Editing Sydney Opera House (section)

====Stage II: Roof====
<gallery mode="packed" heights="150">
File:SYDNEY OPERA HOUSE under construction and ferries including BELLUBERA and KARINGAL 1962.tif|Podium structure complete, 1962
File:SYDNEY OPERA HOUSE under construction 1965.tif|Shells structure, {{Circa|1965}}
File:SYDNEY OPERA HOUSE under construction circa 1965.tif|Roof and shell structure, {{Circa|1965}}
File:Sydney Opera House construction 1968.jpg|Tiles complete, {{Circa|1968}}
</gallery>
The [[Thin-shell structure|shells]] of the competition entry were originally of undefined geometry,<ref>Arup, Ove and Zunz, G.J.: Article in ''Structural Engineer'' Volume 47, March 1969</ref> but, early in the design process, the "shells" were perceived as a series of [[parabola]]s supported by precast concrete ribs. However, engineers [[Arup Group|Ove Arup and Partners]] were unable to find an acceptable solution to constructing them. The [[formwork]] for using ''[[in-situ]]'' concrete would have been prohibitively expensive, and, because there was no repetition in any of the roof forms, the construction of precast concrete for each individual section would possibly have been even more expensive.

[[File:AUS NSW Opera House DSC05118.jpg|thumb|right|Sydney Opera House shell ribs]]
[[File:Sydney Opera House Ceramic Tile Pattern.jpg|thumb|right|The glazed ceramic tiles of the Sydney Opera House]]
From 1957 to 1963, the design team went through at least 12 iterations of the form of the shells trying to find an economically acceptable form (including schemes with parabolas, circular ribs and [[ellipsoids]]) before a workable solution was completed.

The design work on the shells involved one of the earliest uses of computers in [[structural analysis]], to understand the complex forces to which the shells would be subjected.<ref name="PJones">Jones, Peter: ''Ove Arup: Masterbuilder of the Twentieth Century''. Yale University Press, 2006.</ref><ref name=bertony>{{cite web |url=https://www.bbc.co.uk/news/world-australia-47880938 |title=Joseph Bertony: The spy who helped mastermind the Sydney Opera House|website=BBC News |first=Ashitha |last=Nagesh |date= 13 April 2019}}</ref> The computer system was also used in the assembly of the arches. The pins in the arches were surveyed at the end of each day, and the information was entered into the computer so the next arch could be properly placed the following day.

In mid-1961, the design team found a solution to the problem: the shells all being created as sections from a sphere. This solution allows arches of varying length to be cast in a common mould, and a number of arch segments of common length to be placed adjacent to one another, to form a spherical section. With whom exactly this solution originated has been the subject of some controversy. It was originally credited to Utzon. Ove Arup's letter to Ashworth, a member of the Sydney Opera House Executive Committee, states: "Utzon came up with an idea of making all the shells of uniform curvature throughout in both directions."<ref name=autogenerated3>page 199</ref> Peter Jones, the author of Ove Arup's biography, states that "the architect and his supporters alike claimed to recall the precise [[Eureka effect|''eureka'' moment]] ...; the engineers and some of their associates, with equal conviction, recall discussion in both central London and at Ove's house."

He goes on to claim that "the existing evidence shows that Arup's canvassed several possibilities for the geometry of the shells, from parabolas to ellipsoids and spheres."<ref name="PJones" /> Yuzo Mikami, a member of the design team, presents an opposite view in his book on the project, ''Utzon's Sphere''.<ref name="sphere">{{cite web| author=Bentley, Paul| date=September 2001| title=A Matter of Integrity – A Review of Yuzo Mikami's ''Utzon's Sphere''| publisher=The Wolanski Foundation| url=http://www.twf.org.au/research/mikami.html| access-date=30 January 2007| archive-url=https://web.archive.org/web/20070102161608/http://www.twf.org.au/research/mikami.html| archive-date=2 January 2007| url-status=dead| df=dmy-all}}</ref><ref>Mikami, Yuzo: ''Utzon's Sphere'', Tokyo: Shoku Kusha. 2001.</ref> It is unlikely that the truth will ever be categorically known, but there is a clear consensus that the design team worked very well indeed for the first part of the project and that Utzon, Arup, and Ronald Jenkins (partner of Ove Arup and Partners responsible for the Opera House project) all played a very significant part in the design development.<ref name="findarticles">{{cite news|author=Hunt, Tony |date=October 2001 |title=Utzon's Sphere: Sydney Opera House—How It Was Designed and Built—Review |publisher=EMAP Architecture, Gale Group |url=http://www.findarticles.com/p/articles/mi_m3575/is_1256_210/ai_79759827 |archive-url=https://web.archive.org/web/20061219120138/http://findarticles.com/p/articles/mi_m3575/is_1256_210/ai_79759827 |url-status=dead |archive-date=19 December 2006 |access-date=30 January 2007 }}</ref>

As [[Peter Murray (architectural writer)|Peter Murray]] states in ''The Saga of the Sydney Opera House'':<ref name="PMurray" />

{{blockquote|... the two men—and their teams—enjoyed a collaboration that was remarkable in its fruitfulness and, despite many traumas, was seen by most of those involved in the project as a high point of architect/engineer collaboration.}}

The design of the roof was tested on scale models in [[wind tunnel]]s at [[University of Southampton]] and later [[National Physical Laboratory (United Kingdom)|NPL]] to establish the wind-pressure distribution around the roof shape in very high winds, which helped in the design of the roof tiles and their fixtures.<ref>{{cite web |url=http://www.powerhousemuseum.com/mob/collection/database/?irn=12041&img=7593 |title=Model of Sydney Opera House, 1960 |work=Powerhouse Museum – Collection Database |year=2014 |access-date=6 May 2014 |archive-url=https://web.archive.org/web/20140506212436/http://www.powerhousemuseum.com/mob/collection/database/?irn=12041&img=7593 |archive-date=6 May 2014 |url-status=live }}</ref><ref>{{cite web |url=http://www.npl.co.uk/content/conWebDoc/8580 |title=Building the Sydney Opera House |work=npl.co.uk |year=2014 |access-date=6 May 2014 |archive-url=https://web.archive.org/web/20140506200203/http://www.npl.co.uk/content/conWebDoc/8580 |archive-date=6 May 2014 |url-status=dead }}</ref>
[[File:Sydney Opera House At Night 2.jpg|thumb|The shells of the Opera House at night, viewed from the south]]
The immensely complex design and construction of the shells was completed by [[Bilfinger Berger|Hornibrook Group Pty Ltd]],<ref>{{cite web |url=http://www.bilfingerberger.com/C1257130005050D5/vwContentByKey/W26U3AX8814LUNADE/$FILE/bb_historie_en.html |title=Bilfinger Berger corporate history |publisher=Bilfingerberger.com |access-date=23 September 2013 |url-status=dead |archive-url=https://web.archive.org/web/20100324054618/http://www.bilfingerberger.com/C1257130005050D5/vwContentByKey/W26U3AX8814LUNADE/%24FILE/bb_historie_en.html |archive-date=24 March 2010 }}</ref> who were also responsible for construction in Stage III.<ref>{{SLQ-CC-BY|url=https://www.slq.qld.gov.au/blog/archives-reveal-more-history-hornibrook-innovation-building-sydney-opera-house|title=Archives reveal more history of Hornibrook innovation in the building of Sydney Opera House.|date=3 November 2021|author(s)=Julie Hornibrook|accessdate=1 June 2022}}</ref> Hornibrook manufactured the 2400 precast ribs and 4000 roof panels in an on-site factory and also developed the construction processes.<ref name="PMurray" /> The achievement of this solution avoided the need for expensive formwork construction by allowing the use of precast units and it also allowed the roof tiles to be prefabricated in sheets on the ground, instead of being stuck on individually at height.

The tiles themselves were manufactured by the Swedish company [[Höganäs Keramik]]. It took three years of development to produce the effect Utzon wanted in what became known as the Sydney Tile, 120mm square. It is made from clay with a small percentage of crushed stone.<ref>{{cite web| url = https://www.sydneyoperahouse.com/our-story/sydney-opera-house-history/spherical-solution.html| title = sydneyoperahouse.com}}</ref>

Ove Arup and Partners' site engineer supervised the construction of the shells, which used an innovative adjustable steel-trussed "erection arch" (developed by Hornibrook's engineer [[Joe Bertony]]) to support the different roofs before completion.<ref name=bertony/> On 6 April 1962, it was estimated that the Opera House would be completed between August 1964 and March 1965.