Friday, October 31, 2014
Mike Butler: Quake hysteria hits Opera HouseLabels: earthquake-prone buildings, Hawke's Bay Opera House, Mike Butler
Building owners throughout New Zealand are being penalised by faulty advice from earthquake engineers. Banks have climbed on the bandwagon by insisting on earthquake risk reports on buildings that have no structural issues whatsoever as a condition of mortgage finance, creating a new industry for engineers to print out largely pre-written reports for $600 to $1000.
The 99-year-old Hastings council-owned Opera House was suddenly closed on March 4 of this year after advice from engineers that parts of the building were less than 34 percent of the new building standard of earthquake resistance.
The Municipal Building, also owned by the council, was closed later that month citing issues with a central pillar. The stability of Opera House balconies became a further concern last month.
Totally overlooked in the Hastings council’s reaction to claims about building safety is the fact that councils must in law apply the legal definition of earthquake prone, and not the much tougher earthquake engineers’ standard, which is not lawful.
Economist Ian Harrison, who produced a cost-benefit analysis as detailed in Error prone bureaucracy: Earthquake strengthening policy formulation in New Zealand 2003-2013 – a study in failure, pointed out that building owners take guidance from earthquake engineers whose standards are not lawful while ignoring the legal requirements.
If you follow the legal definition of what is earthquake prone, there would be few earthquake-prone buildings in New Zealand. Section 122 of the Building Act 2004 says a building is earthquake-prone if (a) it will have its ultimate capacity exceeded in a moderate earthquake, and (b) would be likely to collapse causing (i) injury or death, or (ii) damage to any other property.
In more commonly understood terms a “moderate” earthquake in Hastings can be roughly equated to an event measuring 6 on the Modified Mercalli Intensity scale.
Such earthquakes are not destructive. A MMI 6 event is felt by all. People and animals are alarmed and may run outside. Furniture and appliances may move on smooth surfaces and objects fall from shelves. Glassware and crockery break. Slight non-structural damage to buildings may occur, according to the Ministry of Business Innovation and Employment.
If a building is so structurally unsound that it would collapse in a moderate MMI 6 earthquake as described it is clearly earthquake prone. Bear in mind the 2010 Canterbury earthquake was MMI 10, and the 1931 Hawke’s Bay earthquake, that the Opera House survived, was MMI 12.
The detailed information provided in last month’s report by former Waitakere City Council chief executive Harry O'Rourke and structural engineer Win Clark shows that both the Opera House and the Municipal Building are far from collapsing in a moderate MMI 6 earthquake.
This means that the Hastings District council could deal with the problem of alleged earthquake proneness of the Opera House and Municipal Building by applying the law as they must.
The O'Rourke Clark report details all earthquake risk assessments of both buildings.
Hastings engineers Loughnan Hall and Thompson did an assessment in 1998 that noted areas of possible weakness but concluded that the buildings were not an earthquake risk. At that time, Loughnan Hall and Thompson obtained plans of strengthening work done on the building after the 1931 earthquake, and noted that the building code in effect during the 1990s did not require strengthening unless a change of use was intended.
In a report released on March 20 this year, Strata Group assessed the Opera House by looking at sub soil category and scanning concrete for reinforcing size and location and concluded that the fly tower was 48 percent of new building standard (a pass mark on the much tougher earthquake engineers’ standard), that the stall area masonry walls were 17 percent NBS (fail), the steel columns were 22 percent (fail), the foyer masonry walls 34 percent (another engineers’ pass).
EqStruc assessed the Municipal Building in a report also released in March by looking at the geology, masonry wall and column composition, brick masonry bedding joint capacity, and brick and mortar compression strength of. Three-dimensional computer modelling concluded that in-plane masonry wall and out-of-plane wall and parapet capacity were less than 34 percent of new building standard.
A further report by Holmes Consulting, also in March, that reviewed the reports by Strata Group and EqStruc, agreed that both the Opera House and Municipal Buildings were earthquake prone due to likely failure of masonry walls, but deemed EqStruc’s use of modal response spectrum computer modelling as inadequate.
Faced with an apparent triple whammy by three consulting engineers, the Hastings District Council apparently felt compelled to close the buildings even though the buildings achieved a number of passing marks on the unreasonably stringent and non legal engineers’ assessments against new building standards.
The decision to close the buildings ignored the legal definition of earthquake-proneness as compelled to do so in law.
With strengthening work done after the 1931 earthquake, and with further such work done in 2005 as part of the upgrade, neither the Opera House nor the Municipal Buildings are like to collapse in a moderate quake, causing death, injury, or damage other property.
The O'Rourke Clark report concedes that use of the “percent of new building standard” tool to determine a building’s capacity is “inappropriate and has caused significant loss of value in New Zealand building stock”.
But Mr Harrison points out that the O'Rourke Clark report is not independent. “Win Clark is the executive officer of the NZ Society of Earthquake Engineering and has an interest in protecting their interests,” he said.
The O'Rourke Clark report has errors. On page 110, “the first statement that government legislation has set a 33 percent trigger point is not true. There is no reference to this in the legislation”, Mr Harrison said.
“Similarly the statement that regulations define a moderate earthquake as one that will cause the failure of a building with a 33 percent rating is not true. The regulations define a moderate earthquake as one that is as one that it a third as strong as that used in the new building code. There is no reference at all to failure,” he said.
Aside from earthquake issues, the Hastings council deserves a good bollocking for allowing the project to proceed in a manner, as the O'Rourke Clark report said, that “left a lot to be desired”, and allowed costs to balloon from the 1996 Option 1 estimate of $2.145-million to a final cost of $13.6-million.
With a rule-of thumb that earthquake strengthening costs 50 percent of replacement value, and with a replacement value of $23-million for both buildings combined, Hastings ratepayers could be slugged with a further $13-million bill for two buildings that struggle to pay their way.
In making a decision on the Opera House and Municipal Building, the Hastings council must ask: 1. Whether the buildings are legally earthquake prone, which they clearly are not, and 2. Whether they are as strong as the council wants them to be having regard to the costs, Mr Harrison said.
The second point is a matter for expert advice that shows the life safety consequences of different strengthening levels, and political judgement. The NZ Society of Earthquake Engineering framework is an unreliable guide to how safe a building is because it tells you nothing about life safety risk
Readers with concerns about their buildings should refer to Mr Harrison’s report at http://www.tailrisk.co.nz/documentlist
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