Survey of Central District Buildings Finds Many Issues
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 Day One and Two and Day Three of Biggs' diary if you have not already.
The day started with calls back to the States and email catch up. The L.A. Times did a piece on the earthquake earlier in the week and called for additional information for an article to be published this Sunday (unless something else comes up). Led by Jason Ingham, we published a blog of a transect we made of the Central Business District (CBD) the previous day. It was posted to the New Zealand Earthquake Engineering Society Web site. A Japanese newspaper with a 10 million readership picked up the post and asked for more information for an article. That’s amazing because all of New Zealand has only about 4.5 million people.
Jason, our team leader, attended a briefing and received our team assignment. We were given two special assignments for the morning. The assessment coordinators wanted experts with high-rise experience to perform Level 2 inspections of buildings of concern. Those "high-rise" buildings ended up being only five and nine stories high.
The five-story building did quite well. The ground floor experienced some repairable cracking and water damage from liquefaction. The ground floor slab is a diaphragm tying the foundations together. We did not have drawings but we assumed a deep spread footings or piles. That’s a problem with many assessments -- the plans are rarely available, yet decisions have to be made. The building received a green tag.
The nine-story building had significant wall panel cracking on one wall. Some were fractured and the Level 1 assessment team had taken these to be precast shear walls. Our assessment was they were likely to be cladding panels that worked like shear walls and underwent significant distress. Anchorages were likely compromised. We red-tagged the building and called for a reassessment once the engineer of record could be found and questioned, or the drawings made available. Either the building had a lateral load capacity problem or the cladding was in severe distress.
Our afternoon assignment included Level 1 assessments of an entire block of the CBD just south of the cathedral. Only the telecommunications building was partially operational.
In general, the CBD continues to be off-limits to all except inspection teams and search and rescue personnel. Some demolition of the pancaked buildings had begun the day before as part of the recovery of remains process. Several search and rescue teams with dogs were roaming the CBD to check selected buildings for bodies.
Christchurch officials thought that the media were reporting inaccurate information because they had not been allowed access. They organized several buses for media to travel through portions of the CBD to see for themselves the condition of the buildings and streets. That was interesting because many were impassable. Overall, the streets they were able to traverse should have been sufficient to report on city conditions.
Our afternoon inspections produced several green, yellow and red tags each. Buildings ranged from the two-story heritage building that is the Visitor Center and was in excellent condition, to an Ibis Hotel, to a huge telecommunications building and others. Red tags went out to an unreinforced masonry that had been retrofitted and the retrofit did not hold up. Again, restating what I said in previous correspondence, this earthquake likely exceeded code design levels. Here in New Zealand, heritage buildings are commonly strengthened to 33 percent of code. After the September earthquake, the move is toward 67 percent. Christchurch implemented that upgrade but no buildings had likely been strengthened to that level yet.
The CBD and surrounding area changed in one day. The large number of inspectors then produced enough assessments to identify serious conditions so that fencing and barricades were springing up quickly. The traffic pattern around the CBD, and for official vehicles leaving the CBD, was altered to avoid buildings that were recently deemed as likely collapses.
As for aftershocks, the day was rather calm until the late afternoon and early evening. Then, three hard jolts hit at about 45 minute intervals. Small crowds assembled around various buildings in anticipation of new collapses. Sinkholes were forming near the Avon River. We did not stay to wait; we’d seen plenty for one day.
Our day in the field ended at about 7:30 p.m. Every night goes to midnight with reports and diary-blogging (like this one). Tomorrow is our last day in Christchurch. We have more inspections in the CBD. In addition, we were tasked to develop a list of indicator buildings and provide assessments. These are intended to be a generalized representation of building categories. Not sure where we are going with this.
Read on for Day Five of Biggs' diary.