Future of Christchurch Depends on Lessons to Be Learned
David T. Biggs, P.E., S.E., Dist.M.ASCE, HTMS, a consultant and former principal of Ryan-Biggs Associates, a structural engineering firm in Troy, N.Y., continues his diary of experiences surrounding the 6.3 magnitude earthquake that struck Christchurch, New Zealand. Biggs happened to be delivering a seminar lecture on structural engineering and seismic forensics when the earthquake hit on Tuesday, Feb. 22, and he immediately went to work assisting New Zealand engineers in the assessment of buildings for safety.
Read Biggs' diary entries in sequence if you have not already -- Day One and Two, Day Three, Day Four, and Day Five.
It has been comforting to return to Auckland. However, I still am startled occasionally by vibrating floors in buildings. The Christchurch aftershocks are still a fresh memory.
Our team members, Ingham, Biggs and Moon, assembled to plan the digestion of our field data and plan future publications. Each took on one article; all are digesting data.
On Monday, Feb 28, I was requested to provide a forensic plan for the concrete industry to requisition consultant services to evaluate concrete buildings in Christchurch. They decided to retain consultants to perform these investigations and assessments and not rely on volunteers because it was assumed that the consultants would be otherwise engaged with clients following the earthquake and might not be able to provide the necessary studies in a timely manner.
New information coming in from Christchurch has been interesting. The Grand Chancellor hotel has crushed columns on the 12th story in addition to the previously mentioned damage. The owner has stated we would not be allowed to show any photographs taken within the hotel. The plans to get in to perform stabilization safely have still not been made public. The risk will be significant!
A consistent question coming in from reporters has been whether the seismic codes need to be revised. Our response has been that the codes need a reassessment. The magnitude of the earthquake was so significant that it warrants a review. In addition, the spurs of the fault line that were activated by the earthquake were generally unknown before last September. That will probably prompt changes.
One issue not yet discussed to my knowledge relates to many of the collapses that have occurred. Following the September earthquake, shoring or stabilization was installed on many buildings. Many repairs worked but many did not. Reportedly, the question asked by engineers following the September 2010 event was what strength level should they design the temporary repairs and shoring? Engineers wanted to know if they were designed for another design level earthquake or a lesser aftershock. We have no official answer on this, but some engineers indicated they were told to design to a lesser aftershock because that was what was historically what was expected. Unfortunately, the Feb. 22 aftershock was twice the design level earthquake. Given that, there is no surprise there were failures! The public response is, why didn't officials demand demolition or full strengthening? Officials did what was historically correct, but this aftershock did not follow the pattern.
It was comforting to finally hear officials acknowledge that the earthquake was as much as twice the design-level earthquake for new buildings. They are listening to the engineers and giving correct information. That is critical. Otherwise, people wonder if buildings collapsed due to faults in design or construction. Certainly, the collapsed buildings should and will be investigated for design or construction flaws. However, it might not be surprising if the investigation indicates the collapses were simply due to overload from excessive accelerations and liquefaction. We’ll wait to hear the outcome.
Christchurch city officials are proposing a concept to move the CBD temporarily to keep business going. The new CBD work being proposed is for low-rise buildings only. This will be an interesting program in urban planning. The most significant technical issue to be resolved will be liquefaction.
Newspapers report people are leaving Christchurch in the short term and many will not return. The government wants to rebuild the city, but the timing and funding are still to be determined. I expect the public will be wary of multi-story buildings and unreinforced masonry.
An ASCE-SEI team is slated to return in April and reassess the remaining structures they inspected after the 2010 earthquake. Lessons learned will then be released over the following months.
Unless there are new developments or I return to Christchurch, this will be my last installment. New Zealand paused today for two minutes of silence at the minute one week ago when the quake struck -- 12:51 p.m. It was very moving.
Thanks to all who have expressed concern for my safety!