// Client -
Tony and Vanessa Merritt
// Location -
// Size -
// Services -
// Fire Engineering // Geotechnical Engineering // Project Management // Structural Engineering
// Project value -
// Status -
Young Hunter House (YHH) is a 3-storey, 1,900m2 office building in central Christchurch. A finalist in the 2015 INNOVATE Awards, it was designed to have easily repairable damage at code level seismic events, but capable of withstanding drifts associated with a 1 in 2500 year seismic event. YHH is self centring and dissipates energy. It is the application of these principles through post tensioned LVL beams and columns that makes this building an example of world best practice. Damage is concentrated to replaceable ductile links.
It was the first internally post-tensioned structural timber multi-storey building in New Zealand. It utilises PRESSS technology (PREcast Structural Seismic System) and applies it to laminated veneer lumber (LVL) columns and beams. The building system was chosen to satisfy the client’s passion for a safe, low damage and easily repairable structure, while using timber as an architectural feature.
Young Hunter House represents the first full commercialisation of a structural system researched and developed by the Structural Timber Innovation Company (STIC). The STIC consortia included Government, private New Zealand companies and University schools of engineering in both Auckland and Christchurch. The building was designed and built while the post-tensioned timber design guidelines were still being developed under the auspices of the University of Canterbury and the Structural Timber Innovation Company consortia.
Our team used both force based and displacement based design technologies and specific emphasis was attached to making the new technology cost effective and commercially viable. The post-tensioned timber concept (Pres-Lam) technology had been developed and extensively tested (beam column, wall / column – foundation, 3D frame and wall structure) in the structural laboratories of the University of Canterbury School of Engineering (Newcombe et al, 2010) (Palermo et al, 2005).
“This is one of the safest new technology buildings in Christchurch. If built again I wouldn’t change a thing.” – Tony Merritt, Property Developer and Building Owner
A New Zealand First
YHH applies innovative new engineering principles that were originally designed for concrete to NZ manufactured Laminated Veneer Lumber. Consent was gained and construction commenced late 2012, immediately outside the red zone, despite the uncertain and frequently changing regulatory landscape.
The structural engineering of YHH necessitated engineering vision and an investment of time and resource at a time when conservatism and risk aversion was the order of the day. As a landmark building for the Canterbury Rebuild, YHH also highlighted the value of engineering excellence across such criteria as; cost efficiency – due to its rapid erection and lighter weight than comparable buildings, sustainability in terms of a locally sourced and manufactured building material with known fire-resistant properties and building aesthetics derived from exposing the building frame due to the highly visual and tactile use of LVL.
“As a product it has a feeling of warmth and permanence… It is frequently showcased by the University of Canterbury, School of Engineering to visiting groups.” – Tony Merritt
Post-tensioning technology initially overcame the challenge of connecting large concrete structural elements. Its adaption and application to relatively new laminated veneer lumber provided advantages by reducing construction time (concrete curing time avoided) and reducing construction cost (a consequence of faster erection and the lighter weight).
The beam-column connection is designed as a rocking mechanism, allowing gap opening at the beam column interface. The post tensioned steel tendons within the beam are rather like a large elastic band – they elongate as the frame moves and the joint opens up. As the post-tensioned strands stretch they work to pull the frame back together removing all residual displacement in the building.
At the out tension and compression zones, externally mounted mild steel energy dissipaters are installed. These have been designed to hit first yield at a 1 in 500 year seismic event. Control of the stiffness and displacement of the frames is achieved by opening and closing the joint interface enabling the structural elements to be protected from damage.
Kirk Roberts designed multiple iterations of the joint connections, targeting economy in design, ease of construction, and architectural expression. One of the key challenges posed by the LVL over concrete is its low compressive strength perpendicular to the grain and its lower stiffness. Being more flexible than timber, the beams can deform more in the elastic range than concrete , meaning larger drifts are required before gap opening can occur.
The gap opening was targeted through stiffening up the beams by making it composite with the concrete slab, although a zone around the columns was allowed to remain non-composite. The columns were protected by steel plates to protect the member from the high perpendicular compression resulting from the moment at the beam face.
Continuing with the timber theme, the flooring system on levels one and two was timber-composite concrete. This consisted of LVL joists (every other joist doubled for fire), with plywood infill and a concrete topping.