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Master Geek
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Topic # 106758 31-Jul-2012 12:24 Send private message

Animation and article on the Christchurch rebuild

http://www.nzherald.co.nz/property/news/article.cfm?c_id=8&objectid=10823289

Disappointing to see a maximum height restriction of only 8 stories. Same amount of land but now there will be less office space available than before

Sky Tower in Auckland completed in 1997 is 222 metres tall. According to wikipedia a magnitude 8.0 earthquake is not expected to collapse the tower

http://en.wikipedia.org/wiki/Sky_Tower_(Auckland)

Look how tall buildings are in Tokyo

http://en.wikipedia.org/wiki/List_of_tallest_structures_in_Tokyo

I am assuming the height restriction could be legally removed if the Government/Council wanted to so if you are like me and want the height restriction removed as long as the building complies with earthquake standards here are the contact details for the appropriate people

http://cera.govt.nz/contact
http://www.ccc.govt.nz/thecouncil/contactus.aspx
http://www.national.org.nz/MP.aspx?Id=28

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Uber Geek
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  Reply # 664507 31-Jul-2012 12:34 Send private message

Yeh I totally agree, buildings will need to be built to withstand earthquakes anyway, what difference does the height make? The only thing this will be doing is help those who probably have a fear of tall structures since the quake. 





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  Reply # 664526 31-Jul-2012 12:53 Send private message

I think one of the main reasons for the height restriction is to allow light into the central city. Previously even in the height of summer large portions of the central city were dank and dark thanks to tall buildings. The square wouldn't see light for large parts of the day thanks to surrounding high buildings. The new central city plan shows short buildings on the north side of the square to allow light through. I don't agree with the height restrictions and I don't see them being viable in the long run.

gzt

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  Reply # 664569 31-Jul-2012 13:27 Send private message

Is the height restriction justified by the geology or is it because many chch people will not lease/buy/work there otherwise?

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  Reply # 664573 31-Jul-2012 13:33 Send private message

kingjj: I think one of the main reasons for the height restriction is to allow light into the central city. Previously even in the height of summer large portions of the central city were dank and dark thanks to tall buildings. The square wouldn't see light for large parts of the day thanks to surrounding high buildings. The new central city plan shows short buildings on the north side of the square to allow light through. I don't agree with the height restrictions and I don't see them being viable in the long run.


Yes, I believe the height restriction is in place to allow light (and heat) to pass unimpeded down to ground level.
I totally agree with this policy.




Michael Skyrme - Instrumentation & Controls

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  Reply # 664580 31-Jul-2012 13:41 Send private message

Sky tower is 46?m into the ground. We had a bore hole here at work to test, it went 4m before it hit slush, and 7 before it was pissing sand and moisture

I think you will find the ground structure being on a swamp and river area has something to do with it. A little bit different to Aucklands volcanic rock structure.

We also now need to put piles 3-4m appart in at areas of the CBD as deep as 26m to stabilise the ground area around where foundations are to be poured/dug.

Japan CBD was also designed from day dot being in a prone area, they are mostly on deep stilts o rollers and built to sway like reeds in the wind. Whereas here in CHC, only the government designed Ministry of works decided to make their building like brick poo houses, and guess which ones are still standing...

The ground here has moved up to 3ft up and down in the space of a split second. Some areas are now ~2m altitude different to what they were pre quakes. Simply put the stability of the ground structure here will not be the same again. As a result, you can't compare canterbury to the rest of the world/country anymore.

We are now a special case, in some parts of the world this city would not exist anymore had they they experienced the same.

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Ultimate Geek
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  Reply # 664606 31-Jul-2012 14:13 Send private message

The height restrictions (7 story or 28 m) in the core and 4 story elsewhere)  are a balancing act. They are trying to balance the economic viability of any development with the desire to create a neat place to be. That place won’t have overpowering tall buildings, light will get through, wind tunnel effects will be minimised. That’s a plus! I think there is some discretion which may enable some buildings to be taller –but the overall theme is 28 metres and less.

 

Lets face it – Christchurch had loads of empty building space pre E1 with grotty old buildings whose only economic viability rested on sex shops and second hand dealers. It was turning into a spread out city with no heart and a Council who hasn’t had the mental capacity to turn the tide.  This plan will do us all a favour – and hopefully keep the useless council at bay.

 

So far I’m pretty happy with the overall concept. It will be a city with a real heart and I can imagine an inner city resident could be a great place to be.

 

I’m struggling to find a negative – even though I’m opposed to building a 35,000 seat rugby stadium But if I put that into a 20 year context with a megacity of Christchurch, Rolleston and Rangiora I’m not so opposed  especially if they make it multi function and covered.

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  Reply # 664612 31-Jul-2012 14:21 Send private message

The issue in Christchurch is not one of earthquake resistance, but liquefaction and settlement.

Big buildings are built on deep foundations, these foundations transfer the loading on the structure to the soil through base bearing (what the end of the pile is pushing down on) and skin friction.

When a soil layer liquefies, it cannot take shear stress and the foundation looses it's friction resistance, therefore transferring all the structures mass onto the base layer. This then causes the base layer to settle, as the soils in Christchurch are around 5000 years old, this means they can settle a considerable distance.

Studies have shown that structures on slight tilts are safe structurally. Unfortunately they have also shown that being in an environment that is tilted past a certain angle will mess with your internal balance and can drive you insane; not joking here, this is why NZ and other nations have severe limits on floor angles.

Their engineering studies of Christchurch soils have shown that the level of risk for buildings exceeding 8 storeys exceeds acceptable levels adopted in NZ and other earthquake prone nations such as Japan. They have larger buildings in Japan because the soils are older (and therefore less prone to liquefaction) and they have a good base layer that Christchurch lacks.

Source: My final year Civil Engineering professors at Canterbury Uni




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  Reply # 664615 31-Jul-2012 14:26 Send private message

I think part of the height restriction (combined with buying up properties for that green frame) is about creating artificial scarcity. As others have mentioned here, there was a lot of empty office space, which had a negative effect on vibrancy.

Limiting higher buildings to a small area, and limiting the height of them, will create artifical scarcity of office space, which aside from helping developers & landlords make more money, is a pretty standard recipe for a vibrant CBD.

About the rest of the plan: Im disapointed with the covered stadium (waste of money imho), and the convention center being so central. Convention centers are basically big warehouses that experience a lot of truck movements (including big b-trains) for setting up and packing down, and while worthwhile economically, dont contribute a whole lot to the vibrancy of a city. Would be just as successful if they plopped it out towards the four avenues rather than the center.

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Ultimate Geek
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  Reply # 664617 31-Jul-2012 14:26 Send private message

  Same amount of land but now there will be less office space available than before 
???? Look at the plan - there is significantly less land. There is a whole tract of land that runs North/south, west of Latimer square which is no longer full of buildings. That’s pretty much half of Manchester street and east gone! There is no more Crown Plaza hote – that will all be park. But rather than office space it will be parks and that’s neat. I think what the planners are looking at is a basic supply and demand model. Limit the supply of land, limit the height of the buildings and you'll attract the higher end developers. Less office space perhaps - but space that will be better quality at a high rental. Office in a new CBD or stay in the suburbs. The rif raff won’t be able to call the CBD home. We might end up with a city where you can walk the CBD streets safely at night.

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  Reply # 664651 31-Jul-2012 15:02 Send private message

MikeSkyrme:
kingjj: I think one of the main reasons for the height restriction is to allow light into the central city. Previously even in the height of summer large portions of the central city were dank and dark thanks to tall buildings. The square wouldn't see light for large parts of the day thanks to surrounding high buildings. The new central city plan shows short buildings on the north side of the square to allow light through. I don't agree with the height restrictions and I don't see them being viable in the long run.


Yes, I believe the height restriction is in place to allow light (and heat) to pass unimpeded down to ground level.
I totally agree with this policy.


But you can do that with 'podiums', and you push the height of the building back into the middle of the block. Large cities all have tall buildings and light isn't a problem if it is well designed. Having a height restriction means that you are going to end up with more height at the footpath edge as developers will need to maximise the floor area, which could create more light problems. This could also create some very bad wind tunnels.

I can't understand why they have a height restriction, and I think it is a stupid restriction. Tall well designed building are no more likely to fail than shorter ones, and I think they could be stronger as they will have better foundations. Not one tall building collapsed in the earthquakes, it was actually the buildings around the 5-7 level that failed. I had heard that that was partly because building of that height may have been more susceptible due to their natural resonance with the ground movements, which increased the forces on it. I can't believe they have put that restriction in place before the royal enquiry has even concluded their investigations.
I think this was a rushed in plan. Giving only 100 days to plan a cities structure isn't long enough, and I think the guys on closeup last night summed it all up pretty well. It was almost as though it was a design by a committee, and you know what you get when that happens, you get a donkey (the perfect horse designed by a committee)
I think it would have been better to have an international urban design competition and attract some of the worlds and NZ's leading urban designers.

gzt

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  Reply # 664662 31-Jul-2012 15:13 Send private message

The Grand Chancellor did not collapse but it was a close thing wasn't it?

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Ultimate Geek
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  Reply # 664676 31-Jul-2012 15:35 Send private message

Lets not forget the old waterways that lie under the CBD.



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  Reply # 664700 31-Jul-2012 15:53 Send private message

gzt: The Grand Chancellor did not collapse but it was a close thing wasn't it?


I don't think that was height related though, and I don't think that building is any great loss, probably one of NZ's ugliest buildings. I think the verdict on that has still to be released, but I had heard that that building wasn't initially that tall, someone may know more on the history of it. But new modern buildings shouldn't have any problems with EQs up to 8.

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  Reply # 664701 31-Jul-2012 15:54 Send private message

minimoke: Lets not forget the old waterways that lie under the CBD.




Yeap, I think any foundations really need to go down to the bedrock, otherwise you can get the foundations tilting, as it will be like building on jelly.

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  Reply # 664711 31-Jul-2012 16:10 Send private message

minimoke: Lets not forget the old waterways that lie under the CBD.
 



I get the feeling most people over looked the fact I subtly pointed it out this and the reasoning behind restrictions.. if you shake a carpet.. it takes a bit to straighten it out. If you fill a bucket with mud, it doesn't dry in 5 seconds.

People have to look a little deeper than old building vs new asthetics - This puppy didn't just write off a building here and there.. the entire city GROUND has been affected (at the least warped). (fyi the greater city has rotated clockwise about 2-6ft)

Lets remember the reason for the residential redzone.. it is not viable to build on the GROUND - the land cannot be re-mediated. It turned to slush which can take 20+years to re-settle as pointed out by our resident engineer.

And as pointed out by the CBD enquiry and old river mapping zones.. the CBD is no different with pockets of ick underfoot.

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