Digital heritage construction: Testing the heritage value of construction documentation and building processes through Virtual Reality

Abstract

This research paper examines the heritage value of construction documentation and processes via Virtual Reality (VR), with a focus on the Sydney Opera House (SOH). It underscores the importance of comprehending and documenting transient construction techniques for heritage valuation. Utilising VR, the study offers an immersive portrayal of the SOH's construction, emphasising its innovative methods, craftsmanship, and environmental challenges. The paper draws from the Digital Heritage Construction project, showcased at the Heritage Exposition of the ICOMOS General Assembly 2023. This project featured two VR simulations, developed through analysing 200 original shop drawings, historical photographs, and site minutes and reports. The first simulation illustrates the formwork systems used for the SOH's iconic sails, while the second elucidates the assembly methods for the precast vaulted roofs, including the operation of the telescopic erection arch and the installation of concrete segments. The paper examines the novelty of this approach through a survey conducted at the Heritage Exposition. Analysis of the survey's result reveals VR's effectiveness in deepening the appreciation of architectural heritage's intangible qualities, providing new insights into the historical construction processes of the building and their cultural significance.

Headnote

KEYWORDS

Digital heritage;

Virtual reality;

Construction history;

Cultural significance;

Twentieth century;

Intangible heritage;

Archival studies

Abstract This research paper examines the heritage value of construction documentation and processes via Virtual Reality (VR), with a focus on the Sydney Opera House (SOH). It underscores the importance of comprehending and documenting transient construction techniques for heritage valuation. Utilising VR, the study offers an immersive portrayal of the SOH's construction, emphasising its innovative methods, craftsmanship, and environmental challenges. The paper draws from the Digital Heritage Construction project, showcased at the Heritage Exposition of the ICOMOS General Assembly 2023. This project featured two VR simulations, developed through analysing 200 original shop drawings, historical photographs, and site minutes and reports. The first simulation illustrates the formwork systems used for the SOH's iconic sails, while the second elucidates the assembly methods for the precast vaulted roofs, including the operation of the telescopic erection arch and the installation of concrete segments. The paper examines the novelty of this approach through a survey conducted at the Heritage Exposition. Analysis of the survey's result reveals VR's effectiveness in deepening the appreciation of architectural heritage's intangible qualities, providing new insights into the historical construction processes of the building and their cultural significance.

1. Introduction

In the realm of Twentieth-Century Architectural Heritage conservation, the pivotal role of archival documentation is paramount. Recognising this, the International Council on Monuments and Sites (ICOMOS, 2017) highlights the primary importance of these records in gaining insights about specific places or sites. Indeed, architectural archival entries and records are invaluable; they encapsulate the essence of the design process, offering scholars vital insights into its evolution. Thus, they serve as essential resources for architects and heritage experts committed to the preservation and advocacy of historic buildings. Furthermore, these documents are often the starting point for assessing the cultural significance of heritage buildings and developing policies for their preservation and respectful treatment (Armstrong, 2006).

Building upon such principles, and recognising the diverse innovations, forms, construction techniques, and materials introduced in the twentieth century, ICOMOS recommends maximising the potential of archival records by gathering information from the original designer, builder, planner, client, or others intimately associated with the site (ICOMOS, 2017). In fact, these sources should be utilised not only for evaluating the original design intent against the as-found physical state, but also for shedding light on other critical historical settings that may form an integral part of the site's significance, and as such extend and corroborate its cultural value. In terms of settings and archival sources, this study narrows its focus to the inherent socio-technical environment of architectural heritage, which encompasses the application of local building methods, the development of new processes and techniques, and the expertise of skilled builders. It does so through an archive-based cross-analysis of constructionfocused documentation including original site reports, minutes, layout diagrams, and shop drawings. This approach highlights the significant but transient narratives of construction processes, emphasising their role in understanding the identity and cultural value of architectural artifacts of heritage importance.

This interplay between the tangible constructs of architectural heritage and the intangible and transient aspects of their construction settings and processes aligns with Goncalves and Deacon's (2003) notion that tangible and intangible heritage are two sides of the same coin. Echoing this idea, Prosalendis's (2003) concept outlines that tangible heritages inherently possess associated intangible values. Accepting this dynamic adds complexity to the relationship between architectural heritage and its original construction, influencing how heritage significance is investigated, assessed, and managed, thereby affecting conservation management practice. Architectural heritage practices for significance assessment have already demonstrated that, in some instances, the construction process transcended the mere physical act of building, emerging as a key factor in dynamically transforming design intents into physical reality. Consequently, the act of construction not only contributed to the creation of built heritage but also became an integral and foundational part of it (UNESCO World Heritage Centre, 2007). In other instances, the role of construction techniques and processes are key in laying the groundwork for the protection of architectural heritage sites, including facilitating the allocation of funds for their conservation and restoration (Getty Foundation, 2022).

By drawing from these examples, this study aims to expand the traditional focus on the tangible "masterpiece" by emphasising the transitory and performative aspects of its physical creation, in an effort to evaluate their contribution to the significance assessment of cultural heritage. This approach raises several epistemological questions: Can the mere physical presence of a building sustain the intangible value of its construction? How should the transient nature of construction processes be documented, and how can their value be assessed and interpreted? Furthermore, what is the role and weight of construction processes in the evaluation of a building with heritage value?

In seeking answers to such questions, this paper elucidates an innovative approach for understanding, reconstructing, and then assessing the intangible value of construction processes. This study specifically focuses on the construction of the Sydney Opera House (SOH), a building that exemplifies the complex relationship between design requirements and constructional performance in terms of heritage value. This relationship is already recognised in its designation as a UNESCO World Heritage site (2007), corroborating the universal acclaim of the building for "its unparalleled design and construction", "its exceptional engineering achievements and technological innovation", and the "collective creativity of architects, engineers, and builders". The significance of the performative construction of the SOH is further emphasised in the report provided by the Australian government for its inscription on the World Heritage list (Carter and Hannah, 2006). The report describes the Opera House as "literally becoming a testing laboratory and a vast, open-air precasting factory", and whose construction site "was characterised by an outpouring of plans and drawings, the building and testing of numerous prototypes", marking "a radically new approach to construction".

Practically, this study employed Virtual Reality (VR) simulations as a novel method to reconstruct, analyse, assess, and preserve the complex processes integral to the physical making of heritage sites. The integration of VR technology in the field of building heritage and conservation represents a significant advancement in preserving and understanding historical structures. Indeed, VR offers an immersive, interactive platform that enables architects, conservators, and historians to explore and analyse heritage buildings in a detailed, three-dimensional environment. This technology surpasses traditional methods by providing a virtual reconstruction of historical sites, allowing users to examine aspects of artifacts that might have been inaccessible or deteriorated over time (Arenghi and Pane, 2016; Paladini et al., 2019). Additionally, VR has been adopted as a powerful tool in restoration processes, enabling conservators to plan and visualise restoration practices before any physical work begins, thus reducing the risk of errors and preserving the authenticity of heritage sites (Dellepiane et al., 2011). However, to date, the adoption of VR in architectural heritage has not been fully explored with regards to original fabrication processes. This underutilisation overlooks a key advantage of VR technology in its ability to immerse users not only in a digitally developed environment that closely mirrors reallife scenarios but also to augment the same with simulations rendering the original construction site. Moreover, VR technology could include and showcase the operation of historical machinery and equipment, as well as provide dynamic visualization and utilisation of these at real scale.

All in all, VR technology enables users to virtually explore every aspect of a construction site, both internally and externally, providing a realistic sense of space and context (Ahmed, 2018; Whyte and Nikolic, 2018). As a result, the use of immersive VR can significantly enhance the understanding of complex and dynamic environments, offering enriching learning experiences and potentially unveiling technical insights and environmental conditions that might have been challenging to gain and appreciate through conventional means.

Furthermore, in evaluating the fabrication process of architectural heritage, the use of VR in the context of construction practices and sites is particularly relevant. This relevance stems from the potential of VR technologies to facilitate new investigative and interpretative methods, where original construction documentation and process can be archived, accessed, and reconstructed. By presenting its potential, VR can also aid in understanding the meaning and value of highly specialised technical documentation, empowering interpretation of cultural values associated with construction processes.

For example, in the exemplary case of the SOH, the complex bespoke falsework systems were part of the tangible testimony of the building's "unparalleled design and construction". Yet, the technical value of these demolished, and therefore forgotten, temporary structures is barely investigated, explained or acknowledged while discussing the significance of the building. While the relationships and contributions of the Danish architect Jorn Utzon and the British engineering firm Ove Arup to the completion of the iconic roof are addressed, the local expertise and ingenuity of the Australian builder Hornibrook Ltd is often overlooked despite being briefly mentioned in the universal value of the building. This gap in scholarly evaluation of the SOH significance has been confirmed and investigated in a multi-year research project targeting the Australian contribution of the general contractor to the making of the SOH (Stracchi et al., 2023a; 2023b). One of the outcomes of this research is the discovery of thousands of shop drawings issued by Hornibrook (Figs. 1 and 2), along with weekly site minutes covering the entire duration of the iconic sails' construction. After the building's completion and since their storing in the Museum of History New South Wales, these records have not been accessed, meaning their value has not been assessed and included in the nomination for inscription of the SOH on the world heritage list by the Australian government (2006). The neglected and forgotten nature of the construction documentation of the SOH, together with the overlooked intellectual contribution of its general contractor, are the stepping stones of the research project underpinning this paper.

This project aimed to test VR technology's affordances in identifying heritage attributes and values in construction and technical documentation, evaluating the opportunities and limitations in recreating building processes for structures with heritage values, and implementing a research methodology able to use archival records as entry data for VR simulations. The testing and validation of the innovative aspects of this project, particularly the capabilities and effectiveness of VR technology in identifying heritage attributes within construction documentation and processes, led to a collaborative research initiative between the University of Sydney and the University of New South Wales, named "Digital Heritage Construction" (DHC). The output is a 14-min immersive experience accessible through the use of a VR headset. The DHC project reconstructed two key episodes of the construction of the SOH sail-like roof, including the innovative open-air factory to fabricate the 2400 segments forming the ribcage of the iconic sails (Fig. 3), and the sophisticated movable and telescopic centering specifically designed for the roof assembly (Figs. 4 and 5).

The testing and validation ground for this output was offered at the ICOMOS Heritage Exposition ( 23) during the ICOMOS General Assembly 2023, where the DHC project was submitted and subsequently selected. This event, held at the ICC Sydney International Convention & Exhibition Centre from September 5-9, 2023, was attended by approximately 1400 delegates focused on heritage issues, including a majority of the World Heritage Committee members. DHC provided VR headsets for delegates to try the immersive experience. To test and validate the outcome and consequently achieve the projects' objectives, a post-experience survey was conducted addressing two specific research questions:

Can fully-immersive VR technologies and experiences support the identification of heritage values in construction and technical documentation (RQ1)?

Does the construction documentation produced by the Australian General Contractor Hornibrook contribute cultural value to the evaluation of the heritage significance of the Sydney Opera House (RQ2)?

In synthesising these elements, the study presents a multifaceted examination of the SOH's construction, blending traditional archival research with cutting-edge VR technology. By doing so, it not only seeks to provide a deeper understanding of the building's construction process but also aims to establish a precedent for the use of VR in architectural heritage research. The findings from this study are anticipated to contribute significantly to the evolving discourse on heritage assessment, particularly in how modern technology can be leveraged to enhance our understanding and appreciation of historical construction documentation and processes, which are the focus of this project, and their impact on architectural heritage.

2. Materials and methods

To address the two research questions and achieve the project aim, a storyboard for the VR simulation was initially conceived. In order to test Each VR experience was designed to develop a specific "cognitive experience", depending on the unique qualities of the selected topic. The VR storyboard was structured in two parts, addressing the following scopes:

(1) The meaning and significance of the construction drawings of the SOH.

This part aimed to introduce the archival documents, guiding the user to understand the subject of the document without influencing the user's assessment of its cultural significance. This was achieved by creating an associative link between the archival document and a virtual 3D model of the object depicted in the drawing. Given the complex and technical nature of these shop drawings, this link was deemed essential to assist those not familiar with the Architecture, Engineering, and Construction (AEC) industry in interpreting these specialised forms of communication. To recreate the consultation archival experience, the digital environment here was conceived as a virtual archival gallery with few selected original and scanned drawings in front of the user.

(2) The actions and construction tasks the drawings illustrate, focusing on their technical, logistical, and procedural dimension.

The second part of the VR experience was designed to offer a fully immersive experience at the realworld scale of the construction process within the environment of the original site, as described in the construction documentation. Upon the preliminary theoretical introduction of the drawings, the aim of this second part was to enable a complete appreciation of the actual construction challenges and tasks (conveyed by the original drawings) as they occurred on site between 1963 and 1966.

To select specific aspects of the construction process for the VR experience, the authors drew on previous studies conducted on the archival material of the SOH between 2020 and 2023 (Cardellicchio et al., 2021; Stracchi et al., 2023a; Tombesi et al., 2023a, 2023b). These studies provided a qualitative analysis of the shop drawings produced by the general contractor Hornibrook Ltd for the construction of the roof, revealing the contractor's significant agency and contribution. The records indicated that the Hornibrook drawings primarily focused on erection procedures of the roof's concrete segments (48%), casting procedures and manufacturing of the roof's components (30%), and construction layout and site organisation (18%). Within these categories, two major building tasks were selected for the VR experience due to their non-standard, complex, and innovative nature. These building phases were chosen as follows: 1) the manufacturing of the precast concrete segments through the Hornibrook's bespoke formwork system and casting yard; 2) the additive assemblage of the same precast segments through the operation of a customised travelling and aerial scaffolding system, known as the Erection Arch, still invented by Hornibrook.

Once the building phases were identified, the research team selected the most relevant drawings for the first part of the VR experience, considering the scale of representation and the degree of innovation. Consequently, three drawings each for the formwork system and the Erection Arch were chosen. Overall, the VR experience was designed to communicate the real scale of the building site, the complexity of the fabrication and erection procedures, and the innovation in the building process. Based on these aims, the research team developed a storyboard and script for each part of the VR experience. As mentioned, the VR experience debuted at the Heritage Exposition organised during the ICOMOS General Assembly in Sydney. After selection by the organising committee, the project was allocated a booth (3 m by 3 m). Due to the limited space and the aim to maximise user engagement, the simulation was designed and developed to avoid the need for physical movement to navigate and appreciate the experience. The VR experiences were thus designed as follow:

The Casting Yard, Part 1: Understanding Shop Drawings. This section features a 1:50 scale 3D reconstruction aimed at helping users identify and understand the shop drawings presented. In this virtual archive gallery scene, users stand before a consultation desk with three of Hornibrook's shop drawings (Fig. 6). These drawings collectively depict the automated formwork designed by Hornibrook for manufacturing the first five segments of each rib that forms the main sails of the SOH's roof. As users interact with each drawing, their understanding of the technical content deepens. Clicking on specific areas of the drawing brings forth a 3D model, or training model, representing the 2D content (Fig. 7). With this 3D model at a 1:50 scale, users gain familiarity not only with the drawings but also, more importantly, with the formwork's geometric characteristics. This knowledge is crucial for the subsequent scene, where users will immerse themselves in a digital casting yard, recognising and operating the formwork at full scale. The 3D training models thus serve to bridge the gap between the 2D archival records and the construction environment.

The Casting Yard, Part 2: Procedural and Logistic tions. part reconstructs the original casting yard and its essential operations to convey the logistical and procedural challenges encountered during the original construction. In this scene, users witness and interact with the fabrication of a few precast concrete segments of the SOH's roof. After an introductory overview of the casting yard, users are placed atop the formwork analysed in the previous scene. Here, they occupy the exact positions of workers who constructed the segments (Fig. 8). While standing on the formwork, users witness and interact with the production of the fifth segment of each rib, chosen by the research team for its complexity. Following the completion of the fifth segment, users move to ground level to observe the next stage of Hornibrook's manufacturing process. To ensure complete adherence between concrete segments produced in different formworks, the fifth segment is lifted and placed at the beginning of the next mould before pouring the concrete for the sixth segment (Fig. 9). After this operation, users return to the virtual archive gallery for the next scene. e

The Erection Arch, Part 1: Shop Drawings' Significance. Similar to the Casting Yard, this part uses a 1:50 scale 3D training model to aid users in understanding the shop drawings employed in building the travelling centring system. The Erection Arch, designed to follow the spherical geometry of the sails, provided temporary aerial support for the concrete rib segments before their final connection through post-tensioning cables. Once a rib was completed, the Erection Arch moved to the next position to support the subsequent rib. In the virtual archive gallery, users focus on the detailed connections and components that facilitated the movement and functioning of this unique falsework. Three of Hornibrook's drawings on the consultation desk depict three critical parts of the Erection Arch: the telescopic side trusses, the top crown connection for radial movement, and the needle beam invented by Hornibrook as a bespoke harnessing device for connecting the concrete segments. Unlike previous interactions, users start with a 3D model of the entire Erection Arch in front of them. Clicking on specific areas of each drawing highlights the corresponding part of the scaffolding, changing its colour and moving it closer to the user (Fig. 10). These 3D models also create a link between the 2D archival content and the construction environment seen in the following scene. e

The Erection Arch, Part 2: Procedural and Logistic Actions. This section aims to reconstruct the original erection procedures, enabling users to grasp the intervention's scale and the logistical and procedural challenges that occurred during the original building process. Users are placed atop the main western sails, overlooking the eastern sail under construction (Fig. 11). Here, they confront the scale and height of the assembly operation. After completing a rib, users observe the Erection Arch moving to its next position, followed by the placement of the first six segments of the rib. The erection and assembly of the sixth segment are detailed more thoroughly in the experience to showcase the complexity of the needle beam and its function. To achieve this, users are positioned on a temporary platform at the very top of the rib, close to the segment being positioned, mirroring the exact location of the workers responsible for assembling the concrete segments (Fig. 12).

In every scene, a voice-over commentary provides key historical and technical information while guiding users through the various phases of the experience.

2.1. Virtual Reality (VR) and User Interface (Ul) development

2.1.1. 3D model preparation and import to a gaming engine

The 3D models of the SOH construction elements and assembly were developed using Rhino 3D (Rhino, 2023). The 3D models and procedural scenes were reconstructed based entirely on the construction records and drawings used at the time. The data and procedures from the Hornibrook drawings were validated by the weekly site minutes meetings found in the Archive Collection of the Museum of NSW and construction photos housed at the State Library of NSW.

The Rhino 3D modelling environment supports the use of NURBS-Non-Uniform Rational B-Splines. NURBS modelling, widely adopted in architecture, utilises parametric functions to describe curves and points, which are then used to create surfaces and B-Rep NURBS geometry. NURBS are ideal for modelling complex curvilinear and smooth surfaces, such as those of the Opera House sails.

The development of the VR environment was undertaken using Unity software-a cross-platform game engine (Unity, 2023). However, the Unity platform does not support direct import of NURBS geometry from Rhino. Unity geometry import only supports polygon mesh-simple flat planes connected at straight edges to form a 3D shape. Consequently, it was necessary to convert all NURBS geometry modelled for the Opera House project into polygons before exporting the 3D model and importing it into Unity. Effectively converting a Rhino 3D model to the Unity platform was a critical task. This process involved several steps and potential issues, which can be effectively managed with the right Rhino 3D to Unity pipeline. The transition begins with the preparation of the model, which includes reducing mesh complexity to ensure adequate performance in VR. A high polygon count in the scene requires more computational power to visualise and navigate the environment and may result in a "laggy" visual experience, often leading to nausea and physical discomfort for VR users. The 3D model preparation also involved handling overlapping mesh and fixing non-unified normal directions of the geometry. While in Rhino, overlapping surfaces and non-unified normals might not affect the rendering result, in Unity, this can cause a "surface flickering" effect (mesh overlap) or lead to "missing" parts of geometry (normals facing away from the camera), as Unity only displays one side of the surface when non-double-sided shaders are applied.

Lastly, when importing the mesh into Unity from Rhino, texturing and material application can become complicated. By default, the texture tiling of the exported model is not scaled based on the object's size in the scene but on the composition of polygons. Most of these issues can be overcome if the developer follows a systematic pipeline, which can be subdivided into the following steps:

Reducing Mesh Complexity when Transforming NURBS Geometry into Polygons. This involves simplifying the 3D model without compromising its structural integrity or visual clarity to enhance performance within Unity.

Resolving Overlapping Mesh and Non-unified Normal Direction. Overlapped mesh can cause rendering issues, while non-unified normal direction can lead to visual inconsistencies. These issues must be addressed before exporting the model.

Applying Box or Surface Mapping to All Mesh Geometry. This is done before exporting to avoid texture tiling inconsistencies.

Organising Objects within the Scene. Objects should be organised in a hierarchical manner, with consistent naming of all layers and sublayers, to ensure smooth shared application, animation, and real-time interaction in the VR environment.

Exporting 3D Models in FBX or OBJ Formats. These formats facilitate easy import into Unity.

2.1.2. VR scene development

After importing the 3D models into Unity, the development pipeline shifted towards creating an immersive and engaging environment (Globa et al., 2022). Firstly, the selection of materials significantly influenced the aesthetic and immersion of the virtual environment, thereby shaping the user's perception and interaction with it (Beza and Globa, 2023). Our aim was to achieve a semirealistic portrayal of both the archive gallery and the construction sets of VR scenes (the Casting Yard and the Erection Arch).

Historic photographs were imported into Unity to foster an engaging context for the archive scenes. The on-site materials, such as concrete, metal, dirt, and wood, were either imported from Unity's asset library or created from scratch to achieve the desired effect (Figs. 13 and 14). This meticulous approach to material choice and scene setting was vital to deliver a coherent and authentic virtual experience, mirroring the historical accuracy and texture of the original construction sites of the SOH.

The creation of the archive gallery with the desk for the virtual consultation of the drawings, though not essential for the envisioned functionality, was undertaken to simulate the ambiance of the archive gallery. The objective was to immerse the viewer in the context of a SOH's construction archive, utilising available archive photographs and drawings. For the construction site experiences, a simplified 3D model of the Sydney Harbour area was imported into Unity as a textured mesh to create a realistic setting.

Lighting played a pivotal role in defining the scene's ambiance and visual aesthetics, essential for a believable and immersive experience. In all four VR scenes, we employed Unity Mixed lighting (baked + real-time). Most of the geometry utilised baked lightmaps, where Unity precalculated the illumination from light sources before runtime. This approach enabled us to achieve better performance in VR and a more realistic rendering of the geometry.

Additionally, Unity Post-processing effects such as colour grading, depth of field, and bloom were used to further enhance the visual fidelity of the scene. These enhancements contributed significantly to a more immersive and engaging VR experience, elevating the overall quality and realism of the virtual environment. The integration of background and ambient sounds plays a crucial role in enhancing the overall immersive quality of the VR experience. Sound adds a layer of realism and guides user interactions within the virtual environment. Sound effects were particularly impactful in the construction site scenes, where the animation of heavy equipment was paired with spatial sound effects. For example, the sound of a crane moving above the user's head increased in volume as the tower crane jib approached the user. Audio narration was implemented to guide users through the step-by-step process of the VR experience.

The incorporation of animated objects, such as moving cranes, building elements, and concrete pouring, along with interactive elements within the scene, infused a sense of dynamism and realism. This approach significantly enhanced the user's immersive experience. The animations were synchronised with the narration script (audio) that was recorded for the experience, following the storyboard prior to the development of animated scenes and interactions.

2.1.3. Ul development

For the DHC SOH VR experience, we developed a straightforward Ul system (Fig. 15). The aim was to ensure the Ul was user-friendly and intuitive, particularly as many of the ICOMOS delegates were anticipated to have no prior experience with VR. Consequently, we focused on providing essential guidance and control without compromising the immersion and presence of the scenes. The strategic timing and placement of Ul elements were key, ensuring they were easily accessible to users. Additionally, event triggers were effectively implemented to respond to user interactions, enhancing the overall user experience.

2.1.4. Output to VR headsets

The delivery of the VR experience was facilitated using Pico3 VR headsets (Pico Neo 3. 2023). In this project, the Pico headsets were chosen for their user-friendliness, comfort, performance, and, most importantly, security considerations. Previously, our VR experiences were developed with Meta Quest headsets (Meta, 2023); however, due to changes in Meta's ownership and policies, the use of Meta headsets necessitated login options that could potentially compromise privacy. Consequently, we opted to shift to using Pico VR instead.

The exhibition space at the ICOMOS event accommodated 2-3 VR headsets for simultaneous use. To prevent the tangling of wires, the headsets were used untethered. This arrangement required charging the devices between VR experiences. To ensure continuous availability, several additional VR headsets were kept on hand, guaranteeing that at least 2 or 3 charged headsets were accessible at any given time.

2.2. Implementation and testing

Over the course of five days at the ICOMOS Heritage Exposition, more than 200 individuals participated in the VR experience ( ). To assess the efficacy of the VR experience and thereby answer the research questions, a questionnaire was designed.

As outlined in the National Statement on Ethical Conduct in Human Research (NHMRC 2018), involving human participants in research interviews is classified as human research. Accordingly, such interviews should be conducted in accordance with the principles of research merit and integrity, justice, beneficence, and respect. In this research, participants were interviewed about their experiences in Virtual Environment (VE) projects without being asked any personal questions. Therefore, the risk of discomfort for interviewees was minimal, classifying this research interview as low risk.

Following the VR experience, users were invited to complete a questionnaire to gauge their background knowledge in heritage and conservation, their familiarity with the history of the SOH, and their ability to interpret construction and architectural documentation.

To address КОЛ, the following questions were included in the survey:

(023) Regarding the on-site digital experience, did the VR enhance your understanding or appreciation of what happened on-site during the construction of the Sydney Opera House?

(025) Has the VR experience improved your knowledge of the cultural significance of the Sydney Opera House?

(Q26) Based on this experience, do you think Virtual Reality technology can help convey the cultural cance of documentation and on-site processes for heritage buildings? To

(RQ2) these questions were incorporated:

(Q19)Considering that this VR experience aimed to increase your appreciation and understanding of the heritage value of construction documentation and on-site processes, how would you rate your experience overall? e (020) Which part of the VR experience most effectively increased your appreciation of the heritage value of construction documentation and on-site processes? e

(Q21) Regarding the archival documentation, did the VR experience enhance your understanding or appreciation of the content of the original drawings? e

(Q22) Based on your current understanding of the original drawings shown in the VR experience, please assess (agree/disagree) the following statements: (1)

The drawings have no cultural significance (Statement 1). (2)

The drawings express the outstanding technical organisation as part of the exceptional engineering and technological innovation (Statement 2). (3)

The drawings express the builder's contribution to the collective creativity at the base of the universal value of the Sydney Opera House (Statement 3). The

survey results were analysed statistically using IBM SPSS software. A significance value of 0.05 (p < 0.05) was set for all tests. Independent t-tests, one-way ANOVA, and linear regression analysis were employed to assess the association between independent and dependent variables. For the association between dependent variables, linear regression analysis was conducted. Data visualization was achieved using RStudio software, where the results of the independent variables (from Q14 to Q26) were inputted with numeric values. 3.

Results

The survey was completed by 89 individuals, comprising 63% female, 36% male, and 1% non-binary participants. All participants were over 18 years old, with the following age distribution: 30.5% aged 35-44, 22.0% aged 45-54, 19.5% aged 25-35, 14.6% aged 55-64, 8.5% aged 18-24, and 4.9% aged 65 or older. The participants' ancestries were varied, including Australian (50%), European (23%), Asian (22%), and North American (5%). In terms of field of study, participants came from heritage and conservation (70%), architecture (13%), and other fields (17%).

Professionally, 72.2% worked in heritage and conservation. Regarding expertise in built environment heritage, 26.6% were extremely familiar with building conservation, 26.6% very familiar, 12.7% slightly familiar, and 5.1% not familiar at all. The most common level of expertise among participants was senior (55.1%), followed by intermediate (24.4%) and junior (14.1%).

To evaluate prior knowledge in building and construction, participants were asked about their familiarity with reading technical drawings and their general understanding of construction organisation and onsite building processes. Most were familiar with reading technical documentation (22.8% extremely familiar; 29.1% very familiar; 16.5% moderately familiar), with only 12.7% not familiar at all. In terms of construction organisation and onsite building processes, 13.9% were extremely familiar, 19.0% very familiar, and 26.6% moderately familiar, while 21.5% were not familiar at all.

We also assessed participants' familiarity with the SOH and its construction history. 59.5% had visited the SOH, 22.8% had studied it in a professional or academic context, and only 6.3% had no relation with the SOH. In terms of familiarity with the project's history, 35% were slightly familiar, 30.4% moderately familiar, 15.2% very familiar, and 5.1% extremely familiar, whereas 13.9% were not familiar at all. Regarding VR technology, 56% of participants had used it before.

This background information portrays the participants as well-prepared to understand the aim of this experience, with solid prior knowledge and substantial awareness of the SOH and building processes and documentation.

Subsequent results highlight how participants responded to the key research questions:

RQ1: 98.7% felt the VR enhanced their understanding of on-site events during the construction of the SOH (Q23). 74.7% believed the VR experience "definitely" improved their knowledge of the SOH's cultural significance (Q25), and 18.7% thought it "probably" enhanced their knowledge. 81.4% believed VR technology can help convey the cultural significance of construction documentation and on-site processes for heritage buildings (Q26).

RQ2: 89.2% rated their experience positively in terms of increasing appreciation and understanding of the heritage value of construction documentation and onsite processes (Q19). 71.6% felt both the archive space and onsite reconstruction increased appreciation for construction documentation the most, while 27.0% found the onsite scenes more effective (Q20). 93.2% believed the VR experience enhanced their understanding or appreciation of the archival documentation (Q21). Regarding the cultural significance of the drawings, 86.9% disagreed that the drawings had no cultural significance, and 9.8% agreed with that statement (Q22). Most agreed (43.8% strongly, 37.5% somewhat) that the drawings express outstanding technical organisation as part of the exceptional engineering and technological innovation at the SOH, with 12.5% disagreeing (Q22).

Finally, a majority (79.5% strongly agree, 16.4% somewhat agree) believed the drawings express the builder's contribution to the collective creativity at the base of the universal value of the SOH (Q22).

Some survey results were statistically compared and analysed for further insights. To address Research Question 1 (RQ1), we used a statistical method called a one-way ANOVA to see if participants' areas of study influenced their answers to question 23, as shown in Fig. 19. Our findings showed that the answers varied significantly between participants from different study groups, with a statistical test result indicating a clear difference [F(2, 72) = 3.46, p < 0.05]. After that, we applied a technique called Tukey's Honestly Significant Difference Test, which helps compare multiple groups without increasing the chance of error. This test showed that there was a noticeable difference in the average scores for Q23 between participants studying heritage and conservation and those studying architecture. (Mean Difference = 0.10, 95% CI [2.00-1.90], р < 0.05). As a result, participants from heritage and conservation, as well as other fields, felt that the VR experience enhanced their understanding of on-site activities during the construction of the SOH more than participants with an architectural background.

Still regarding to RQ1, we used a one-way ANOVA to lookat how people's relationship with the SOH affected their answers to Question 26. The analysis showed a clear difference in opinions among various groups, indicating that people's connections to the Opera House significantly influenced their responses (Fig. 20). After conducting further analysis using Tukey's HSD Test, we found that people who had studied the SOH or hada personal connection to it gave notably different ratings compared to others (Mean Difference = 0.80, 95% CI [2.00-1.20], p < 0.05). Specifically, those with both academic and personal experiences of the Opera House were more convinced that VR technology can accurately represent the cultural importance of how heritage buildings are documented and constructed.

To tackle Research Question 2 (RQ2), we looked at how people's relationship with the SOH influenced their views on whether a VR presentation could enhance their understanding of the building's cultural meaning (Q25) (Fig. 21). Using oneway ANOVA, we found significant differences in how different groups responded. Those with firsthand experience through study, visits, or work at the Opera House more positively rated the VR's ability to deepen their understanding of its cultural worth [F(4, 70) = 2.66, p < 0.05]. Furthermore, we also applied a one-way ANOVA to examine how the sphere of study affects perceptions regarding the cultural value of the Hornibrook drawings (Q22, Statement 1) (Fig. 22). Here, we observed that those who have studied or work in the heritage and conservation area are notably more likely to refute the view that these drawings lack cultural significance, implying a different perspective on the importance of the Hornibrook drawings among subject-matter experts [F(2, 56) = 3.58, p < 0.05]. This group significantly recognised their importance, underlining how background and personal contacts with heritage material shape viewpoints.

Following our previous analyses, we conducted another one-way ANOVA to see how participants' academic backgrounds influenced their agreement with the idea that "the drawings express the builder's contribution to the collective creativity at the base of the universal value of the Sydney Opera House" (referred to as Q22, Statement 3) (Fig. 23). This analysis revealed a significant difference in how various groups responded, indicating that people's field of study affected their views on the statement [F(2, 70) = 3.35, p < 0.05].

The detailed comparison, using Tukey's Honestly Significant Difference (HSD) Test, showed that the average agreement level on Q22, Statement 3 was significantly higher among those in the field of heritage and conservation compared to participants from other disciplines (Fig. 23). Specifically, this means that individuals with backgrounds in areas other than heritage and conservation, and architecture were less likely to see the drawings as a significant expression of the builder's creative contribution to the SOH's universal value. This difference underscores the impact that specific academic and professional experiences can have on perceptions of cultural heritage connected to construction process and documentation.

We conducted another analysis to see how different levels of connection with the SOH influenced people's views on a specific statement (Q22, Statement 3) (Fig. 24). The analysis showed that there were significant differences in how much people agreed with the statement based on their relationship to the Opera House.

Through detailed comparison using Tukey's HSD Test, we found noteworthy differences in agreement levels. People who had visited the SOH agreed with the statement significantly more than those who had no connection to the building, with a clear difference in opinion (Mean Difference = 0.98). Similarly, individuals who had studied the Opera House showed even stronger agreement compared to those without any relation to it (Mean Difference = 1.25). This suggests that firsthand experience or academic study of the SOH leads to a greater appreciation of the role of the builder's contributions to its universal value, compared to those with no direct connection to the building.

Through linear regression analyses to explore how responses to these questions were interconnected, we found significant relationships:

e Participants' overall rating of the VR experience (019) strongly influenced their views on the cultural insignificance of the drawings (Statement 1 of Q22), their enhanced understanding or appreciation from the VR experience (Q23), and their belief in VR technology's ability to convey cultural significance (Q26).

Opinions on the cultural significance of the drawings (Statement 1 of Q22) had a significant impact on the enhanced understanding or appreciation participants gained from the VR experience (Q23).

Views that the drawings express the builder's tion 3 of Q22) had a notable effect on the belief in VR technology's ability to convey cultural significance (Q26). e

An enhanced understanding or appreciation from the VR experience (Q23) also significantly impacted the belief in VR technology's effectiveness (Q26). e

The broadened knowledge of the Sydney Opera House's cultural significance through the VR experience (Q25) was a strong indicator of the belief in VR technology's effectiveness (Q26).

These findings illustrate the strong influence of the VR experience on participants" perceptions and understanding of the heritage and cultural significance of the SOH and similar heritage buildings.

The survey also included open questions allowing participants to share opinions about future improvements and learning outcomes. While no common trend emerged in suggested improvements, several recurring comments were noted. Seven participants suggested enhancements to the background graphics and the presentation of archival drawings, including the addition of a zoom feature. Six participants recommended incorporating the ability to move around the construction site. One participant suggested adding subtitles to increase accessibility in multiple languages.

Two participants expressed reservations about the general aim of the experience. Participant 67 felt the VR focused on technical rather than cultural aspects, while Participant 75 questioned whether construction history falls within the same category as cultural significance.

Regarding learning outcomes, many participants acknowledged gaining insights into the complexity and sophistication required in constructing the SOH. Participant 74 appreciated how the VR experience effectively broke down the complex construction process, while Participant 29 gained a deeper understanding of the construction's complexity. Participant 28 learned about the role of the travelling scaffolding frame (i.e., erection arch). The recreation of the original site helped some participants appreciate the site-specific building techniques and craftsmanship. Participant 39 valued the engineers' and craftsmen's contributions, and Participant 50 recognised the SOH as not only architecturally unique but also an example of stunning engineering and craftsmanship. Finally, Participants 38 and 25 commented positively on the effectiveness of VR in conveying construction methodologies and the translation of shop drawings into construction methods.

4. Discussion and conclusion

This paper introduces a novel perspective on evaluating twentieth-century Architectural Heritage, highlighting the considerable promise of VR in deepening the comprehension and appreciation of intangible heritage values related to construction practices developed for it. This is particularly evident in the analysis of complex structures such as the SOH, which was adopted here as a case study.

4.1. Impact of VR on the heritage sector

The overwhelmingly positive feedback from survey participants confirms VR's effectiveness in enhancing understanding of the construction process and its heritage significance. This aligns with the growing trend in heritage conservation of incorporating digital technologies for educational and preservation purposes.

It also showed that VR emerges as a powerful medium in the heritage sector, particularly when cultural values intertwine with the act of building. Participants' ability to grasp complex technical details and appreciate the craftsmanship of the SOH's construction underscores VR's potential as an effective interpretative tool for intricate aspects of cultural significance. Notably, the immersive experience provided participants with a deeper insight into the complexity and craftsmanship of the Opera House's construction, aiding their comprehension of its universal value, as characterised by its unique design and construction, in line with UNESCO's Outstanding Universal Value of the building.

VR technologies offer immersive experiences surpassing traditional methods, effectively conveying ephemeral messages and values. However, based on this experience, its effectiveness varies based on participants' backgrounds and pre-existing knowledge. Heritage and conservation experts found the VR experience more enriching than those from other fields. The same can be said, noting that architecture experts appreciated the DHC project more than general experts, indicating the potential for tailored VR experiences at different expertise levels.

The study's findings also have implications for heritage policy and practice, especially in documenting and preserving the intangible, transient processes of architectural heritage. This could lead to more comprehensive documentation and conservation approaches, encompassing the physical preservation of construction narratives and documents.

4.2. Heritage value of construction documentation through VR

At the ICOMOS Heritage Exhibition, VR participants recognised the cultural and technical importance of the SOH's construction documentation. This suggests VR's effectiveness in elucidating and disseminating construction documentation content, enhancing appreciation for the intricate processes in making heritage projects.

The study reinforces the cultural significance of the construction process in the SOH, often overshadowed by the final architectural product. More specifically, the SOH's construction documentation, including technical drawings and builders' contributions, is identified as a crucial part of its heritage narrative. This view complements traditional assessments, advocating for a more inclusive approach that considers both the creation process and the final result.

However, the extent of cultural value recognition varied among participants. Those with a personal or academic connection to the Opera House were more likely to recognise the importance of construction documentation. This suggests that recognising the value of the construction process and documentation requires prior engagement with the building. The diverse backgrounds of participants, encompassing heritage, architecture, and other fields, highlight VR's potential to bridge the gap between technical expertise and general appreciation of construction documentation and processes. The technology's ability to transform complex technical drawings and construction processes into immersive, accessible experiences is noteworthy, potentially leading to wider public engagement in heritage conservation.

Additionally, as the linear regression analysis revealed, appreciation of the drawings' cultural value correlates with participants' depth of understanding of building processes through VR. This implies that the research methodology and development employed in DHC project could be replicated in future case studies where documentation and assessment of construction processes are vital for heritage evaluation.

4.3. Feedback and future directions

Feedback on the VR experience highlighted areas for improvement, such as enhanced graphics, interactivity, and accessibility. These suggestions point to future directions for VR technology in capturing and sharing heritage values. As technology advances, VR could become a crucial component of the heritage sector, offering engaging and informative experiences.

Subsequent to the Heritage Exhibition, a revised VR experience was developed, incorporating simulations of construction workers to boost user engagement. Future plans involve exploring multi-sensory aspects of VR, including implementing haptic feedback. Haptic feedback (Kun et al., 2023), achieved through vibrations in VR controllers or potentially VR haptic gloves using the HaptX pneumatic system (HaptX, 2023), could enrich the archive scene interaction. Additionally, future iterations may collect real-time user behaviour data in VR, offering insights for further refinements.

Aside from technical advancements, the study underscores the need to balance technical detail with cultural storytelling in VR experiences. Future VR developments in heritage education should integrate these aspects, providing a comprehensive understanding of the building process, documentation, and their significance.

Following the Heritage Exposition, the DHC project was selected to feature two public events organised for the celebration of the 50th anniversary from the opening of the SOH.

The first event was hosted at the Centre for Creativity of the SOH, as part of their public conversation series within the official SOH BUILD education initiative (Sydney Opera House, 2023), while the second event occurred at the Museum of Sydney (The Museums of History NSW, 2023), serving as a spin-off to the commemorative exhibition "The People's House: Sydney Opera House at 50". These events, closely align with ICOMOS's conservation strategies for twentieth-century cultural heritage, aiming to promote and celebrate such heritage and facilitate its interpretation and appreciation within the broader community, thereby engaging key audiences and stakeholders (ICOMOS, 2017). Beyond the heritage sector, the SOH BUILD education initiative successfully allowed a broad range of university students in the built environment to test the VR. The effectiveness of this initiative confirms the success of using digital simulation technologies in education as media to increase productivity in learning and training processes (Ardiny and Khanmirza, 2018). Since the COVID-19 lockdowns and face-to-face restrictions, the application of such technologies has demonstrated a diversity of applications in different fields, mainly through an ability to combine different technologies, processes, and user experiences. After architectural visualisation and design, the second largest application of VR in construction education is in health and safety training (Wang et al., 2018). In academia, desktop VR environments for educational settings of engineering and technology concerning teaching students about the construction processes of steel, concrete, and lightweight structures (Haque, 2005) can be seen as a clear application development in the future.

In conclusion, this study underscores VR technology's significant potential in enhancing heritage value understanding, particularly in complex construction projects like the SOH. VR's integration into architectural heritage and conservation offers a novel and effective means to deepen appreciation of both tangible and intangible heritage values. As the field evolves, the applications of VR in conservation appear extensive, promising a richer, more immersive approach to preserving and understanding our architectural heritage.

Ethics statement

The survey presented in this paper was approved by the Human Research Ethics Committee of the University of Sydney, as per the approval for the project titled "Mixed Reality Presentations in Architecture" (Protocol Number: 2019/701).

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors express their gratitude for the assistance in the 3d modelling adopted in the VR and VR simulation to Aidan Walbran, Xinlin Lin, Yingying Chen, Yuxin Tang, and Hang Xu. The model reconstructions are based on original archival material, especially the site journals and shop drawings of contractor Hornibrook Limited held at the Museum of History New South Wales, as well as photographic material at the Mitchell Library, State Library of New South Wales. Special thanks are extended to museum staff, particularly Bonnie Wildie and Norm Ricaud, for their support and assistance. Finally, the authors would like to express their gratitude to Michael Elfick, the original surveyor who worked on the Sydney Opera House, for his invaluable construction photographs.

This work was supported by the University of Sydney School of Architecture, Design, and Planning, and the University of New South Wales School of Built Environment.

Sidebar

Received 14 January 2024; received in revised form 20 February 2024; accepted 26 February 2024

Footnote

* Corresponding author.

E-mail address: [email protected] (L. Cardellicchio).

Peer review under responsibility of Southeast University.

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