Tension-Only Braces Make for a Cost-Effective Seismic Retrofit

In this project, tension-only ReidBrace braces combined with Tectonus RSFJs provided for a cost-effective, low carbon and lightweight solution to surprisingly high seismic demands on this downtown Auckland office refurbishment.

Dealing with High Accelerations

48 Greys Ave is an existing 10-storey concrete office building in central Auckland undergoing a major refurbishment that will see the addition of a new 900 square meter upper level.

The development is targeted at high-end commercial clients, attracted to the central city location and sweeping views over Myers Park and Auckland Harbour.

Although the seismic risk at this site is relatively low, the addition of the new floor, 40 meters above ground, meant that it could experience some very high accelerations in a significant seismic event.

Recently the National Seismic Hazard Model was updated, increasing shaking hazard in Auckland up to 3 times. Although not a statutory requirement yet, the prospect of having a below-code building in the future is something any building owner would want to avoid.

Seismic Design Solution

Client Krukziener Properties engaged structural and seismic engineers TEKTON Consulting Engineers Ltd to come up with a cost-effective and comprehensive solution.

Proposing a lightweight steel frame structure, TEKTON Consulting Engineers wanted to avoid heavy steel bracing and unnecessary additional loads and inertia forces on the existing concrete structure below.

Searching the local and international market for an efficient solution led them to explore the combination of ReidBrace with Tectonus tension-only dampers.

This combination delivered sufficient damping at a high global ductility, removing the need for any additional members or strengthening to the existing structure.

In addition, the low damage design philosophy adopted by TEKTON Consulting Engineers, will cope very well with a seismic event, concentrating forces at the RSFJs which do not require repair or replacement even in the maximum design level earthquake (MCE).

Tension-Only Braces with High Seismic Capacity

ReidBrace is an off-the-shelf system that utilizes ReidBar, a continuously threaded reinforcing bar system, arranged as tension members. The system is lightweight and easy to install with minimum extra processes onsite. However, ReidBrace by itself could not provide the level of damping required.

To deal with the higher loads, Tectonus RSFJ was configured in tension-only format (the standard being tension and compression), sized at 100kN each. Each ReidBrace member had a RSFJ at the top and the bottom – requiring 32 RSFJ devices for the whole upper level.

Comprehensive Technical Support

Tectonus in-house engineering team provided support to TEKTON Consulting Engineers on the design concept and non linear time history analysis, as well as through peer review and consent.

‘’We found TECTONUS very knowledgeable and supportive throughout the process. These guys are easy to collaborate with, and they talk the same ‘’seismic expert’’ language with TEKTON’’ – Ioannis Prionas, CEO TEKTON Consulting Engineers.