by Estelle van Staden, Johannesburg, 23 June 2005

A DEFINITIVE DOME : Bentel Associates International have designed an unusual and spectacular dome for the 35-storey Michelangelo Towers in Sandton - one of the company's newest and most outstanding design ventures due to be completed in September 2005. The 13.6t dome is 15m high and takes the building to its full height of 146m above the ground making it the tallest building on the imposing Sandton skyline and the sixth tallest building in Johannesburg.
 
The Michelangelo Towers was designed to encompass a timeless and elegant feel and it was always envisaged that the architectural icon would be capped by a classically inspired dome. The original dome concept consisted of enclosed glass covering the lift motor rooms and water tanks required by such a structure. 
 
However, as the project evolved and "the Observation Suite" on the top floor was designed along with a pool deck, Franc Brugman, project and design architect from Bentel, felt that a dome with a lot more character and iconic design was called for to give the building the capping design element it deserved. 
  
"We realised that with the design of the Observation Suite at the top of the building, and with the decision to build around the lift motor rooms housed on the top floors, this was our chance to design something truly spectacular and in keeping with the tower block we were creating," says Brugman. Bart Dorrestein of Legacy Holdings, the developer of the Towers, was also excited about the new dome concept and was equally responsible for pushing the design envelope in creating what will become one of Sandton's more memorable landmarks.
  
As the top levels and the penthouse developed, a decision was made to alter the original concept of a closed glass dome by opening up the dome, with two main design objectives. "We wanted the dome to be aesthetically appealing and an enhancement of the building and we wanted the dome to be spectacular and iconic, something completely different and innovative, something original compared to any other similar building in the world," says Brugman. The final design consists of a crown of stainless steel ribs topped by a "jewel" in a floating circular support. "Stainless steel was chosen for the dome to give the required iconic status and a strong design identity to the classically inspired but modern building which incorporates the latest building and materials technology." 
 
The dome has three elements: a lower centre section incorporating a pressure ring, 12 arches spanning over 20m, and a 7.2m wide inverted dome. Fabricating Bentel's spectacular design from 304-grade stainless steel took Betterect, highly experienced stainless steel fabricators, three months to complete the main elements. The ribs were made in sections that were then welded together. Extreme care was taken to choose cost effective material that could withstand welding without rippling. A brushed stainless steel finish was chosen, as it is easier to work with and requires minimal buffing to remove scratches sustained during the erection of the dome.
 
The erection of the stainless steel structure took two weeks. Consulting engineer, Tony Ritchie from Ritchie Midgley Consulting Engineers, utilised the 160m tower crane on the site to place the three elements of the dome into position, and after levelling, the elements were bolted to the surface.
 
"From an aesthetic point of view we wanted to create a building that would be spectacular during both the day and at night," says Brugman. "We decided to do it all in stainless steel, the idea being that during the day this design would sparkle and create an absolutely amazing feature on the skyline, and at night changing lighting would spectacularly enhance the dome as well as the rest of the building." 
 
The day concept has been a stunning success. During the day the stainless steel arches sparkle magnificently from any viewing angle. The lighting plans for night are at the design stage and will be finalised shortly. Brugman says that one of the challenges of designing the lighting for the dome and the rest of the building is to finalise the design in a manner that will not disturb the residents of the building. 
 
The concept includes an intricate lighting design that will produce unusual and memorable effects. "We are talking about lighting up the ribs, lighting up the floating "jewel," and colours and effects that will be constantly changing. The buttress walls at the side of the observation suite will also be lit in various ways. We are really excited about the fact that the top of this building will be in visual motion all the time - not just a static feature like so many other buildings."
 
The decision to use stainless steel for the dome also had a practical aspect. Brugman says that in addition to stainless steel's aesthetic appeal, the material is inherently corrosion resistant and thus requires little or no maintenance. "Choosing stainless steel for the top of the building makes sense because of its low maintenance factor which is necessary due to the relative inaccessibility of this part of the building." 
 
The ribs are made of what is known as Austenitic 304 stainless steel. This is a chromium and nickel-containing alloy with molybdenum additions. The steel is non-magnetic. Austenitics have excellent corrosion resistance; good formability; good weldability, and excellent mechanical properties over a wide range of temperatures. The low maintenance factor makes it ideal for this type of project.
 
Managing director of the Southern African Stainless Steel Development Association (SASSDA) Dr Oliver Damm says that the visibility of the stainless steel structure on the tower is a shining testimony to the success of the utilisation of the material in the architecture, building and construction sector and one that will surely inspire others to follow suit. 
 
"We have also used stainless steel in smaller elements - the idea being that although it is a classical building there are a lot of modern elements," says Brugman. The dome design picks up on the contemporary theme in the design. "Though the Michelangelo Towers is classically inspired through the use of classical arches, sandstone finish and mouldings, the detail is purely modern including stainless steel and glass balustrades, aluminium framed sliding, folding and stacking doors and windows, all capped by the spectacular shining 'jewel' of the dome design at the top," says Brugman.
 
"I like to believe that the dome has given the building a contemporary look, it's not just a classical building, it's a contemporary building with classical lines but with modern material and technologies." The design of the dome is indeed the crowning glory of the Michelangelo Towers.

  
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