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Abstract: To promote the understanding of shrinkage related behaviour of concrete used for tunnel linings the experimental and theoretical investigation including numerical and analytical approach was performed on ring-shaped specimens. Overall one analytical (an.) and two numerical models, namely (i) and (ii) were also developed. Models (an.) and (i) considered the restraining steel ring to be rigid, thus not exhibiting any deformation. Numerical model (ii) considered the steel ring to be deformable. The experimental set-up consisted of a large concrete ring with an inner diameter of 120 cm, an outer diameter of 160cm and 20 cm in height. The restraining steel ring was 5.5 cm thick. Two concrete rings were made, namely R1 with a low compressive strength of ~26MPa and the other, R2, with medium compressive strength of ~40 MPa. The strain was measured in the hoop direction on the inner circumference of the steel ring and on the outer circumference of the concrete ring. Concrete rings were subjected to circumferential drying. Numerical model (ii) predicted critical time to the formation of the first crack to be between 13 and 14 days. The experimentally determined critical time is found to be 11 to 13 days with cracks gradually opening over several days. This was indicated by changes in measured concrete and steel strain. Modelled concrete strain just before cracking was between -20 and -30 % 10-6 m m-1 however, measured concrete strain was ~150 % 10-6 m m-1. Modelled steel strain was between -30 and -40 % 10-6 m m-1 while measured steel strain was between -10 and 20 % 10-6 m m-1. These discrepancies, in particular the positive steel strain obtained in experiments, require further investigation and improvements of the experimental set-up.
Keywords: concrete, tunnel lining, restrained shrinkage, Reissner beam theory, modelling
Published in DiRROS: 19.01.2024; Views: 196; Downloads: 86
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Abstract: The construction sector is recognised as having a key impact on the life on Earth. Consequently, the EU has set clear environmental goals for 2030 and 2050, and is developing policies and tools to achieve them. One of the tools for achieving these goals is to establish a system for the evaluation of the environmental performance of buildings, with the priorities of reducing GHG emissions, saving with natural resources and preserving the environment, while maintaining sustainable development and ensuring a healthy living environment. Slovenia has joined in achieving this goal with a study on the state-of-play, commissioned a few years ago by the Ministry of the Environment and Spatial Planning, as the starting point for the development of sustainable building indicators (SBIs). The research, which included an analysis of the Slovenian legislation, commercial certification systems for sustainable buildings and development in the field of green public procurement, exposed complementary but rather different goals and views. It further showed that the Level(s), which provides a common EU approach in assessing the environmental performance of buildings, seems to be the most appropriate framework and the basis for the development of the Slovenian system of SBIs. The development of the Slovenian SBIs is currently underway within the project LIFE IP CARE4CLIMATE with the preparation of guidelines, data sources and procedures for determining the value of individual indicators for the assessment of buildings. Initial research with key construction stakeholders has shown that the solution must be linked to the national building legislation, computational methods and software tools, and also to the established planning procedures. The analyses have also shown that, parallel to developing such a system, it is essential to provide a functional supporting environment and a specific, purposely designed information platform to connect the stakeholders with the developers of the sustainable building indicators system.
Keywords: sustainable building indicators, evaluation, assessment, Level(s), CARE4CLIMATE
Published in DiRROS: 19.01.2024; Views: 152; Downloads: 74
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Abstract: Explosivity of basaltic eruptions is related to the efficiency in which exsolved gas can separate from the melt during ascent, which is controlled by magma permeability. However, basaltic pyroclasts from eruptions of varying explosivity can show similar permeability, indicating a possible complex relationship between permeability, outgassing and eruptive style. Here, we provide 3D measurements of basaltic pyroclasts using X-ray microtomography. We investigate the role of permeability and outgassing on magma ascent dynamics by using a numerical conduit model. Among the permeable parameters, bubble number density and friction coefficient largely affect explosivity. However, for fast ascending basaltic magmas, gas-melt coupling is maintained independent of magma permeability. In this case, magma storage conditions may determine eruptive style, driving rapid magma ascent, crystallisation and bubble nucleation, producing a highly explosive eruption. Monitoring parameters which reveal pre-eruptive conditions may assist hazard mitigation, particularly for basaltic systems which exhibit a wide range in eruptive style.
Keywords: natural hazards, petrology, volcanology
Published in DiRROS: 12.01.2024; Views: 190; Downloads: 108
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Abstract: A J-value assessment was carried out to quantify the costs and benefits of sprinkler system installation in car parks, both with respect to life safety and property protection. Nine scenarios were established based on collected input data. All car park types were considered for the USA, England, Scotland, Wales and the UK nations collectively, while separate considerations were made for multi-storey car parks (MSCPs) in the UK and for MSCPs, underground and other parking types in England. Even when assuming 100% sprinkler effectiveness, the J-values for the nine scenarios were all larger than unity (ranging from 5 to 555), thus indicating that the installation of sprinklers is not a cost-effective investment for car parks from a societal point of view. The analysis showed that different car park types must be treated separately, due to specifics of structure and fire statistics. The lowest J-values were obtained for MSCPs and underground car parks. Sprinkler installation mainly provides property protection benefits, because of property loss savings substantially outweigh those associated with life safety. Even though sprinklers were not cost-effective for car parks in the current analysis, the scarcity of data and new emerging technologies suggests that further investigation is needed.
Keywords: cost-benefit analysis, J-value, life quality index, Car parks, Sprinkler systems
Published in DiRROS: 09.01.2024; Views: 175; Downloads: 61
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Abstract: Concurrent flame spread data for thermally-thin charring solid fuels are presented from Saffire and BASS experiments performed in habitable spacecraft for three duct sizes, five sample sizes, two materials, and two atmospheres. The flame spread rates and flame lengths were strongly affected by duct size even for the relatively large ducts (> 30 cm tall). A transient excess pyrolysis length (i.e., flame length overshoot) was observed for the cotton fabric that burned away, which indicates that the transient excess pyrolysis length phenomenon is caused by more than just the flame moving into the developing boundary layer thickness as was the case with the SIBAL sample. A burnout time, defined as the pyrolysis length divided by the flame spread rate, normalized the pyrolysis length histories into a single curve with a steady burnout time of 22 s for the SIBAL fabric. The transient excess pyrolysis length is hypothesized to be a post-ignition flame growth transient for the essentially two-dimensional flames where the burnout time becomes very long until the preheat and pyrolysis lengths develop. The three-dimensional flames over narrow samples have lateral thermal expansion and lateral oxygen diffusion which allows them to transition to a steady state length without the transient excess pyrolysis length. Surface temperature profiles, nondimensionalized by the pyrolysis length, indicate that the temperature profiles exhibit the same shape across the pyrolysis zone. A surface energy balance calculation in the preheat region revealed that the heat flux increased rapidly at the pyrolysis front to near the critical heat flux for ignition. An estimate of the acceleration of the inviscid core flow in the duct due to thermal expansion and developing boundary layers on the duct walls and the SIBAL sample surface seems to explain the observed spread rate trends across three duct sizes and multiple sample sizes.
Keywords: concurrent flame spread, microgravity, duct size, sample size, cellulose fabrics
Published in DiRROS: 08.01.2024; Views: 169; Downloads: 36
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