Recently, standard fire resistance testing has been questioned for combustible products. A part of the comments address the thermal boundary conditions and the different thermal exposure of combustible products in comparison to incombustibles. These comments are evaluated in this technical note.To compare heat flux measurements of combustibles and incombustible products when tested in a furnace, furnace tests were performed. The furnace was controlled by plate thermometers to follow the EN 1363/ISO 834 standard temperature-time curve. It could be proven that (a) the heat flux measurements at the specimens surface behind the plate thermometer (PT) are not higher than in front of the PT. The reason for this is most likely that no flaming combustion is possible near the surface due to the low oxygen content typically for a furnace. It could be further shown (b) that the heat flux measurements when combustibles are tested follow the trend reported in literature for incombustibles. Further, (c) that the lower burner fuel used in furnaces is due to the contribution of the specimen (ca. 30% in the presented tests) and due to the lower thermal inertia (ca. 20% in the presented tests). Finally it can be concluded that the thermal exposure of combustibles and incombustibles is equivalent in furnaces simulating a ventilation controlled fire development for a pre-defined duration.
The reduced cross-section method (RCSM) is included in Eurocode 5 (EN-1995-1-2) for the design of timber members in fire conditions. The method considers the strength and stiffness reduction beneath the charred layer by adding an additional depth (known as the ‘zero-strength’ layer) to the charring depth. The zero-strength layer is one of the key parameters for the fire design of timber members. Recently, some concerns have been raised that the zero-strength layer might be non-conservative in some applications. This paper presents the background to the RCSM, followed by a short discussion on the mechanical assumptions, simplifications and possible limitations of the method itself. Further, it discusses determination of the zero-strength layer thickness for members in bending, tension and compression, and provides guidelines on the use of standard experimental tests to determine this quantity. For demonstration of the determination procedure, the results of fire tests in bending, tension and compression were analysed following the described procedure. Results show that the zero-strength layer exceeds the value used in practice, indicate that the method of Eurocode 5 may be non-conservative and should be revised.
The Reduced Cross-Section Method (RCSM) provides a popular method for the design of timber members exposed to fire, using an effective cross-section and mechanical properties at normal temperature. The RCSM was adopted from a single publication and was originally developed for single-span beams exposed to bending load. It has been introduced in Eurocode 5 for a large range of timber members, including columns under compression and members under tension. Recently, the applicability of the method and its extended applications were called into question on the basis of limitations and contradictions found by advanced simulations. This paper analyses a total of 153 fire resistance tests (117 members in bending, six members in compression and 30 members in tension) with respect to the RCSM. The analysis shows that (i) most of the references are of too poor quality, or are incomplete, to validate a design model, (ii) results with adequate information content showed a significant deviation from the RCSM, and (iii) that the RCSM may lead to a non-conservative design. For members in tension, results fit well with the RCSM, while significant deviations were found for members in compression. Members in bending show very large scatter. It is therefore recommended that the existing design approach inEurocode 5 should be revised in order to include the results of advanced calculations and appropriate tests.
Cross-laminated timber, typical abbreviations CLT or XLAM, is currently one of the most innovative product in building with wood. This solid engineered timber product provides advantages compared to other solid timber slabs as the dimension stability, i.e. swelling and shrinkage, is controlled by the crosswise laminations. As for other components, the fire resistance has to be verified for this type of product. While fire testing is time consuming and costly, simulations provide flexibility to optimize the product or to develop simplified design models for structural engineers. In this paper, a simulation technique is presented which can be used to determine the fire resistance of CLT. The technique was then used to develop simplified design equations to be used by engineers to predict the behavior of CLT in fire resistance tests and verify its fire resistance. Following existing models, the simplified design model aims for a two-step process whereby in a (i) first step the residual cross section and in (ii) a second step the load bearing capacity of the partly heated residual cross section is determined. The presented simulations consider the effective thermal–mechanical characteristics of wood exposed to standard fire and perform an advanced section analysis using a temperature profile corresponding to the actual protection and the location of the centroid together with the possibility of plasticity on the side of compression. It was shown that simulation results agree well with test results and that they can be used to determine layup specific modification factors used by the reduced properties method or zero-strength layers used by the effective cross section method. It was shown that the use of the zero-strength layers is favorable compared to the modification factors to calculate the resistance of the residual cross section. This is due to the large range of modification factors answering the typical layup of CLT comprising layers with their fiber direction cross the span direction. Subsequently, the methodology was used to determine design equations for initially unprotected and protected three-, five- and seven-layer CLT in bending and buckling. While the zero-strength layer for glulam beams in bending is assumed to be 7 mm (0.3 in), for CLT the corresponding value is in most of the cases between 5 mm and 12 mm but is different for other loading modes such as buckling (wall elements) and depending on the applied protection.
The load resistance of timber members exposed to fire is determined from the uncharred residual cross section. Owing to elevated temperatures in parts of the residual cross section, the strength and stiffness properties are lower than under normal conditions. The effective residual cross-section model provides a simplified user -friendly design concept to account for the reduced properties of timber exposed to fire. A fictitious zero-strength layer is removed from the residual cross section obtained after removal of the char layer, and the remaining cross section is assumed to have normal strength and stiffness properties. The method is implemented in Eurocode 5 as the reduced cross-section method. This paper deals with the background of this method, originally developed for rectangular cross sections of glued laminated timber, and shows extensions to other types of cross sections such as solid timber frame members and I-joists. While the thickness of the zero-strength layer was originally given as 7,6 mm, the results of simulations presented here show that the thickness of the zero-strength layer depends on a number of parameters, such as the dimensions and geometry of the cross section, the stress conditions (compression or tension) of the fire-expose d side(s), the load ratio and the duration of fire exposure. It is concluded that the assumption of a fixed value of 7,6 mm is often non-conservative.
Cross-laminated timber (CLT) is increasingly used in medium-rise timber buildings, among other reasons for cost effectiveness and robustness. This paper presents a simple design model using the effective cross-section method for the structural fire design, i.e. the determination of the mechanical resistance with respect to bending (floors). Performing advanced calculations for a large number of lay-ups of various lamination thicknesses, using the thermal and thermo-mechanical properties of wood, charring depths and the reduction of bending resistance of CLT were determined as functions of time of fire exposure. From these results zero-strength layers were derived to be used in the design model using an effective residual cross-section for the determination of mechanical resistance. The model also takes into account different temperature gradients in the CLT in order to include the effect of slower heating rate when the CLT is protected by insulation and/or gypsum plasterboard. The paper also gives results from fire-tests of CLT in bending using beam strips cut from CLT with adequate side protection in order to achieve one-dimensional heat transfer. Reference tests at ambient temperature were performed to predict the moment resistance of the beams being tested in fire. Both, calculations and tests show that results can be highly dependent on the temperature profile caused by e.g. protection.
Fire resistance is an important characteristic for all building structures regardless the building materials used. Methods for fire resistance testing were developed already before 1900 to measure the response of the structure in fire and compare different products. In the last decade, the increased popularity of timber buildings has led to a renewed interest in the performance of timber structures in fire and timber products were frequently tested in furnaces. Currently, some discussions question the validity of furnace test results for timber members which are carried out according to standards. Generally, it was stated that combustible and incombustible products are exposed to different thermal exposures when tested in furnaces or exposed in real fires. Additionally, some experts think that massive timber elements, e.g. cross-laminated timber (CLT), cannot be tested in furnaces as these products increase the fire load and, thus, statements in the framework of fire resistance testing are not possible. This paper investigates the validity of furnace resistance testing for combustible products and its limitations. It is shown that, firstly, the thermal exposure in fire resistance tests of incombustibles and combustibles is similar. Secondly, in addition to thermal exposure, the term fire exposure should be introduced where the oxygen concentration is described as the oxygen concentration significantly influences the behaviour of combustible material in fires. Thirdly, the furnace and compartment environment in flash-over fires is similar with respect to this fire exposure. Finally, it is not possible to directly use furnace test results to predict a compartment response in real fires including the cooling phase but recent investigations indicate that results from fire resistance tests can be used to predict burn-out when the mass loss of the timber specimen is measured.
Cross-laminated timber (CLT) is increasingly being used in medium-rise timber buildings for a number of reasons, such as rapidity of construction, cost effectiveness and robustness. Like for other building materials, verification of the load-bearing performance in fire conditions is an important issue. Experimental fire tests have been performed on loaded CLT wall elements at research institutes in Sweden and Italy. In total, three large-scale and four medium-scale tests have been carried out. The aim was to gain information about initially protected and unprotected elements, to be used for classification and also for validation of calculation models. In the test series, reference tests at normal temperature were included to obtain information (e.g. stiffness, strength) about the material tested in fire conditions. In addition, model-scale fire tests were performed to investigate the loss in stiffness resulting from fire exposure and the effect of different protection types. Loaded fire tests varied in the range of 41.8 min to 120 min, depending on the CLT structure, the level of load, and the type of protection. Data on temperature within specimens and residual cross-sections were collected. Charring rates evaluated from experimental results were comparable with values proposed by Eurocode for the design of timber structures. Conservative solutions were obtained by using simplified design methods and comparing their results to test results and results of advanced modelling. It was shown that the load-bearing performance of CLT may show abrupt changes due to its layered structure. It is strongly recommended that a minimum residual depth depending on the CLT structure should be required in order to ensure robust building products.
Purpose – The purpose of this study is to investigate the influencing factors on the charring behaviour of timber, the char layer and the charring depth in non-standard fires. Design/methodology/approach – This paper summarizes outcomes of tests, investigating the influences on the charring behavior of timber by varying the oxygen content and the gas velocity in the compartment. Results show that charring is depending on the fire compartment temperature, but results show further that at higher oxygen flow, char contraction was observed affecting the protective function of the char layer. Findings – In particular, in the cooling phase, char contraction should be considered which may have a significant impact on performance-based design using non-standard temperature fire curves where the complete fire history including the cooling phase has to be taken into account. Originality/value – Up to now, some research on non-standard fire exposed timber member has been performed, mainly based on standard fire resistance tests where boundary conditions as gas flow and oxygen content especially in the decay phase are not measured or documented. The approach presented in this paper is the first documented fire tests with timber documenting the data required.
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A high shake-out temperature after casting is beneficial from a production point of view due to the need of a shorter cooling line in the foundry. However, a higher shake-out temperature might also lead to increased residual stresses due to faster cooling. In order to get a good agreement between simulated and measured temperature curves it is important to adjust material data and heat transfer coefficients accordingly. A reduction of the thermal conductivity of the sand by 25% and a drastically increased HTC were the main adjustments. From the residual stress simulation, the most important lesson learned was the necessity to include the sand in the calculation. Especially internal sand cores can greatly restrict the thermal contraction of the casting. After this fine-tuning of the simulation a good agreement with measurements was obtained. It could be verified that an increased shake-out temperature will lead to significantly increased residual stresses.
Trä används mycket i provisoriska konstruktioner framför allt i form och formställning för betongbyggnad samt i väggar i schakt och ställningar vid byggande eller renovering. I rapporten refereras det mycket omfattande arbete som utförts vid det engelska träforskningsinstitutet TRADA avseende trä i provisoriska konstruktioner. Arbetet inbegriper Skandinavien men slutsatserna och rekommendationerna gäller de olika EG-länderna, främst Storbritannien. Många av synpunkterna är dock intressanta för oss. T ex understryks behovet av en funktionsstandard för ytbildande material till betongform. Att materialneutralt utröna laster på betongform och partialkoefficienter för provisoriska konstruktioner är också viktigt.
Interfacial properties of bulk polymer samples have been characterized by direct measurements of long-range and adhesion forces using a non-interferometric bimorph surface forces apparatus. For this purpose we developed a method where bulk polystyrene was melted and formed into drop-shaped surfaces with a cylindrical shaft. In the case of very smooth polystyrene samples the adhesion in air and water was very strong and when brought into contact a cold welding of the polymers sometimes took place. Upon separation, it was found that a cohesive failure occurred and the surfaces were locally damaged. In the case of less flat polystyrene surfaces, the adhesion increased with the applied (external) load to a saturation value. We attribute this to a local flattening of nanometer sized protrusions. The long-range interaction in water is dominated by a weak electrostatic double-layer force. At separations below about 10 nm, an attractive force component predominates the interaction. The adhesion in aqueous solutions decreased dramatically in the presence of a nonionic surfactant, n-octyl b-D-glucopyranoside. The surfactant adsorbs onto hydrophobic surfaces, such as the polystyrene surface used here, and close to the critical micellar concentration it forms an oriented monolayer where the polar sugar units are directed towards the solution. The range of the short-range repulsion between polystyrene surfaces coated with a monolayer of n-octyl b-D-glucopyranoside is about 2-3 nm, slightly larger than observed previously for such surfactant layers adsorbed onto very flat hydrophobized mica surfaces. Further, a considerably stronger attractive force is observed upon separation of the surfactant coated surfaces in case of polystyrene compared to when hydrophobized mica is used. The influence of the substrate surface on the interaction can be rationalized by their differences in surface roughness.
'Green Memes' proposes an online social network and local kiosks for people to learn about energy consumption. Based on electricity data collected from smart grids, meters and sensors, data visualizations depict consumption per building, per person and at many other scales. A social networking function is attached to these — text messages, or ‘green memes’, invite users to engage with energy-savings advice, current events and sustainability research. Accessible online, through mobile devices, or installed locally, Green Memes combines ‘hard data’ with the ‘soft power’ of personalized information, public opinion and face- to-face communication. The project is currently seeking partners to further develop the system and interface design.
In biogas processes, methane production from acetate proceeds by either aceticlastic methanogenesis or through syntrophic acetate oxidation (SAO). In the present study, the pathway for methane production from acetate was analysed; i) during a gradual increase of the ammonia concentration (final concentration 7 g NH4+ - N/L) in a semi-continuous lab-scale anaerobic digester (4.3 L), operating at mesophilic temperature (37°C) or ii) in diluted enrichment cultures (100 ml) experiencing a gradual increase in ammonia, sodium, potassium and propionic acid. The pathway for methane formation was determined by calculating the 14CO2/14CH 4 ratio after incubating samples with 14C-2-acetate. In the anaerobic digester, as well as in the enrichment cultures, the 14CO2/14CH4 ratio clearly increased with increasing ammonium-nitrogen concentration, i.e. as the ammonia concentration increased, a shift from the aceticlastic mechanism to the syntrophic pathway occurred. The shift was very distinct and occurred as the NH4+ - N concentration rose above 3 g/l. No shift in pathway was seen during increasing concentrations of sodium, potassium or propionic acid. The shift to SAO in the biogas digester resulted in a twofold decrease in the specific gas and methane yield. © IWA Publishing 2008.
Städer växer och förtätas, våra mobilitetsmönster förändras med teknologin som möjliggörare – men först och främst har personer ett behov av att ”lösa” mobilitet i vardagen utan att tänka för mycket på den. Det måste vara ”lätt att göra rätt” från början, och början och slutet av många resor är just fastigheter, antingen bostäder eller olika sorters verksamheter. Vilka mobilitetslösningar de erbjuder och möjliggör är därför avgörande för hur vi rör oss. Våra nuvarande planeringsnormer gynnar en bilburen mobilitet i och med att det finns regler om parkering per bostad resp. arbetsplats, så kallat parkeringstal (se plan- och bygglagen, förkortad PBL). På sistone har det dock varit ett flertal fastighetsaktörer och kommuner som har börjat experimentera med alternativ till parkeringen. Som så ofta inom begynnande innovationsområden saknas det kunskap och erfarenhet hos aktörerna, samt att nya samarbeten måste utvecklas och fördjupas. Under 2020 fick en grupp forskare på RISE möjlighet att undersöka a) hur en samarbetsprocess mellan två hittills oberoende aktörer eller branscher (”gränsland”) kan se ut och b) vilka som är de främsta utmaningar i det nya gränslandet mellan mobilitet och fastigheter, som exempel för ett gränsland som håller på att växa fram – bland flera andra som uppstår i omställningens spår. Till vår hjälp har vi haft flera experter som frikostigt delade med sig av kunskap och insikter, samt kollegor som har ett ben antingen i samhällsbyggnads- eller mobilitetsforskningen. I den här rapporten föreslår vi en process för samarbete mellan två branscher/ sektorer; och vi har sammanställt våra resultat och gör en bedömning av i vilken riktning mobilitet i fastigheter kommer ta vägen samt vilka förutsättningar som behöver förändras så för att bidra till att det blir just lätt att göra rätt, och därmed öka chanserna att lyckas med klimatomställningen i våra städer och samhällen.
One way to contribute to more sustainable travel patterns is involving real estate actors who assume responsibility for mobility services. This paper presents results of two projects that developed or tested MaaS-like mobility solutions for residential or mixed-use areas in Gothenburg (Sweden): A field trial of a mobility broker in a housing unit in a project called (1) DenCity, and a concept study for a mobility system for multiple real-estate actors within a district in the (2) Gamlestaden concept study. The evaluation of (1) adds insights to end-users’ experiences of MaaS. It also showed that expanding mobility solutions to cover multiple housing and facility providers in a district could remedy some of the shortcomings of MaaS for residential units. This would require a different organizational setup since a natural procurer is missing, an insight the concept study (2) was based on.
There are many regions in the developing world that suffer from poor infrastructure and lack of connection to the Internet and Public Switched Telephone Networks (PSTN). Delay Tolerant Networking (DTN) is a technology that has been advocated for providing store-and-forward network connectivity in these regions over the past few years. DTN often relies on human mobility in one form or another to support transportation of DTN data. This presents a socio-technical problem related to organizing how the data should be transported. In some situations the demand for DTN traffic can exceed that which is possible to support with human mobility, so alternative mechanisms are needed. In this paper we propose using live carrier pigeons (columba livia) to transport DTN data. Carrier pigeons have been used for transporting packets of information for a long time, but have not yet been seriously considered for transporting DTN traffic. We provide arguements that this mode of DTN data transport provides promise, and should receive attention from research and development projects. We provide an overview of pigeon characteristics to analyze the feasibility of using them for data transport, and present simulations of a DTN network that utilizes pigeon transport in order to provide an initial investigation into expected performance characteristics.
This report describes a study done as a masters thesis during 1998 within the Complex Operations Laboratory (COL) at SICS. The report describes a vehicle routing and scheduling problem occurring in the planning of rail traffic at the Swedish State Railways (SJ). The report contains a comprehensive description of the problem and describes several techniques that can be used to address the problem: Constraint Programming with a particular model (due to Helmut Simonis) of the routing problem. This model requires an efficient implementation of a particular called global constraint: the geometric diffn constraint. A propagation algorithm for a 2-dimensional version of this constraint is outlined in the report. The use of insertion heuristics to solve this class of problems have been in general use for some time. And adaption and evaluation of some of these heuristics are also analyzed in the report.
Within the framework of a European project, two partial discharge calibrators were circulated to thirteen laboratories for an intercomparison of impulse charge measurements in the range between 1 pC and 500 pC. The deviations of the charge values q reported by the laboratories were, with a very few exceptions, within ±(0.1 pC+0.03·q). Furthermore, the characteristics of several partial discharge measuring instruments were investigated. The indication of some of the instruments showed deviations of more than ten percent from the correct values.
A new concept has been developed for characterizing the real-time evolution of the three-dimensional pore and lamella microstructure of bread during baking using synchrotron X-ray microtomography (SRµCT). A commercial, combined microwave-convective oven was modified and installed at the TOMCAT synchrotron tomography beamline at the Swiss Light Source (SLS), to capture the 3D dough-to-bread structural development in-situ at the micrometer scale with an acquisition time of 400 ms. This allowed characterization and quantitative comparison of three baking technologies: (1) convective heating, (2) microwave heating, and (3) a combination of convective and microwave heating. A workflow for automatic batchwise image processing and analysis of 3D bread structures (1530 analyzed volumes in total) was established for porosity, individual pore volume, elongation, coordination number and local wall thickness, which allowed for evaluation of the impact of baking technology on the bread structure evolution. The results showed that the porosity, mean pore volume and mean coordination number increase with time and that the mean local cell wall thickness decreases with time. Small and more isolated pores are connecting with larger and already more connected pores as function of time. Clear dependencies are established during the whole baking process between the mean pore volume and porosity, and between the mean local wall thickness and the mean coordination number. This technique opens new opportunities for understanding the mechanisms governing the structural changes during baking and discern the parameters controlling the final bread quality. © 2023 The Author(s)