Hello. I used the link for the web app and all I got was an “Oh no :-(” error message. I’m not kidding, it literally has an emoticon in the error message.

That aside, I think it would be good if Standards NZ release Table 3.4 in an excel compatible format.

Why? Say I discover my building has a different period to what I first assumed. If I had Table 3.4 in my spreadsheet I could just change my T1 input and it would auto-update Cd and everything I had made dependent on Cd.
But if I need to use an app I would need to alt-tab to the app; then change T1 in the app; then read the app’s output for Cd; then alt-tab back to my spreadsheet; then change Cd on the spreadsheet to match the app output.

(obviously I’m making some assumptions about how the app input/output will function).

Apologies all – we are aware of the issue with the web app and will have it back up and running as soon as possible.

The web app is now up and running.

Tables 3.4 and 3.5 are available from Standards NZ in Excel compatible (CSV) format via the link in the “Referenced Documents” section of TS1170.5.

Additionally, in the current beta version the web app enables download of the generated spectra in CSV format. This should be amenable to rapidly updating design calculations.

SESOC will be discussing adding features to the web app. If you have suggestions, or wish to report bugs, please do so in response to the post at this link.

TS1170.5 High Level Comments (Opinion):

Dunning Thornton Consultants is a specialist structural design consultancy based in Wellington with broad experience in building design from single storey residential and commercial through to multistorey buildings, with particular experience in low-damage design structures.

It is in this context we have reviewed the proposed draft technical specification TS1170.5 and have the following high-level comments.

We believe the potentially unintended resulting costs and risks associated with issuing this document in its current form significantly outweigh any benefits. The basis for this statement follows:

1. Major Impacts in Wellington Region

It is our opinion that as it currently stands the draft TS1170.5 will result in a significant increase in seismic structure in the Wellington region, increasing the financial and carbon costs of development. We are concerned the resulting costs are likely to have a disproportionate effect on small/medium projects including affordable housing. These costs may result in perverse outcomes that do not align with broader goals including delivery of resilient infrastructure, development of low carbon buildings, and the broader uptake of low damage structures.

2. Review Period Extended

We believe the timeframe for review of TS1170.5 should be extended so that additional supplementary information provided to allow an informed feedback process by diverse stakeholders. There is not sufficient time for the engineering fraternity to appropriately convey (at their own cost?) the effects on the financial stakeholders – all building owners – affected by the proposed changes.

3. Cost / Benefit Analysis

Of key concern is any suggestion that alterations be made to codified hazards prior to a wide ranging and thorough cost/benefit study as we believe the potential impacts and unintended consequences are significant. Seismic Engineering requirements and decision making have real impacts on the feasibility of projects, these costs and potential benefits need to be assessed against other national priorities. A clear ‘business’ case must be made for updating NZS1170.5 as proposed in the draft TS1170.5. This study should not be aggregated nationally but reflect the different impacts by region.  The scope of this study should include:

• Review of increased dollar and carbon costs for new construction and for strengthening.
• Review of Opportunity Costs – What are we not able to afford because of increased structural costs? Townhouses/densification, Affordable Housing, schools, Hospitals, Infrastructure,
• Review of risk mitigation likely to be achieved and comparison with other life hazards.
• Effects on property values for existing buildings. Even if the EQP benchmarks will not alter, the market will differentiate due to NZ’s historic approach and the (mis)understanding of “New Building Standard”.
• Increased insurance costs arising from both higher replacement costs and higher perceived risk.

4. Partial NZS1170.5 Update Problematic

We believe NZS1170.5 does need updating, however the approach to this update should be holistic rather than de-coupling hazard and design provisions. The proposed approach of just increasing the hazard penalises good and bad buildings alike. We believe it is important for the standard to encourage the forms of building that would more appropriately respond to the updated hazard, and incorporate the significant changes in the way buildings should be/are designed and constructed in the last 20+ years.

Any review of NZS1170.5 review should include significant incentives to develop buildings with the 4 Rs – robustness, resilience, redundancy, regularity. ASCE7 provides an example model for this.

We are concerned the proposed design hazard for Wellington is so great when constrained by the current design provisions of 1170.5 that some current structural forms that are considered robust will not be feasible. The added complexity and/or lack of precedent in designing for these hazard levels without update of the design provisions we believe will cause heavier and more expensive structures without necessarily an improvement in performance. The general adoption of lower ductility systems in Wellington since the Canterbury and Kaikoura Earthquakes is an example of design practice exceeding the minimum code requirements. It should be noted that limiting ductility is recognised in US design standards as one of the greatest drivers of collapse prevention and is the performance basis for their importance level system rather than longer return periods.

5. More “Guidance”

This document will also be added to the high number of non-cited “guidance” documents which design practitioners and BCAs have to grapple with outside the NZBC. This will require additional interpretation and judgement, adding to issues of inconsistency, reduced productivity and cost. We are concerned that as another “guidance” document the TS1170.5 will be interpreted as the new standard and will be used for design, which will affect projects immediately. Further coordination is required with the BCA’s and Worksafe to clarify their positions in relation to this document prior to it being formalised.

6. Significant Differences from US approach to Design Risk

The west coast of the United States has many similarities to New Zealand, with a series of major active faults regions and subduction zones. Code development committees in the US have had to develop building and infrastructure design provisions to account for their seismic hazard, for a much larger economy and population base. Code development organisations like the American Society of Civil Engineers (ASCE), International Code Council (ICC) and infrastructure regulators like California Department of Transportation (CalTrans) have all included Deterministic Seismic Hazard Assessments (DSHA) in developing seismic loading requirements. This approach is often referred to as the “Deterministic Cap”.

The National Earthquake Hazards Reduction Program (NEHRP2020) recommendations outline the basis for DSHA’s inclusion in design codes as noted below (our highlight in bold). These recommendations are adopted in the latest ASCE7 provisions.

“The amplitude of the MCER shaking, except where the deterministic limit applies, generally is somewhat less than a ground motion hazard having a probability of 2% of being exceeded in 50 years. The deterministic limit is imposed on the MCER ground motion, because the large uncertainty in our ability to predict ground motion at a site, given an earthquake of known magnitude at a known location, drives the probabilistic computation to predict very large ground motions where the return period of the characteristic earthquake is only a small fraction of the return period of interest for failure. The alternative calculation effectively places a bound on that uncertainty in ground motion while preserving the occurrence of a rare and large earthquake at a known location with some conservatism in the prediction of ground motion for that event as the design basis. Compared to less seismically active regions where earthquake records are rare, there is much more data available on the likely magnitude of earthquakes that active faults in such regions are capable of generating. It is also true that very large ground motions make some types of construction economically impractical, and there is insufficient experience to validate that design for such extreme ground motions without the deterministic limit is necessary.”

Extract 1 Source: https://www.fema.gov/sites/default/files/2020-10/fema_2020-nehrp-provisions_part-1-and-part-2.pdf (pg5-6)

NZS1170.5:2004 already contains a deterministic cap on design seismic loading however this rarely applies as the value is not site specific. The deterministic “cap” provisions appear to have been removed from TS1170.5 as there is no reference to this in the commentary or main body.

We believe the TS1170.5 committee should consider keeping the current the deterministic “cap” provisions but apply them on a site-specific basis. This approach has provided a rational and pragmatic means of conditioning large uncertainties around active faults in the US. This approach can be combined with improved seismic design provisions for high seismic intensity areas (Refer item 8) that is more reflective of current practice.

An appropriate estimation of the seismic hazard is not only a fundamental input into building design but also of societies perceptions (and pricing) of risk. It may not be considered reasonable or “fair” to apply a higher bar for seismic design requirements then in other jurisdictions with similar risks. The hazard is only one part of the overall risk equation and suitable design provisions to incentivize the design of robust resilient buildings are likely to be a more effective way to reduce risk and account for high levels of uncertainty. The decision around an appropriate approach to design hazard levels is fundamental to all other discussion and review of TS1170.5.

7. NSHM Translation:

The translation of the NSHM2022 hazard to the TS1170.5 document has resulted in higher accelerations than we believe the NSHM2022 hazard implies. There are three main areas which appear to cause this and suggest and these should be reviewed to ensure they are not unduly conservative.

1. The inclusion of NZS1170.5:2004 Near Fault Effects in the TS1170.5 does not appear to be supportable. The current 2004 provisions are not site specific and GNS’s own reporting (GNS report 2022/1) suggests that a maximum NFF for NZ would be around 1.1 with Wellington City having a neutral / negative directivity factor. Large NFF are explicitly a function of deterministic hazard thinking as any specific near fault effects on a particular site are extremely unlikely on a probabilistic basis. It may be appropriate to include these factors in a determinist hazard assessment to cap PSHA hazard risks.
2. The parametrisation of the NSHM curves from a composite Uniform Hazard Spectra (UHS) curve to a two-period curve has created large variations from the original NSHM data. Aside from capping a small portion of the short period hazard these variations all appear to be towards greater seismic demands then the NSHM. 
3. The creation of site soil classes within VS30 velocity bands, appears to have been carried out on an envelope basis to address the significant spectral variability within the bands. This generally means that all sites will have a conservative UHS.

Design values for a site in Wellington with VS30 of 275m/s and a period of 3 seconds are tabulated below. This translation results in a >60% increase in design acceleration over NSHM2022.

8. Hazard Zones

The current NZS1170.5 is largely agnostic to the magnitude of seismic shaking in design provisions. It allows buildings of the same configurations and systems to be designed in Whangarei and in Wellington (PGA 0.1g vs 0.9g – NSHM2022). Blanket rules are applied over all differing hazard levels. This approach has the potential to be overly conservative in Low Seismic Zones and un-conservative in High Seismic Zones. It also creates complexities for materials code development as the requirements to achieve minimum safety in a poor performing building (irregular, high drift etc) may unduly punish well configured buildings. This is apparent in the fragility analysis that accompanies TS1170.5 where the poor performing “tail” has a significant impact on the average fatality rate. Consideration should be given to varying the design provisions for low, medium and high hazard area.

9. Geotechnical Considerations

The impacts of the proposed changes under TS1170.5 have the potential to be even more impactful on geotechnical assessment and design. Increased PGA levels increase the scope of issues (slope instability, liquefaction etc) and the designs required to mitigate these issues (Foundation, Pile , Retaining size). As geotechnical considerations also extend outside of building design this impact is likely to be wide ranging on infrastructure projects. This is already obvious with the increased that have been associated with the Module 1 changes. We would recommend that deterministic assessment be considered for geotechnical considerations High Hazard Zones as is the case for buildings (ASCE7) and transport infrastructure (California Department of Transportation) in the United States.

Summary:

Society relies on engineering leaders to assess what are appropriate levels of risk, and practitioners to design structures to perform accordingly. Life safety is always the prime concern, but we are failing in our duty of care if we do not acknowledge that elimination of structural risk is not going to be affordable or have too great an impact on other priorities. Society does, of necessity, limit what it spends on life safety; traffic safety improvements are limited by available money and Pharmac does not fund every available life-saving drug. As Engineers we need to consider seismic risk in a wider context and understand that undue conservatism in our codes and design practice has real implications which may outweigh our small section of the overall risk pie.

The standard needs to clearly define (perhaps in the commentary) whether, or not, the 30% loading needs to have a separate eccentricity applied from the 100% direction.

https://www.sesoc.org.nz/forum/technical-issues/interpretation-of-accidental-eccentricity-to-nzs1170-5#post-179