Michael is an architect, working in New Zealand, where buildings can be subject to sudden earthquakes. How do you create structures that will withstand abrupt lateral and vertical movements? And how do you strengthen existing buildings to preserve life in the event of a big quake? What about the School’s building? Read on to understand more about these challenges; this is necessarily quite a technical article. Michael is a senior student in Wellington, shown here in front of the School building in Wellington.
Designing for Earthquakes
Michael Davis, Wellington
New Zealand is located on what is known as the Pacific Ring of Fire – a string of volcanoes and areas of earthquake activity around the edges of that ocean caused by the junction of two tectonic plates. This has produced some dramatic scenery like our Southern Alps, but also active volcanoes and geothermal areas. In addition there are thousands of earthquakes every year in New Zealand, of which an average of 250 are felt in some part of the country.
When is the big earthquake?
Despite growing up in Wellington I’m still uncomfortable when there’s a detectable earthquake, asking myself: ‘Will this be the big one?’ Some quakes are short and sharp; others are gentle with prolonged swaying. Often preceded by a low rumbling as they approach, they usually go sideways but sometimes up and down. Although I’ve not experienced it, they can be large enough to knock you off your feet. Their power can cause major structural damage, landslides, liquefaction where shaken water causes the loss of soil strength, or even cause tsunamis.
Wellington – HQ for earthquakes!
Wellington is something of the earthquake headquarters of New Zealand because it is located over a number of fault lines. Some are in evidence as large visible steps in the ground while others are yet to be discovered. Seismologists and geotechnical engineers have worked hard to assess the hazards and forces our buildings will be subject to for timescales up to 2500 years. The longer the period, the greater the likelihood of a large event. In Wellington, this could easily shift the ground a metre or more, in less than a second.
Training as an architect I learned the basics of good seismic design and various techniques to achieve it. But I must acknowledge that structural engineers have the detailed understanding. Whilst working in the UK for a time, it was shock to see how slender the structural members were in buildings. Typically UK buildings only have to deal with the loads imposed by gravity and strong winds. The lateral forces that we have to consider in Wellington can be as high as 1g or more – in other words – applying the force of gravity sideways on the building.
How do houses perform in earthquakes?
Much of New Zealand’s housing stock consists of lightweight timber framed houses. They perform quite well in earthquakes by swaying from side to side and in the process absorbing the imposed forces. For small earthquakes, damage is usually nil or limited to some cracked plaster. A vase or ornament might be slid sideways or knocked over. A slightly larger earthquake might knock over shelving or a TV. Encouraged by a government campaign a few years ago, many households make sure their ornaments are adhesive-fixed to the shelves. The shelves themselves are screw-fixed back to the walls. Larger earthquakes can topple an unreinforced brick chimney, dislodge a brick cladding, or push a house off its foundations . The worst situation for houses is when they are impacted by a major landslip caused by the quake.
Lessons from the Christchurch earthquake
The approach to designing buildings (large and small) to withstand earthquakes in New Zealand has always been focused on life safety. Our building code sets out requirements to ensure that a building remains standing in a large event and that people can exit the building safely. This was well demonstrated in an earthquake centred on Christchurch city in 2011. This was part of a series of earthquakes in the Canterbury region, leading to the loss of 185 lives – 115 of which were due to the unexpected collapse of a single 1980s building.
Many modern buildings remained standing but with irreparable damage. Their demolition imposed significant cost but we learnt valuable lessons about how the design of ceilings, services and exit stairs had impacted on the egress paths of those trying to leave these buildings.
Engineers from around the world visited Christchurch to see first-hand how buildings performed. The sharing of seismic knowledge continues, within both academia and engineering practices across the globe.
What can we do to mitigate the effects of earthquakes?
I have worked on several projects that demonstrate a range of approaches to earthquake-resistant design. These range from simple approaches involving cross-bracing and stiff concrete shear walls to more sophisticated technologies.
In 2010 I worked on a project which included the strengthening of an 18-storey 1960s building. Massive shock absorbers called viscous dampers were added to dampen the impact of an earthquake. This is similar to the function of shock absorbers on a motor vehicle.
More recently I led a project for a major addition to New Zealand’s first ‘base isolated’ building. Base isolators are a technology developed in New Zealand whereby the building is placed on top of a series of rubber bearings (isolators) which incorporate a core of lead. When the ground moves, the lead absorbs the energy and turns to liquid while the rubber moves from side to side isolating the building from the earthquake’s movement. The building consequently moves a lot less than it might otherwise have done.
What is the situation for School’s building?
The Wellington School of Philosophy is based in Philosophy House in an area known as the Aro Valley. Originally built for the Salvation Army in 1913-14, the School bought this magnificent building in 1982. In 2011 it was identified as being ‘earthquake prone’ by the City Council and is required to display a ‘yellow sticker’. This identifies the building as meeting less than 34% of the New Building Standard (NBS). Therefore it must be strengthened (or demolished) within a certain timeframe.
In 2016, we commissioned a structural engineer to carry out a detailed seismic assessment to better understand the building’s seismic performance. Then the School embarked on a programme to strengthen the building to 67% of NBS.
While the land has good ground conditions, the unreinforced brickwork of the building could perform poorly in a large earthquake. Technologies like base isolators could be adopted but the costs to retrofit these would be extremely high. So the approach has been to remove, strengthen or restrain the existing brick walls, and to create what is called a structural diaphragm in the roof.
Strengthening of brick walls against earthquakes
One way to restrain an unreinforced brickwork wall to prevent it toppling over in an earthquake is to build a new steel or timber framed wall next to it. Then we tie that to the bricks as shown in the photograph. The steel members are then covered up with lightweight timber framing and plasterboard. The skirtings and cornices are then reinstated so the strengthening is reasonably discreet.
Preventing the brick parapets from toppling is particularly important for main building exits. The photograph shows how steel members are used to restrain the parapet that sits above the front door.
Creating a diaphragm at roof level
Imagine that you have a cardboard box in the shape of a cube with an open top. Without a top, the sides of the box can be moved around quite easily when you push on them. It’s the same for a building when it is subjected to the sideways forces of an earthquake. If you tape a lid on the box, made from stiff card and cut to the same size, the box becomes strong and not easily distorted. That piece of stiff cardboard is known as a structural diaphragm – something that is strong in its own plane.
In the case of Philosophy House the diaphragm is concealed in the roof space. It’s made of braced steel members. These members are attached to the perimeter and some interior walls to stiffen up the building. They make it resist the horizontal forces of an earthquake much better.
How has practical philosophy influenced your work?
The teaching of the School of Philosophy has helped in many ways, but three main areas stand out.
Calmness – people I work with often comment on my calmness in stressful circumstances. This can range from difficult team dynamics to unexpected changes or cancellations to projects. I think meditation is a key reason for this calmness.
Patience – I am currently leading a project that commenced in 2015 and won’t be completed until late 2027. I maintain my enthusiasm and passion for this large, complex and protracted project by bringing to mind some of the teachings about work – in particular that the work is more important than my thoughts about it.
Problem solving through questioning – I often use a dialectic approach to seek out the ‘truth’ of a situation. This can range from trying to get a deeper understanding of a user’s requirements for a project, to working with a consultant to come up with ideas to solve a technical issue.
And finally,
Architecture is an extraordinarily satisfying career. There are always so many challenges and no two projects are ever remotely the same, so I never tire of the problem solving element. It is also a great expression of the values and technologies of the time of construction. Ultimately though it is about the way that the built environment can support and enrich people’s day-to-day lives.
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