| 1. |
- Ahn, Namhyuck, et al.
(författare)
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Circular economy in mass timber construction : State-of-the-art, gaps and pressing research needs
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier. - 2352-7102. ; 53
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Tidskriftsartikel (refereegranskat)abstract
- The building and construction sector is a major contributor to human environmental impact on the planet. It follows that the sector's contribution is also crucial for transition towards a low carbon society and circular economy (CE). Mass timber products, are one of the sustainable alternatives to traditional building materials and have led to the recent revolution in timber construction. While environmental benefits of mas timber manufacturing and construction is well documented the end-of-life (EOL) and the post-EOL options for mass timber buildings, their environmental benefits and CE potential are discussed much less. Short history of construction technology involving prefabricated mass timber panels compared to traditional building types results in virtually no documented cases of panelized mass timber structures reaching the EOL stage and no practical examples of incorporating CE concepts in such projects. In this study, a two-step systematic literature review was used, to define and classify 23 CE-based governing principles from six categories in the construction industry, and to use those principles to analyze the state-of-the-art circular approach in mass timber research. The study covered a total of 90 papers, of which 68 focused on the general construction industry and 22 specifically on the mass timber construction. Results of this review suggest substantial gaps in knowledge and pressing research needs for the development of holistic approaches to prepare the mass timber construction for circular economy.
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| 2. |
- Du, Linpu, et al.
(författare)
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Shaking table test on a novel mega-frame suspended structural system
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier. - 2352-7102. ; 52
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Tidskriftsartikel (refereegranskat)abstract
- This paper designed a 1/20 scaled two-segment 19-story mega-frame suspended structure. The seismic behaviors of the structure equipped with viscous dampers (named damping suspended structure, DSS) or rigid connecting rods (named normal suspended structure, NSS) were studied and evaluated by a series of shaking table tests, where three seismic ground motions with two intensities were selected as input motions. Both acceleration and displacement responses of the primary and suspended structures were recorded. The results revealed that the mega-frame suspended system showed good seismic behaviors and viscous dampers could effectively improve its energy dissipation capacities. For DSS, the maximal acceleration and displacement reduction of suspended structures were 75.4% and 39.8% while those of the primary structure were 29.4% and 35.3% respectively. White noise tests showed all models were at the elastic stage under all cases. Evident relative displacements between the primary and subordinate structures were observed for DSS, in this case, the suspended floors were considered as the additional mass of the primary structure and the energy could be dissipated by the swing of suspended floors. The energy dissipation mechanism of DSS was theoretically analyzed while the effect of connection forms on vibration reduction was discussed.
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| 3. |
- Hussain, Syed Asad, et al.
(författare)
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Dissimilarity-driven ensemble model-based real-time optimization for control of building HVAC systems
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier BV. - 2352-7102. ; 52
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Tidskriftsartikel (refereegranskat)abstract
- Model-based real-time optimization (MRTO) is proven as an effective tool that can capture the complex dynamics of heating, ventilation, and air conditioning (HVAC) systems and improve its energy performance. Despite the energy benefits offered by MRTO, these approaches are rarely implemented in actual buildings. This is due to the reason that these approaches are very difficult to implement because they require the synthesis of a reliable and accurate performance model of the system. The reliability of decision-making with MRTO is directly related to the accuracy of these performance models. In addition, the model has to be computationally efficient for practical implementation. The development of such a model requires the most effort and is a major challenge in the implementation of MRTO. Several HVAC performance models are already available in the literature, and these can be classified as semiphysical models and data-driven models. The semiphysical models are generalized models with simplification assumptions that can provide consistent performance, however, with reduced accuracy. Contrastingly, the data-driven models can offer better accuracy; however, they lack robustness in terms of operational ranges. These factors affect the energy performance of MRTO, and an improper parametrized model could result in performance that is even worse than the conventional fixed setpoint or rule-based approaches. A dissimilarity-driven ensemble model-based real-time optimization (DEMRTO) approach is presented in this study that incorporates a dissimilarity-driven ensemble model in the framework of real-time optimization. The dissimilarity-driven ensemble model combines semiphysical models and data-driven models in a systematic manner to use one's strengths to address others' weaknesses, rather than developing a new form of a model. The performance of the proposed integrated approach was examined using case studies over three weather seasons in Hong Kong. The results showed as compared to the fixed setpoint approach the DEMRTO approach can provide significant energy savings up to 11.085% setpoint, and around 2.785% reduction in energy use as compared with the conventional MRTO approach. It was demonstrated that the proposed approach can capture diversity in load conditions and provide consistency in model prediction to improve reliability in decision-making with real-time optimization.
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| 4. |
- Jin, Hesong, et al.
(författare)
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An experimental study on the influence of continuous ambient humidity conditions on relative humidity changes, chloride diffusion and microstructure in concrete
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier BV. - 2352-7102. ; 59
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Tidskriftsartikel (refereegranskat)abstract
- Most engineering structures are exposed to various harsh environments, such as temperature fluctuations and humidity cycles, simultaneously. Additionally, moisture transfer and corrosive ion transport in concrete are driven by humidity gradients. Therefore, studying Chloride transport in concrete under constant humidity conditions is a meaningful research project. In this work, a new experimental setup was designed, and the Chloride diffusion behavior of concrete under a continuous humidity environment and NaCl immersion was investigated. Meanwhile, to accurately evaluate the internal humidity of concrete, humidity sensors were applied to the concrete. Additionally, the impacts of the water-binder ratio (w/b) and ambient humidity on the humidity diffusion coefficient, free Chloride content and bound Chloride content in concrete were evaluated. The microstructure was characterized by scanning electron microscopy, X-ray diffraction and mercury intrusion porosimetry. The results show that the content of free Chloride increases with an increasing w/b ratio. The humidity diffusion coefficient of concrete during water absorption (continuous high humidity environment) is significantly higher than that during water loss (continuous dry environment). Furthermore, under the drying condition, the Chloride content and the humidity diffusion coefficient on the concrete surface gradually increased, while during the wetting procedure, the Chloride content inside the concrete increased, and the humidity diffusion coefficient gradually decreased. However, the bound Chloride content inside the concrete is not affected by the humidity level in the environment. In the wetting environment, the calcium hydroxide in the matrix is gradually consumed, and the Chloride diffuses to the matrix to form more Friedel's salt and calcium carbonate. Moreover, lowering the w/b ratio or increasing the ambient humidity can enhance the formation of more hydrated compounds (C–S–H gel), which can reduce the total porosity and can also improve the ability of concrete to resist Chloride diffusion. Overall, this study provides a better understanding of and insight into the design and maintenance of seaside RC infrastructures.
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| 5. |
- Li, Yongqiang, 1992, et al.
(författare)
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Assessment of compositional changes of carbonated cement pastes subjected to high temperatures using in-situ Raman mapping and XPS
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier BV. - 2352-7102. ; 45
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new method for assessing the compositional changes of carbonated cement pastes subjected to high temperatures. In this new method, in-situ Raman mapping combined with X-ray photoelectron spectroscopy (XPS) was used to monitor the phase transformation in carbonated cement pastes subjected to various high temperatures from 30 to 950 degrees C. Two kinds of carbonated areas, i.e., vaterite dominated and calcite dominated, were found in the in-situ Raman measurements. With the elevation in temperature, most of the vaterite was converted to calcite at 500 degrees C and completely decomposed at 600 degrees C, while the decomposition of calcite started at 600 degrees C and finished at 720 degrees C. Meanwhile, the depolymerization of the calcium modified silica gel to the silicate phases with a lower degree of polymerization was initiated at 500 degrees C, which led to the crystallization of beta-C2S at 600 degrees C. The generation of beta-C2S was found to increase with the elevation in temperature and became the dominant phase at 950 degrees C. In conclusion, the high temperature could affect the stability of carbonated cement pastes at 500 degrees C and above. The in-situ Raman mapping measurement has provided an extraordinary view of the spatial distribution of interesting phases subjected to high temperatures in a nondestructive way, which should be more consistent with the true condition in the material.
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| 6. |
- Mahaki, Mohammadbagher, et al.
(författare)
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Experimental and numerical simulations of human movement effect on the capture efficiency of a local exhaust ventilation system
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier. - 2352-7102. ; 52
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Tidskriftsartikel (refereegranskat)abstract
- In local exhaust ventilation systems, external turbulence from e.g. human movements can affect the capture efficiency of the system considerably. In this study, experimental and numerical (CFD) approaches were utilized to evaluate the effect of human movement on the capture efficiency of a local exhaust ventilation system with an exterior circular hood. Human movements were simulated by back-and-forth movements of three human-sized moving objects: a flat plate (CFD + experimental), a cylinder (CFD) and a human-shaped manikin (CFD), respectively. The experiments consisted of tracer gas measurements in a full-scale test room. The numerical simulations included dynamic mesh methods to handle object movements. The results showed reasonable agreement between numerical and experimental results regarding the capture efficiency at different movement frequencies and exhaust flow rates, indicating that CFD is a feasible method for investigating complex flows of the studied kind. In comparison with the moving manikin, the moving plate caused significantly lower capture efficiency, whereas the moving cylinder yielded higher values. Overall, the results with the cylinder as moving object proved more similar to those of the manikin than the results with the flat plate. These findings have particular relevance towards existing test standards that stipulate the use of a moving flat plate in similar test situations. Further, some parameter variations verified that local exhaust capture efficiency increases by increasing the exhaust air flow rate and movement time interval, and also by decreasing the distance between contaminant source and exhaust hood opening. Also increasing the distance between the movable object and the contaminant source, as well as decreasing the diameter of the exhaust hood opening increased the capture efficiency.
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| 7. |
- Pieskä, Henrikki, et al.
(författare)
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Thermodynamic and thermal comfort performance evaluation of two geothermal high-temperature cooling systems in the mediterranean climate
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier BV. - 2352-7102. ; 56, s. 104738-104738
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Tidskriftsartikel (refereegranskat)abstract
- The European Commission aims to reduce the greenhouse gas emissions of the European Union's building stock by 60% by 2030 compared with 1990. Meanwhile, the global demand for cooling is projected to grow 3% yearly between 2020 and 2050. High-temperature cooling systems provide cooling with lower exergy use than conventional cooling systems and enable the integration of renewable energy sources, and can play a crucial role in meeting the growing cooling demand with less energy use. The aim of this study is to analyse and critically evaluate two high-temperature cooling systems in terms of their energy and exergy use in a case study. We also consider thermal comfort performance, CO2 emissions, and sensitivity to changing operating conditions. The two systems considered are a mechanical ventilation system with heat recovery combined with geothermal cooling (GeoMVHR) and a radiant cooling system with ceiling panels connected to the same geothermal cooling (GeoRadiant) system. The study is conducted using building energy models of a typical office building belonging to a three-building school complex located in Sant Cugat near Barcelona, Spain. IDA ICE 4.8 simulation software was used for the simulations. The results show that the two different installations can produce near-identical thermal comfort conditions for the occupants. The GeoRadiant system achieves this result with 72% lower electricity use and 60% less exergy destruction than the GeoMVHR system. Due to the higher electricity use, the CO2 emissions caused by the GeoMVHR system are 3.5 times the emissions caused by the GeoRadiant system.
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| 8. |
- Sadrizadeh, Sasan, et al.
(författare)
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Indoor air quality and health in schools : A critical review for developing the roadmap for the future school environment
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier Ltd. - 2352-7102. ; 57
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Tidskriftsartikel (refereegranskat)abstract
- Several research studies have ranked indoor pollution among the top environmental risks to public health in recent years. Good indoor air quality is an essential component of a healthy indoor environment and significantly affects human health and well-being. Poor air quality in such environments may cause respiratory disease for millions of pupils around the globe and, in the current pandemic-dominated era, require ever more urgent actions to tackle the burden of its impacts. The poor indoor quality in such environments could result from poor management, operation, maintenance, and cleaning. Pupils are a different segment of the population from adults in many ways, and they are more exposed to the poor indoor environment: They breathe in more air per unit weight and are more sensitive to heat/cold and moisture. Thus, their vulnerability is higher than adults, and poor conditions may affect proper development. However, a healthy learning environment can reduce the absence rate, improves test scores, and enhances pupil/teacher learning/teaching productivity. In this article, we analyzed recent literature on indoor air quality and health in schools, with the primary focus on ventilation, thermal comfort, productivity, and exposure risk. This study conducts a comprehensive review to summarizes the existing knowledge to highlight the latest research and solutions and proposes a roadmap for the future school environment. In conclusion, we summarize the critical limitations of the existing studies, reveal insights for future research directions, and propose a roadmap for further improvements in school air quality. More parameters and specific data should be obtained from in-site measurements to get a more in-depth understanding at contaminant characteristics. Meanwhile, site-specific strategies for different school locations, such as proximity to transportation routes and industrial areas, should be developed to suit the characteristics of schools in different regions. The socio-economic consequences of health and performance effects on children in classrooms should be considered. There is a great need for more comprehensive studies with larger sample sizes to study on environmental health exposure, student performance, and indoor satisfaction. More complex mitigation measures should be evaluated by considering energy efficiency, IAQ and health effects.
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| 9. |
- Yan, Zidi, et al.
(författare)
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Performance of reversible timber connections in Australian light timber framed panelised construction
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier BV. - 2352-7102. ; 61
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a novel insight into using reversible mass timber connectors in light-timber framed (LTF) construction to create dismountable, panelised LTF construction systems that enable adaptable building design and panel reuse in the context of a circular economy. The study presented in this paper focused on Australian LTF panelised construction:. A total of 10 IdeFix 304 connectors by SIHGA GmbH, and 20 M20 connectors by SHERPA Connection Systems GmbH were installed in Australian machine graded pine and subjected to monotonic tensile and shear loads to assess their feasibility in the given application. Two strength prediction models were evaluated in comparison to experimental results: Formulae given in the manufacturers’ European Technical Assessments (ETAs) and a prediction model adapted from literature. On average, the latter was more accurate in the given configuration. Considering the set goal of repeated assembly and disassembly, the connectors with a tight fit faced tolerance issues due to moisture fluctuations. Furthermore, rupture of the connector was observed in some instances, owed to higher screw withdrawal capacity in Australian timber. A reduction of the number of screws or their length is suggested to achieve a more ductile response with screw withdrawal. Finally, following comparative analysis of experimental tests and prediction models, recommendations were made for future design of novel LTF panel connectors in the context of disassembly and reuse.
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| 10. |
- Younis, Adel, et al.
(författare)
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Cross-laminated timber for building construction : A life-cycle-assessment overview
- 2022
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Ingår i: Journal of Building Engineering. - : Elsevier. - 2352-7102. ; 52
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Forskningsöversikt (refereegranskat)abstract
- The building industry is a large contributor to greenhouse gas (GHG) emissions and a vast consumer of natural resources. It is estimated that, in the next 40 years, around 415 Gt of CO2 will be released as a result of global construction activities. Therefore, improvements in construction technologies are essential to reduce GHG emissions and thereby attain national and international goals to mitigate climate change. Cross-laminated timber (CLT) has emerged as an innovative alternative material to steel/concrete in building construction, given its relatively low carbon footprint, not to mention its high strength-to-weight ratio, simple installation, and aesthetic features. CLT is a structural composite panel product developed in the early 1990s, and the contemporary generation of CLT buildings are yet to reach the end of their service life. Accordingly, there has been growing interest to understand and optimize the performance of CLT in building construction. In view of that, this paper presents an overview on the feasibility of using CLT in buildings from a life-cycle assessment (LCA) standpoint. The authors performed a brief review on LCA studies conducted in the past decade pertaining to the carbon footprint of CLT buildings. On average, the findings of these studies revealed about 40% reduction in carbon footprint when using CLT in lieu of conventional construction materials (steel/concrete) for multi-story buildings. Furthermore, the paper explores the challenges associated with conducting LCA on CLT buildings, identifies the gaps in knowledge, and outlines directions for future research.
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