ACSE AWARD SUBMISSION 2017

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BARANGAROO R1

Introduction

Barangaroo R1 is a landmark example of modern architecture within the Barangaroo precinct. The building is an integral part of the entertainment and leisure precinct within the Barangaroo foreshore, housing 3 restaurant and bar tenancies all operated by a single tenant. Arcadis delivered an innovative structure to suit this new landmark project.

Arcadis provided structural engineering services building and tenancy works, working with the client, Lendlease, from concept through to construction – we were able to ensure that the engineering challenges including 8m cantilevers, inclined columns, limited structural depth, and a curved façade could be overcome with minimal architectural impact.

The Barangaroo R1 design commenced in 2013 and the building was opened to the public in December of 2017, including the flagship restaurant for Matt Moran and Solotel. The construction cost of Barangaroo R1 was approximately $14 million.

Project Brief

The project brief for Barangaroo R1 was straightforward; to give the design-competition-winning architectural design a structural frame that worked within the architectural requirements.

Inevitably, such a striking architectural concept will pose challenges for any design team; the curved floorplate was to be supported by only 4 columns and a core, and fringed by 8 metre cantilevers on three sides. This was to be achieved within a limited structural depth of 700mm, and with deflection criteria restricted by a curved façade.

Design & Construction Process

Barangaroo R1 was a technically challenging structure. The structure employs a post-tensioned waffle slab and high strength concrete puddles to provide the significant cantilevers and inclined columns that make the building unique. A post-tensioned waffle slab was chosen as a means of minimising structural mass and maximising stiffness whilst maintaining an irregular floorplate.

Architectural impression of Barangaroo R1

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RAM Concept was chosen as the method for the analysis of the slab; the requirement for detailed deflection analysis, the irregular structural layout, as well as the unusual design solution led to the use of the FEA software. The waffle pod system was modelled as a mat of beams consisting of a single rib with post tensioning running through each.

Alongside the detailed modelling in RAM Concept, Arcadis worked closely with the construction team to provide predictions of deflections that were then correlated with survey results to ensure the construction team were meeting the project requirements. The waffle pods were developed alongside the construction team and included inclined walls and were constructed of fibreglass to ensure ease of removal following the pour. The inclined columns employed flowable concrete within a moulded form to ensure a high-quality finish and performance. We were able to provide detailed deflection models of the structural performance such that the client could match the first 6 months of the building performance to our calculations. This was done as a form of verification and also to assist in the programming of the construction team – they were able to better understand the delivery constraints of their façade and external elements. The project was initially to have a period after construction prior to the tenant taking possession where creep deflections would be allowed to occur. Programme delay reduced this float and the Arcadis engineering team were engaged to conduct detailed deflection analysis and review the impact of extended propping at the cantilevers. This was completed and an additional month of propping to the main cantilevers was occurred following construction. Deflection was then verified against the model on a monthly basis.

Before and after waffle pods during construction

Images of the R1 modelling in RAM Concept

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To meet the clients design intent the project required highly specialised concept design and a strong internal review process. The original concept was developed by Arcadis Technical Director and senior team members and an external consultant was engaged to provide additional assurance and expertise. Arcadis engaged in peer reviews at several points in the design process to further ensure confidence in our design. In addition to our standard verification process we also provided verification of the structural performance between designed as and as-built deflections to provide further assurance to the project team. In submitting our design to several peer reviews and providing a way of allowing assurance between the design and the as-built structure, we developed a strong relationship with the client team that appreciated our focus on their needs.

Creativity & Innovation

Barangaroo R1 presented a highly challenging structural profile for the team. The curved floorplate is supported by only 4 columns and the core, and is fringed by 8 metre cantilevers on three sides. The key design innovation for the project is the use of the post-tensioned waffle slab. This structural system is highly unusual and makes use of a ribbed slab in two directions to reduce the overall mass of the profile. This allowed the team to provide 8m cantilevers with a 700mm thick slab. All levels were modelled in finite element software with deflections plotted over the first 6 months to allow for cross-checking as mentioned above. Another challenge was ensuring continuity of the column reinforcement through a heavily congested post-tensioned slab. The bars had to be sketched and detailed in drawings showing heights of bar termination, bars to be terminated and additional lap bars where required. This was then matched and inspected on site.

Sustainability

The project was built to adhere to the strict standards of the Barangaroo precinct. Although the option was not fulfilled, the roof has been designed to a live load that allows for the installation of solar panels.

Snapshots of the structural Revit model, highlighting R1’s unique structural system

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Built Environment & Heritage

Barangaroo R1 is a landmark example of modern architecture within the Barangaroo precinct. It is an integral part of the entertainment and leisure precinct within the Barangaroo foreshore, housing 3 restaurant and bar tenancies all operated by a single tenant. The project is sustainable, complying with the strict sustainability requirements of the Barangaroo stage 1a development, and also offers engineering excellence within a striking architectural design.

The Challenges and Resolutions

The timing of the project created unusual challenges that Arcadis’ team had to overcome. The initial design deadlines were tight with the concept developing rapidly and requiring several levels of peer and internal review. The construction schedule required rapid turnaround for inspections and several inspections per level due to the complex nature of the floorplate. Our responsiveness during the construction phase cemented our relationship with the construction team.

Numerous challenges were encountered associated with the construction of a new project over an existing basement. The existing basement is heavily reinforced and included starter bar allowances that did not suit the R1 columns. Arcadis had to develop post installed bar solutions that provided connectivity for the inclined columns that could be managed and installed by the construction team. This was achieved through several inspections and detailing.

A similar issue occurred at the ends of the inclined columns – the solution to congestion at column locations was driven by detailing of individual bars and providing details on drawings and identifying where bars could extend or where bars had to terminate.

The major driver of cost for the project was construction cost. Due to the elegant architectural profile and difficult structural system the cost of construction was high. Arcadis was receptive to this and made several labour and material saving changes. The structural system for the top level was value engineered to a more traditional system during the tender phase to minimise cost for the roof whilst maintaining architectural intent.

The profile of Barangaroo R1 R1 opened to the public in December 2017