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Povzetek: When creating a simulation model to assess the performance of buildings, there is usually a lack of feedback information. Only in the case of measurements of a real building is a direct comparison of the measured values and simulated results possible. Parameter data related to users’ behavior or other events can also be obtained. Their evaluated frequency, magnitude and duration, along with boundary conditions, are crucial for the results. It is clear that none of them can be predicted very accurately. Most of them, however, are needed for computer modeling. In this paper we analyzed the well-defined TRNSYS simulation model of offices equipped with radiant ceiling panels for heating and cooling. The model was based on real case offices and was validated based on measurements for 1 year. The analysis included simulations in order to define what effect the parameters related mainly to users have on the energy use and the indoor air temperatures. The study confirmed that specific human activities influence the annual energy use to a relatively small degree and that their effects often counteract. It also confirmed the even more important fact that although small, these activities can influence the thermal comfort of users. It is believed that despite the fact that this research was based on an analysis of offices equipped with radiant ceiling panels, most of the results could be applied generally.
Ključne besede: measurements, modeling, simulation, validation, analysis, energy use, temperature
Objavljeno v DiRROS: 15.09.2023; Ogledov: 122; Prenosov: 63
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Povzetek: Bridge weigh-in-motion systems use instrumented bridges or culverts to weigh vehicles as they pass over the structures. They also provide data to allow the calculation of several bridge performance indicators. The article starts with the basics of a bridge weigh-in-motion system and briefly describes two key bridge performance indicators, girder distribution factor and dynamic amplification factor, which are also derived from B-WIM measurements. The central part of the article focuses on monitoring of influence lines, the third key parameter that characterises the bridge performance under traffic loads. First, the method of calculating the bending moment influence lines from random heavy traffic is described. A coefficient of rotational stiffness is introduced, which defines the shape of influence lines around the supports as a linear combination of the ideal simply supported and fixed supported influence lines, to allow quantifying the influence line changes. Then the long-term monitoring of influence lines is investigated on four different single-span test bridges. The initial focus is given on the examination of the effect of temperature on the shape of influence lines. Finally, two sets of influence lines are compared on one test bridge, one from before and the other from after replacing the expansion joints and bearings. The work done so far confirms that calculating of influence lines from random vehicles with a B-WIM system is entirely feasible and that differences in their shape can be detected on single-span bridges. What remains to be investigated is the comparison of these differences to the actual damages and under which circumstances the proposed procedure can compete with or better the routine bridge inspection and the conventional monitoring techniques.
Ključne besede: bridge loading, bridge response, temperature dependency, influence line, monitoring
Objavljeno v DiRROS: 12.09.2023; Ogledov: 190; Prenosov: 62
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Povzetek: The influence of different curing temperatures on the hydration of belite-calcium sulfoaluminate cement was investigated at 20, 40 and 60 °C. The hydration kinetics and the hydrated phase assemblages were studied by isothermal calorimetry, X-ray powder diffraction, differential thermal analysis and thermogravimetric analysis, as well as field emission scanning electron microscopy. The compressive strength development of the cement pastes was also determined. Results showed that, at early ages, hydration was faster and early compressive strength was higher at elevated temperatures than at ambient temperature. On the other hand, at late ages in cement pastes cured at 60 °C, the amount of ettringite decreased, leading to lower compressive strength, indicating that the degree of hydration was lower at higher temperatures. Moreover, at elevated temperatures prismatic ettringite crystals became smaller due to faster hydration. Other hydration products present were aluminium hydroxide, which is formed together with ettringite from the hydration of calcium sulfoaluminate and gypsum, and C–S–H which precipitates as a main hydration product of belite. Belite hydrated in a lesser amount, especially at 60 °C, when the lowest amount of C–S–H was observed.
Ključne besede: hydration, cement, temperature, belite, calcium sulfoaluminate, open access, hidratacija, cement, temperatura, belit, kalcijev sulfoaluminat
Objavljeno v DiRROS: 04.08.2023; Ogledov: 118; Prenosov: 86
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Povzetek: The influence of temperature on the early hydration of belite-calcium sulfoaluminate cements with two different calcium sulfate to calcium sulfoaluminate molar ratios was investigated. The phase composition and phase assemblage development of cements prepared using molar ratios of 1 and 2.5 were studied at 25, 40 and 60 ◦C by in situ X-ray powder diffraction. The Rietveld refinement method was used for quantification. The degree of hydration after 24 h was highest at ambient temperatures, but early hydration was significantly accelerated at elevated temperatures. These differences were more noticeable when we increased the temperature from 25 ◦C to 40 ◦C, than it was increased from 40 ◦C to 60 ◦C. The amount of calcium sulfate added controls the amount of the precipitated ettringite, namely, the amount of ettringite increased in the cement with a higher molar ratio. The results showed that temperature also affects full width at half maximum of ettringite peaks, which indicates a decrease in crystallite size of ettringite at elevated temperatures due to faster precipitation of ettringite. When using a calcium sulfate to calcium sulfoaluminate molar ratio of 1, higher d-values of ettringite peaks were observed at elevated temperatures, suggesting that more ions were released from the cement clinker at elevated temperatures, allowing a higher ion uptake in the ettringite structure. At a molar ratio of 2.5, less clinker is available in the cement, therefore these differences were not observed.
Ključne besede: in situ X-ray diffraction, hydration, temperature, cement, rietveld analysis
Objavljeno v DiRROS: 26.06.2023; Ogledov: 173; Prenosov: 111
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Povzetek: Single edge-notched three-point bending tests (SEN-TPB) for mode I were utilized to experimentallyevaluate fracture properties of adhesive bondlines in European beech (Fagus SylvaticaL.). Thebondline was examined at two anatomical planes with TR and RT orientation and at control andtwo elevated temperatures (70°C and 140°C). Among epoxy (EPI), melamine-urea formaldehyde (MUF), and polyurethane (PUR) adhesives, the highest average critical energyGcwith 0.80 N/mmand fracture energyGfwith 1079.4 N/mm were obtained for EPI in the TR plane and understandard climate conditions (20°C/65% relative humidity), followed by MUF (Gc= 0.50 N/mm andGf= 620 N/mm) and PUR (Gc= 0.25 N/mm andGf= 290.9 N/mm), respectively. PUR was leasteffected by elevated temperature, and no significant differences forGcandGfbetween TR and RTbondline orientations were found for MUF and PUR treated at 20°C/65% relative humidity whilecomparisons between other factors varied significantly. Treatment of specimens at elevatedtemperatures resulted in reduced fracture performance regardless of wood grain orientation orthe adhesive system.
Ključne besede: crack, fracture, grain orientation, temperature, European Beech, odprti dostop
Objavljeno v DiRROS: 03.05.2023; Ogledov: 256; Prenosov: 173
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