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How safe are our structures? – Conceptual paper of the DGGT Working Group 2.15 "Reliability‐Based Methods in Geotechnical Engineering" The future Eurocode 7 will explicitly allow the use of reliability‐based methods in geotechnical planning and design. In Germany, there is hardly any experience in the practical application of such methods so far and thus the reservations towards these methods are plenty. The new DGGT Working Group (WG) 2.15 "Reliability‐Based Methods in Geotechnical Engineering" has set itself the goal of providing a practical access to those methods by means of practice‐oriented instructions and recommendations as well as accompanying training and further education courses. The aim is to clarify the possibilities and limitations and, above all, to exploit their potential. This article presents the general principles as well as the future fields of work of the WG 2.15. Starting with the introduction of relevant technical terms, the implementation of reliability‐based methods within the current codes of practice and regulations is shown. Using the life cycle of a geotechnical structure, the uncertainties in geotechnical designs and assessments are described. Subsequently it is outlined, in which situations and to what extend reliability‐based methods can aid engineers, clients and inspectors in verification and decision‐making processes. In the future, WG 2.15 will develop recommendations on individual topics and publish them successively. [ABSTRACT FROM AUTHOR]

Hydraulic heave in round excavation pits with relief boreholes – calculation approach The use of relief boreholes to reduce the effect of a vertical upward flow has proven to be a constructive measure to avoid the risk of hydraulic heave in excavation pits in groundwater. The applicable standards and regulations, however, only provide general information on the use of relief boreholes. A concept for the verification against hydraulic heave failure using relief boreholes is missing as well as defined information on the arrangement of the relief boreholes and the influence of the excavation geometry. Therefore, the aim of the research work at the Chair of Geotechnical Engineering of RWTH Aachen University was to develop a concept for the proof against hydraulic heave failure with the arrangement of relief boreholes. The result was a calculation approach that determines the decisive fracture body under consideration of the flow conditions due to the relief boreholes. This fracture body can then be used for the proof against hydraulic heave failure. Based on this, dimensioning diagrams were finally generated for typical excavation pit geometries in dimensionless representation. [ABSTRACT FROM AUTHOR]

New definition and measurement of the boundary layer thickness on a wall – Determination of thermodynamic and aerodynamic quantities This publication describes the theoretical basis and a measuring device to measure the convective heat transfer coefficient and the shear stress on a wall exposed to the flow. For this purpose, the Convective Heat Transfer Meter (CHM) measures the temperature gradient within the flow boundary layer. For exponential time processes, the time constant τ is defined as the period of time after which a quantity A(t) has declined to a fraction of 1/e of the initial value, with the Eulerian number being 2.718... Analogous to this, the boundary layer thickness d is proposed for spatial processes with exponential approximation instead of the time constant τ. Such a process occurs in the viscous boundary layer area of a wall exposed to flow. The flow velocity U(y) running parallel to the wall surface is decelerated due to the viscosity of the air and the friction of the wall surface until it reaches the condition of adhesion to the wall surface. The newly defined boundary layer thickness d is the distance from the wall y = d for which the local flow velocity U(y=d) has reached the fraction of (1–e–1) from the macroscopic flow velocity U(y=∞). In contrast to the frequently used boundary layer thickness δ, for which the threshold is by definition 99 % of U(y=∞), the new definition of the boundary layer thickness d offers advantages in terms of its measurability and the determination of the convective heat transfer and the determination of the shear stress on bodies in contact with the flow. [ABSTRACT FROM AUTHOR]

Validation of the AVISA model Despite advanced design technologies, construction on cohesive soils is still a challenge. Especially when dealing with cyclic loading conditions combined with the time‐dependent behavior of cohesive soils, such as offshore structures or even dams, the tools to predict the long‐term deformations of fine‐grained soil are limited. Due to the complex influence of loading rate, preloading, and soil structure, it is necessary to understand the effects of these influences on cohesive materials through laboratory testing and describe them numerically through accurate and physically based constitutive equations. Researchers (continue to) develop many hundreds of material models each year. Most of them are used for PhDs and not investigated further. In this work, such a model, developed in the first author's PhD, is be validated. The performance of the AVISA model has been previously demonstrated on experiments of various fine‐grained soils. In this paper, a new experimental study on Malaysia Kaolin is used for the validation of the model. Furthermore, the reproducibility of the so‐called Krey and Tiedemann criteria, parameters φ′s , c′ und φ′ is investigated by simulations of simple shear tests. It should be noted that many constitutive models for fine‐grained soils fail in this task. [ABSTRACT FROM AUTHOR]

Steel tube struts in braced excavations – Simplified design for cross section class 4 Steel tubes are often used as excavation struts. When designing long struts without intermediate supports, tubes with large diameter and small wall thickness are particularly economical. This may lead to reaching the limit of cross section class 4 requiring a shell buckling analysis according to EN 1993‐1‐6. In this article a simplified design method using section‐related buckling stresses based on EN 1993‐1‐6 Annex D is described. Ready‐to‐use section‐related buckling stresses are given for commonly used steel tubes of cross section class 4. [ABSTRACT FROM AUTHOR]

Failure criteria for foam‐grouted gravel under multiaxial loading Foam grouting is an innovative method for improving the mechanical properties of cohesionless, coarse‐grained soils. Despite this, only a few experimental studies have been conducted to assess the failure of foam‐injected soils under multiaxial loading. This paper aims to fill this gap in knowledge. The stiffness and strength of the natural soil, which serve as reference values for the evaluation of the improvement effect due to the injection, are derived from drained triaxial tests. The mechanical behaviour of the foam‐injected soil is investigated using uniaxial, triaxial, and splitting tensile tests. The foam‐injected soil, exhibits significantly higher strength and stiffness but lower ductility than the untreated soil. The ductility of the foam‐injected soil increases with increasing lateral pressure. The splitting tensile strength is only a small fraction of the compressive strength. The adequacy of the failure criteria Mohr‐Coulomb, Hoek‐Brown and Lade for the description of the failure of foam‐injected coarse‐grained soils is verified. All three failure criteria are basically suitable to describe the state of failure in triaxial compression. For compressive and tensile loading, the Hoek‐Brown and Lade failure criteria seem to be more appropriate compared to Mohr‐Coulomb. [ABSTRACT FROM AUTHOR]

Simple and fast dynamic model for the prediction of PV self‐consumption The widespread use of renewable energy plays a crucial role in increasing the energy efficiency of the building stock. The significantly decreased PV system prices and the high flexibility in electricity use for all loads in a building, i.e., space heating (and cooling) and domestic hot water in combination with heat pumps, auxiliary energies, household appliances, and also increasingly electric mobility leads to a wide use of PV. However, the integration of PV into the building is complex and requires the use of electrical and/or thermal energy storage and appropriate control strategies. Therefore, evaluating and optimizing the part of PV electricity that is used directly or stored in the building is a challenging task. Thus, for a detailed analysis of PV and energy storage at the building level, extensive building and system simulations were performed using reference buildings. [ABSTRACT FROM AUTHOR]

Building Performance Simulation at RWTH Aachen University – Series: Building simulation and calculation tools in teaching This series of articles presents the use of computer programs in university teaching of building physics and building technology for architects and civil engineers. Since 2013, the subject "Building Performance Simulation" has been offered at RWTH Aachen University at the Institute of Energy Efficiency and Sustainable Building E3D. The target group is the core courses "Civil Engineering", "Environmental Engineering" and Business Administration and Engineering: Civil Engineering in the Master's program at the Faculty of Civil Engineering. The aim of the current course is to teach the students the theoretical and practical basics of building performance simulation. For this purpose, the theoretical basics are prepared in a modular way and presented in detail in the lecture. In the exercise, the basics of programming are taught or refreshed. Subsequently, modular subcomponents for a simulation are implemented in the Modelica language. This enables the students to progress through the complex collection of topics in an appropriate manner and to deal in depth with topics that would certainly be neglected in a purely application‐oriented view of an existing building simulation program. [ABSTRACT FROM AUTHOR]

Development of a model to evaluate the environmental properties of common outdoor plasters and mortars A requirement of the Construction Products Regulation (CPR) in the European Union states that construction materials and works must be designed in a way that throughout their entire life cycle, they have no exceedingly high negative impact on the environment. The objective of the current work was to develop a model capable to evaluate the environmental properties of outdoor plasters and mortars. Therefore, the extensive database recollected during 10 years of field and laboratory experiments by Fraunhofer IBP for these products was used as a basis and for validation, respectively. A three‐stage model was set up. In "Level 1", runoff volumes are calculated for a specific façade. In "Level 2", leached inorganic substances and their concentrations in runoff water are identified. As a final step, the evaluation of the environmental risk of stormwater runoff from façades covered with plasters and mortars takes place in "Level 3" using a groundwater risk assessment including leachate prognosis. It could be shown that vanadium, chromium and lead can be leached from mineral plasters and mortars during rain events in relevant concentrations. However, the evaluation showed that within usual application scenarios threshold values at a defined point of compliance are not expected to be exceeded. [ABSTRACT FROM AUTHOR]

Use of software tools at the Chair of Building and Indoor Climate Technology at RWTH Aachen University – Series: Building simulation and calculation tools in teaching This series of articles presents the use of computer programs in university teaching of building physics and building technology for architects and civil engineers. The goal of sustainably providing a healthy indoor climate determines research and teaching at the Chair of Building and Indoor Climate Engineering at RWTH Aachen University. Computer‐aided analysis and simulation techniques are important tools for implementing energy‐efficient and environmentally friendly construction, retrofitting and operation of buildings and neighborhoods with all their complex interactions in the overall system. Students are introduced to the fundamentals of modeling and simulation. The course covers the consideration of all life cycle phases of the building. The knowledge can be further deepened in final theses. The developed tool chains and open source libraries of the institute guarantee a good manageability of the software tools without too long training periods for the students. [ABSTRACT FROM AUTHOR]

Diese Artikelserie stellt den Einsatz von Computerprogrammen in der Hochschullehre der Bauphysik und Gebäudetechnik für Architekten und Bauingenieure vor. An der TU Kaiserslautern wird der E‐Learning‐Kurs „Building Simulation in Design and Operation" für die Master‐Studierenden im Studiengang „Immobilien und Facilities – Management und Technik" angeboten und ist dort im Pflicht‐Curriculum verankert. Darüber hinaus können Studierende des Bauingenieurwesens und des Umweltingenieurwesens den Kurs als Wahlpflichtfach belegen. Der Fokus wird auf das Durchführen von Parametervariationen auf Basis von fertigen Modellen gelegt. [ABSTRACT FROM AUTHOR]

Dynamic CO2 emission factors for the German electricity mix. In recent years, the German Energiewende has led to a significant increase in the renewable energy share of the electricity generation. While being characterized by lower specific CO2 and greenhouse gas emissions over the life cycle in comparison to conventional power generation, the expansion of electricity production from wind and solar energy makes a vital contribution to climate protection. In the context of emission balances, adjustments of the specific emission factors continue to account for the ongoing improvement of the electricity mix. However, an expedient evaluation of innovative and electrified energy supply concepts is virtually impossible using static emission factors based on the annual energy demand. Therefore, this paper describes a methodology to calculate CO2 and greenhouse gas emissions for the German electricity mix 2017 dynamically with a temporal resolution of 15 minutes. For this purpose, open source time series for the electricity production are processed, adjusted to national energy balances and transformed into time‐variable emission factors. A case study demonstrates that CO2 emissions of a building determined on an annual basis differ significantly from those calculated using dynamic CO2 factors. The adaption of these factors to the specific case reveals a potential for emission reductions of a building's heat supply around 12 %. [ABSTRACT FROM AUTHOR]

Approaches to the economic valuation of living wall systems. Vertical greening can make a significant contribution to sustainable urban development. Greening can not only improve the building‐physical properties of buildings and contribute to improving air quality as a pollutant filter, but can also have a major impact on the people affected. A greening measure to be carried out as part of an existing renovation or a new construction is highly dependent on the costs incurred and the potential benefits. The aim of the research carried out is to develop a basic model with which the costs and benefits for wall‐based greening systems can subsequently be estimated on an object‐related basis. For this purpose, an entire life cycle is considered for each system, from installation through use to final disposal. Due to the lack of measurability and quantitative evaluability of many positive effects of building greenery, no holistic model can currently be presented, but only the developed, easily extensible approach to economic evaluation can be shown. Thanks to this model, it has already been possible to gain valuable insights into system optimisation and to define starting points for further evaluation options. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of the spread of the temperature plume of small borehole heat exchanger systems. Small shallow borehole heat exchanger (BHE) systems with a heat capacity smaller than 30 kW can be found mostly in the private housing sector. The heat extraction of the BHEs causes temperature changes in the ground. The form of the temperature changes depends on the project relevant parameters such as geothermal ground conditions, operation of the BHEs and groundwater movement. During the approval processes the approval authority claims for global and non‐project related border distances of the BHEs. The compliance can be difficult due to smaller property sizes. The use of an analytical method for the determination of the length of the temperature plume is needed in order to allow the determination of border distances fitting to the project while taking into account the groundwater velocity, the operation mode as well as the number of BHEs of small shallow geothermal systems. [ABSTRACT FROM AUTHOR]

Abstract: On validating predicted shading duration in built‐up areas: We present a prediction model of shading duration in complex building structures. The model is based purely on the laws of maths and physics, with no conventional values, standard figures or hypotheses. We checked the predicted shading times by observing the shading periods in the areas surrounding four high‐rise buildings in Berlin: our figures were in line with predictions, within the expected margin of error. This margin arises mainly from rounding the coordinates for both the building's cubature and the position of the observer to the nearest whole metre. Hence the calculation model presented here is not used to visualise building shadows for shading studies, but instead for a precise, validated calculation of shading duration at specific reference points based on a 3‐D building model which is as quick and easy as possible to generate. This can be used in existing scenarios, as well as in planning new builds and renovations. The ProShad prediction model is also used to calculate shading duration around building complexes as a three‐dimensional matrix, so that horizontal and vertical sections through the shading (duration) area can provide a comprehensive overview, for example as ground shading maps or with façade shading shown as isosurfaces at intervals during the shading period. [ABSTRACT FROM AUTHOR]

Abstract: Comparative contemplation of reference climates regarding their influence on the energetic building performance. There is a steady increase of the importance of component and building simulation as a part of a holistic building information modeling (BIM). The quality of the simulation results is highly influenced by the selected ambient climatic conditions. Currently the user is forced to use different reference climates depending on the focus of the preferred assessment. In this paper, the impact of different German reference climates on the energy consumption of a sample building is assessed. Therefor the steady state heating degree days as well as the transient heating load of the building are compared using different ambient reference climates. Finally, the results generated with the reference datasets are set into relation to the naturally fluctuations of the local climate. [ABSTRACT FROM AUTHOR]

Abstract: Geotechnical rich due to loss of stability. In this paper the geotechnical risk as expected value of sizes of geotechnical events within an operation region and time is specified. Causative losses of stability are related with domino‐like chain reactions and losses of control which as yet cannot be calculated. Their physical extent is given by the released energy. The bigger this is and the more something or someone is exposed to a chain reaction, the higher is the damage. Due the “wild” randomness the number of chain reactions depends on the energy which is released at least by a power‐law. The exponent of it is nearly –1 as the reaction of geo‐matter is nearly rate‐independent. The power‐law has physically justified lower and upper cut‐offs. Thus the geotechnical risk is the product the lower damage cut‐off and the logarithm of the ratio of upper and lower cut‐offs. Expected values of cut‐offs have to be determined for scenarios by means of ground data, technical and other actions. Thus the risk can be calculated objectively, insurance fees can be estimated and total expenses from feasibility study to use can be reduced. [ABSTRACT FROM AUTHOR]

Abstract: Pile driving of open‐ended steel piles in offshore wind industry – comparison of prognosis and measurements. Today popular foundation methods of offshore wind turbines (Jackets, Tripods or Monopiles) are mainly realised with steel pipe piles. Against the background of cost effectiveness, the selection of a driving system as well as design fatigue calculations it is of importance to run driveability analysis prior to the installation process. Results and criteria for that are amongst others (e.g. propagation of underwater sound, not discussed here) blow count and duration of a driving process as well as the soil resistance at the moment of driving (with or without driving stops) being the so‐called static resistance to driving (SRD) and compressive and tensile stresses within the pile. At real pile driving usually dynamic pile tests are performed in order to record real blow counts und stresses in the pile and furthermore, to verify pile capacity. In the present paper theoretical driveability analyses and thus SRD models will be compared with results of dynamic pile tests in certain offshore wind farms in the North and Baltic Seas in order to check their applicability based on sand or chalk dominated soils. [ABSTRACT FROM AUTHOR]

Abstract: Energy consumption forecast for redevelopment concepts for buildings and districts Elaboration of a forecast model to predict realistic thermal energy savings for renovations on building and district levels, in consideration of prebound and rebound effects. Within the scope of redevelopment concepts, consumption forecasts are being compiled to quantify and evaluate energy saving potentials. It should be considered that the ratio of the calculated energy demand and the actual energy consumption before and after the renovation is not linear. The calculated heat demand typically exceeds the measured heat consumption before a renovation, while it is usually lower after the renovation. These phenomena are known as ”prebound effect“ and ”rebound effect“. They can cause an overestimation of potential energy savings and can have a negative impact on the overall economic efficiency of renovation measures. Therefore, they should be included in the development of renovation strategies. For this purpose, a forecast model will be presented which allows for realistic heat consumption forecasts based on an adaptable, empirical data basis. It is applicable to residential as well as non‐residential buildings. These forecasts can be extrapolated from the building level to large building stocks and are thereby also applicable to the holistic renovation strategies on district level. The model will be demonstrated by the example of the university campus ”Campus Lichtwiese“ of TU Darmstadt, outlining the significance and impact of prebound and rebound effects. [ABSTRACT FROM AUTHOR]