Avian forms in the okavango delta

Introduction

The confluence of pristine wilderness, tensile engineering and specialist knowledge.

Set in the famous Moremi Game Reserve on the breathtakingly beautiful floodplains of the Okavango Delta, Xigera is the apex of innovative form and function. Tucked away in a pristine labyrinth of waterberries, leadwoods and papyrus islands, the verdant fluvial forests and iconic wildlife is the natural habitat to this unique luxury African experience.

As the appointed tent technologists, Tenthouse Structures called upon their expert team of design engineers, remote project management and site specialists, as well as their long-standing local manufacturing partners to create this extraordinary project.

From traditional roofing to tensile engineering.

With the initial ambitions of the owners, a leading global hospitality group, to design and build the leading luxury camp in Africa, standards were set extremely high and originally, the architects and owners considered only the idea of rolled rigid roofing for their new concept design. With this lofty mandate, they had not fully considered the use of textiles as the basis of the natural roof form they had in mind for the ultra-luxury design.

It was our groundbreaking work at (Mombo Camp) which initially piqued our client’s interest in Tenthouse Structures. Due to our proven ability to create highly complex and iconic roof forms with superior performance specifications, in remote wilderness locations, it was at this juncture in the design stage that the client decided to actively explore Tenthouse Structures’ advanced performance fabric technology in order to deliver on their mandate.

The Brief

Our scope as the turnkey tent technologists was to design-engineer, supply and install the tensile membrane systems, shade flyouts, canvas walling and ceiling systems.

We were further consulted to provide the steel frame modelling and detail for manufacture by other service providers.

The guiding principle of the project was to be as efficient (lightweight) as possible with no compromise to aesthetics and engineering standards whilst adhering to strict environmental guidelines.

The Technical Design-Engineering

Tensile Structure

Tensile membrane design-engineering is an iterative and integrated discipline (bionic design) where form and function are inseparable and influenced by multiple factors. Key factors at Xigera were:

  • Design demands and limitations
  • SANS Building code compliance
  • Strong summer Thunderstorms (Wind loading and ponding)
  • High Temperatures (40°C+ in summer)
  • Maintenance (Tree and wildlife damage)
  • Site Remoteness
  • Guest security and wildlife passage

These material factors presented substantial technical challenges to creating the membrane form, detailing the steel structural elements, selecting the correct textiles, positioning anchoring systems, and resolving interfacing detail and behaviour.

Analysis (frame & membrane as one)

Biomorphic Design Challenge

In shaping the roof to align with the architectural brief for a natural form that is reminiscent of the local Pels Fishing Owl, the correct synclastic curvature had to be resolved so we could integrate the membrane system effectively. The more shape (curvature) the more its ability to resist live loads, especially during serious summer storms.

This, in turn, influenced the fabric selection, reinforcement techniques, water run-off and shading for the main areas and suites. Advanced simulation software and skilful design enabled us to manage the shallow roof angle to avoid ponding and the membrane touching* the steel superstructures beneath during high wind loading events.

*Membrane rubbing against framework is not an acceptable outcome as this creates points where fabric can wear. Were solved this by adapting the shape of the surface, the height of the outrigger connection points and introducing strategic under-fabric rolled steel arches where needed.

Detailing

Confection

Welding and stitching of technical fabrics into performance membranes, flyouts, facades, shaped ceilings and blinds is a suite of highly specialized confection skills.

Tarso

Tarso refers to the engineering design of connection joints in tensile membrane structures. Tarso is critical because it affects the entire structure’s stability, durability, ease of installation, maintenance, aesthetic and cost. Vector aligned connection systems, swaged tensile cables, high tensile steel U-bolts, specialised washers and fabric reinforcement techniques were employed.

Steel Framework

Rolled ridge spines, arched branches and slender outriggers of these extraordinary structures are supported by a vertical frame and a series of tension cables. These make up the ‘bones’, which in turn hold the membranes, flyouts, facades, floors and ceilings.

These homogenous ‘bionic’ structures were all developed and detailed for fabrication by Tenthouse to comply with wind load criteria approved by the Engineer on Record (EoR).

The frame connection elements are a series of precision-engineered non-orthogonal plates that follow predetermined force vector ranges to ensure stability and manage eccentricities as the structures deflect and move over their design life – a living organic structure!

Visuals

Aesthetic Performance

Working closely with the architects and interior designers, we proposed an organic muted colour palette for the various textile layers to blend and harmonize with the surrounding environment and to offset the contemporary tent architecture and eclectic interior design to optimal effect.

The roof, flyout canopies, ceiling and wall textile systems make up four layers, the properties of which are respectively different and are carefully considered for the technical solutions they offer.

Layer 1Outer Membrane‘Taupe’ Architectural PVC
Layer 2Flyout canopies‘Grass mix’ Textured shade-mesh
Layer 3exterior walling & blinds‘Kalahari sand’ Technical canvas
Layer 4Interior ceiling, blinds & wall liner‘Natural’ textured weave

Layers 1, 2 and 3 although all quite different in aesthetics had to compliment.

Layer 4 had to tie in with the interior look and feel.

All fabrics had to meet International Fire and Safety standards.

All overhead fabrics had to be laboratory tested for their modulus characteristics under specified pre-stress and design-life load scenarios.

In collaboration with our textile partners each layer has been selected for and/or developed with special features:

Layer 1 (membrane):

  • Custom built-in heat shield to block all transmitted light energy.
  • Custom natural matt colour
  • Custom Surface lacquer for extra UV resistance
  • Structural characteristics suitable for the complex loading criteria

Layer 2 (flyouts):     

  • Composite knit structure to enable on-site install flexibility
  •  Triple yarn to create a natural texture and depth, with the light finish on the top side and a warm finish beneath

Layer 3 (External canvas):

  • Neutral, complimentary natural colour
  • Refurbishable coating with UV resistance and colour stability

Layer 4 (internal canvas):

  • Emulate the luxuriant, soft handle & textured weave of duck cotton canvas
  • Synthetic performance yarns
  • Upholstered backing for walls
  • topical treatments for easy maintenance and dimensional stability.

Delivery

Tenthouse Structures managed the international logistics supply, including:

  • Consolidation
  • Packaging and labelling
  • Export manifests
  • Loading
  • Sea, air and road freight
  • Debunking

Site Management & Assembly

Site Operations is an extensive and highly specialised service that covers the following:

  • Storage
  • Preparation
  • Programming
  • Crew supervision
  • Tensile rigging
  • Canvas fitment
  • Snagging

Building Around Nature

Building in a National Park (Moremi Game Reserve) and a globally recognized and protected UNESCO Wildlife Reserve comes with its unique challenges that had to be identified, planned for and overcome. In urban construction projects, the build can be held up by traffic jams. In a wilderness National Park in remote Africa however, this project was held up by lions inhabiting the building site. This delay in construction was overcome with rigorous forward planning and after-hours contactability of senior project managers and site personnel alike. The entire team was forced to build around and work with nature, as causing a disturbance with the natural flora and fauna was simply not an option.

Frame

Tenthouse Structures detailed the steel superstructures and their outrigger systems to tie into submerged footings.

Working with the local contractors, the steel frame and timber cladding had to work as a homogeneous building system. Connection detailing and complex structural behaviours were resolved.

Tensile membrane engineering is a precise DFMA (Design for Manufacture and Assembly) discipline. The construction of the frame footings had to be set out according to design and surveyed post-build to ensure accuracy. However, our contained (return-to-frame) design facilitated the off-site production process and in turn the overall project programming as we were not waiting on multiple perimeter mast footing surveys before we could finalise detailing to as-built variances.

Envelope

All our canvas cladding and linings were detailed to connect to a timber stud wall envelope. This entailed complexities such as tensioned fabric ceilings, upholstered canvas stud panels, top fitted wall profiles, ring beam profiles canvas clad corner trim and eave valence systems.

Rigging the Tensile Rooves

Large span membranes are vulnerable to wind and snagging damage during erection.

Expert tensile rigging teams from South Africa planned accordingly for these conditions by:

  • Saddle-strapping the membranes along with horizontal boom rigs.
  • Lowering them into position over cones with one man positioned at each cone head.
  • Fixing the coneheads with the membrane partially wrapped to avoid flapping.
  • Rapidly unfolding the membrane during calm conditions, with one man per connection point.
  • Connecting perimeter points to pre-installed masts, raising the membrane and achieving the first fix in one rapid process.
  • This ensured the entire membrane had enough pre-stress to afford adequate structural stability for the protracted final fix process.

Troubleshooting

The locally constructed habitable shell was a typical clad-stud wall frame with PU insulated fill as-built vs design tolerances were at times a little beyond the tighter acceptable tolerances for patterned fabric systems.

Our expert technical supervisors were able to make complex on-site corrections to the shells and our interfacing systems.

Team Culture

As with all Tenthouse Structures projects outside of our home turf, cultural assimilation between professional and site teams is a valuable soft skill developed over the years of working globally with different cultural teams and languages and we relished and excelled in the opportunity to work with people from different backgrounds.

Role Players

Collaboration

Client/OwnerRed Carnation Hotel groupLondon, UK
Tent TechnologistsTenthouse StructuresCape Town, RSA
Architecture and InteriorsAnton De Kock & Malan Vorster ArchitectsCape Town, RSA
Tensile & textile façade supplyTenthouse StructuresCape Town, RSA
Frame manufacturingProkon SteelCape Town, RSA
ConstructionLodge Builders BotswanaMaun, Botswana

Conclusion

These iconic tent style-suites pioneer the future for performance fabric technology in the Okavango Delta’s rustic eco-luxury hospitality landscape. Tenthouse was called upon and answered the brief with iconic, efficient, high-performance design structures and created a discreet, yet highly engineered solution within the broader natural habitat of the Okavango Delta where the owners’ guests can intimately immerse themselves in and reconnect with nature.

Xigera is Made for the Wild.