14 | REGIONAL DEVELOPMENT PSA House: Maycroft Construction PSA House: Maycroft Construction The building as it will look when Stage 2 is complete. T T Lindy Andrews The combined cost of the Canterbury earthquake sequence of 2010-2011 and the 2016 Kaikoura earthquake to private insurers and the Natural Hazards Commission Toka Tu Ake was more than $31 billion. Total economic losses are estimated more than $40 billion. The two events – which tragically claimed 187 lives between them – have cast the spotlight on the seismic safety of thousands of commercial buildings, including Wellington’s PSA House. For Project Lead, Brett Denham, the seismic strengthening of PSA House is first and foremost centred around Health and Safety considerations for the organisation’s 125 staff and the building’s commercial tenants. “We moved out a year ago and the work is scheduled to be finished next year,” says Brett, who estimates the completed project will cost in the order of $20 million. Brett’s role involves close collaboration with John MacDonald, of McKenzie Higham Architects, and Maycroft Construction. Key to the future safety of PSA House is a new external reinforced concrete shear wall, and a latticework of internal steel beams beneath each floor to prevent the building’s lightweight hollow core concrete floor panels dropping to the floors below in an earthquake. The steel bracing also redistributes the weight of PSA House to the new and three existing shear walls, which act to resist lateral forces – or swaying – during a seismic event, John explained. Engineering and architecture are inextricably entwined in the project. “We first got involved after Clendon Burns and Park - the engineers – had completed preliminary. They encouraged us to get involved because there is a significant architectural component to any earthquake engineering, when you have to strip away a building’s layers and put it back together again. “There are a lot of physical and practical elements to deal with.” Among the many considerations taken into account for the classic 1970s six storey, seven level building were fire and accessibility upgrades, durability, weathertightness and its unequal shear strength distribution. With the enactment of the Building (Earthquake-prone Buildings) Amendment Act 2016 an initial full steel exoskeleton design was set aside, although its construction would have allowed tenants and PSA staff to remain working in the building. “With the 2017 Codes, it became harder to work out how to do it while the building was occupied,” John remembers. “With the floors being pre-cast panels, there was a risk the frame would flex, and the panels wouldn’t follow. They could become loose at one end and just drop out or break up. A further problem is that the floors have to act as a diaphragm to distribute the weight to the shear walls.” The solution avoided the installation of massive brackets around the internal periphery of PSA House, by substituting a latticework of steel underfloor bracing connecting to the existing concrete frame and ultimately the shear walls, managing the effects of both lateral forces and torsion (twisting) caused by seismic activity. Extensive strengthening work in the basement included a leviathan steel reinforced concrete beam with ground anchors at each end. The exposed concrete shear walls offered benefits from both an engineering and aesthetic perspective, as well as environmental benefits. “They have a lower carbon imprint than a steel exoskeleton, and suit the building better,” John says. The seismic strengthening project provided an opportunity to instal a new roof and hightech electrical infrastructure. “Because the work is so extensive PSA House will have all new fire, electrical, data and HVAC systems,” says Brett, who also sits on the PSA leadership team. Also, the scissor stairs will be separated from the building to allow them to move independently, as well as the reconstruction of fire separation walls. Retaining Walls - Concrete | Timber | Steel | Reinforced Anchor Systems - Seismic | Pre grouted | Post grouted | Self-drilling Piling - Bored | Driven | Micro piles | Grouted columns Concrete Works | Spray | Boxed | Steel works Phone (04) 383 5050 | Mobile (027) 44 33 625 roan@keenekrib.co.nz | www.keenekrib.co.nz RAISING THE BAR HIGHER +64 27 386 0630 www.matikasreinforcinglimited.co.nz • REINFORCING STEEL • STEEL TYING • PLACING REBAR • MESH PROUDLY PSA HOUSE SUPPORTING
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