Anzac Memorial Centenary Project

Medium ProjectACSE Awards 2019

1. IntroductionThe Anzac War Memorial is a landmark building located at the southern end of Hyde Park, Sydney. The original building completed in 1934, is a concrete structure, clad in stone, designed by Charles Bruce Dellit.

As part of the NSW Centenary of Anzac, the redevelopment intent was to construct new education and interpretation facilities, including a water cascade that completes the original 1930’s vision for the Memorial. The redevelopment enhances the Memorial serving as a focal point for future generations to learn about our Anzac legacy and Australia’s war history.

The new underground facilities include education and exhibition areas organized around a new central chamber, the “Hall of Service”, visually connected to the Memorial through an open oculus. A new stair flanked by inclined lifts connects the new underground spaces with the existing ground floor.

The structure is the column free space in the new Central Chamber Hall of Service, with a visual connection to the Memorial through the Oculus.

The structure within the Hall of Service features dramatic precast cantilevers towards the central oculus, leaving the space free of columns.

Project CreditClientThe Trustees of the Anzac Memorial

ArchitectJPW

Structural, Civil & Facade EngineerTTW

BuilderBuilt

Project Value$40M

2. Response to the Project Brief ■ The project’s aim was the seamless integration of heritage and

contemporary architecture – with new building designed to complement and respect the existing Memorial and the site’s heritage.

■ Our brief was to establish a structural language that works with the existing Memorial and offering large open spaces with high degree of flexibility for future planning.

■ TTW worked closely with architect JPW and builders Built to ensure the client’s brief was realized. Special consideration was taken to ensure the structural elements aligned with the architectural vision.

■ Our design approach was to use pre-stressed precast concrete T-beams and planks span east west and cantilever in the center of the Hall of Service. The regular architectural precast T-beam structure offered up to 15-meters clear span that allows a high degree of flexibility in both the exhibition and education spaces and provided clearance for services reticulation.

■ The use of precast elements for the underground area reduced on-site construction time, thereby reducing disruption to the Memorial and Hyde park during construction and provided high quality of finish in keeping with the existing Memorial.

■ The prestressed hollowcore plank was utilised in lieu of T-beams or standard planks to assist with the economy of the project, on the structure where the soffits were not exposed, e.g back of house and plantroom areas.

■ The new extension of the Memorial has now become a new iconic public space in Sydney. A hallmark of this project is how close collaboration between the Architect, Engineer, Builder and Precaster has resulted in a stunning combination of structural integrity, beauty and utility.

3. Design and Construction Process ■ TTW were engaged to take the structural design from preliminary stage in

2015 to the construction phase services through to completion in late 2018.

■ Productive design meetings were hosted by Built to resolve the significant detailing challenges, including large spans with high loads requiring the necessity for prestressing in the horizontal elements, maintaining the relatively small geometry in the member sizes requiring innovative connection and reinforcement detailing, logistical challenges working in a confined space on a major Sydney inner CBD site, and other buildability and practical constraints.

■ JPW were intimately involved in those discussions, ensuring that the design integrity was not compromised. This flowed through to the manufacture phase, with frequent visits to the precast yard in Brisbane to ensure the high standards were being achieved.

■ TTW Optimized the details, the geometry and the material to achieve simple and elegant self-supporting conic shaped doubly curved glass oculus. It’s a minimalist design where the structural design empowers the architectural vision.

Precast Structure

4. Creativity & InnovationStructure of the Service and Oculus

■ Architecture and structure in the Hall of Service are mutually enriched. Structural elements are expressed directly and organised along the major north south axis of the building. Dramatic cantilevers towards the centre of the chamber draw the visitor’s gaze towards the central oculus and the Memorial beyond.

■ The structure over the Hall of Service and Foyer offers a 15 by 21.5 metres clear space featuring a 6 metres diameter open oculus. Beams and columns supporting the cantilevering beams are organized in the galleries adjacent the Hall of Service.

■ The off-form finish for all structural elements is obtained through careful sampling of off-white cement and titanium oxide considered against different pouring methodologies for different structural elements.

■ Custom 8.5 metres precast planks infill the central section of the Hall of Service soffit between the cantilevering T-beams. In situ post tensioned beams, as long as 20.5 metres, were poured above the planks to distribute loads towards the east and west structural supports.

Proposed structural scheme

Oculus Void

5. Sustainability ■ The project structural works achieved sustainable outcomes through smart

use of long-cycle, durable material to ensure durability and integrity of the building without large cost interventions to maintain during its life span. Offering great flexibility for the Memorial in the future.

■ Not only is the finish of the raw, off form coloured concrete aesthetically pleasing, it has reduced the environmental footprint of the structure as there were no artificial coatings required during construction or maintained throughout the life of the structure.

■ In areas where the roof structure was not visible, prestressed hollowcore flooring was utilised. These planks are extremely efficient as they hold only half of the concrete volume in comparison to more conventional flooring solutions.

■ In comparison to traditional in situ construction, precasting the concrete elements removed most of the structural works from the site to a controlled factory environment, with less disruption to the City Centre, more efficient use of materials and a superior finished product.

■ In the park, adjacent to the water cascade, a large fig tree was relocated 16 meters east following extensive research on feasibility. The relocation allowed safer construction, cleared the view to the Memorial from Liverpool street as originally designed, whilst preserving a significant tree for visitors to enjoy.

Underground stair link to existing Memorial

■ The new underground facility required access to the existing podium level from the southern side of the memorial with allowances for excavation and shoring under and adjacent to the existing Memorial structure were made.

■ The existing podium stair of the memorial was temporary supported by a series of steel beam above the stair spanning between existing walls. Once secured, the demolition / excavation and underpinning process were carried out. Movement and vibration monitoring were carried out regularly to ensure no impact.

Demolition of the stairs

Underground stairs complete

Central stair and ramp

7. The Challenges and Resolutions ■ Being in central Sydney CBD, the prefabrication system had constraints to

consider such as transportation from Queensland yard to site, limitation on the working hours and truck access to site.

■ Site of precast T-beam was carefully considered to achieve ease of transportation and delivery with additional joint to T-beam proposed to fit in with project team approved, regular connected trucks during construction.

■ The project site was constrained with mature trees, paving and access paths radiating in every direction and the Pool of Reflection to the North. Thereby the construction sequence and staging were considered to minimise major disruption to existing public use and keep the Memorial operational throughout the works.

■ Over the Hall of Service and around the Oculus, a hybrid precast and in situ post-tensioned system were used to minimise the weight of the precast plank for transportation and erection. Each precast panel was constructed with a built-in pre-camber to ensure no noticeable differential deflection between precast panels.

■ Excavation adjacent to and under the Memorial had been a challenge for the construction team. A buildability review was organised by the Anzac Memorial Centenary Project PMO, to identify risks and mitigations to the existing Memorial due to the impact caused by potential displacement and vibration during shoring and excavation works. Innovative solutions including construction staging sequence and advanced monitoring methods were developed to reduce potential impacts caused by displacement and vibration.

6. Built environment and Heritage ■ From Liverpool Street, the visitor walks into the underground addition

through the water cascade walkway, inviting the sound of cascading water to replace the noise of the city.

■ Underground, The Hall of Service is visually connected to the Memorial and its heritage, the park and the city beyond through the open precast Oculus void, a direct reference to the existing Well of Contemplation. Surrounding this, artwork conceived by Fiona Hall: names of 1701 New South Wales locations with a jar of earth, each representing where soldiers of the Great War enlisted from. Under the Oculus, earth from 100 significant battlefields is inlaid in the floor.

■ Functional spaces articulated around commemorative ones, in keeping with the original tradition of a “working Memorial”, now used by staff.

Architectural considerations about Precast

■ Precast concrete was selected for this project to ensure a high level of finish, suitable for a civic landmark, and to meet program and site constraints.

■ An extensive sampling process was carried out to select the appropriate finish through different ratios of cement and admixtures. The outcome is a crisp yet warm finish that contributes to the changing natural light conditions in the Hall of Service and via the Oculus.

■ The structural composition and detailing of the precast concrete elements directly contribute to the architecture of the underground spaces. The dramatic cantilevers in the Hall of Service reinforce the main North South axis of the precinct while supporting and drawing the visitor’s gaze to the central precast oculus and the Anzac Memorial beyond it.