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CaseStudy

From CAD User AEC Magazine  Vol 22 No 3 - FEBRUARY/MARCH 2009

Bentley’s GenerativeComponents has been used in the design of the Okhta Tower for Gazprom in St Petersburg

Take 5 squares, and then rotate each of them at a rate of 1.5 degrees on each floor, around a central axis, and, in addition, gradually increase the footprint of each floor, as you rise, up to the middle floor, and then decrease it at a similar rate. You end up with a slender, sinuous, exciting shape that might almost have been derived from a dancing, flickering flame - an appropriate enough symbol for the leading gas exploration company in Russia, Gazprom!

It’s not the sort of thing you can do in standard architectural design packages. And, whilst you may be able to create such interesting shapes in a freeform modeller, turning them into a detailed construction model tends to be a bit of a poser, too! So, when architects RMJM came up with the initial concept for the controversial Okhta Tower, a 400metre, 75 storey tower, to be used as the headquarters for Gazprom, in St. Petersburg, Russia, which they had developed using Rhino, structural engineers Ramboll Whitbybird had to resort to some pretty special software to turn their ideas into a workable structural model. Although RMJM used Rhino as their preferred CAD package for setting out the 3D geometry of the building, RWB were happier to use Bentley's Microstation for all of their structural modelling and draughting. They believe it is a robust piece of software for solid modelling, and use it for producing all of their structural drawings. Microstation, alone, however, could not cater for the complexity of this particular design, and GenerativeComponents was employed to drive the structural steel geometry - and also to allow RWB to react quickly to any design changes to the building geometry.

The building envelope models were provided by RMJM in Rhino format. Rather than accept the Rhino geometry to build the GC model, though, RWB decided to sample the data instead, using just key information, instead, to develop its 3D structural model. This was an important decision, as it gave greater flexibility to the way in which GC could then develop the building.

GENERATIVECOMPONENTS

GenerativeComponents uses sets of rules to develop 3D geometry. Starting from a basic configuration, an infinite number of iterations of a design could, theoretically, be developed and tested, merely by inserting appropriate algorithms acting on each GC component.

In the case of the Okhta Tower, the task was simplified somewhat, as the inherent rules for the extent and the structural elements setting out each floor plate of the tower were all essentially the same. The floor plate extent of each of the five squares was rotated symmetrically and evenly five times round the centre, enabling each one to be defined by just 5 points - 3 corner points, 1 core radius point and 1 centre point. Actually, because of the flexibility of GC, the number of rules required to run the generation were decreased even further by using a couple more points.

The extents were then used to generate the steel beam structural elements by adding further parameters - the circular core radius, the offset distance to column centre locations and the maximum span of composite floor slabs between beams. The software was also capable of adding further steel beams as and when required. Thus a typical floor plate was defined, with a set of parametric rules that could be used to propagate its development throughout the entire structure - and on every level where there is a floor plate - with just a few mouse clicks! Refining the solution further, a GC script was written to colour each line individually with rules depending on its level and its location within the floor plate, each colour being a unique section property.

A macro was then developed within Microstation to read these colours, and to assign the section property to each line with its steel section - enabling the software to produce a solid model for the steelwork.

Not everything could be handled in so neat and efficient a manner though. The reinforced concrete core was drawn in 3D manually using Bentley Structural, and final drawings were also extracted manually from the completed 3D model.

BENEFITS OF USING GENERATIVECOMPONENTS

Using GenerativeComponents, RWB was able to set out every steel beam and column within a very short time on receiving a new, or revised Rhino model of the building from the architects. The use of GC's parametric technology in conjunction with the rules set up by RWB allowed them to re-generate the model every time rather than resorting to redrawing it using conventional methods.

The process was not perfect, however, and there were several areas that needed refinement, such as the ability to automate the cutting of holes for services in the steel beams and the addition of coping between steel elements - repetitive tasks that still needed the services of a technician. Other steel elements were not included either, such as outrigger trusses. Overall, though, the project proved that developing high rise towers, with changing or evolving floor plates, can benefit greatly from using such software techniques.

The GC geometry was able to be used to extract x.y and z data, which was imported into the Etabs analysis package, to validate the design. This was not that easy, and required a bit of manipulation of both the Rhino or the Microstation model.

CONTROVERSIAL!

Actually, the inspiration for the Okhta Tower comes from the concept of energy in water, with the site located on St. Petersburg's main waterway - the River Neva. The shape of the building reflects the changing nature of water, reflections and refractions. The design also features a unique environmental touch - a double layered skin that maximises the amount of daylight received and minimises heat loss in the Northerly-based St. Petersburg environment.

And yet controversy has surrounded the building itself. Originally, it was to be funded by both the St. Petersburg city authorities and Gazprom itself. The tower is the focal point of what was to be known as the Gazprom City business centre; and the tower itself, the Gazprom Tower. That was changed in 2007 to Okhta Centre, named after another local river. In January this year, however, after St. Petersburg withdrew from the funding of the project because of the worldwide global recession, Gazprom took over full funding itself. (It's also said that the Mayor of St. Petersburg switched the funding to a new football stadium instead!) Another slight glitch that appears to have been overcome is the fact that St. Petersburg is a World Heritage Site. The project is also very close to the Smolny Cathedral, an iconic emblem for the city. Previously, no construction was allowed to be greater than 40 metres in height. At 398 metres I would say that the Okhta tower comfortably exceeds that!

www.rambollwhitbybird.com

CaseStudy

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