How do you strengthen a very large building, whilst maintaining safety, confidence and full occupancy?
New Zealand is an extreme seismic region—the seismic hazard in Wellington is comparable to San Francisco. The Majestic Centre building was assessed in 2011 and demonstrated lower than expected seismic capacity. Over the course of five years, costing NZ $83.5M , it was strengthened to 100% of code requirements, while remaining fully tenanted. The project demanded highly complex and innovative analyses, and the design and construction of a wide array of detailed strengthening measures. Our assessment used non-linear time history analysis (NLTHA) and was performance based, in accordance with ‘ASCE-41 (American Society of Civil Engineers, USA), Seismic Rehabilitation of Existing Buildings’.
Choosing a sustainable solution
Holmes Consulting were the lead Structural Engineers and Holmes Farsight led the compliance. Originally completed in 1991, the Majestic Centre is a 30 storey (116m) modern tower, providing 25,000 square meters of office space. When the seismic capacity was assessed as between 35-45% of current code requirements in 2011, the building’s value reduced from NZ $101M to NZ $67M.
Demolition was considered, with the Demo/re-build cost estimated at NZ $120M. Instead, it was elected to strengthen the building to 100% current code requirements, while maintaining tenant occupancy. This was the most sustainable solution. Significantly less energy and new materials were used in the strengthening scheme compared to what would have been required for demolition and redevelopment, not to mention less waste generated. The project also prevented the relocation of 2,700 people and loss of business/activity in this part of the city. If a large seismic event does occur, the project will also have likely prevented catastrophic failure of the structure, the associated loss of life and long term impediment to the function of this part of Wellington
The strengthening cost was NZ $83.5M, but NZ $41M was earned in rent during construction and upon completion of strengthening the building’s value increased to NZ $121M. Tangible value for the client.
The Holmes strengthening scheme design made this solution possible and was recognised by being awarded runner-up in the sustainability category of the 2017 Institution of Structural Engineers awards (the global Oscars of Engineering). Designing to minimise loss of occupied space and allow strengthening to be installed while the building remained occupied made this an economic choice for the owner as well as a sustainable one.
Some of the challenges
- The challenge was how to carry out significant invasive seismic work, ensuring stakeholder’s continued confidence, whilst taking the lead in a new era of uncharted regulatory compliance issues.
- From early engagement Holmes Farsight acted as the coordinator, guide and translator between the project team and the Council.
- The solution required the parties to be focussed on ‘the real compliance risks and needs’, so a clear evaluation of all parties needs and concerns was established and agreed with Wellington City Council.
- Holmes Farsight provided a project specific ‘smart regulating’ solution. ‘The ‘Compliance Pathway’. It achieved a comprehensive and clear compliance process, which is both cost effective and efficient.
- It now creates precedence nationally for successful seismic improvements.