Advances in Design for Improved Seismic Performance
New Zealand Low Damage Seismic Design Guidance
By Stuart Oliver (SESOC President) and Kelly Cobeen (SEAOC)
Guidance documents for Low Damage Seismic Design (LDSD) have been published in New Zealand. A key goal of LDSD is to deliver buildings that are less likely to be damaged and thereby limit disruption and losses in future earthquakes. The adoption of LDSD on projects is non-mandatory. The guidance documents were developed in response to the 2010-2011 Canterbury earthquake sequence and the 2016 Mw 7.8 Kaikoura earthquake. Both of these events caused significant damage to numerous modern buildings, with many of these eventually being demolished as a result. In light of such events industry has recognised that a life safety focus is insufficient to meet community expectations about the likely performance of buildings in earthquakes.
LDSD emphasises thoughtful early decisions in design, including site selection and structural regularity. Stiff, regular buildings on good ground have been shown to perform well in earthquakes when secondary and non-structural elements are adequately restrained (e.g. partition walls and ceiling systems). In many cases it will not be necessary to include novel anti-seismic devices into structural systems (i.e. seismic isolators or supplemental dampers) to achieve LDSD performance goals. LDSD performance goals can often be achieved using conventional structural systems, applied in a thoughtful way, in regular, well-coordinated buildings. An exception to this is buildings located in areas of very high seismicity when very high levels of seismic performance are being sought. For such buildings novel anti-seismic devices may be required.
The LDSD guidelines provide for both prescriptive and performance-based verification pathways to demonstrate a building meets specified LDSD performance goals. It is envisaged the simpler Prescriptive Design Method will be applicable to most buildings. For design teams using this pathway, the LDSD design process is similar to the current design process in the New Zealand Building Code system, albeit there is an increased requirement for design collaboration and reporting. Provided the prescribed design parameters and/or methods are used, then the Prescriptive Design Method is deemed to satisfy the LDSD provisions.
The performance based Direct Design Method is used for building systems or components that don’t meet the requirements of Prescriptive Design Method pathway. It is for those building systems or components that are considered innovative, new or alternative solutions via the New Zealand Building Code system. Demonstrating compliance using this method requires design team to follow recognised analytical methods, or experimental testing in accordance with recognised standard testing procedures, to validate the performance of potentially affected building systems or components will not compromise specified LDSD performance goals.
All three LDSD volumes are available on the design.resilience.nz website.
United States Functional Recovery Design Guidance
In a parallel effort in the United States, a first-generation version of functional recovery (FR) design guidance is nearing completion. To develop these requirements, a Functional Recovery Task Committee (FRTC) under the Provisions Update Committee (PUC) of the Building Seismic Safety Council (BSSC) was formed in late 2022. The PUC FRTC’s overarching goals included reducing vulnerability, minimizing losses, improving access to essential services, avoiding significant population displacement, and, ultimately, improving recovery time of new buildings and nonbuilding structures. Over the course of approximately three years, the PUC FRTC developed first-generation seismic functional recovery code provisions, and related commentary, which achieve quantitative targets for a new performance objective of functional recovery. These provisions and commentary were developed as a proposed non-mandatory appendix for inclusion in the 2026 NEHRP Recommended Seismic Provisions for New Buildings and Other Structures. The provisions and commentary were developed, debated, balloted, and revised by the FRTC and the PUC through a deliberate process and forwarded to the ASCE 7-28 Seismic Subcommittee (SSC) for consideration as a proposed non-mandatory appendix for inclusion in the ASCE 7-28 standard Minimum Design Loads and Associated Criteria for Buildings and Other Structures.
The functional recovery provisions are written as a stand-alone appendix but one that shares many aspects of current code-based seismic design. It is intended that new building design that implements FR will follow a standard seismic design process in accordance with the adopted building code and ASCE 7, and then an additional design using the appendix. Both a prescriptive and a performance procedure are included; conventional as well as innovative structural systems (e.g., seismic isolation) are supported by the appendix.
Important aspects of the functional recovery provisions include the assignment of buildings and structures to Functional Recovery Categories ranging from A through E based on the service the structure provides to the community. Rather than relying on past categorization of buildings, significant studies were conducted by subject-matter experts regarding the role that different services play in recovery following earthquakes and similar events.
A primary design measure used to achieve increased FR performance is design for reduced deflection and drift. Drawing on several decades of development of performance-based seismic design procedures and tools developed to evaluate performance-based design outcomes, as well as new FR specific studies, seismic design parameters for many common seismic force-resisting systems have been developed for FR performance. Both a prescriptive and a performance procedure are included; conventional as well as innovative structural systems (e.g., seismic isolation) are supported by the appendix.
Another key measure used to help ensure intended performance is a very extensive set of quality assurance provisions. This recognizes that improved performance can only be realized if construction implements the intended designs. Added measures include establishment of a Functional Recovery Coordinator, conduct of functional recovery meetings and walkthroughs, and more extensive special inspection requirements, among others.
At time of writing, versions of the functional recovery provisions are anticipated to be published in the 2026 NEHRP Provisions and ASCE 7-28. Thank you to Ryan Kersting and Reid Zimmerman for their leadership in the FR effort and review of this article.