Shells for the senses: the multidisciplinary success of “Stage by the Sea”

When we speak of “aesthetics”, the first sense that comes to mind is sight – when appreciating the “aesthetics” of a structure, we often refer a structure’s beauty. But a secondary definition in Merriam-Webster reminds us that aesthetics can also be defined as “appreciative of what is pleasurable of the senses.”

In Professor Adriaenssens’s words, “a formal analysis, deprived of tactile, auditory and olfactory experiences, seems only to capture to a certain extent the esthetic intent of curved surfaces.” How might structures embody acoustics and the auditory senses? Today we examine Stage by the Sea, a small concert stage in Littlehampton, England that does just that.

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Image courtesy of Flanagan Lawrence Architects.

Context-driven design

The design brief first set out by Littlehampton was for a stage and a shelter to occupy its beach and “reinvigorate the town’s gentility of the early 20th century.” The project, being publicly funded, had an extremely tight budget of £100,000.

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Beach view from the shelter shell of Stage by the Sea. Image courtesy of Flanagan Lawrence Architects.

There were, of course, additional implied constraints due to the setting of the project. Situated on the beach, the structure had to be durable enough to withstand a harsh marine environment. The public structure also needed to be able to withstand vandalism such as arson or graffiti. Above all, the performance stage of course needed to function well, so acoustic requirements would serve as a particularly major driver in this project.

“[We brought the] notion of a traditional bandstand forward to the 21st century, where social media has democratised the production and distribution of music. No longer the preserve of elite musicians, music is now being made by anyone, and played anywhere. The Stage by the Sea is a response to this context, bringing back an old ideal, an architecture that can represent ‘sound’ and the people [who] made it.” – Flanagan Lawrence Architects and Expedition Engineering

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Littlehampton’s Nautical Training Corps Brass Band playing at Stage by the Sea’s performance shell on opening day event, May 2014. Image courtesy of Flanagan Lawrence Architects.

It became clear that effective coordination of the various goals – acoustics, architectural qualities, and structure – would be the key to getting the most value and benefit from a stringent budget. Read on to see how this design team achieved these goals within budget, making such a compelling structure that eventually earned them the 2015 Award for Small Projects from the Institution of Structural Engineers.

The collaborative design process

The successful design team consisted of three firms that excelled in their respective roles: Flanagan Lawrence Architects in acoustic architecture, Expedition Engineering in unusual structural engineering, and Arup Acoustics in technical acoustic consulting. However, even three experts would not have been able to design such a successful project without effective collaboration.

“None of the design disciplines had to make major compromises; it was about working together to achieve the best possible overall outcome.” Pete Winslow, Expedition Engineering

To be more precise about the key to the team’s successful collaboration across disciplines, a single Rhino geometry model was passed between architect and engineer “over twenty times for rapid design iteration and analysis.” Since acoustics were a key driver, the team did not necessarily seek a structure that was shaped to optimally carry dead load.

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Iterative structural engineering analysis (in Oasys GSA) and optimization of the shell geometries. Image courtesy of Expedition Engineering.

We were lucky to speak to Expedition Engineering associate Pete Winslow about the process of working on the project in a multi-disciplinary context. “We [structural engineers] did not prescribe a funicular, or pure compression, structural form,” Winslow says. “Rather, we developed and communicated an understanding of how much bending could be accommodated – for example, in the peak, and close to springing points – without needing to unduly thicken the shell or disproportionately increase the amount of rebar.” But likewise, “acousticians did not prescribe every internal dimension. Rather, they put forward key ratios, such as height/width, or shell peak cantilever distance / depth of stage.

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Concept sketches and acoustic diagram. Image courtesy of Expedition Engineering and Flanagan Lawrence Architects.

“One of the most interesting things about the project is that, in my view, none of the design disciplines had to make major compromises,” Winslow says. “Nobody was saying, ‘every aspect of the form must be like this’ to the detriment of other disciplines. It was about communicating and understanding the main drivers for from each discipline.”

Sustainability in the long term

A final driver guiding the design decisions and compromises was the structure’s durability. “Whilst conventional thinking says that reducing the absolute value of embodied carbon in a structure is desirable, once this figure is spread over the expected design life / life to first major maintenance, the situation can significantly change. Therefore, we decided to explore all practical measures for increasing durability and life, and then within those constraints looked to minimise quantities of material and embodied carbon.”

As an example of how this approach affected the design process, Expedition Engineering pointed out that “in terms of ultimate load capacity, a thinner shell could have been possible. However, the overarching requirement for durability translated to limiting crack widths to 0.15mm.” The team thus optimized thickness around the resulting constraint – stresses within the shell.

Construction

An unconventional construction technique was used for this project: shotcrete. Unlike traditional concrete construction, shotcrete applies concrete by spraying it at high velocity onto a surface. It is often reinforced by steel bars or a mesh.

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Spray concrete application of Stage by the Sea. Image courtesy of Pete Winslow, Expedition Engineering.

“When [conversations] went towards construction, the base method proposed was to build up a formwork and cast concrete in situ, since many contractors can do this,” says Winslow. “Conversations with Shotcrete Ltd, who are experts in tunneling, highlighted that they could very economically do it as a spray-concrete shell, which required no formwork required and achieved a high quality finish.”

“The judges greatly admired the way in which value for money has been delivered to great effect through the structural engineers’ creative thinking and confidence in eschewing complex construction techniques – instead putting faith in simplicity and skilled craftsmanship.” – IStructE award judge comments

Winslow admits that “getting the right shell geometry built on site to tight tolerances on a very limited budget” posed a challenge in construction. Since the project was so small, the team knew it would be uneconomical to use “clever (but expensive) high-tech things like CNC’d polystyrene, laser scanning, or computer simulated or bent rebar.” They improvised: “the thoughtful use of BIM and integrated common models allowed key information to be communicated to the small construction team, who could quickly and simply set out the doubly curved form on site using a conventional scaffold on a 1m x 1m grid. A modest survey and cross-check against the BIM model ensured the geometry was correct, prior to curving and fixing the bi-directional rebars over the top of this scaffold framework, therein defining the complete shell shape.”

 

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BIM model setting out used for construction. Image courtesy of Flanagan Lawrence Architects.
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Shell reinforcement with temporary scaffolding used for construction. Image courtesy of Flanagan Lawrence Architects.

The final result

Today you can find Stage by the Sea, two thin concrete shells oriented back-to-back, on the East Beach of Littlehampton. The larger shell faces inland and serves as the performance stage; the smaller shell sits along the East Beach promenade and faces the sea to provide shelter for passersby and buskers.

 

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Site landscaping of Stage by the Sea. Image courtesy of Flanagan Lawrence Architects.

The impressive thinness of the shells demonstrate that formal elegance were not compromised for acoustic function: “the shells are 100mm thick reinforced concrete, increasing to 150 mm at the more highly stressed springing points, and bi-directional rebar. At the crisp leading edge, a stiffening strip is introduced with minimal increase in overall thickness; instead, additional rebar is introduced with smaller cover.”

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Reinforcement details and stage cross-section. Image courtesy of Expedition Engineering.

As for acoustic function, the performance stage delivered – the violinist playing on the windy opening day could still be heard perfectly well from 50m away.

“The wave-like form follows the acoustic function beautifully.” – IStructE award judge comments

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Acoustic form refinement. Image courtesy of Flanagan Lawrence Architects.

The shells are also well-loved by the community. “I particularly love the public booking system open to anyone,” Winslow says. “It very much makes it an accessible community facility.”

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Sea-front shelter for local residents. Image courtesy of Flanagan Lawrence Architects.

Winslow shares a final touching story demonstrating Stage by the Sea’s place in the hearts of the people: “Over the weekend, a vandal had painted graffiti on one of the shells. It was reported to the council, but almost immediately a group of locals got some paint and painted over the graffiti to restore the shell to pristine condition!”

Visit the team: Expedition Engineering | Flanagan Lawrence Architects | Arup Acoustics

See more at Expedition Engineering’s project page.

Expedition Engineering’s close collaborations with Flanagan Lawrence in acoustic architecture continue. Check out their Soundforms project!

Any quotes not attributed to Mr. Winslow are taken from Expedition Engineering’s pamphlet about the project, which he provided for us. We thank Mr. Winslow for all of his help in making this post possible!

Author: Demi Fang ’17

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