Browsing by Organization "Department Bauingenieurwesen"

A wall construction, used in civil engineering, requires not only good acoustic insulation to protect people from the harmful impact of noise exposure, but also efficient thermal insulation to minimize energy consumption. Experimental, analytical and numerical studies are usually conducted to analyze and optimize the acoustic and thermal properties of a wall structure. In general, experimental measurements are time-consuming and expensive, while analytical studies suffer from restrictions of the boundary conditions and geometry of the problem. By using appropriate numerical methods, however, all relevant physical phenomena can be included. The present work develops a virtual multipurpose laboratory, which is capable to determine the acoustic and thermal insulation of a geometrically complex wall construction. A strongly coupled fluid-structure interaction problem (FSI) in the frequency domain is solved to determine the acoustic insulation. The simulation follows the conditions of an experimental setup. Therefore, the characteristic values for the sound insulation calculated by the virtual multipurpose laboratory are comparable to experimental measurements. The heat equation is solved to estimate the thermal insulation. In the case of structures including cavities and gaps filled with air, an equivalent thermal conductivity is used. The virtual multipurpose laboratory calculates the characteristic values of the acoustic and the thermal insulation for a large number of geometry parameters of the wall structure. To increase the accuracy and speed of the calculation, the spectral element method (SEM), which is an advanced finite element method (FEM), is used. Convergence studies are conducted to analyze the efficiency of the developed SEM. The characteristic values for the acoustic and thermal insulation, which are calculated in the virtual multipurpose laboratory are verified by experimental data and compared to the characteristic values derived by other estimation methods. Examples for the use of the virtual multipurpose laboratory in the optimization procedure of wall structures are given.

This dissertation deals with the continuum-mechanical behavior of multi-phase mixtures, untreated soils with organic matters and treated soils with organic matters. Organic matter content in soils can determine the deformation behavior of soils totally. Soils with organic components such as peat are well known for their high compressibility. Depending on the content and degradation of the organic matter, as well as the resulting water content a correlation to the bearing capacity of the soil can be established. The aim of the performed investigations on multi-phase mixtures (soil/soil with bonding agent) within the scope of this dissertation is to establish the compression and shear behavior of soils with organic content after adding different fractions of binding agent. The ultimate target is to develop a high-performance building material/soil that can be utilized. Hence, three peats with different soil-mechanical properties were investigated to cover a wide range of parameters and to gain trusted results. The results show that it is possible to stabilize the peats by conditioning with cement, thus a peat layer can be stabilized through special ground engineering methods (e.g. Mixed-in-Place- or Mixed-in-Plant-Methods) to become stable construction ground. However, the precondition for the success is to carry out laboratory investigations on the conditioned soils to obtain their precise soil-mechanical properties. In doing so, the selection of the initial stress and the timing for load increase are of eminent importance for the future deformation behavior of the improved soils.In this dissertation a new far-reaching approach in construction ground design for soils with organic content is introduced – till now it was possible to apply such concepts on granular soils using Mixed-in-Place and other methods – utilizing conditioning methods to stabilize soils with organic content instead of excavating and depositing the soil on landfills for replacement or instead of constructing deep foundations. This would minimize the pressure on the cycle of materials.

Sea and estuarine dikes protect more than 2.4 million people in Germany, making them one of the most important coastal protection structures. A failure of these structures would have serious consequences as e.g. during the Hamburg flood in 1962, where one sixth of the city were flooded and more than 300 people lost their lives as a result of several dike failures. Therefore, early recognition of dangers and disaster prevention are elementary to ensure reliable coastal protection. Existing early warning systems for coastal protection in Germany are based on water level measurements and forecasts provided e.g. by the Federal Maritime and Hydrographic Agency in cooperation with the German Weather Service. The predictions of the water level are currently provided selectively for individual tide gauge locations. However, it is known from water level records and their investigations that such tide gauge based water level information is not representative for a larger area, e.g. for the German Bight, or for smaller geographical units, e.g. a Hallig. Thus, local effects and nonlinear interactions can result in spatial water level differences in a range of decimetres along a single coastal section. Especially along complex coastlines, such as the German North Sea with islands, bays, estuaries and tidal flats, a simple interpolation between tide gauge locations is inaccurate. This thesis deals with the development of a new methodology for the prediction of water levels at higher resolution based on existing approaches and models for the entire German North Sea coastline. A hydrodynamic numerical model is used to simulate water levels for the entire coastline of the German North Sea. The modelling is carried out on the basis of currently available bathymetric information, meteorological and astronomical boundary conditions as well as the observed changes in the mean sea level. Next, the water level information is separated into tidal and non-tidal components. The non-tidal residual is applied to derive empirical-statistical models using multiple linear regression relationships. Regression coefficients are derived using meteorological boundary conditions as input. The statistical approaches presented here also aim at incorporating the nonlinear interaction between tide and non-tidal residual into the model chain (tidal synthesis and non-tidal residual prediction). As a result, a first of its kind water level prediction at high spatial and temporal resolution along the entire coastline of the German North Sea (including islands and Halligen, point distance ~1 km, hourly values) is presented. Based on the 2013 storm surge “Xaver“, the procedure was applied practically and then successfully integrated into an operational test operation. This work thus makes a significant contribution to the extension and optimisation of existing early warning systems for coastal protection.