on the same flight. But if it’s true that you save the best for last, today was no exception! We were escorted into several red-placarded buildings today by representatives of one of the highest regarded New Zealand structural engineering firms.
In the morning we were taken around the city by one of its top Urban Search and Rescue engineers, and shown some of the more spectacularly damaged buildings. We saw one building, the Copthorne Hotel, which had severe beam and column damage because there were shear walls atop them that did not continue to the basement. Apparently, New Zealand had the same issues U.S. engineers did with discontinuous shear walls; only in the past 20 years are they beginning to adequately address this and steer engineers away from their use.
The next building we looked at was a concrete wall and frame building where the shear wall core settled differentially with respect to the rest of the building, due to the underlying soil liquefying. Here is Owen Rosenboom standing next to a door opening in the core wall that originally was probably about 7 feet tall, but has shrunk to less than 6 feet.
After leaving that building, we walked over to the tallest building in Christchurch – the Grand Chancellor. We were all excited to be able to go in and see the damage in this building. A load-bearing wall and two columns supporting a large transfer girder had failed, causing the southeast corner of the building to drop about 3 feet. The building was so noticeably leaning that emergency crews cordoned off a radius of about 4 blocks around the building. The failed wall and columns had been encased in an inordinate amount of concrete to strengthen and stabilize them. It was amazing to see how much the floors had dropped. The floors in the picture should be flat.
After walking through the Grand Chancellor, we broke for lunch.
After lunch, we met up with another engineer from the Holmes group who was going to take us into three buildings this afternoon. We first headed to Clarendon Tower. It’s a tall building in which the stairs had dislodged and there were some failures in the floor diaphragm. In fact, there was such a severe failure where the precast double-t sections actually dislodged from the beams and are being help up solely by adhesion to the 2-inch topping slab which is spanning like a catenary. Unfortunately, it was not safe for us to go up to the floor under that to observe. However, we did get some very sobering pictures of the failed stairs. Being in this building and the Grand Chancellor were probably the two most unnerving points of the trip.
We then walked over to the Christchurch Cathedral. We were very lucky to find out that the engineer taking us around was going to be the one designing the repairs to the cathedral. They had previously upgraded the cathedral by adding some shotcrete to the front face and then strengthening the roof diaphragm.
At the time they were not permitted to do any work in the spire, which in my opinion was was unfortunate, because that is what collapsed. The remainder of the cathedral was damaged, but according to that engineer, it was essentially what their complex nonlinear models had predicted would happen.
Following the cathedral, we had the opportunity to walk through another tall concrete shear wall building. That building had some damage to the wall and also to the floor diaphragm. In September, cracking was found in the floor diaphragm topping slab. The Holmes Group then began an upgrade of adding FRP sheets to the floor. The FRP appeared to have performed well and there were no additional or wider cracks observed in the floor.
This has been an amazing trip. We’ve learned a great deal and have several observations that we will be taking back to incorporate into ASCE 31 and 41. What has been most amazing is how receptive the New Zealand engineers have all been to us. It turns out they hold our standards in high regard and want nothing more than to be a part in helping to improve them. They see the value in understanding what happened in this great tragedy and moving forward from it with better provisions for everyone to use. Several engineers have actually volunteered to become members of our standards committee. We’re all very grateful for their help this week and the collaboration that this event and the one in September have forged.
• Day 1 | Day 2 | Day 3 | Day 4