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Exposed structures

Charles Grimes Bridge

The aesthetic appeal of exposed structures, in which the structure becomes the architecture, can result in very expressive buildings that pose challenges and opportunities to designers.

Ben Coxon, Country Manager for China and Hong Kong, and Aurecon’s previous Building Structures Leader, speaks to some of Aurecon’s experts in the engineering of exposed structures about the potential to enhance the functionality of spaces and the user experience while still optimising buildability and cost.

• Ben:                    In your opinion, what is the most pressing design challenge for engineering exposed structures?

Nikolaos Tsoukalas: The juxtaposition of the interpretation of the design philosophy (right brain thinking) into the physical form representation (left brain thinking). It is not always the case that ‘iconic’ is achieved via very technical, highly tuned and engineered solutions. In some cases, the simpler and not as highly technical physical form interpretation is just as ’iconic‘. For example, Santiago Calatrava Palau De Las Artes in Valencia versus the great pyramids of Giza.

Peter Murenu:             Exposed structures represent the culmination and integration of form and function. Creating a structure that is true to form, aesthetic and practical is the result of working closely with the architect.

Francisco Pantano:   Efficiency - a lot of effort has to be placed when designing an exposed solution, as the harmony and elegance of the final solution will come after each single component of the structure is optimised to its limit.

Damian Murphy:        The challenge and the reward with detailing these types of design elements are wrapped up in the collaboration required and the way a solution is borne of understanding the primacy of its purpose.

The most elegant solution is always the one which reflects most directly the forces in the system. Over the many generations of evolution, industry standards detailing the inclusions and requirements for elements can sometimes be assumed and not challenged. The devolution of expectation and exposure of true purpose is always a journey worth taking.

• Ben:      What methods or approaches are applied to maximise functionality and spatial requirements?

Nikolaos:    Integration, Integration, Integration. There are many technical manners that can be utilised, but the symphony of two designers (architect and engineer) not just engaging in polite conversation but in seeing issues from the other’s vantage point.

Francisco: Parametric. It is becoming a key factor to be able to work with multiple solutions, as it will let us run optimisation algorithms to find the best compromise.

• Ben:      Are there special considerations for the long term protection of exposed structures that need to be considered?

Nikolaos:    Again, this depends on the design response. If the response is interpreted in a physical form that heavily exposes structure, then depending on material selection, there are technical considerations that need to be considered.

Peter:          Like all structures and, in particular, exposed structures, corrosion protection needs to be considered. Exposed structures, in their nature, are often outdoors and exposed to the elements; thus, in a more aggressive environment. Any deterioration of the protective coating will have aesthetic implications; therefore, considerations such as design life, access and maintainability need to be considered.

Francisco: Quality. It is imperative to work with high-quality materials to prevent undesired behaviours of the aesthetical look.

Damian:     The coating of the structure has to consider design life, installation processes, coating technologies, material compatibilities, size of fabrication plant and likely damage during construction.

• Ben:      How critical is wind engineering on an exposed structure? What are the key parameters that need to be considered?

Nikolaos:    Important, especially when the design response is interpreted in a physical form that exposes structure in a light and delicate manner. The response of the structure to wind dynamics as a whole as well as the parts that make the whole.

Peter:          Slender, circular elements can be susceptible to wind-induced vibration. During the design, the engineer will consider the possibility of vortex-shedding, whereby an element could oscillate uncontrollably at resonance at generally low-wind speeds – with the aim to mitigate this occurrence through stiffness of the elements or roughening the surface to break the wind flow.

Francisco: Very critical, as most of these structures would require a precise wind study to really understand its effects. The dynamic behaviour of the structure plays a significant role in this item.

Damian:     Understanding the wind pressures and the behaviour of the structural response in the wind is one of the key issues for the façade elements of the building. The modern architectural design is about transparency and lightness. The most lightweight and transparent façades are glazed cable walls. The effects of local pressures and global pressure across each elevation need to be considered.

Modern cable façades can have design deflection profiles up to span / 33. Each design has to be developed from first principles and developed in collaboration with all parties.

• Ben:      Exposing the structure can be a detriment to acoustical performance. What treatments can be integrated with the structure to maintain acoustical performance while maintaining design intent?

Nikolaos:    The interpretation of this question that jumped to mind is the ‘whistling’ effect that a structure may create because of wind excitation; and, hence, a response would be the integration of any wind deflectors into the main form of the structure to eliminate their need because of synergies between form selected and wind response around that form.

Peter:          Exposed surfaces can be treated with an acoustic diffractive coating to scatter reflected sound; so that the surface does not dominate the acoustics of a space. This was recently used in the refurbishment of Hamer Hall in Melbourne, an existing concert hall with exposed concrete walls.

Francisco: Not always. Acoustic behaviour has to be considered at the beginning of the design process, to let the structure evolve all together at once.

Damian:     While not addressing the issue of acoustics, an allied matter is fire protection. The fire rating performance of exposed structures is often the main impediment to being able to expose steel. In many instances, the types of buildings which will more than likely relish the use of structural architecture also require first principle analysis of occupant behaviour and a fire engineered solution.

Hamer Hall

• Ben:      What systems promote the most efficient design of an exposed structure?

Nikolaos:    It depends on what the exposed structure is. It can vary from very complex geometry studies using NURBS modelling to simple hand calculations. As stated earlier, one must understand the design philosophy to respond with a physical interpretation, which may require complex or simple systems to provide efficient design.

Peter:          Exposed steel cables and tension systems are a very efficient means of obtaining large spans with low steel weight. This could be applied to glazed atrium roofs or bridges, for example. Exposed concrete surfaces are a great way of combining structure, aesthetic and finish, all in one. This deletes the need for applying additional cladding layers and provides a robust finish.

Sustainable advantages can be gained with exposed concrete walls and soffits by exploiting the thermal mass of the concrete to store and release air within the occupied space to maintain comfortable temperature levels.

Francisco: It depends on the requirement of functionality for each specific project.

• Ben:      Are there aesthetic features you particularly love about exposed detailing?

Nikolaos:    The elegance of the form selection and material choice, coupled with the texture and colour of the particular area of detail, can create some amazing aesthetic features which are sometimes quite complex, in terms of engineering and other times are quite simple.

Peter:          Detailing for exposed structures showcases the structure for what it is. It highlights the pure and raw form of a structure in which the individual detailing elements are there for a reason and are doing a particular job.

Francisco: Slenderness!

Damian:     The way in which each detail reflects the ways in which the forces are transferred and the magnitude of these forces. The restraints and releases of the connection, the installation process and the adjustments are embodied in the detail.

Quite often, the details which are considered aesthetically pleasing are the ones which most directly reflect these considerations.

Canon Performing Arts Centre

• Ben:      Exposing the structure can pose challenges with the reticulation of building services. What techniques have you used to integrate the building services and the structure while maintaining the design intent?

Nikolaos:    Placing the services within the structure in areas that are not efficient places for structure to be placed. Simply put, “creating opportunities from the areas where structure is inefficient to be placed”.

Peter:           The philosophy of exposed structures could be applied to services in that there is nothing to hide. It’s possible to have exposed structure alongside exposed ductwork. The importance of high-quality detailing, jointing, modularisation and clean lines is, therefore, as important for services as it is for structures.

Damian:     Often, the reliance on hidden risers and ducts simply allows the building to be divided into parts suitable for the use of conventional mechanical systems. When the space is open, the building has to be considered as a unit.

Solutions such as air-spill and localised supply become methods to avoid vertical risers.

• Ben:      Where does buildability and cost fit into the exposed structures equation?

Nikolaos:    Integration of efficiency. When one considers exposed structure in its purist physical form, then buildability is a key parameter within the equation, and hand-in-hand with that comes cost. The use of the final solution in the temporary solution with heavy modification.

Peter:          While there is an inherent cost in the detailing, fabrication and protective coating of exposed structures, this is offset by minimising cladding and other finishes. The aim is to achieve a cost-neutral solution.

Francisco: Efficiency, when successful, an exposed structure will match the best cost-effective solution.

Damian:     It is somewhat ironic that the cost associated with exposed structural architecture is usually anticipated by some in the industry to be more than conventional detailing. The endeavour of exposed detailing is to reduce the amount of cladding and to refine connections; so that they reveal the elegance of their design, thus reducing the amount of material required. In many instances, this type of detailing becomes unconventional and the cost rise is simply because they are not what contractors are used to. In many instances, the level of fabrication required to achieve tighter tolerance and finish standards requires additional labour. Regardless, striving for appropriate cost-effectiveness underpins all good design


Peter MurenuPeter Murenu
Peter is a Technical Director of Aurecon and has worked for over 18 years as a structural engineer with extensive experience in conceptual and outline design, working closely with architects and clients from the outset, to provide practical and innovative solutions, to meet the project goals.

Now based in Melbourne, Peter has been involved in delivering a diverse range of projects, including transport hubs, stadiums, pedestrian bridges and commercial construction in Australia, United Kingdom and Dubai.  

Francisco PantanoFrancisco Pantano
Francisco Patano specialises in the design, analysis and optimisation of structures to deliver breakthrough innovations on high-profile public infrastructure, long-span and large custom tensile structures.

Francisco has worked on numerous projects internationally, developing his expertise in a wide spectrum of projects that involve non-linear analysis, seismic calculation--both conventional and unconventional materials--and systems, including stressed cables, net structures and tensioned membranes.

Nikolaos TsoukalasNikolaos Tsoukalas
Niko Tsoukalas is a Technical Director with Aurecon who specialises in concrete, steel, glass and architectural building structures.

Niko's creativity and innovation are key attributes which he uses to excel in complex architectural structures as well as outside the square construction and delivery solutions for projects. He has led many multidiscipline engineering teams in complex major projects over his career.

Damian MurphyDamian Murphy
Damian Murphy is a Technical Director at Aurecon with 18 years of experience in the design of structural projects internationally.

With specialist knowledge of long-span structures, lightweight and glass structures and façade systems, Damian is at the forefront of structural engineering in these fields. He regularly presents at industry conferences.

Ben Coxon
Ben Coxon

Ben Coxon is Aurecon’s Country Manager for China and Hong Kong, and was previously Building Structures Leader. He is passionate about delivering solutions that maximise the outcome for the client, together with all stakeholders and the community. As a structural engineer, he appreciates that we have a tremendous ability and opportunity to effect innovative and sustainable outcomes for all types of building structures.

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