Christchurch Arts Centre, with Owain Scullion of Holmes Consulting

In memoriam

As with earlier posts about Christchurch, the post following is written with  respect and sympathy for the victims of the quake sequence and for their families. As students who want to work with heritage buildings, we can learn from Christchurch and be part of doing better. Ka mate te kāinga tahi, ka ora te kāinga rua. HT

Christchurch Arts Centre, tower restored by stonemasons.

What I did on my holidays

With exams out of the way, I was delighted to be offered the opportunity to go down to Christchurch and have a look at the reconstruction and strengthening work taking place at the Christchurch Arts Centre. The Arts Centre is a cluster of historic buildings, the majority of which made up the original campus of the University of Canterbury. It’s a closely-spaced collection of good-sized masonry structures, dating from the second half of the 19th century and the early years of the 20th: more or less the exact kind of buildings that copped a fair hiding in the Canterbury earthquake sequence. A ~$300 million, multi-year programme is restoring and strengthening the buildings in the complex.

Christchurch Arts Centre, Girls’ High entrance. A Corinthian column is cased for protection during the building works.

I had the great pleasure of going through the site with Owain Scullion of Holmes Consulting. Owain patiently explained the strengthening programme to me, and showed me the current state of the works. What I thought I’d do, for the audience of this blog (who are mostly clustered up here on Pig Island) is talk about a few of the technical details that I was able to see, and try to give an impression of how the work is proceeding. I can hardly claim to be comprehensive, but I’d like to give a snapshot of what I saw. There’s a site map here to see where the buildings are as I refer to them; scroll down a bit on the linked page to find it.

Christchurch Arts Centre, Chemistry building. Horizontal and vertical stainless steel cables are connected to the structure through junction boxes, enhancing the compression in the wall caused by gravity loads to ensure that the wall stays in overall compression during shaking.

A stitch in time

Buildings at the Arts Centre had been strengthened before the quakes began. (Holmes’ involvement with the Arts Centre stretches back well before the 2010 quake.[update]) Regular attendees of Heritage Now events may remember Peter Boardman talking about his involvement with applying post-tensioning to the Chemistry building at the Arts Centre, which happened in the 1980s. As Peter told us, there was controversy over the appearance of the post-tensioning, which takes the form of a visible network of cables wrapped around the building. But what is undeniable is that the system largely preserved the Chemistry block during the quakes, despite the collapse of the building’s (unstrengthened) tower. As a measure of the post-tensioning system’s success, it has been renewed and reinstated, this time using stainless steel cables. (For more about how the post-tensioning cable system performed, you might like to read Dmytro Dizhur (et al)’s paper from 2013, which also talks about the post-tensioning of College Hall at the Arts Centre. TL;DR: it worked bloody well, and had some fringe benefits like increased out-of-plane capacity that weren’t predicted by the retrofit designers.)

Christchurch Arts Centre, Chemistry building. The post-tensioning terminates at steel plates. Note the cable entering the structure on the right to travel along the inside face of the wall. The stone buttresses to which the plate is attached were the original design mechanism to resist out-of-place forces in the gable end walls, but unfortunately their capacity to do so is insufficient.
Christchurch Arts Centre, Girls’ High, pre-quake tension brace retrofit, attaching to gable end. Note valley beam at springing of arches.

Not all of the pre-quake work was suitable for unmodified reinstatement. However, I did see examples of earlier retrofits being integrated into the new strengthening systems. For example, in the Girls’ High building, a system of tension braces had been installed to restrain the gable end and to transfer loads towards the core of the building. In the 2010-11 quakes, the loads were transferred pretty successfully, but in doing so, the valley beam at the base of the tension braces pushed on an internal wall, moving it by 50mm. This internal wall is now being beefed up and stiffened to drag loads out of several surrounding rooms.

Christchurch Arts Centre, Girls’ High. A brick internal wall is being strengthened to collate loads from adjoining rooms.

As an aside, Owain mentioned that a fringe benefit of working on these unique structures is that you get to see examples of fine nineteenth-century crafting. In the Girls’ High building, tusk tenons connect the floor joists to the beams, a detail that points to the relative cost of fasteners vs. workmen’s time in the early days of the NZ construction industry!

Christchurch Arts Centre, Girls’ High. A profusion of materials require strengths to be assumed or determined: timber sarking; bricks and mortar; timber beams; steel tension braces (upper left), plus masonry walls (not shown).

The right ANSR?

Owain explained that it has been important for Holmes to test the properties of the materials at the site—particularly for critical structural elements. For example, the internal wall mentioned above that’s aggregating loads has been subjected to pull-out testing to determine the cohesion value of its mortar, in a process analogous to the bed joint shear tests I’ve written about on this blog. The testing allows the engineers to close the loop on their modelling.  Having made assumptions about the material properties of the elements, the engineers model the structures in a software package called ANSR. Using data recorded in the last few decades of earthquakes around the globe, the engineers subject the model to a succession of simulated earthquakes. This modelling identifies structural hot-spots that need to be addressed. Materials testing allows the team to to be satisfied that their underlying assumptions are valid and that they can therefore trust the results of the modelling.

Christchurch Arts Centre, Girls’ High. First floor interior, showing lower edge of timber ceiling trusses with hammerbeam-style half-arches. Hidden structural steelwork supports the gable end.

Variations on a theme

For an all-too-brief moment, I got to put my steelies on and go up the scaffolding, even if I did have to wear the hard-hat-of-shame marked Visitor. At the top of the walls of block DA, aka Girls’ High, below a steeply-pitched roof, some supplementary structural steel has been inserted. The frames support the gable end, and diagonal braces lead down to a PFC that runs along the top of the wall. (Jargon alert! PFC = “parallel flange channel”, eg a C-shaped section.)

Christchurch Arts Centre, Girls’ High. Taken from the scaffold outside the room in previous picture. Note the PFC running along the top of the wall, and at left the diagonal brace heading towards the gable end. The thicker timber beams at the left are the upper chord of the trusses shown in the previous picture.

At the time I visited, the workers were setting up to drill some three-metre holes horizontally down through the wall. My first thought was that what I was looking at was similar to what’s being done at the University of Auckland’s ClockTower Annexe, where a series of drilled holes accommodate rods that are putting the entire wall into compression. I was wrong. In fact, here the drilling was to allow for Macalloy bars to be inserted, which will hold down the PFC securely and hence restrain the gable end against excessive rocking. The three metre length of the drill holes won’t get them to ground level—it’s just to allow the Macalloy bars enough space to develop good friction. Plenty of length is needed, because the drillholes tend to be smooth, meaning that the grout or epoxy that holds the bars in place doesn’t get a very strong bond to the walls of the hole.

Christchurch Arts Centre, Girls’ High. In a ground-floor room, a concrete core has been created and attached to the existing masonry. This necessitates building up and moulding window reveals. Dowels secure the concrete core to the masonry.

In another part of the building, however, there was a remediation technique being used that’s closer to what’s happening at the ClockTower. (Incidentally, although the ClockTower is about 50 years younger than the Girls’ High building, the coursing of the masonry is similar.) A ground floor space is being converted into a movie theatre, and shotcrete has been used to create a concrete core inside the masonry. This concrete core is connected to the exterior material by a closely-space system of dowels, similar to the Helifix screws that are being used at the ClockTower. (At the ClockTower the concrete core was part of the original design.)

Christchurch Arts Centre, Great Hall

The great Great Hall

One of the best things about the site visits we’ve done is getting to see some of the unique and remarkable interiors of heritage buildings. (St Matthew-in-the-City is a standout example for me.) While I’m sure that College Hall aka the Great Hall at the Arts Centre is well known to many people, it was a complete (and stunning) surprise to me. It’s an incredible interior: ornate, stately, and imposing. My first reaction was that I’d never seen anything like it in New Zealand; but then, as I looked more closely, I realised that it reminded me a little of St Paul’s Church on Symonds St which we visited earlier this year.

Christchurch Arts Centre, Great Hall. Successive layers of materials. The piers contain concrete cantilevers and post-tensioning systems.

There’s a roundabout connection to be made between the two buildings, in that Benjamin Mountfort, who designed the Great Hall, also worked on  ChristChurch Cathedral, to which St Paul’s Church has been compared by Heritage NZ. That part I’ll confess I looked up: what spoke to me immediately, though, was the palette of materials and the hierarchy of how they were deployed. At the Great Hall, moving horizontally upwards, timber panelling gives way to fine red bricks, then to Oamaru stone, then timber hammer beams and a a patterned timber ceiling. St Paul’s follows a similar pattern of material proportions and transitions. Gothic Revival, innit? One day St Paul’s will look as stunning as the Great Hall does.

At the Great Hall, the strengthening has involved inserting concrete cantilever columns inside the piers of the long side walls, enhancing the in-plane and out-of-plane capacity of the walls. Post-tensioning was also re-installed and enhanced. I suspect that the much larger ground accelerations expected in Christchurch compared to Auckland meant that a rocking-pier model that EQ STRUC proposed for St Paul’s wouldn’t have worked for the Great Hall—and, of course, the site topography’s different.

(Here’s an interesting article on Newsroom about the work at the Great Hall and the UNESCO prize it won, including a few images.)

Christchurch Arts Centre, Engineering building. Note missing gable end, steel wire strapping, vertical cracks through masonry.

Next up

Once the Girls’ High work is complete, the works will move on to the eastern end of the Engineering building, where extensive damage is still visible. A gable end is missing; there are deep vertical cracks in the masonry; and, in the building’s tower, the Oamaru stone quoins and the basalt wall have parted company. Steel ropes lash the structure together for temporary support. When works begin, tall steel buttresses will be attached to the walls, allowing the connections between walls and diaphragms to be cut and reinstated without triggering a collapse. Stonemasons are working to recreate the lost finials and many other decorative elements of the building, using archival photographs as visual references.

Christchurch Arts Centre, Engineering building. Steel buttress frames await re-use in supporting the structure. Cut off at bottom centre is the poster for the Teece exhibition.

A colossal amount of work has been done to restore the Arts Centre complex. While planning for the Engineering Building restoration is doubtless far advanced, I’m sure that lessons learned from working on the other buildings will be carried into the final part of the project, and will go on to inform strengthening and repair of similar buildings.

ChristChurch Cathedral

Christchurch

Walking around the city, it was sad and sobering to see the two hulks of the great churches standing unrestored, the Cathedral and the Basilica. The first sadness is for the human tragedy, certainly, but then you feel the loss of the buildings and the stories they contained.

Inside the Chemistry building at the Arts Centre, I spent time at a small exhibition in the Teece Museum which contained artefacts from Greek and Roman burial sites. One way of reading the objects in this collection was suggested by the inclusion of a Piranesi engraving, emphasising the splendour of decay and Romanticism of ruin.

The Cathedral of the Blessed Sacrament, aka the Christchurch Basilica. Shipping containers as temporary supports are a not uncommon sight in the city.

Without a doubt the Cathedral and Basilica would fit the bill for the Piranesi treatment, and I do love Piranesi. But for me, the most affecting object in the Teece show was the tiny child’s sarcophagus, and the memorial plaques beside it. Death and loss seem overwhelming, all-consuming, and hope is lost. But what can survivors do in response except make beautiful objects, and offer dedications to the memory of those who (to quote the plaques) “well deserved” to be remembered? As hopeful humans, we keep piling up stones, making new, making good, even though we know that nothing we make can truly last forever.

I’ve just been reading Joseph Conrad’s Nostromo, and my thought above is expressed far better by him. “…for life to be large and full, it must contain the care of the past and of the future in every passing moment of the present. Our daily work must be done to the glory of the dead, and for the good of those who come after.” From afar, I’ve been unconvinced that it’s worth reconstructing the Cathedrals. But, faced with the sight of them, and seeing them on the same day as the Arts Centre, I’ve changed my mind. It’s worth trying to restore those churches, just as the Arts Centre has been restored. What else are poor hopeful humans to do? We’re fortunate, then, to have engineers, architects, historians, stonemasons—and many others—to shoulder the task.

Thanks!

With sincere thanks to John Hare, Owain Scullion, and Alistair Boyes of Holmes Consulting, for inviting me to visit the Arts Centre and for their generosity with their valuable time.

Update

back to article

John Hare checked in to provide some more background on Holmes’ involvement with the Arts Centre project.

“The strengthening being done now is now part of a much more comprehensive programme that was always intended, but is now being amalgamated into the repairs. That commences in 1978 or thereabouts, when the Arts Centre came into existence. The general approach was:

  • Stage 1 – secure the buildings to make them a good as they could be, ie tie in the floors and roofs and add a few elements to take out the worst of the structural weaknesses, and address the most critical life safety falling hazards – chimneys for example.
  • Stage 2 – protect as much as possible of the fragile heritage secondary structural and non-structural elements
  • Stage 3 – full seismic upgrading.

“In practice, money was always short so Stage 1 was done bit-by-bit with parts of stage 2 added in where practical. A big push in the late 90s saw most of the Stage 1 worked completed with outside help, but most of the work to that time was done by Jim Loper, the on-site Master of everything! And later in the piece, with Chris Whitty, now the Site and Restoration Manager.

“We did a few big studies, starting as far back as 1996, as I remember it, for the Stage 3, but other matters were judged more important, such as fire protection (which I supported at the time – fire would be hugely destructive there).

“As a consequence, only the Old Registry (HA) and the Old Girls High (DA) were strengthened to anything like what we now regard as a reasonable level (I think both were to 67% at the time, therefore around 50% against current code).

“The original post-tensioning (College Hall and Chemistry) was quite adventurous at the time! Done to a relatively low level and as such, prevented the worst of the damage, but needed significant upgrade for the current work.”

ClockTower East Wing, University of Auckland, with Neil Buller and Peter Boardman

UPDATE 15 October 2018: Tiago Almeida of Structure Design got in touch to let me know about a paper that the participants in the job had written and presented at the concrete conference. I highly recommend a read of it: it contains a good overview of the full scope of the works and has some great illustrations.

We’ve been doing these site visits for a while now. In March last year, a large group of site visitors heard Neil Buller of the U of A’s Property Services talk about planned works on the University ClockTower’s East Wing. Peter Boardman of Structure Design was along that day, too—he was there primarily to talk about the work he’d done on the Symonds St Houses. This week, we got the band back together, and went to see the progress at the ClockTower.

ClockTower, view from the site gate.

The ClockTower, the East Wing, the Annex(e), B119, B105, the Cloisters…

All the above are legitimate names for some part of the building you can see above. The East Wing was built as part of the original construction of the ClockTower, in 1923-26. The great Roy Lippincott was the architect—I’ve written about another Lippincott building, Nelson House, on this blog. The ClockTower, aka the Old Arts Building (there’s another name!) will likely need no introduction to the audience of these posts, but its East Wing is less iconic.

Originally built as student accommodation, the East Wing has served as offices, meeting rooms, and administrative space for much of the last few decades. It’s undergoing a major seismic upgrade, targeted at 67% NBS. The target is based on a 500-year return period earthquake, and the building is designated Importance Level 2. The interior has been modified considerably since the building was first constructed. At the moment it is fully stripped out, and it will be getting a contemporary refit. It’s also going back to being a teaching space.

Plans, proposed refit of ClockTower East Wing. Note the symmetrical plan of the East Wing itself. Extending at the top right are the cloisters which link the East Wing to the main ClockTower building. Image courtesy Neil Buller, drawn by Architectus, all rights reserved.
The drilling rig atop the stair tower, ClockTower East Wing. Image courtesy Neil Buller, all rights reserved.

Stronger, tougher, independent

The most arduous part of the work at the East Wing is to strengthen the walls. The building has a reinforced concrete inner shell, which is clad in an outer shell of masonry. The strengthening regime requires inserting long steel rods down the walls from top to bottom. The rods will be tensioned, squeezing the stones more tightly together.  In the horizontal direction, the masonry is being tied more firmly to the concrete. The ClockTower connects to its East Wing by a covered walkway, known as a cloister. In the cloister, rods have been inserted horizontally as well as vertically, binding the open-walled space together. A seismic joint has been cut mid-cloister, separating and de-coupling the ClockTower and the East Wing and giving each of them room to wobble about at their own rate if an earthquake strikes.

Capstones removed, top of the exterior wall, ClockTower East Wing. Picture taken in December ’17.
Capstones marked with Roman numerals to allow them to be correctly replaced. Roman numerals are used, says Neil, because they’re much easier to carve with a grinder–all straight lines!

Drilling the walls

At the roof level, the capstones have been carefully removed. At regular intervals, the drill has been worked down through the masonry parts of the wall to the foundations. As the drill is lowered, the workers add on extra length to the drill bit, carving holes down to the foundations as far as eleven metres below. If the drill jams—and sometimes it does!—in some cases a pilot hole needs to be drilled through from the inside to release the bit.

Once the hole is drilled, steel rods are inserted, then grouted into place. Grouting a wall can be tricky—unseen cavities and naturally porous materials can leave you pumping oceans of grout into a small hole. To prevent this, the hole is lined with a fabric “sock”, which deforms to fit snugly into the drilled void, but prevents the grout from branching out into the wide blue yonder.

Holes drilled down through masonry wall. Holes ~120mm diameter?
Photo taken in December ’17.

With the rods installed, a stainless steel plate connects the rod-tips together. They’re then mechanically tightened, binding the whole system into a whole. Post-tensioning works by putting the entire wall into compression. When the wall gets shoved by a quake, it wants to rock or overturn. The side that’s being shoved up gets put into tension. (To understand this, put your hands on your hips and bend sideways: you’ll feel your muscles getting stretched on the side you’re bending away from.) Stone, brick, concrete—these materials don’t like tension. They’re good at squashing, bad at stretching. By adding extra compression through the post-tensioning system, the walls get to stay in an overall compressive state, even when tensile stresses are created by rocking. The tensile stresses aren’t big enough (hopefully!) to overcome the pre-existing compression created by the post-tensioning.

Once the rods have been tightened, the capstones are drilled out to conceal the protruding rod tips and nuts. Then they’re mortared and dowelled back into place. It’s important to fix the capstones back tightly so that a shake doesn’t dislodge them. They are not something you’d want landing on your head.

Rod inserted into hole and grouted. Yellow cap is for worker safety. Note stainless steel plate connecting rods and generating compression in wall. Note shaped edge of capstone, to avoid water running into wall cavity (?) Picture taken Feb ’17. Roof of cloisters.
Stainless steel plates overlap. Tensioning rod through centre. Capstone will be hollowed out to cover bolt heads, etc. Feb ’17.

A bigger, sturdier foundation

So much for the walls, but what are the vertical rods going down into? They’re not going to help much unless they’re sturdily connected to the ground! Significant work is going into upgrading the foundations and increasing their capacity. The ground has been dug out on the outside of the building, and a new foundation strip poured against the existing one. In the interior, digging is in progress to create a second new foundation inside the existing wall. The new foundations, inner and outer, are interconnected at intervals. Soon, the base of the original wall will be sandwiched between two new foundations, with the vertical post-tensioning wall rods tied into this newer, larger foundation unit.

ClockTower, East Wing. New external foundations being prepared. Photo courtesy Neil Buller, all rights reserved.
Base of exterior wall, ClockTower East Wing. The timber is formwork for poured concrete foundation. This new concrete foundation abuts existing foundation. The dark layer of stone at the base of the wall is granite, creating a damp proof course through which water cannot travel up the walls. This was very hard to drill through! Picture Feb ’17.
Interior, ClockTower East Wing. Preparation for new internal foundation to be poured, abutting existing foundation. Note at corner in foreground, reinforcement coming through hole. This is where the new inner and new outer foundations connect.
Horizontal drilling, ClockTower cloisters. Photo courtesy Neil Buller, all rights reserved.

 Tie me up, tie me… across

In the cloisters, the drilling work has been carried out horizontally as well as vertically. Workers have drilled through the concrete vaulting of the arches, installing horizontal ties to bind the open-air structure together. The tie rods have been hidden with round pattress plates, designed to imitate the tie rod end plates that are pretty ubiquitous on older buildings. At the moment, they’re a bit shiny, but they’ll soon dull down and become essentially invisible.

Cloisters. New steel pattress plate spreads bearing load. At centre of plate, rod extends through cloister arch into wall of ClockTower. Photo courtesy Neil Buller, all rights reserved.
Cloisters. Steel bracket, used in location where drilling is not possible. Bracket styled after decorative newel post in main ClockTower building.

In one spot, drilling proved impractical, owing to the geometry of what was above. To increase the capacity of that area, a steel bracket was designed and inserted, taking up the work that the internal tie rods would have performed. In keeping with heritage principles, the bracket has been designed to be sympathetic to the character of the building, but not to pretend to be an original feature.

ClockTower, ground floor interior. Black dots on walls are the location of ResiTies, inserted to bond masonry outer wall to existing concrete inner wall.

(Not) losing face

To prevent the masonry and the concrete shell delaminating, they are being bonded together with a close-spaced grid of special ties. They’re called ResiTies, and they’re a stainless steel twist, which looks not dissimilar to a decent-sized drill bit. The system uses a resin to bond both ends of the tie, locking the masonry layer and the concrete layer together. Apparently they go in pretty easily, but it certainly seemed like a big job to install these throughout the building. The manufacturers reckon they’re good for holding together brick cavity walls, too. You can read about them here: the link goes to a commercial site but, just to be clear, I have no relationship of any kind with Helifix.

ResiTie inserted. Note epoxy blob holding stainless steel tie.
ClockTower, East Wing. First floor. Concrete floor slab, patches of drummy concrete removed. Photo courtesy Neil Buller, all rights reserved.

Augmenting the concrete

The internal floor of the building is concrete. As you will know, reader, internal floors can be pretty important when buildings are strengthened. They transfer forces between walls, and allow the structure to act as a box. Diaphragm improvement is one of the most common things we’ve seen on our tours—it’s often in the category of low-hanging fruit when it comes to improving a building’s NBS score. The East Wing is no exception.

Over the years, a certain amount of moisture has found its way into the building. This, combined with the fact that the concrete was made with unwashed beach sand, has led to some deterioration of the internal steel reinforcement. (You can tell that you’ve got unwashed sand when you find shells in your concrete, as they did at the East Wing—it’s a dead giveaway.)

On the ground floor, the undersides of some of the concrete beams have been carved away, the surface rust removed from the internal steel, and then they’ve been re-sealed. On the first floor, the team went over the floor slab with a hammer, inch by inch, whacking the concrete, listening for the ringing sound that means the concrete is drummy. That’s happened where steel has rusted and expanded, cracking the concrete, or where salts in the sand have caused adverse reactions, or both.

The drummy bits of the concrete floor slab have been raked out, leaving the floor surface more than a little Lunar. Neil pulled out a bit of the reinforcing mesh and snapped it. Not much capacity left there!The engineers have prudently decided to discount the existing reinforcement in the floor slab entirely. So, to reinforce the floor and help it do its lateral-load-transferring work, the plan is to use strips of fibre-reinforced polymer (FRP). The FRP strips will create a lattice which will resist both tension and compression. A thoughtful site visitor double-checked: FRPs? Compression? Yes, says Peter Boardman. The lattice pattern allows the FRP strips to act like a truss.

 

ClockTower, first floor. Drummy concrete removed from floor slab. Blue lines indicate proposed location of fibre reinforced polymer strips which. Lattice of strips creates truss which can resist tension and compression.

Speaking of trusses

ClockTower, East Wing. Timber ceiling battens. Timber trusses above.
Trusses, slightly better image. The trusses are mostly sound, with minor water damage in the area shown. Steel brackets will mitigate lost connection strength.

A brief note at the end, then, to say that the timber trusses that form the roof are in pretty good nick, bar a few rotten ends which are getting bypassed with steel brackets. The building’s going to be sealed and air-conditioned, and some of the plant is going up into the roof void, with the rest perching discreetly beside the cloisters. On the day we visited, the roof-level scaffold was going up, and soon the building will be wrapped to allow the concrete roof tiles to be replaced with more authentic clay ones. There’ll be the usual plywood ceiling diaphragm enhancement, too.

It’s good to be back, and thanks!

Having seen the building last year, it was great to get a chance to come back and see how the work is being done. As our ad-hoc society continues to mature, expect more “return to-” tours further down the line.

We’re sincerely and warmly grateful to Neil Buller for organising the site visit, to Peter Boardman for sharing his time and his knowledge, and to Todd and the Argon team for letting us come and get in the way of a tight timeframe. As University of Auckland students, it’s great to have the chance to use our own campus as a learning tool. We really appreciate your co-operation. Thanks also to Phillip Hartley of Salmond Reed Architects for taking me on-site at the East Wing over the summer.

 

 

University of Auckland heritage buildings with Neil Buller and Peter Boardman, March 2017

Yesterday a large group defied the weather forecast and enjoyed a tour of several of the University’s heritage buildings.

Neil Buller, architect and project manager for the UoA, battles a sore throat and traffic noise, talking to the crowd about 10 Grafton Road.
Neil Buller, architect and project manager for the UoA, battles a sore throat and traffic noise, talking to the crowd about 10 Grafton Road.

For me, the recurring theme of the afternoon was the University’s special nature as a client. It’s unusual to have a client whose heritage properties span such a range of ages, styles, and typologies. The University’s buildings mostly have high levels of occupancy and usage, making it more critical that they be demonstrably safe and sound. And the University also has a kaitiakitanga role and a concern for preserving its history. For all these reasons and more, the University seems to take a more scrupulous position about how much retrofit it is prepared to do. The projects we saw were targeting 100% of the New Building Standard (NBS), which is a higher target than many clients choose to set.

It’s also a target that necessitates more physical intervention. Some of the conversation on the tour turned around questions of the practice of making these interventions visible, of leaving good records of work done, of reversibility, and of the suitability or otherwise of certain building technologies for heritage sites. Sometimes repairs can bring problems with them, if, for example, they bring moisture where it’s not wanted. We also heard a familiar story about working on heritage buildings–starting to fix one problem leads to finding several more!
Neil describes the proposed post-tensioning system for the Clock Tower Annexe, where work is due to start in October 2017.
Neil describes the proposed post-tensioning system for the Clock Tower Annexe, where work is due to start in October 2017.
I enjoyed the opportunity to hear and see some details about the specific problems heritage buildings experience, and how these are addressed. At Bayreuth (the 1903 Italianate building at 10 Grafton Road), tie rods have been inserted both parallel and perpendicular to the floor joists, binding the structure together. The brick and concrete Merchant Houses Belgrave, Okareta and Mona (12-16 Symonds St), dating from the 1880s, were suffering from water intrusion, and required structural improvement. The basement slab was relaid, with a ventilation system designed to improve airflow and remove moisture. Floors were taken up, the joists re-fixed to the walls, tongue-and-groove floorboards re-laid, plywood diaphragms used to stiffen the structure. Roof timbers were refreshed. All in all, a major refit, and one that necessitates tradeoffs between the future of the building as a whole and the integrity of its heritage fabric.
Crossing the road, we saw an elegant intervention at the General Library, where the services and stairwell were too stiff and inflexible in comparison to the abutting structure. In a decent shake, they’d likely knock the rest of the building to pieces. The solution proved to be “strengthening through de-strengthening”, in that vertical saw-cuts were used to weaken the walls, while the structural members of stairwell and library were tied together. There was an interesting conversation about the value of taking the time to allow designs to be re-thought. In this project, the initial design proposed masses of steel, strapping the disparate parts of the structure together. The final solution proved to be far more minimal, essentially a steel rod lashing elements together across the stairwell, forming a lattice. A conference panel on Alistair Cattanach of Dunning Thornton’s design for the library, with some photos, drawings, and some more information, can be found here.
After the tour, we moved inside to examine drawings and photographs. Above my not-so-hot picture of the design for the Library. Look up, next time you're on Alfred St!
After the tour, we moved inside to examine drawings and photographs. Above my not-so-hot picture of the design for the Library. Look up, next time you’re on Alfred St!
Lastly, we looked at the Annexe to the Clock Tower (aka the Old Arts Building), built in the 1920s. Peter Boardman, of Structure Design, who accompanied the tour, was responsible for the highly effective post-tensioning system on the Christchurch Arts Centre, which saved it from major damage. If you’re not familiar with the Christchurch project, imagine a netting of steel cables wound around the outside of a stone building and tightened! The Clock Tower Annexe is getting a more high-tech version of this treatment, where steel rods are being inserted through the major structural members of the building. The Annexe is made from concrete faced with stone, and the steel rods, once tightened, will add some very necessary tensile strength to the building.
I’ll finish by mentioning that in response to a question from the audience about the most important lessons from the Christchurch quakes, the presenters agreed that the biggest lesson was this: doing something is better than doing nothing. Buildings which had been strengthened, even those with ad hoc solutions, survived better than those which had not. Peter suggested, as an example, that shoring up verandahs at a cost of a few thousand is often a way to reduce stresses throughout the structure, and provide protection from falling decorative elements. The two presenters also reinforced the importance of communication and compromise between members of allied professions (like architecture and engineering), and I’m sure you will all concur with this sentiment. We’re very grateful to Neil Buller and Peter Boardman for their generosity, frankness, and expertise.