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A proposal for the Triangle Centre site in central Christchuch:

This was sketched for a competition hosted by the NZSEE as an adjunct to their 2012 conference. The site chosen was that formerly occupied by the Triangle Centre on the block bounded by High Street, Colombo Street and Cashel Street. At the time I understood that the Triangle Centre site was to be cleared and that the art-deco buildings on High Street had been demolished, but the Hallensteins building was to remain. The block has now been entirely cleared.

The concept:

The complex consists of three buildings connected with glass atria. Each block is base isolated at first floor level, assembled from a kitset of precast concrete components stitched together with enough simply formed in-situ concrete to ensure durability and structural coherence. There is a relatively small number of different window, arch and pier modules, though this still gives plenty of texture. Extra variety is achieved in the timber attic floor and roofline. The building would be clad in local Port-Hills andesite trimmed in concrete coloured by the local greywacke aggregate, though red brick could be substituted for the stone. The building is in a sense a medieval market or guild hall, but it is also an arcade or mall with a mixed use apartment and office building above. Its richly ornamented gothic from and detail are a true expression of its very modern construction, systems and materiality, while its romantic turreted outline is a true and overt expression of its embodied energy efficient circulation and air handling systems.

presentation panel
The entire A1 size drawing (all in 2B 0.5mm mechanical pencil)

The site is a well known one in central Christchurch, with High Street and Cashel Street both being major pedestrian thoroughfares, and Colombo Street being the primary North-South axis through the middle of the city plan. The three main blocks surround a central courtyard with paving, grass and large deciduous trees, accessed through the atria and an arcade.  The buildings themselves are in effect open arcades at ground floor level, with only the circulation towers extending to the ground. Each stair tower is an entrance to the building, with an ornate concrete staircase lit by large windows winding around a timber and steel cage elevator. The arcade is subdivided by light weight partitions and of course large shop windows into a range of shops. None of these partitions is load-bearing and they can easily be reconfigured. The intention is that a couple of the smaller shops are let at a low subsidised rate to carefully chosen tenants who might not otherwise be able to afford the rent in such a complex, but nonetheless attract the right kind of customers to the building. These might include an antiquarian bookseller, a rather artsy and unconventional boutique, or a contemporary art gallery. Other courtyard spaces, arcade spaces and setbacks around the perimeter are let to carefully chosen stallholders. The centre of the courtyard might hold a restaurant pavilion.

The upper floors are simply loft space, naturally lit and ventilated, suitable for use as offices or apartments. Most likely they would be offices on the lower levels and apartments above. Again, some spaces might be let at a subsidised rate to creative organisations and people who might help attract other more lucrative tenants and their clients.
floor plans
Counterclockwise from top right: Site plan, ground floor plan, first floor plan.

The building has a high and open ground floor, and the stories above also have high ceilings. The exposed ceiling in each case is precast concrete double tees, with a timber framed raised floor above to fit the building services. The second and third stories are of concrete construction, with the attic stories framed in timber (though steel could be substituted). The top part of the building would probably be clad in sheet metal, though it could just as well be roofed in slate, terracotta or concrete tile.

The building is base isolated at first floor level, with the break line at about 2.7 metres above the floor (just above the tops of all the door-cases), this being the top of the column capitals. Between the top of each of the column capitals and the springing of the arches is a lead-rubber bearing or a friction-pendulum slider. The stair towers are also broken at this point, and the lift-rails would be suspended from above below this point. The break would continue through the relevant stair riser too, and all services crossing this point would need to be detailed to cope with perhaps 300mm of movement.  There would be a bearing at each corner of each stair tower at this point. All of the partitions and shop fronts would also break at the same level, with everything above that point fixed to the ceiling, and everything below fixed to the floor. A joint allowing for up to 300mm movement at this level is relatively simple to detail, and being under an arcade is not difficult to make weathertight.

The turrets atop the stair tower are a wind scoop intake to the air handling system, and a solar stack with a venturi cap acting as outlet. The stairwell would work as the outlet plenum, while the vertical services plenum behind the stairway acts as the intake plenum.

cross section
Note the base-isolation break line, continuing though the stair tower. The stair tower window faces the courtyard and so isn't seen here. The oriel window in the atrium visible in the background is intended to flex when the two blocks move independently of each other.

The three main elevations to the complex are of course composed for visual effect, but aside from the main tower don't really take any great liberties with function.

High Street elevation

Colombo Street elevation

Cashel Street elevation

The construction of the base of the building is shown in more detail in the larger section. As can be seen here the stubby columns that form the base of the building are cantilevered out from a massive ground beam. The ground beams form a substantial 'egg-crate' structure over the site of each block of the building, ensuring that the foundation system behaves as a coherent unit. This 'egg crate' rests on the pile caps of a deeper foundation below (the ground here is rather soft), here shown as bored piles though driven piles may be used instead. The ground beams are not fixed to the pile caps, and jacking points are included too, so if the foundation do settle it is a relatively simple matter to dig to the pile cap, jack the foundation level and shim and grout it in place.

detail section of base
The base of the structure, showing the base isolation bearings and also the foundation system

And here is the construction of the upper part of the building. Note that there is a combination of precast concrete, in-situ concrete and masonry cladding securely tied to the concrete wall structure behind. A concrete wall is a much stiffer structure than a frame, and as it will not deform significantly under load (especially in a base-isolated structure), it is well equipped to keep masonry cladding in place even under extreme seismic loads. Note the role of the precast concrete window frames.

detail section of top
The upper part of the structure, showing the layered construction and the combination of precast and in-situ concrete

James Carr - June 2012