BUILDING SEISMIC PERFORMANCE: CONSULTATION · PDF fileBuilding Seismic Performance Consultation ... in the seismic design of ... the entire 1- NZSEE Submission to MBIE Building Seismic

NZSEE Submission to MBIE 1 of 25 Building Seismic Performance Consultation 8th March 2013

New Zealand Society for

Earthquake Engineering

BACKGROUND TO NZSEE NZSEE is a Collaborating Technical Society of the Institution of Professional Engineers, New Zealand, Incorporated. The objectives of the Society are to: a) Foster the advancement of the science and practice of earthquake engineering. b) Retain a close liaison with the Institution of Professional Engineers of New Zealand Incorporated by being a Collaborating Technical Society of the Institution. c) Further the objectives of the International Association for Earthquake Engineering as applicable to New Zealand viz: “to promote international cooperation among scientists, engineers and other professionals in the broad field of earthquake engineering through interchange of knowledge, ideas, results of research and practical experience.” The Society has over 700 individual and corporate members within New Zealand and internationally.

EXECUTIVE SUMMARY The key issues and recommendations addressed in this submission are related to: 1) Clarification of objectives for the earthquake resistant performance of buildings,

and better definition of seismic risk, target level of earthquake, minimum threshold for Emergency Response Plans (ERP), and targeted retrofit capacity level to resist earthquake effects.

The accurate and consistent assessment of building seismic resistant performance is a critical requirement for the improvement of earthquake-prone buildings.

The current Initial Evaluation Procedure (IEP), to determine a percentage of New Building Standard (%NBS) for the earthquake resistant capacity of the building, was originally intended to identify buildings most at risk from earthquake effects, using minimal information. The quality of the result is improved with more information, and where there is extensive knowledge and experience brought to the procedure by the assessing engineer. It should be recognised that the environment in which the procedure was developed to assist Territorial Authorities, consultants and building owners meet their obligations under the 2004 Building

BUILDING SEISMIC PERFORMANCE: CONSULTATION DOCUMENT Submission to the Ministry of Business, Innovation and Employment Provided by the New Zealand Society for Earthquake Engineering Inc

8 March 2013


Act with respect to identifying Earthquake Prone Buildings (EPB), has now changed dramatically as a consequence of the Christchurch earthquakes. The use to which %NBS has now been put, beyond the original “coarse screening” of EPB buildings, is inappropriate and is unlikely to provide acceptable guidance for the general public. In recognition of the changing environment for building assessment, the IEP process requires review and adaption to meet the current needs for the structural assessment of existing buildings and their earthquake resistant capacity.

• More clarity is required in the definition of performance objectives for existing buildings and for risk = seismic hazard x vulnerability

• The current “scoring approach”, evaluated against the requirement of a newly designed building and referred to as %NBS, needs revision to incorporate lessons learnt from the Canterbury earthquakes, recent experience with the application of the IEP process nation-wide, and more recent research-based evidence on building element and overall performance.

• Critical vulnerabilities which can lead to catastrophic collapse under a design level event (severe earthquake, as used in the question 33 of the consultation document) should be identified and brittle collapse mechanisms prevented. It is recommended that structural drawings should be used to facilitate the capture of critical vulnerabilities in the building under assessment. These vulnerabilities would trigger the definition of EPB based on the second part of the new suggested definition (see below).

• Since the IEP is only a screening tool, a Detailed Engineering Evaluation (DEE) procedure must follow the IEP to evaluate the building’s earthquake resistant performance to a greater level of certainty and to identify any requirements for structural improvement in the building’s resilience. The assessment of building performance against the severe (design level) earthquake as well as, or instead of, the moderate earthquake needs to be included in the DEE.

• Similarly, parts of the building whose collapse can threaten life should be identified and remedied.

• NZSEE recommends to improve the definition of Earthquake Prone Building (EPB) in the Building Act to incorporate a check for potential critical vulnerabilities which can lead, under a severe (design level) earthquake event, to a catastrophic collapse and loss of life.

2) Performance-based Retrofit strategy and targeted level

• The strengthening and/or retrofit intervention should aim at increasing the earthquake resistant performance of the structure and reduce its likelihood of collapse under a design level (severe earthquake). In order to achieve this, a performance-based approach is required and improvement of the failure modes from brittle to ductile may be necessary. It is recommended that, regardless of the minimum threshold used to define an EPB the targeted performance on a retrofitted EPB building should not be limited to %33NBS, but be improved as much as reasonably possible towards 67%NBS.

• In developing any retrofit solution, a clear understanding is required of the relative stiffness, and displacement compatibility in the response of the existing building to that of the new work. It is imperative that the retrofited building can respond effectively as a whole to the earthquake effects.


3) Management of Engineering Resources – Development of Risk-based Framework to assist with the implementation of the policy

• It is likely that there will be a heavy demand on resources to assess and improve the seismic performance of the existing building stock within the proposed timeframe. It is thus probable that, without proper coordination, there could be a bottle-neck on resources (engineers, contractors, Building Consent Authorities (BCA)) towards the end of the implementation timeframe.

• It is proposed that a “Risk Management Framework” be developed to assist prioritization of the timing of actions required on detailed assessment and retrofit, and thus allow better allocation and use of limited resources during the assessment phase, but more importantly during the implementation phase. Such a framework should have a national focus and allow for the most-dangerous buildings to be strengthened first and less-at-risk (also considering occupancy levels) buildings to a longer time-frame.

4) Retrofit of Heritage Buildings

• It is suggested that the “Risk Management Framework” particularly cater for heritage buildings with the objective of identifying and retaining heritage values.

• Once a building is identified as having heritage values, a seismic risk assessment should be carried out to determine the risks, mitigation measures and the cost of such measures. From this analysis a process can be put in place that develops a programme of works to protect the heritage values and how the protection works are to be financed.

5) Education, training, benchmarking exercise

• It is a critical recommendation to develop a comprehensive education and training campaign, using benchmarking and piloting workshops, to ensure consistency in the evaluation approach as well as in the retrofit strategy and solutions adopted. Such activities must be organized at an early stage, prior to proceeding with Detailed Engineering Evaluation and the implementation of the retrofit solutions.

6) Improvement of cost-benefit analysis, communication to the owners, and possible incentives towards implementation

• The proposed cost-benefit analysis of retrofit on a national scale needs to be improved by introducing full direct costs (including repair/demolition/strengthening costs, injuries and homeless) as well as indirect costs (business interruption for the single building as well as for the whole city, increase in the insurance premiums, impact on the GDP and flow of the economy, impact on tourism etc.) It is suggested that the current cost-benefit analysis be significantly improved prior to defining a nation-wide implementation strategy. The benefits of strengthening/retrofit of buildings can be better appreciated by the wider community when full direct and indirect costs are given.

• It is also important to clarify that, depending on the structure and the level of target performance, as well as on the selected technique, the cost of retrofit may not proportionally increase with the target level. For example in some cases retrofitting to 67%NBS might cost significantly less than twice as much as retrofitting to 33%NBS, when most of the initial costs are based on the invasiveness of removing and reinstalling linings, partitions, ceilings etc. On the other hand, for some structural


systems, and depending on the technique involved, the cost of improving the level of performance can suddenly escalate.

• In order to achieve best outcome, even in terms of preliminary conceptual design and cost of a retrofit intervention, it is fundamental to develop and disseminate a set of practical design guidelines on alternative retrofit solutions.

• For special buildings (such as but not limited to those of heritage value), it is suggested that the government develop ad-hoc incentive strategies, in the form of subsidy, tax rebate/deductions, free loans etc, such as those implemented in the past few years for improvement of insulation in buildings and limitation of air-pollution from open fire-places.

Coordination of Submission The NZSEE management committee at a meeting held on The 26th February 2013 provided the principal input for this submission. This meeting distilled various discussions held over the previous months. Discussions were also held with executives of IPENZ and SESOC. A high level of consensus was evident at these discussions. The draft of this document was circulated to members on 5th March 2013 for comment and the final submission amended as required to reflect the feedback.

SUBMISSION

GENERAL COMMENTS Background to the Current NZSEE 2006 Assessment Procedure

The current Initial Evaluation Procedure (IEP) and “scoring” methodology in terms of % NBS value is based on the NZSEE 2006 guidelines Assessment and Improvement of the Structural Performance of Buildings in Earthquakes .

The document was prepared with the aim of providing a set of guidelines that assisted Territorial Authorities, consultants and building owners to meet their obligations under the 2004 Building Act with respect to identifying Earthquake Prone Buildings (EPB), and that can be applied consistently to assess the earthquake performance of a building.

The main purpose was to assess the building’s capability to reach a minimum required level of performance. That minimum level of performance was defined in the Building Act 2004, and referred to as a “moderate earthquake”, or 1/3 of the intensity of the design-level earthquake for an equivalent new structure.

The assessment procedure was developed based on information available at a national and international level until the late 1990s. In those years, there was an increased awareness of the vulnerability of, and risk posed by, pre-1970s reinforced concrete buildings (e.g. designed prior to the establishment of capacity design or hierarchy of strength principles). Such types of buildings were recognized as requiring a vulnerability screening, similar and in addition to the previously recognized at-risk Unreinforced Masonry Buildings (URM) buildings, already considered as Earthquake Risk in the Building Act 1991.

It is worth noting that the IEP was always intended to be a “coarse screening” only involving as few resources as reasonably possible to identify the highest risk or potentially most dangerous buildings. It was moreover expected that those carrying out the IEP would be NZ


Chartered Professional engineers with experience in the seismic design of buildings and various forms of construction.

The NZSEE guidelines had the expectation that the IEP would be followed by a more detailed assessment, currently referred to as a Detailed Engineering Evaluation, DEE, to evaluate the building’s earthquake resistant performance to a greater level of certainty and identify any critical structural weaknesses and hence any requirements for structural improvement in the building’s resilience. The 2006 document concentrated on matters relating to Life Safety, that is to say, performance at the Ultimate Limit State (ULS). Emphasis was therefore placed on the identifications and elimination of possible collapse modes that could effect either part of a building or the entire structure. As well as considering the relative strength of structural members, the assessor was reminded to evaluate the consequences of critical structural weaknesses that could lead to collapse. The concept of critical weaknesses, herein proposed to be included in the Building Act as part of an amended definition of Earthquake Prone Building, was thus already included in the general approach of the guidelines. Lessons from past earthquakes and research will inform the preparation of a more comprehensive list of potentially critical vulnerabilities and associated evaluation tools. It was also stated in the guidelines that the assumptions for existing building assessment were less stringent than for a newly designed building. As a particular example, it was mentioned that the general lower ductility exhibited by older buildings implies more brittle behaviour and more sudden loss of structural integrity. An existing building with 33% NBS, subject to a one-third earthquake, would generally represent a higher probability of loss of life than a new building subject to a design earthquake. In the 2006 document the Society gave its opinion that reference to a “moderate earthquake”, defined in the Building Act 2004 as “one third as strong” as a design-level event was considered (“at the present time”) to be a reasonable balance between imposing a requirement to upgrade all non-complying buildings (<100%NBS) and the previous position of the Building Act 1991 where only URM buildings were addressed. It was thus anticipated that “the threshold of 33%NBS could be lifted over time, but if the proposed NZSEE grading scheme worked as intended, this lower level might suffice as a legislative backstop".

Nevertheless, it was recommended that building with <67%NBS be seriously considered for improvement of its structural performance, at least when major alterations or refurbishments were contemplated. The NZSEE maintains this view on this recommendation.

Recommendations for improvements As the 22nd February 2011earthquake in Christchurch has shown, an earthquake (with a low probability of occurrence) can occur that will severely damage buildings designed and constructed to the current Building Code. It then follows that a building with an earthquake resistant capacity less that the Building Code has a higher probability of damage, or even collapse, in an earthquake. A building with a capacity of 33%NBS has a relative risk of its strength being exceeded that is 20 times greater than a code compliant building.

1- Clarification of definition of seismic risk, target level of earthquake, minimum threshold

For the technical and non-technical audience, including the public and various stake-holders, more clarity is required around the definition of desired performance objectives for existing and retrofitted buildings (in comparison with new building design expectations). This will require agreement over a wide range of stake-holders.


As a starting point, it is important to clarify and communicate that the “seismic risk”, intended as the potential consequences of an earthquake, according to its basic definition is a combination of two factors: 1) the seismic hazard (probability of occurrence of an earthquake with a given intensity)

and 2) the seismic vulnerability (probability that a building will be damaged or collapse

under a given earthquake). Too often, and inappropriately, the concept of “seismic risk” is confused with the first factor, e.g. seismic hazard. As far ad the first factor is concerned, we clearly cannot change the probability of occurrence of a given earthquake for any known or unknown fault, but we can and must continue to study their source mechanism and ground motion effects, to improve the knowledge of the seismic hazard in a given region or site and provide information on the required design level for new buildings/structures and for the strengthening/retrofitting of existing buildings/ structures. However the reduction of the vulnerability of the built-environment is an issue that we can and should directly operate on to reduce the consequences and impact of the earthquake event, and hence reduce the overall seismic risk. Eliminating/improving critical weaknesses in existing buildings, which can lead to catastrophic collapse and loss of human life, is a way to achieve the objective of enhancing life safety.

2- Definition of performance objectives for assessment and retrofit. Use of moderate

earthquake vs. severe (design level) earthquake Clarification on performance objectives and expectation for new buildings is required. Current performance-based seismic design philosophy defines “a set of engineering procedures for design and construction of structures to achieve predictable levels of performance in response to specified levels of earthquake, within definable levels of reliability”. Figure 1 shows a traditional performance design objective matrix used at international level to define the expected performance of new buildings with increased level of earthquake intensity


Figure 1. Seismic Performance Design Objective Matrix for New Building Design as defined by SEAOC Vision 2000 Guidelines (1995).

An ordinary importance (Basic Objective, taken as 100%NBS reference) building (IL2) would be expected to achieve Life Safety under a severe or Design Level Earthquake (DLE, 1/500 years), and be Near Collapse under a very rare event (or Maximum Credible Earthquake, MCE, 1/2500 years earthquake). As a corollary, the actual comparison of the performance of an existing building or a retrofitted building with a newly designed building, would require that under the design level of earthquake (DLE) the existing building would suffer extensive damage (possibly over the repairable threshold). If subject to a so called Maximum Credible Earthquake, MCE (represented by an intensity of 150%-180% the DLE), the building would be near to collapse. Thus the capacity of a new building to go beyond its ULS limit state, before collapsing, is expected to be quite substantial. As a result, and as indicated by the Christchurch Earthquakes Royal Commission, the current %NBS should be more properly referred to (evaluated against) Ultimate Limit State (Life Safety), not (near) Collapse.

Assuming the evaluation of %NBS has been carried out in accordance with the Royal Commission recommendations (e.g. referring to Life Safety thus ULS, not Collapse), we could look at what are, and if uniquely defined, the implications on the seismic performance expectation for an EPB building sitting at 33%NBS (Fig. 2).

By current definition of an EPB, the building will be likely to collapse under a moderate earthquake, defined as a 1/3 of the intensity of a severe (design level) event. This level, according to the NZS1170.5 would approximately correspond to a 1/50 year event (frequent earthquake, R=0.35).

Under the design level earthquake the 33%NBS building (either existing or retrofitted only to that level) would have a relatively high probability of collapse. This however, would assume that the building is in fact capable of developing a robust/ductile rather


than brittle behaviour. A less ductile or brittle mechanism, or the possibility of triggering some critical weakness would lead to a more premature failure (likelihood of collapse) at less than the design level earthquake. In other words, for brittle buildings, such as URM or buildings with critical vulnerabilities which can lead to catastrophic collapse, the “distance” between the ULS and Near Collapse events might be dramatically and dangerously short. It might thus not take too greater intensity of earthquake, or simply amplification due to soil conditions, to move from ULS to Collapse.

The suggested revised definition of EPB should be able to capture these effects. .

Figure 2. Tentatively Modified Seismic Performance Objective Matrix for an ERP Buildings Policy using

33%NBS and 67%NBS as references.

A similar example can be carried out for a 67%NBS building (either existing or retrofitted). Such a building, according to the performance matrix, would reach Life Safety with an earthquake at a return period between 1/100 years (R=0.5) and 1/250 years (R=0.75). (For simplicity the occasional earthquake is herein used as reference). Under the design level of earthquake the 67%NBS building would reach near collapse but still have good probability of avoiding total collapse, depending on the nature of its failure mechanism. The preferred performance would be where the building continues to displace without failure (ductility) after reaching its ultimate strength. The evident conclusion is that “scoring” against a 1/3 of a real design level earthquake does not provide robust information on the actual performance of the building under the real, expected, design level earthquake. The robustness of the capacity of the building should be checked against not only a moderate but also a severe earthquake. The latter can be achieved by checking the ultimate capacity (displacement/ductility capability) of the structure to sustain gravity/vertical loading without catastrophically collapsing under the “real” (severe) earthquake.


It is thus suggested to modify the definition of Earthquake Prone Building to identify this performance objective for existing and retrofitted buildings. The reference to a moderate earthquake in the Building Act, defined as 1/3 of the intensity of the ”real” design level earthquake (or “expected” event with a return period of approximately 1/500 years, as it could be the Alpine Fault or Wellington fault event) is considered to be insufficient. Therefore, it is suggested to integrate the definition of EPB in order to capture critical vulnerabilities that can lead to catastrophic collapse under a severe earthquake as per the CTV building.

The Society proposes a change to the definition of earthquake prone building, such as: An earthquake prone building is a building that either:

under a moderate earthquake is likely to reach, in part or as a whole, its ultimate capacity, in a way that can lead to death or injury of people within or outside the building;

or under a severe earthquake could result in catastrophic collapse due to the

presence of critical vulnerabilities that can lead to the development of brittle global failure mechanisms that can lead to death or injury of people within or outside the building.

It is acknowledged that the wording of the second part of this definition would require special care, as well as a technically sound and clear explanation of those critical vulnerabilities which could lead brittle global failure mechanism. 3- Clarification on use of strength-only approach assessment vs. expected “seismic

performance” which include strength and ductility

One of the main reasons for possible lack of consistency in the evaluation of the expected performance of an existing building is, in addition to the complexity of the problem itself, related to the inherent, and thus difficult to modify, the force-based approach of traditional code design.

In recent years it has been proven that displacement capacity is an equally important if not even more important characteristic for the ability of a structure to sustain severe earthquakes. A trend towards displacement-based design and assessment is happening in NZ as well as overseas.

Notably, the NZSEE2006 guidelines already introduced a displacement-based assessment procedure in its Detailed Engineering Evaluation, also referred to as SlaMa, (Simple Lateral Mechanism Analysis). Such procedure was built on state-of-the-art knowledge in the field of structural analysis, and is still recognized today as having a sound basis.

However, education and training of engineers is required to shift from a force-based to a more displacement-based design of new buildings. Similarly, in the assessment of existing building, the natural tendency would be to think and calculate/check using forces only (or in the main).

Also, in the first phase of the IEP process, again intended to be only a first level screening of the worst cases, the method is basically force-based and it is apparent that when looking at the more refined evaluation of the %NBS, engineers might (incorrectly) tend to


refer to strength-only assessment, without checking the ultimate displacement capacity associated with the probable mode of failure.

The potential problems of such an approach, is clarified in Fig. 3 (Kam et al., 2013).

From a force-based assessment perspective, only case F & G with the lateral strength < 67%NBS and <33%NBS would be, inappropriately, considered earthquake-risk and earthquake-prone buildings respectively.

From a seismic performance perspective, cases E, F and G are seismically-vulnerable as they will be vulnerable to collapse under moderate-to-large earthquakes (with >67%NBS displacement demand). The new definition of Earthquake Prone Building, might be able to capture the presence of a critical vulnerability leading to catastrophic collapse of such buildings under a severe event.

On the other hand, cases C and D are expected to perform better, despite having a lower strength capacity. The strength of such buildings might be low but the displacement capacity would allow them to survive a higher level of earthquake, thus their actual %NBS (in terms of performance) should be recognized to be higher than E and F and their overall ductile behaviour be preferred and recognized.

Figure 3: Behaviour of a structure after its maximum strength is achieved. Brittle vs. Ductile mechanism. The figure illustrates that a %NBS based on force/strength only is not adequate. Current Detailed Engineering Evaluation in the NZSEE2006 guidelines proposes the use of either a displacement-based or a combined force-displacement approach.

In order to overcome potential inconsistencies in the evaluation of the actual performance of an existing building, it appears clear that it would be necessary to make more explicit reference to the displacement based component, even at early stages of the IEP. The suggested modifications to the definition of the EPB would help in that sense, as it would enforce an explicit check of critical displacement-driven vulnerabilities such as


excessive drift demand in non-ductile columns, unseating of precast floors, stairs, inelastic torsional amplification of deformation. In parallel, brittle forced-based local failure mechanisms such as shear failure etc. will continue to be followed at increasing level of displacement demand.

This displacement type failure is likely to be more of an issue with multi-storey buildings.

As anticipated, it is our opinion that the introduction of a performance check against a severe earthquake, in addition to or in replacement of the check against moderate earthquake, could naturally overcome most of the aforementioned sources of inconsistencies or misinterpretation of the guidelines, as it will inevitably require the assessor to check the behaviour of the structure in the post-yielding range and limit brittle global (and local) failure mechanisms.

4- Improvement of Assessment procedures: IEP, %NBS or similar parameter

In light of the above issues with building performance , the current “scoring” approach, evaluated against the requirement of a new design building, %NBS, requires review and possible modification to account for the twofold performance objective, e.g. ultimate limit states achieved under a moderate earthquake and catastrophic collapse avoided under a design level earthquake.

To this purpose, NZSEE is planning to look at a short-term revisions of the NZSEE2006 Guidelines (including, but not limited to, the IEP in Phase I by mid-2013). A more substantial and thorough revision of the whole guidelines will be required to incorporate the latest findings in research at national and international level, as well as lessons learned from the Canterbury earthquake. This more significant revision is intended to be carried out within 18-24 months (Phase II, by end of 2014).

As part of the planned revision, a list and clear identifications of “critical vulnerabilities” which can lead to such brittle and catastrophic collapse under a design level event (severe earthquake, as used in the question 33 of the consultation document) will be more explicitly provided. Non-ductile gravity columns, typical of the pre-1995 period, weak diaphragm details and seating, insufficient stairs seating, highly irregular and torsion prone buildings, are only some examples.

Following the increased awareness in the 1990s of the seismic vulnerability of pre-1970s buildings, recent research carried out in the past ten years (non-ductile columns, floor systems etc), and the Canterbury earthquakes have provided a string of evidence that raised awareness of the potential critical vulnerability of post-1970s and pre-1995 buildings (e.g. CTV Building being a very unfortunate example), which are unlikely to have been captured by current EPB building screening processes.

5- Improving consistency in the evaluation and retrofit implementation: role of education, communication, workshops

It was always anticipated that when dealing with the complexity of evaluating the seismic capacity of an existing building, considerable engineering judgement would be required to identify the buildings vulnerabilities.

However, developing a comprehensive education and training campaign, using benchmarking and piloting workshops, can narrow the possible wide range of


assessment results from two different engineers. This is to provide consistency in the evaluation approach as well as in the retrofit strategy and solutions adopted.

Such activities must be organized at an early stage prior to proceeding with DEE as well as the actual implementation of the retrofit solutions.

Furthermore, it is fundamental to improve communication among building owners, occupiers, businesses, territorial authorities, building officials, engineers, architects, building officials, the building sector, CDEM sector, the insurance sector, the media, Central Government and the public.

A better understanding of performance objectives, shortcomings and limitations of the assessment procedure, as well as the potential and costs (see below) of retrofit solutions and available strengthening techniques, can enhance significantly the awareness of retrofit options. This would lead to a reduction in the seismic risk via retrofit mitigation strategies.

6- Management of Engineering Resources – Development of Risk-based Framework

to assist with the implementation of the policy

The demand on resources to assess and improve the seismic performance of the existing building stock might be too high in the suggested timeframe. Without proper coordination at municipality, regional and national level, it is realistic to anticipate that there may be a bottle-neck on resources (engineers, contractors, building consent authorities), near the end of the suggested term/deadline.

It is herein proposed to develop a Risk Management Framework which could assist to prioritize the allocation of limited resources during the assessment phase, but more importantly during the implementation phase. Such a framework should have a national focus and allow for the most-dangerous buildings to be assessed and strengthened first, and less-at-risk (also considering occupancy levels) buildings to a longer time-frame.

Note that a suggestion on a prioritization strategy was already included in the NZSEE2006 guidelines.

7- Considerations of other associated hazard sources

The current model focuses on buildings, but does not adequately consider the hazards associated with the surrounding environment – ground failure, slope stability, rock falls etc, which could lead to life safety considerations. It would be important to explicitly include considerations of such hazards in the Risk- Assessment guidelines and in the education/training courses.

8- Improvement of cost-benefit analysis, communication to the owners, and possible

incentives towards implementation

The proposed cost-benefit analysis of retrofit on a national scale needs to be improved as it can be misleading in its current format. It is acknowledged in the consultation document that the evaluation was based only on life-safety considerations. However, recent research has showen that if using a simple cost-benefit analysis based on life-safety considerations only, it will be very hard to


justify any retrofit intervention. Cost of injuries and providing accommodation for homeless people would be the most immediate inputs to the economic analysis. The wide range of indirect costs and overall economic impact to the community are even higher (as evidenced by the loss of the entire CBD in Christchurch).

It is thus suggested that the cost-benefit analysis be significantly improved prior to defining a national-wide implementation strategy The comparison with road-victims is also not fully appropriate for two main reasons: a) Road/car accidents do not occur, in the vast majority of cases, because of faults in the

mechanical parts of the car. The equivalent of the WOF for a building would be a Seismic WOF with much higher requirements.

b) Isolated car accidents do not lead to an overall major impact on the economy of a city or country. The benefits of strengthening buildings are much greater if all indirect costs are considered.

For individual buildings, it is important to develop, communicate and assist the building owner with the understanding of the actual cost of retrofit options. These different solutions target different levels of performance as well as the long-term benefits, including possible reduction of insurance premiums, increased rentals, and maintaining of market value. In addition, there is less likely to be the need to demolish the building or face expensive repairing costs following an earthquake event. It is also important to clarify that, depending on the structure, the level of target performance, and the selected retrofit technique, the cost of retrofit may not proportionally increase with the target level. For example in some cases retrofitting to 67%NBS might cost significantly less than twice the cost to retrofitting to 33%NBS, when most of the initial costs are based on the invasiveness of removing and reinstalling linings, partitions, ceilings etc. On the other hand, for some structural systems, and depending on the technique involved, the cost of improving the level of performance can suddenly escalate once the limits of a strengthening “plateau” is reached. In order to achieve the best outcome, even in terms of preliminary conceptual design and cost of a retrofit intervention, it is fundamental to develop and disseminate a set of practical design guidelines on retrofit solutions. NZSEE is planning to facilitate and coordinate the preparation of a study group to develop a Retrofit Design Handbook which could assist engineers, contractors and clients in the selection of a suitable set and mixture of cost-efficient retrofit techniques, including use of advanced materials and technology. It is suggested that the government develop, for special buildings (e.g., but not limited to those of heritage value) ad-hoc incentives strategies, in the form of subsidies, tax rebates, reduced compliance costs, free loans etc, as those implemented in the past few years for improvement of insulation in buildings and limitation of air-pollution due to open fire-places.


RESPONSE TO PROPOSALS AND QUESTIONS Proposal 1: Local authorities would be required to make a seismic capacity assessment of all non-residential and multi-unit, multi-storey residential buildings in their districts within five years of the legislation taking effect, using a standard methodology developed by central government, and to provide the resulting seismic capacity rating to building owners. An owner could have their building”s seismic capacity rating changed by commissioning their own engineering assessment. Proposal 2: Assessments would be prioritised faster for certain buildings (eg, buildings on transport routes identified as critical in an emergency). 1. Should local authorities be required to assess the seismic capacity of all buildings covered

by the earthquake-prone building system in their areas, and to issue seismic capacity ratings to owners?

NZSEE supports the proposal for local authorities to carry out an initial evaluation of all buildings within their jurisdiction. This coarse screening process can be based on the current NZSEE procedure, but note that it is to be modified to provide additional information for evaluating engineers so that greater consistency of the %NBS value determined by different assessors is obtained. This value for %NBS, together with a description of any identified “critical structural weakness”, are conveyed to the building owner. Where the building has a %NBS less than 34%, or critical vulnerabilities are found, the building owner has an agreed period of time to engage an appropriate experienced engineer to carry out a “Detailed Seismic Assessment” (DSA) of the building’s seismic resistant capacity as well as further identifying any “critical structural weakness” that can lead to possible collapse of all or part of the building from the “design earthquake”. This detailed assessment will provide the basis for rating the building”s seismic resistant (in terms of performance, not strength-only) capability. The initial evaluation process carried out by local authorities should be to a nationally developed “Risk Management Framework” that identifies “high risk” buildings (e.g. high occupancy multi-storied unreinforced masonry adjacent to main transport routes) through to those that are inherently considered to be “low risk” (e.g. timber framed buildings with low levels of occupancy). 2. Do you think five years is a reasonable and practical time to require local authorities to

carry out assessments in their districts? The assessments should be carried out to a programme that is identified in the “Risk Management Framework”. Under the “Risk Management Framework” programme it is possible that the most critical buildings in high seismic regions will be assessed well within a 5-year period, whereas other, less critical buildings, may require a longer timeframe because of resource constraints. The “Risk Management Framework” will also identify appropriate resources, the development of best practice processes, and training requirements to achieve an inventory of building seismic capacity that the public can have confidence in.


3. Should unreinforced masonry buildings be assessed faster than other buildings? The “Risk Management Framework” will consider the relative risk provided by un-reinforced masonry buildings as against other building types that are also “high risk”. The “Risk Management Framework” should also consider elements of building that may require evaluation before the building structure as a whole. This could include masonry chimneys, parapets, gable end walls and front facades. Other forms of construction that may be considered “high risk” are precast concrete cladding panels, precast flooring systems, other non-structural elements and adjacent hazardous features such as a “high risk” neighbouring building or rock fall. 4. What costs and other implications do you see with these proposals to assess the seismic

capacity of buildings? A major issue will be obtaining appropriate resources to match the workload likely to be identified in the “Risk Management Framework” so that assessments can be completed in an acceptable time frame. It must be appreciated that IEP assessments require a high level of knowledge and experience to identify how a particular building type will perform in a moderate or design earthquake event. To provide the training and benchmarking required will involve significant financial input. To provide the required knowledge on the wide range of building types and material, research input will be a priority. Whereas research has been provided on new construction, there are areas of the seismic performance of existing buildings that is lacking. For example, the dynamic performance of timber floors, and their interaction with the overall response of URM buildings, is still not well understood and requires further research so that assessments are soundly based. Proposal 3: Building information would be entered into a publicly accessible register maintained by MBIE. 5. Do you agree that local authorities should be required to enter information on the seismic

capacity of buildings into a publicly accessible, central register to be managed by MBIE? It is recommended that MBIE setup and maintain a national buildings register. The information on individual buildings should be collected by local authorities and entered into the national register. The information provided should include the seismic capability of buildings in their jurisdiction that has been obtained from detailed assessments and agreed between the local authority and the building owner. This information should be able to be published by the local and national authorities and be publicly available. In addition to informing owners, occupiers, and users, a national, authenticated, maintained and discoverable register of buildings will have benefits for those with interests in building portfolios, including insurers and mortgage holders. Under the governments Open-Data and interoperability policies, the building data will be able to be linked with other data, such as title information (LINZ LandOnLine) and hazard information from regional and national hazard registers.


A requirement of any building register is that all buildings must have:

1. a unique identifier; 2. a geospatial location – preferably represented by the buildings foot print; 3. summary attributes that define the buildings characteristics; 4. all of the above in accord with National standards – that are yet to be established.

A readily accessible database with this type of information will be invaluable following a major earthquake event. It will allow engineers carrying out the “Rapid Assessment” to better understand the structural characteristics of the buildings being assessed. This is likely to lead to greater accuracy in the building assessment. 6. Should information other than a building”s seismic capacity rating be entered into the

register – for example, agreed strengthening actions or information from an agreed building ratings system?

Yes, it is important to include such information as the history of strengthening carried out on the building, and previous earthquake performance. Also to record any agreement that the building owner has entered into with the local authority for a programme of strengthening works and what those works will entail. Again this information would be of great value for Rapid Assessment of buildings following an earthquake. 7. Rather than a central register, should local authorities be responsible for both collecting

and publishing this information? Yes, provided the information is in a standardized form and accessed from a national register managed by MBIE. It is important that the buildings on the register be reviewed on a regular basis and the register updated. This is to pick up deterioration of the building fabric with time that can have a marked bearing on the earthquake resistant capacity of the building. For example, leaking internal gutters can lead to rotting of the timber framing of the roof structure that may be providing lateral support to the building”s masonry façade or parapet. 8. Should there be any other information disclosure requirements – for example, should

building owners be legally required to display information on the building itself about the building”s seismic capacity?

It is recommended that the building owner be required to display a public notice on the building identifying the earthquake resistant capacity of the building in a standardized form. The information displayed should be in “plain English”, which includes the seismic rating of the building as well as vulnerable features.


9. What costs and other implications do you see resulting from the proposal to put seismic capacity information in a register?

NZSEE does not consider it has sufficient information to provide a substantive answer to this question. However, the Society considers that, over time, publicly available information on New Zealand”s building stock is important to assist with the process of informing the public and improving the earthquake resilience of our buildings, as well as other building related matters as noted by the Ministers description of “GeoBuild” on 7 June 2012 - http://www.national.org.nz/Article.aspx?articleId=38691 . Proposal 4: The current national earthquake-prone building threshold (one-third of the requirement for new buildings, often referred to as 33 per cent NBS) would not be changed. However, it is proposed to establish a mandatory national requirement for all buildings to be strengthened to above the current threshold, or demolished, within a defined time period. 10. Does the current earthquake-prone building threshold (33 per cent of the requirement for

new buildings) strike a reasonable balance between protecting people from harm and the costs of upgrading or removing the estimated 15,000 - 25,000 buildings likely to be below this line?

NZSEE does not consider it has sufficient information to provide a substantive answer to this question. NZSEE has always held the view that a building with a 33%NBS earthquake resistant capacity is highly vulnerable to damage that could be a life risk. In addition, the cost of recovery from a major earthquake event can have a severe effect on the economy of the country as a whole. Therefore, over time, it is important that the country’s building stock is brought up to a higher level of earthquake resilience. If the legal minimum level of 33%NBS is maintained to identify “Earthquake Prone Buildings” (EPB), consideration could be given to strengthen an EPB to improve its performance to a higher level than 34%NBS; as much as reasonably possible. The NZSEE maintains its recommendations, written in the NZSEE2006 guidelines, to try to target 67%NBS, and to at least reduce critical vulnerabilities and modify, as much as reasonably possible, brittle mechanisms so they develop sufficient ductility. 11 Should the requirement for earthquake-prone buildings to be strengthened or demolished

take precedence over all other legal, regulatory and planning requirements, such as those designed to protect buildings of heritage or local character?

Public safety is the prime importance. However, other aspects of “public good” must be considered on a case-by-case basis so that the ultimate decision on any outcome is based on clear, well-founded information. Development of the “Risk Management Framework” will provide a mechanism where such information can be identified and given due weight. Where there are other important criteria to be addressed, hasty decisions should not be made. If required, the building can be seismically secured while the information gathering and decision-making processes take place. In the case of heritage buildings consideration should be given to “making safe”, then allowing an extended period of time to identify sources of funding, appropriate strengthening solutions, and for the strengthening works to take place.


Where there is a strong case for retention of heritage that meets public objectives, then public funding of the strengthening works and /or tax relief and/or reduction in compliance costs may need to be allowed for. Where additional funding is provided for an iconic heritage building, consideration should also be given to providing a higher level of earthquake resistant capacity to meets public expectation that the building will be available for many generations. 12. Should local authorities have the power to require higher levels of strengthening than the

earthquake-prone building threshold, or strengthening within shorter timeframes than the legally defined period?

Development of a “Risk Management Framework” on a national basis that has local authority and public input will identify those particular buildings or facilities that require priority action and higher levels of protection, as well as those that can be deferred due to their low risk. By working within a national risk management framework, local issues can be identified, their ranking balanced against the desires of the local people and the cost. This should provide a clearer picture of the local as well as the national cost/benefits, so that well understood decisions can be made. 13. Should certain features of unreinforced masonry buildings, such as chimneys and

parapets, be required to be strengthened to a higher level? NZSEE supports the concept that particular building elements that are identified as having a high potential vulnerability to earthquake effects be identified in the “Risk Management Framework” and assessed as a priority. Refer to the answer to question 3. above. Where it is considered appropriate to manage the risk, these elements may require restraints that have an ability to improve the earthquake resistant behaviour of the element at higher intensities of earthquake shaking. The emphasis should be on earthquake resistant “behaviour” rather than just on strength. Proposal 5: All buildings would be strengthened to be no longer earthquake-prone, or be demolished, within 15 years of the legislation taking effect (up to five years for local authorities to complete seismic capacity ratings, followed by 10 years for owners to strengthen or demolish buildings). Proposal 6: Strengthening would be carried out faster for certain buildings (eg, buildings on transport routes identified as critical in an emergency). Proposal 7: Owners of buildings assessed as earthquake-prone would have to submit a plan for strengthening or demolition within 12 months. 14. Is it reasonable and practical for owners of earthquake-prone buildings to meet the

following timeframes: • 12 months to submit plans for either strengthening or demolishing the building? • 10 years from the date of the seismic capacity rating to strengthen or demolish?

NZSEE do not consider they have sufficient information to provide a substantive answer to this question. Development of the “Risk Management Framework” will assist in identifying


appropriate timeframes for building owners to develop retrofit schemes and carrying out strengthening works. It will also allow different types of buildings that have differing solution complexity to be addressed as resources become available. There must be a nation-wide prioritization plan that is risk-based and resource-based to provide the best possible solutions in a fair and equitable way. 15. What additional powers would local authorities require to enforce the proposed

requirements? NZSEE do not consider they have sufficient information to provide a substantive answer to this question. 16. Should local authorities be able to require faster action on buildings of strategic

importance, such as those: • located on transport routes identified as critical in an emergency • with important public, social and economic functions, such as schools and police

stations • with post-earthquake recovery functions, such as civil defence centres and hospitals.

Yes, in accordance with the “Risk Management Framework”. There must be a clearly identified risk management basis for any equitable national action. The long-term objective is a “resilient New Zealand. 17. Should all unreinforced masonry buildings require strengthening more quickly than other

earthquake-prone buildings? The “Risk Management Framework” will assist to identify the most at risk buildings, no-matter what their form of construction. Any work must be based on reducing the risk whatever the form of construction. Proposal 8: Certain buildings could be exempted or be given longer time to strengthen, eg, low-use rural churches or farm buildings with little passing traffic. 18. Should the owners of certain specified types of earthquake-prone buildings be able to

apply to local authorities for exemptions or time extensions to the requirement to strengthen or demolish?

The “Risk Management Framework” will assist to identify those buildings, and their seismic risk locations, that are of such low risk that they can be exempt from the Building Seismic Assessment process. 19. If yes, what are your views on the following possible criteria:

• the building is used only by the owner, or by persons directly employed by the owner, on an occasional or infrequent basis

• the building is used only occasionally (less than eight hours per week), and by less than 50 people at any one time


AND in each circumstance above • all users are notified that the building is likely to collapse in a moderate earthquake • the building is not a dwelling • the building is not a school or hospital and does not have a post-disaster recovery

function • there is no risk of the building partially or fully collapsing onto a public walkway,

transport route or a neighbouring building or public amenity • effective mitigation measures have been put in place to protect building users from the

risk of collapse in a moderate earthquake? Any criteria must be “risk based”. The main issue here is for informed decisions to be made by all users of these buildings based on sound defensible information that is clearly presented. Proposal 9: Central government would have a much greater role in guiding and supporting local authorities and building owners, as well as in public education and information. 20. Are the advice, information and education activities proposed for central and local

government agencies sufficient to help ensure effective implementation of the new earthquake-prone building system?

NZSEE supports Government, through MBIE, to develop guidelines for local authorities, building owners, and the general public to assist them understand the issues around earthquake-prone building systems. However, the Society has a concern that the public perception around earthquake resistant building performance is not well founded, particularly with the heightened interest following the events in Christchurch. Consequently there is a challenging task to develop soundly based education material for all sectors. Also for engineering practitioners there is a greater demand for guidance material in all facets of assessment and identifying retrofit solutions for a wide range of existing building types. Much research and development of guidelines is required to identify and support best practice. Views are sought on whether the current Building Act fire and disability upgrade requirements are, in practice, a barrier to building owners deciding to carry out earthquake strengthening work. 21. Are current requirements to upgrade buildings to “as nearly as reasonably practicable” to

Building Code fire and disabled access requirements a disincentive or barrier to owners planning to earthquake-strengthen existing buildings?

It is generally perceived that costs associated with upgrading the building is a disincentive to also carrying out seismic retrofit works. NZSEE recommends that the requirement to upgrade at the time of a seismic retrofit be de-coupled. The local authority must be quite clear as to the objective for any particular seismic retrofit, and any decisions based on minimization of risk, be it fire, access or earthquake. Where there is a change of use, the building should be upgraded “to as near as is practically possible” with the current Building Code. During the recovery period following an earthquake, it is important for the recovery to be carried out as expeditiously as possible. Therefore, there could be merit in allowing building owners to carryout repair work only (like-for-like), to reinstate the original capacity of the


building, or provide securing without undue demand to meet other requirements of the Building Code. 22. Should local authorities be able to grant building consents for earthquake strengthening

without triggering the requirement to upgrade the building towards Building Code fire escape and disabled access and facilities requirements?

Refer answer to question 21. 23. Should any change apply to both fire escape and disabled access and facilities

requirements, or to disabled access and facilities requirements only, ie, retain the current fire escape upgrade requirements?

Refer answer to question 21. Each application must to be considered on a case-by-case basis to minimize risk. 24. What would be the costs and other implications of de-linking earthquake strengthening

from current Building Code fire and disabled access requirements? NZSEE do not consider they have sufficient information or knowledge of this question to provide a substantive answer. Views are sought on how important heritage buildings can be preserved while also being made safer. 25. When considering listing heritage buildings on district plans, what factors should local

authorities consider when balancing heritage values with safety concerns? When considering heritage values, the building”s safety assessment is of secondary concern; either the building has heritage values or it does not. Once a building is identified as having heritage values, a seismic risk assessment should be carried out to determine the risks, mitigation measures and the cost of such measures. From this analysis a process can be put in place that develops a programme of works to protect the heritage values and how the protection works are to be financed. This programme is aimed at managing the risks of earthquake related damage and deterioration of heritage fabric with time. In particular cases, seismic securing may be appropriate, and additionally evacuation and cordoning, to allow time to develop solutions and raise the required finance for the protection, repair and seismic strengthening works. 26. What assistance or guidance will be required for owners, local authorities and

communities to make informed decisions on strengthening heritage buildings in their districts?

The “Risk Management Framework” will assist heritage building owners, the government authorities and the general public to place any particular heritage building into the national


and local built environment context. Value judgments must be made with a clear understanding of the heritage values, the risks and the cost of mitigating those risks. 27. What barriers deter heritage building owners from strengthening their buildings? The inability to fund proposed strengthening works is a major barrier. The general concern is that there is little or no financial return from any investment in strengthening works; the work must be paid for out of current income, which may be reduced during the construction activity. Also, liability concerns and how they may or may not impact in the future is of real concern to building owners. The requirements of the RMA with respect to cost and time to work through the process are a barrier in some cases. However, it does highlight the demands on prospective building owners to understand the requirements and implications that go with ownership of a heritage building. Due to the demand on engineering services, the situation can arise where the limits of an engineer”s knowledge or experience may be stretched, or there is insufficient time to fully develop solutions for what can be complex engineering problems. In these cases, the proposed strengthening works may impinge on heritage fabric to an unacceptable degree, or the solution may not be cost effective. These technical demands highlight the need for the development of training material and its dissemination to practicing engineers. 28. Do heritage rules (for example, those in district plans) deter owners from strengthening

heritage buildings? The structural analysis and strengthening of heritage buildings can be a very complex task that requires extensive knowledge and experience of the materials of construction. This is not only the engineering properties of the building materials and its foundations, but also how the strengthening system will affect the building”s dynamic response to earthquakes. Long-term aging of the building fabric is another consideration when developing strengthening proposals. Heritage rules tend to focus on preservation of heritage fabric, which tends to limit the options for structural strengthening towards the more expensive solutions. For these reasons, and as noted in 27. above, cost is a major barrier to carrying out strengthening works, with very little economic return. Where there is a public good aspect to structural upgrading of heritage buildings, support for this work must be provided by public and government sources. 29. What are the costs and benefits of setting consistent rules across the country for

strengthening heritage buildings? Consistent generic rules across the country would provide greater certainty for building owners as to potential requirements. However, consistent rules would work against remote heritage buildings in a low seismic area. The different risks associated with remote areas, provincial centres and metropolitan centres must be addressed. Resources can also vary from region to region, hence working for or against a particular approach to protecting heritage buildings. Again the “Risk Management Framework” would have the potential to identify those differences and provide appropriate direction.


Views are sought on the Royal Commission”s recommendation to allow local authorities the power, following consultation with their communities, to adopt and enforce policies to require specific hazardous elements on residential buildings to be dealt with within a specified timeframe. 30. Should local authorities have the power, following consultation with their communities,

to adopt and enforce policies to require specific hazardous elements on residential buildings to be dealt with within a specified timeframe?

Christchurch has shown that certain forms of construction have a detrimental effect on the earthquake resistant performance of residential buildings. A well-researched national policy should be developed to mitigate the clearly identified hazards. The general public must understand the issues, through a consultation process, so that the proposed policies are well accepted into the communities. If residential buildings are included in the “Risk Management Framework” it would provide for a complete picture of the national built environments risks, which must be understood and addressed. Other questions 31. What would the proposed changes mean for you? The changes would have a direct impact on the Society”s members, as they are involved in various ways with the assessment and improvement of building performance during earthquakes. The development of guidelines to assist the dissemination of knowledge would place a significantly increased demand on the resources of the incorporated Society. We are keen to provide the technical expertise that we have available, but further financial support would be required. With the current demand on engineers and scientists time, the Society should offer payment for any input into Study Groups that would be set up to assist with the develop of technical guidelines and providing technical advice. This would allow the developments to be carried out in a timely and cost effective way, using the wide range of expertise available in the Society”s membership. 32. Are you aware of any problems with current policy and practice around earthquake-prone

buildings, other than those identified in this document? There are significant issues around the consistency of IEP assessments provided by engineers, and the inapropriate use of this “coarse screening tool”. This has led to distortions of the property market with significant loss of value in some areas. The variations in approach taken by different local authories with assessments has also give rise to uncertainty. The “passive” approach has delayed the identification of harzardous buildings that must now be addressed. It is noted that Building Consent Authorities do not necessarily have the expertise to assess retrofit solutions submitted for Building Consent. It is important that a robust and nationally consistent process is established to review retrofit projects in support of the local authories.


An area of concern, as noted above, is the level of expertise that is available to develop appropriate seismic retrofit solutions; this is variable and does not always produce the best solution. This suggests that development of more extensive training programs and supporting tools is an imperative. Some inappropriate retrofit solutions are not cost effective and have turned building owners away from carrying out urgently required structural strengthening. Better solutions must be identified and case studies made available to enhance the outcomes. 33. Do you agree with the following objectives for changes to the existing earthquake-prone

buildings system: • reduce the risk – to an acceptable level - of people dying and being injured in or by

buildings that are likely to collapse in moderate to large earthquakes. • ensure that building owners and users have access to good information on the strength

of buildings they own and use, to help them make good decisions about building resilience and their use of the building.

Yes, over time the reduction of seismic risk in New Zealand is important. Not only from a life risk point of view, but also to reduce the enormous economic cost on the country when a metropolitan centre is hit by a major earthquake event. This is where the “Risk Management Framework”, together with a National Building Register, such as GeoBuild, could provide the necessary information and direction to meet the proposed objectives. An important issue, as highlighted in the question, is to not only set a minimum legal limit for earthquake prone buildings, but also to ensure all buildings have an acceptable performance in large earthquake events. For any building, damage may be severe but total collapse should be prevented. To achieve this objective it will be necessary to not only assess the earthquake resistant capacity of the building but also identify vulnerable elements liable to fail and cause death or injury, including non-structural elements. A very important matter is the need for national consistency in Earthquake Prone Building policies, including professional competencies and practice, and the addressing of health and safety aspects of occupancy and neighboring exposure to risks adjacent to EPBs. Prof. S. Pampanin President NZSEE


FURTHER CONTACT The New Zealand Society for Earthquake Engineering is available to provide further comments if required. For more information please contact: Prof. Stefano Pampanin President e-mail: [email protected]; [email protected] Mr Peter Wood Immediate Past President Mr Win Clark Executive Officer e-mail: [email protected] New Zealand Society for Earthquake Engineering Inc.

Documents

BUILDING SEISMIC PERFORMANCE: CONSULTATION · PDF fileBuilding Seismic Performance Consultation ... in the seismic design of ... the entire 1- NZSEE Submission to MBIE Building Seismic