Off-site Fabrication Research Articles

A Global Snapshot of 3D-Printed Buildings: Uncovering Robotic-Oriented Fabrication Strategies

This paper aims to provide a global snapshot of concrete 3D-printed buildings and to uncover robotic-oriented large-scale fabrication strategies. Therefore, an extensive internet search and literature review was carried out to investigate 3D-printed buildings. In this study, 154 construction projects with 204 buildings were systematically recorded and evaluated from 2013 up to 2023. Using an exploratory mixed-methods approach and a comparative case study analysis, a total of 88 3D-printed buildings were first evaluated descriptively. Thereafter, different existing printing strategies for in situ, on-site, and off-site production were identified, using an iterative approach. In addition to the geographical distribution, the descriptive evaluation also showed the key players as drivers for the spread of the 3D-printing technology and the correlations between printer type, fabrication strategy, and the building size. With regard to the printing strategy, three different approaches for in situ and off-site fabrication can be defined, depending on the printer types and their characteristics (work size and mobility): print-in-one-go, horizontal or vertical segmentation, and the multi-element vs. full-scaled wall strategy. However, the study showed that the data quality was sometimes difficult due to a lack of information and essential details of the printing process and segmentation.

Facilitating Circular Transition in the Construction Industry: Optimizing a Prefabricated Construction Site Layout Using a Novel BIM-Integrated SLP-GA Model

Prefabricated construction is being developed as one of the pathways toward circularity in the construction industry. However, compared to traditional cast-in-place construction methods, the design of prefabricated construction site layouts presents unique challenges, such as managing the space for prefabricated components and lifting equipment, and coordinating the precise timing between off-site fabrication and on-site assembly. Existing research has primarily focused on traditional cast-in-place construction, leaving room for improvement in optimisation models for prefabricated site layouts. This study develops a BIM-based System Layout Planning-Genetic Algorithm (SLP-GA) model specifically tailored for prefabricated construction site optimisation. The proposed model improves the accuracy and visualisation of layout planning through BIM technology, enabling dynamic adjustments and real-time data integration. It also incorporates genetic algorithms to address complex multi-objective optimisation problems, avoiding local optima and overcoming the limitations of traditional SLP methods that rely on subjective judgements. Unlike previous studies that do not consider secondary handling, the optimisation objectives of this study focus on minimising material handling costs associated with secondary handling and maximising comprehensive relationships, including efficiency, safety and space utilisation. The application of this model in a case study shows a reduction in logistics costs of 8.58% and an improvement in comprehensive relationships of 11.61%, indicating significant improvements. This research advances optimisation methods for prefabricated construction site layouts, enriches optimisation objectives by considering secondary handling, and provides practical guidance for improving the efficiency and effectiveness of prefabricated construction projects.

Barriers to achieving satisfactory dropped objects safety performance in the UK construction sector

In 1980 a deadly explosion occurred at a nuclear missile base precipitated by a dropped object. The potential for major catastrophe, an industry call to action and a research gap forms the rationale for this research into dropped objects. The aim of the research was to devise guidance to assist United Kingdom (UK) based construction sector companies to reduce the frequency of dropped object incidents. A mixed research approach that includes literature review, semi-structured interviews and case studies were used to achieve the purpose of this research. The trend data revealed that dropped object incident rates have remained flat in recent years. The quantitative incident reports and qualitative feedback from interviews concluded that design is a contributory factor in a significant number of incidents and possibly in many cases but more research with a larger quantitative research sample is required. The interviews and literature review revealed several useful recommendations to sector bodies, construction sector companies and for further academic research. Recommendations to Individual Construction Sector Companies are grouped into different themes including manage, eliminate and control. The main recommendations to regulators included ensuring that tool tethering and containers are marked and inspected in line with other lifting equipment. Industry bodies could consider liaising with the energy industry to develop a suitable general construction exclusion zone calculator. Initiatives to improve the design of Mast Climbing Work Platforms to provide integral storage and enclosure solutions could be initiated with the vendors of this equipment. Practitioners and companies could consider offsite construction as a strategic means to reduce the number of dropped objects and consider work scopes that could be executed at ground level rather than at height. Consideration could be given to the more commonly deployed off-site fabrication options such as façade panels and bathroom pods. During detailed design, companies could have a high focus on the mechanism of reducing fixings in facades using Building Information Modelling.There are a number of areas which can be investigated further such as the implications of offsite construction on dropped objects accidents when compared with traditional methods. The research findings hint that Business Information Modelling might be a useful tool to reduce dropped objects on construction sites especially related to facades.While there were several limitations of the research including a limited amount of quantitative data and availability of the specific interview group, the findings of the research will still be useful for the construction sector in the UK and overseas to improve safety performance in construction.

Novel Panelized Roof Design for Offsite Fabrication of Residential Light-Frame Wood Homes

Novel Panelized Roof Design for Offsite Fabrication of Residential Light-Frame Wood Homes

MODULAR CONSTRUCTION: A SUSTAINABLE SOLUTION FOR CARBON EMISSION REDUCTION IN THE CONSTRUCTION INDUSTRY

This research focuses on modular construction as a sustainable solution for reducing carbon emissions in the construction industry. The study examines the environmental benefits of modular construction and its potential to mitigate the carbon footprint associated with traditional construction methods. Through a comprehensive literature review and analysis of case studies, the research explores the use of modular construction techniques, including off-site fabrication and assembly, eco-friendly materials, energy-efficient systems, and renewable energy technologies, to minimize carbon emissions throughout the building lifecycle. The findings highlight the advantages of modular construction in terms of reduced construction time, improved resource efficiency, and lower energy consumption, resulting in significant carbon emission reductions. The research contributes to the existing body of knowledge by emphasizing the importance of adopting sustainable practices in the construction industry and provides valuable insights into the role of modular construction as a sustainable solution for carbon emission reduction.

Bundling elastic gridshells with alignable nets. Part I: Analytical approach

Elastic gridshells (EGS) offer a cost-effective and rapid way to construct lightweight structures. This paper focuses on bundlable EGS, gridshells which may be deployed from a compact slender state, thus allowing for off-site fabrication. Some bundlable EGS have the additional property of being self-shaping, an aspect that simplifies considerably the erection phase. Despite recent research interest, there is still a lack of understanding of the design space of bundlable EGS, and a need for intuitive design tools for preliminary design phases – in particular for self-shaping EGS. Based on this observation, this article introduces alignable nets, shapes that inherently fulfill the metrical compatibility constraint of bundlability. This mathematical formulation allows to identify analytical shapes of bundlable EGS, which constitute very accessible design tools. In particular, surfaces of revolution appear to be a valuable tool for the conceptual design of self-shaping gridshells, as they may give instant feedbacks on the mechanical energy required for deployment – allowing notably to design structures that may be deployed with zero total external work.

Synchronising Off-Site Fabrication with On-Site Production in Construction

The aim of this study is to explore how offsite fabrication (OSF) can be tightly coupled with production and assembly on-site. Prefabrication is a production method that has potential to yield significant productivity and sustainability improvements in the construction industry. Failure to synchronise production in the factory with on-site production can lead to financial losses for the client/owner, main contractor and subcontractors as well as to delays in the construction schedule. The study draws on two case-studies and the authors’ experiences in the context of a critical review of literature on the concepts of flow and Just-in-time (JIT) construction delivery. The findings show the value of a buffer between suppliers, fabricators and the site as a way to help the whole supply team create production flow and more environmentally friendly results. A buffer can help while the team is learning to use collaborative short-term planning to create predictable production. The paper recommends ways to synchronise OSF with on-site production. The paper provides practitioners with ideas to reduce both work waiting for workers (or robots) and workers (or robots) waiting for work – and it contributes to theory by raising more questions for further research.

Optimizing the prefabrication finishing level in modular construction

Prefabricated modules in modular construction projects can have a wide range of finishing levels that range from partially completed with only structural frame to fully completed with all structural, wall, mechanical, electrical, finishing and furnishing components. A higher module finishing level increases the offsite fabrication and transportation cost and decreases onsite assembly cost and duration while a lower finishing level produces the opposite results. This paper presents an optimization model that enables construction planners to identify an optimal finishing level for prefabricated modules to minimize the total cost of modular construction projects that includes all offsite fabrication, transportation, and onsite assembly costs. A case study of a modular construction project for a healthcare facility was analyzed to illustrate the use of the model and evaluate its performance. The results of this analysis highlight the original capabilities of the model in minimizing the total cost of modular construction projects by identifying an optimal finishing level for each module type in the project from a set of feasible alternatives with varying building components, weights, and cost rates.

Analysis of neutron physics and thermal hydraulics for fuel assembly of small modular reactor loaded with ATFs

The new small modular reactor (SMR) NuScale has been in the approval process for Nuclear Regulatory Commission by its off-site fabrication and assembly and good safety performance. To ensure the safety of the fuel rod the rod ejection accident at the beginning of cycle (BOC) and the end of cycle (EOC), the traditional fuel rod is replaced by accident tolerant fuels (ATFs). Neutron physics and thermal hydraulic analysis need to be performed before the actual application to ensure feasibility. In this paper, neutron physics and thermal hydraulics for SMR loaded with ATFs are analyzed. The results show that the 4% uranium enriched ATF pellets can meet the lifetime requirements, and the application of silicon uranium fuel pellets can significantly reduce maximum fuel centerline temperature (MFCT). Safety margin analysis was also performed for different ATF material failure criteria. The results show that ATF materials can enhance the safety of NuScale reactors.

FLEXURAL STRENGTH TEST OF PRECAST INDUSTRIALISED BUILDING SYSTEM BEAM-CORBEL CONNECTION

Industrialised Building Systems (IBS) involves offsite fabrication in a systematic and controlled environment. The aim of this research is to determine the structural performance of newly enhanced column corbel support for IBS industry application. However, there is no solid data to support the industry in producing safe and reliable IBS structure with newly enhanced prototype. Hence, the objectives of this research paper are to identify failure behaviour, flexural strength, maximum deflection and ductility of the IBS beam to column corbel connection. Scaled 1:5 IBS beams with column supports were prepared according to Buckingham and Similitude Theorem. Result contribution of five specimens were obtained from the flexural strength test. The scaled beam has maximum flexural resistance of 2.2 kNm and deflection of 7 mm. The projected flexural resistance for full scale beam is 1265.6 kNm with ultimate load deflection of 35 mm. Failure behaviours such as shear cracking, flexural cracking and concrete crushing have been identified. The average ductility of the specimen was 3.23 which is higher than 3.0 from PCI design handbook. The newly improved specimen has the load bearing improvement of 32%. Thus, this research has positive outcome that could improve the confident level of the industry user toward this product.

Assessing the Environmental Implications of Industrialized Housing: a Systematic Literature Review

Industrialized Housing (IH), also referred to as prefabrication, preassembly, modularization, and/or off-site fabrication, is a growing strategy for constructing housing. IH offers potential for significant reduction of environmental impact in comparison to traditional housing construction. Past research used methods such as environmental impact assessment on given case study buildings or expert’s opinions to identify the benefits and drawbacks present on the lifecycle of houses constructed partially or fully using IH methods. Nevertheless, this literature is scattered across several sources and units of analysis. The specific factors of IH that contribute to environmental impact reduction have not been comprehensively reviewed and summarized from design considerations up to the end of life possibilities. In this paper, a systematic literature review is performed on the environmental implications of the industrialized way of constructing residential buildings. From a review of 49 journal publications, this paper identifies 18 key factors that influence the environmental performance of such residential buildings. These factors are categorized into the following lifecycle phases of the IH process: a) system design, b) material design, c) manufacturing and logistics, d) transportation and assembly, e) Operational phase, and f) end of life. Findings reveal the importance of decisions made in design phases such as choice of materials, which in turn show a snowball effect throughout the phases. A final category – g) support and hindrance of IH - includes a discussion of external factors such as building codes and regulatory policies and their impact on IH performance.

Acoustic Emission Sensing for Crack Monitoring in Prefabricated and Prestressed Reinforced Concrete Bridge Girders

Prefabricated and prestressed beams are integral to accelerated bridge construction (ABC) and other construction projects, but concerns exist regarding the development of cracks during curing, form removal, detensioning, transport, installation, and operation. Acoustic emission (AE) sensing techniques have the potential for detecting and locating cracking in prefabricated, prestressed concrete girders used as prefabricated bridge elements and systems (PBES) in ABC as part of a quality assurance/quality control (QA/QC) program. AE measures the elastic waves produced by crack nucleation and growth with an array of point sensors. The AE instrument system is relatively portable, which can allow for it to be an option for off-site fabrication QA/QC and on-site field QA/QC. This paper presents AE measurements and analysis on relatively small laboratory reinforced concrete beam specimens under pullout and three-point bending to demonstrate the efficacy of AE in detecting cracks. It then presents application of AE during detensioning and lifting of full-scale Northeast Extreme Tee (NEXT) beams and Bulb Tee. The results indicate that AE sensing is a practical QA/QC process for PBES elements.

A Coordinated Approach for Supply-Chain Tracking in the Liquefied Natural Gas Industry

With the increased size and complexity of liquefied natural gas (LNG) projects, supply-chain management has become a challenging process due to involvements of the remote location of the project site and the multiple stakeholders. The transparency and traceability of the supply-chain are critical as any surpluses or shortages of materials will put the project at risk. Currently, limited research has been conducted on LNG projects considering the total supply-chain perspective, which refers to all stages of materials tracking in off-site manufacturing, transportation, and site logistics. The purpose of this research is to propose a framework of a coordinated approach for supply-chain tracking in the LNG industry. Two focus group studies were organized to develop the proposed framework: One for LNG construction supply chain process development, and another for alternative tracking technologies selection. In addition, two experiments, namely off-site fabrication tracking and site logistics tracking, were conducted in a field to evaluate the feasibility of the proposed framework. Technology limitations were also discussed in terms of field implementation.

Briefing: Design for manufacture and off-site construction at Woolston Wastewater Treatment Works (UK)

Due to numerous site physical constraints and a tight construction programme at Woolston Wastewater Treatment Works, UK, conventional design and construction practices are being challenged to deliver the project using off-site manufacturing wherever possible. Through early supplier engagement and collaboration, the team has developed design solutions to suit off-site fabrication: most of the permanent civil elements are to be supplied in precast concrete; larger mechanical elements are being designed in a modular arrangement; and mechanical and platform suppliers are developing these elements in factory conditions and delivering to the site with pipework and electrical elements pre-installed. By working within a building information modelling environment, the team manages supplier three-dimensional model sharing within a common data area, ensuring governance and version control. This enhances integration between suppliers, enabling early clash detection and providing confidence in the production of off-site elements. The adoption of an off-site manufacturing strategy has accelerated construction delivery, providing programme and cost savings, and improved the level of safety on-site through reduced working at height, temporary works requirements, lifting operations and plant and vehicle movements.

INDUSTRIALIZED BUILDING SYSTEMS: A BIBLIOMETRIC ANALYSIS FROM 1980 TO 2017

Industrialized building system (IBS) is an innovative building technology that provides faster, cleaner, neater, and more quality construction. Bibliometric quantification has been done to determine the amount of publications for this novel research area considering the scientific literature that are available from the Web of Science and to find the most common terms in this field to enable the researchers to study all the available terms. Bibliometric study is a new trend in scientific publication which statistically analyses the available published scientific paper and provide valuable information about changes in the trends in any field of study. As a result, the researchers have found that the number of publications in the field of industrialized building increased in the last decade. It is also found that the same system has different terms which represent industrialization of construction among the different countries. Industrialized building or industrialized building, Manufactured homes or Manufactured housing, Modern Methods of Construction (MMC), Modular building or Modular construction or Modular houses or modular homes, Offsite Manufacture/Manufacturing, Offsite Construction or Offsite Production or Offsite Fabrication, Prefabrication or Prefabricated and Relocatable homes/houses are different terms that used to refer to the same process that includes manufacturing all or some of buildings’ elements and then transport and install them at construction site. The distribution of publications among the countries has been swung. The term of "Prefabrication" or "Prefabricated" is widely used in China and the U.S., whereas, about 70% of the publications that used the term of "Industrialized building" or "Industrialised building" are from Malaysia. Moreover, there is a noticeable increment in the number of countries that conducted researches in this field.

Considering Materials Management in Construction: An Exploratory Study

While materials count for a considerable amount of construction costs, the way materials are managed seems to be improvised rather than approached methodically. This study investigates the practice of novel techniques used to manage materials in the construction industry. Techniques that have already proven themselves to be efficient ways to manage the production pace within the industry include the pull system, Just-In-Time, Kitting and off-site fabrication. These are explained and assessed in the context of the French construction industry through an exploratory study, supported by a questionnaire completed by contractors. The results reveal that a clear plan to manage materials on-site is lacking among the respondents, creating common inventory problems. This research provides evidence to support the central role played by an efficient management of material flow on-site. It also highlights the obstacles that hinder the adoption of innovative techniques, such as sub-contractor coordination.

Flexural behaviour of headed bar connections between precast concrete panels

The use of headed bars in joints between precast concrete elements allows continuity of reinforcement to be achieved over very short splice lengths. The paper describes a series of flexural tests carried out on specimens consisting of pairs of precast elements connected by overlapping headed bars of 25mm diameter. The headed bars overlapped by 100mm within a 200mm wide in situ concrete joint in which transverse bars and vertical shear studs were installed to provide confinement. This type of joint facilitates the construction of continuously reinforced slabs from precast elements thereby enabling significant reductions in overall construction time and improvements in construction quality due to off-site fabrication. The tests investigated the influence on joint strength, ductility and crack width of concrete strength, out-of-plane offset of precast planks and confining shear studs. Ductile failure with yield of 25mm diameter high strength headed bars was achieved with joint concrete having a cylinder compressive strength of 39MPa. A nonlinear finite element model is presented, which gives good predictions of joint strength as well as providing insight into joint behaviour.

Heathrow Airport Terminal 2B, Phase 2 – a new pier facility constructed in an operational airside environment

With London's Heathrow Airport recently celebrating its 70th year of commercial operation and looking forward to further expansion, this paper describes a major contribution to its passenger handling infrastructure. As part of the redevelopment of the eastern side of Heathrow Airport, destined to become the new Terminal 2 (The Queen's Terminal), Mott MacDonald was appointed to deliver the civil and structural engineering scheme and detailed design for an operationally complex pier, intended to serve 10M passengers a year. The new pier was delivered on a physically constricted site inside the high-security (airside) zone of this major international airport. Building in such a location creates a singular set of conflicting demands, headed by the need to minimise the risks to aircraft operations through carefully planned and executed construction operations that avoid potential security breaches or alarms. This manifests itself in increased logistical challenges, including the need to security screen all staff, plant and materials entering the construction site, manage the execution of major construction works next to passenger aircraft operations, and overcome the effects of aircraft noise on safe working practices. These exacting circumstances demanded an equally singular design approach, focused on the use of appropriate, dependable, on-site construction methods and maximising off-site fabrication. All this was to be achieved while working with the architect to create a passenger experience consistent with a leading international hub airport.

Application of discrete-event simulation to investigate effects of client order behaviour on off-site manufacturing performance in Australia

ABSTRACTOff-site manufacturing (OSM) has implied capabilities that could enhance housing supply in Australia. The OSM system requires the efficient management of two concurrent working locations: the off-site fabrication facility and the construction site. Client order behaviour impacts on the OSM system. Accordingly, client order information flow is an essential component for efficiently managing this system. This paper investigates the effects of client order behaviour on the performance of OSM within the Australian housebuilding context using discrete-event simulation (DES). The data used to develop the conceptual model were based on a review of 21 related technical documents and interviews with 13 OSM experts in Australia. The operational data used for executing the simulation model were collected through a questionnaire survey of 30 builders as well as three one-day site visits to the fabrication facilities and construction sites of three major building organisations in Australia. The simulation model assisted in experimentation with four scenarios that represent client order interaction in the OSM system in Australia. The model simulation results showed noteworthy improvements in house completion time and the number of completed client orders per year.

Simulation Based Validation of Supply Chain Effects through ICT enabled Real-time-capability in ETO Production Planning

According to Industry 4.0, real-time information in production planning and control, shows a high potential for optimizing the whole supply chain. The paper considers the plant building industry, especially the off-site fabrication and on-site installation. Traditionally, production planning is centralized following a Master Schedule that rarely is up to date, ignoring deviations on-site. As a result, components are delivered in advance or too late, which create non-value adding activities and high inventory levels. The paper proposes an ICT-supported nearly real-time capable production planning approach, which by means of a simulation, shows a drastically reduction of the inventory level on-site.