OPTIMUM use has been made of the design freedom afforded by GRC to create the highly-aesthetic external envelope of the Atlantis Hotel, which sits majestically at the Palm Jumeirah in Dubai, UAE. The UK-based consulting engineers BSCP was approached to assist in the complex GRC façade for the hotel, which opened in September 2008.

The hotel consists of two main towers linked by a bridge with a highly decorative arch feature beneath. This arch is approximately 40 m wide at the base and approximately 65 m in height. The entire envelope utilised approximately 80,000 sq m of Grade 18 GRC that was manufactured and supplied by Emirates Precast Construction, Dubai.
GRC was specified for the external envelope for three primary reasons: mass, speed of installation and the full fit to architectural intent.

In terms of mass, GRC is a very good lightweight option when compared with precast or natural stone cladding elements. As a general rule, one can consider a GRC façade solution as being up to 80 per cent lighter than the precast option. Looking at the second reason, GRC units are manufactured in a controlled offsite environment; panel anchors and fixings can be designed and cast into the units, allowing for a rapid installation methodology to be developed. Thirdly, the ability to cast very complex and ornate geometry allowed the GRC façade to achieve a 100 per cent fit with the architectural intent for the structure’s external envelope.
In terms of a design approach, the façade utilised primarily two types of cladding panels – the simple ribbed panel and the stud frame panel.

Simple ribbed panels
Simple ribbed panels forming the majority of the façade envelope were employed on the wing walls and the vertical surfaces of the tower elements. The typical ribbed panel consists of a nominal 15-mm-thick face of GRC with hollow profiled ribs cast into the rear of the panel. In production, the spraying down of the face material and creation of rib profiles is carried out simultaneously. The size, shape, amount and orientation of any rib arrangement are all a function of and dictated by design requirements. The factors affecting the design parameters are usually a combination of: wind loadings, self weight, unit de-moulding loads and loads induced by lifting-installation activities.
The designer has given due consideration to degrees of freedom when using GRC elements. This is because GRC is a cement-rich matrix (approximately 50 per cent) and as it is a thin-walled element, it will react quickly to ambient temperature variations and thus will need to shrink and expand accordingly.
For a simple ribbed panel unit, basic section analysis techniques can often be enough to ascertain the unit’s structural integrity – for instance, the Sectprop software analysis programme, which has been developed by BSCP consulting engineers.

Stud frame GRC panels
Stud frame GRC panels were used to form the complex central arch feature where panels had to be cast in technically challenging geometric forms. Also of major importance was the ‘build-ability’ of this arch feature.
A stud frame panel unit is where a single-skin GRC unit is sprayed down a nominal 15-mm thick face and a support frame is cast into the back of the unit. This frame provides the structural capacity of the unit and is most often manufactured from steel. The method of casting the frame to the GRC is of some importance as the ability of the GRC to expand and contract must not be impinged.
The stud frame consists of gravity and flex anchors. Gravity anchors are positioned at the base of the GRC panel skin and are interspersed around the unit at approximately 500-mm centres in the X and Y vertices. Both anchors are formed by L bars with the gravity anchors being welded to the frame members and the flex anchors bolted to the frame members.
Both the flex anchors and the gravity anchors are de-bonded from the GRC with the L anchor profiles pointing to the centroid of any unit. This facilitates the thermal movements of the panel skin both off and on the cast in anchor positions. The perpendicular aspect of any anchor bar is encapsulated by a local build-up of GRC material known as a bonding pad.
During the process of designing and detailing the arch GRC panel units, several parameters were of key importance – first, the need to rapidly design both the GRC panel skins and stud frames, second, the need to optimise this design in terms of unit mass and financial compatibility, and third, finding an effective way of coordinating set up of stud frame fixing positions and the supporting secondary steelwork. The use of 3D modelling and analysis techniques facilitated these design parameters within BSCP’s scope of works in the most appropriate manner.
During the design process, 3D finite element analysis techniques were employed by BSCP to develop the stud frame unit’s structural capacities. The software utilised is a program that has been developed for use within the aerospace industry. BSCP’s in-house team of software developers have worked with the program, adapting it to work within the structural engineering environment.
Approaching the design of such elements in this way has definite advantages: the GRC panel skin and stud frame units can be designed in unison taking full advantage of the composite action that is derived from both individual elements. Individual reactions between the panel skin and stud frame, or the stud frame and supporting superstructure can be analysed in great depth. The most cost-effective design can be proposed and interface coordination can be carried out using 3D clash detection methodology.
Once the structural design of any element has been completed, it is a simple process to extract from the models completely faithful and ‘live’ drawn details to facilitate the project’s approval process.
In conclusion, it can be seen that a dual approach has been utilised within the design process for the façade elements. The simple ribbed façade panels have benefited from the generally simple 2D process in terms of design, analysis and detail/drawing management. The stud frame elements have been developed using a 3D design, analysis and detailing/drawing methodology which has reaped all the benefits.
BSCP, part of the GHA Livigunn Group, has more than 30 years of experience within the GRC industry acting as façade consultants. Its façade division has been engaged in projects located in the UK, Europe, Scandinavia, Russia, Greece, Turkey, Cyprus, Kazakhstan, the Middle East, Hong Kong, Asia, Korea, the Far East and Bhutan.
BSCP works with building owners, architects, main and specialist façade contractors and advises owners and managers on handling technical, commercial and programme risks associated with façade elements.

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