Sports Stadium Redevelopment

Proposed sports stadium with world-class functionality and beauty and a minimal carbon footprint.

Project Title:

Sports Stadium Redevelopment
Project Type:
Innovative, architecture, 6 greenstar environmental rating
Feature Summary:
Proposed sports stadium with world-class functionality and beauty and a minimal carbon footprint.
Categories:
  • Commercial
  • Products
  • Mid Rise
  • Sustainability
  • Innovation
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Type

Commercial

Structure

  • Lightweight
  • Mass
  • Region
    NSW, Aus
  • Status
    Proposed

When fitzpatrick+partners and ARUP approached Wesbeam to partner with them on delivering a unique and memorable sports stadium, the Wesbeam Tall Timber Building Systems (TTBS) team were quick to appreciate the magnitude of the opportunity. Wesbeam and fitzpatrick+partners worked together to showcase innovative timber engineering in a commercial structure that is highly functional, beautiful and respectful to the environment.

fitzpatrick+partners were tasked with developing an infrastructure that builds on the strengths of the current stadium precinct, activating the site on a daily basis for social and commercial opportunities whilst demonstrating respect for the site’s unique heritage elements.

ENGINEERING DESIGN:

The roof structure was designed in collaboration with ARUP to be an elegant cantilevered timber and steel structure, supported from the main concourse level and potentially structurally independent from the grandstand superstructure. 

In two-dimensions, the roof form is similar to a cantilevered pinned arch, with the horizontal forces resolved at roof level in a continuous ring truss in the roof plane, and at the base at concourse level. 

All vertical forces are resisted at concourse level, and therefore no additional horizontal actions are transferred into the superstructure above this level. The structural form has been carefully conceived and assembled based on both structural performance, economy, and build-ability. 

Timber is used structurally in straight segments only, with simple tapered timber box girders up to 9m deep at the East and West and 4.5m on the North and South assembled from standard LVL supply. To maximise the performance, flange zones are orthotropic (maximise timber strength in direction of chords), and the webs contain some cross plies to assist with shear capacity and out-of-plane stiffness. 

The triangulation in this design is important for structural performance as it:

  • Distributes peak wind pressures across multiple structural bays. This allows the designers to optimise the structural economy based on time-history studies using a wind tunnel. Similarly, it distributes heavy rigging loads – even loads that may exceed the preliminary brief;
  • Provides the diagonal elements in the roof plane ring truss (diaphragm);
  • Self-restrains the box girders by controlling their structural buckling lengths without the need for secondary bracing elements; 
  • Provides redundancy to the structural system in the event or accidental or criminal actions.

Steel shoes are used at the change of angle to connect the straight segments, with the timber to steel connection through multiple flitch plates and timber dowels for chords, and screws for webs. External post-tensioning within the box girder has also been reviewed as a method for connection of the box girder chord forces and is a feasible alternative – potentially with the added benefit of providing the roof with additional stiffness and redundancy. 

STRUCTURAL ANALYSIS:

Detailed structural analysis and initial optimisation was undertaken by ARUP to develop the system. This included:

  • Development of a parametric model integrated with structural analysis software;
  • Loading based provided in the brief including all imposed gantry, lighting, AV, rigging, and club mode screen loading etc;
  • Short-term and instantaneous loading under above, wind, and maintenance live loading;
  • Long-term analysis to accommodate timber creep and additional long-term roof deflection under permanent loading;
  • Buckling analysis to confirm performance of the roof diaphragm (ring truss) and demonstrate adequate flexural stiffness to restrain the inner compression ring;
  • Member strength;
  • Connection capability.

The roof can be erected sequentially to follow the bowl construction. Rafter segments can be pre-assembled with the steel shoes from the transported lengths on the pitch or outside the stadium and lifted into position, propped at the inner ring node. 

Once the full roof has been completed the inner props can be released and removed, with the roof lowering into its final position from its pre-set geometry.

WHY ENGINEERED TIMBER?

The engineering of timber structures is well understood. Engineered Wood Products (EWP) such as Wesbeam LVL offer many of the benefits or steel and/or concrete without many of their constraints.

EWP is a suite of products including LVL, Glulam and Cross Laminated Timber (CLT). EWPs are the products of our generation. They are sourced from sustainable and certified plantations, assuring a continual regenerating supply chain, and the sequestering of carbon for the life of the product. EWPs require little maintenance and perform better than concrete and steel under some key structural scenarios. EWPs fire characteristics are understood and are addressed by product depth and thickness - more material to allow for charring.

The added durability of being an EWP means LVL is less prone to shrinking or warping. LVL can also support heavier loads and span longer distances than standard sawn timber.

Wesbeam LVL Section sizes are cut from 1200 mm wide sheets or “billets”. The ability to cut different shapes from the LVL billets allows for structural innovation using angular and curved shapes.

Wesbeam LVL is a cost-effective and sustainable building material, delivering high structural reliability and strength.

The proposed design by fitzpatrick+partners protects the majority of the LVL beams, locating them behind or below the membrane skin. As such, only occasional wetting would occur through vertical driven rain under the roof canopy, and cleaning.

The exposed “feet” of the structure have the potential to be over-clad with a sacrificial timber veneer composite skin - with an appropriately warranted finish. 

As the leading supplier of LVL in Australia, Wesbeam recommended that a penetrating sealer be applied to the product prior to delivery to site. The maintenance and recoating of this sealer would match the recommended recoat periods for a steel structure - 5-10 years.

The general maintenance regime is similar to that of a coated steel solution - with recommendations for an annual wash down only. As the material is protected from the majority of UV light - little colour degradation of the material would be expected.

The primary timber and steel node structure supporting the roof and facades is currently designed as a stand-alone structural system. 

Most importantly, Engineered Wood Products have an inherent beauty of texture and colour. They are simply nice to be around. Efficient, Durable, Flexible, Natural, Carbon Sequestering, Recyclable, Beautiful and of our time.

Wesbeam worked closely with fitzpatrick+partners and Arup in the development of the design concept and the preparation of the final submission for the Design Excellence Competition submission. Whilst the solution was not successful, the knowledge learned by all parties has successfully transferred to other real projects.

Wesbeam welcomes the opportunity to work with design teams on development of innovative design solutions, always aiming for a successful outcome, and the development of the knowledge base for Engineered Timber solutions.

For more information on Wesbeam Tall Timber Building Systems click here. For more information on architects fitzpatrick+partners please click here and for information on ARUP, please click here.

Architect: fitzpatrick+partners http://www.fitzpatrickpartners.com/
Author:
Wesbeam
Date:
Aug 14, 2019