Universität Stuttgart
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Item Open Access Simulation of cracking and failure of concrete structures(1990) Cervenka, Vladimir; Eligehausen, RolfThe computer simulation of the cracking process in concrete structures is performed by means of the program system SBETA. The program is based on nonlinear hypo-elastic constitutive model, which covers all important, experimentally derived material properties, namely, cracking, nonlinear stress-strain law in compression, softenning in compression and tension, biaxial failure function, etc. The nonlinear fracture mechanics is included by means of the fictitious crack model and smeared crack approach. Two examples of computer simulation of concrete fracture are shown. In the first example, the failure mode of a pull-out test is presented. In the second example, the process of the crack development and shear failure of a reinforced concrete beam is simulated.Item Open Access Comparison of feedforward and model predictive control of wind turbines using LIDAR(2012) Schlipf, David; Pao, Lucy Y.; Cheng, Po WenLIDAR systems are able to provide preview information of wind disturbances at various distances in front of wind turbines. This technology paves the way for new control concepts such as feedforward control and model predictive control. This paper compares a nonlinear model predictive controller and a feedforward controller to a baseline controller. Realistic wind "measurements" are obtained using a detailed simulation of a LIDAR system. A full lifetime comparison shows the advantages of using the wind predictions to reduce wind turbine fatigue loads on the tower and blades as well as to limit the blade pitch rates. The results illustrate that the feedforward controller can be combined with a tower feedback controller to yield similar load reductions as the model predictive controller.Item Open Access Computer simulation of anchoring technique in reinforced concrete beams(1990) Cervenka, Vladimir; Pukl, Radomir; Eligehausen, RolfThe load transfer in reinforced concrete structures by means of anchoring elements is very common in modern concrete technology. Anchoring elements are often inserted in the bottom surface of a structure and the load is transfered by tensile action of the concrete. In case of shear failure, the anchores are located in the most exposed tensile zone of beams. The shear failure can be thus influenced by anchoring elements. This effect was analysed by means of the finite element program SBETA, which is based on the nonlinear-elastic constitutive model. The comparison with experiments for several loading configurations was made. In the second part a computer simulation of similar experiments was conducted.Item Open Access Computer simulation: splitting tests of concrete thick-walled rings(1992) Pukl, Radomir; Schlottke, Bernd; Ozbolt, Josko; Eligehausen, RolfTwo non-linear program systems are used for a computer simulation of splitting failure of thick-walled concrete rings under internal radial pressure. Results of the numerical analyses for plane stress models, axisymmetrical model and 3D model are compared with available experimental data and empirical formulas. It is shown, that the behavior observed in experiments can be simulated, using advanced material models, namely the non local microplane model and SBETA material model based on the crack hand theory. With increasing outer radius of the ring, a size effect can be observed.Item Open Access Size effect of the concrete cone failure load of anchor bolts(1992) Eligehausen, Rolf; Bouska, Petr; Cervenka, Vladimir; Pukl, RadomirThe concrete cone capacity of headed anchor bolts subjected to axial tension load was experimentally investigated using 35 concrete specimens of three different sizes. The dimensions of the test specimens were varied in proportion to the embedment depth h (h = 50, 150 and 450 mm). Material properties were measured on accompanying specimens. The measured failure loads are compared with other experimental and numerical investigations. According to the present results the failure loads increase in proportion to h 16, that means close to the prediction by linear fracture mechanics.Item Open Access Managing uncertainties in LCA dataset selection(2019) Pfeuffer, Simon; Wehner, Daniel; Bouslama, RaedThe selection of LCA datasets requires an understanding of the available datasets in a database and awareness about the uncertainties associated with the dataset selection. Therefore, a graphical presentation technique is introduced to support the communication of information about available datasets and uncertainties.Item Open Access Frequency and safety of small radii on motorway-like roads in greater Stuttgart area - recommendations for future guidelines of motorways(2022) Holzwarth, JürgenThe German Guidelines for the Design of Motorways (RAA 2008) assume sufficient safety of a circular curvature if a vehicle does not slip of the road at a given design speed. Earlier researches indicated a higher accident-risk of small radii R < 1000m frequently used on motorwaylike road with a design speed of 100 kph given in German Guideline for Motorways RAA 2008. With regard to the “Vision Zero”, no fatal accidents, it was examined whether minimum radii should be increased to improve safety. For this purpose, 174 km from the entire 200 km motorway-like road network in Greater Stuttgart Area were selected. The existing circular radii were evaluated according to their frequency and accident risk using databases of the State of Baden-Württemberg about road geometry and accidents including the accident cost rate for each 100 m section. Within the selected network 212 circular curves exist. All radii R ≤ 1000 m were examined for their accident cost rate. Radii with an accident cost rate above the average were classified as risky. The investigation showed that 33 % of all applied radii are below R < 1000m. Circular curves with R < 650m showed a significantly higher accident risk and should be excluded. Circular curves between R ≥ 650m and R < 900m showed a higher accident risk if the ratio of adjacent radii is considerably above R1/R2 ≥ 1.5. After a long straight line the minimum radius should be R ≥ 1000m. The study results in recommendations for the geometric design introduced by the follow-up of German Guidelines for Motorways.Item Open Access Nonlinear model predictive control of floating wind turbines(2013) Schlipf, David; Sandner, Frank; Raach, Steffen; Matha, Denis; Cheng, Po WenIn this work a nonlinear model predictive control method for a floating wind turbine is presented. A reduced nonlinear model including disturbance preview of wind and waves is derived and implemented to compute optimal input trajectories for collective pitch and the generator torque. A cost functional is introduced which fulfills all desired constraints and controller goals for above rated wind conditions. The controller is tested for extreme and fatigue load cases and a significant reduction of the power and rotor speed deviations is obtained. Furthermore, ultimate tower loads and damage equivalent loads on shaft and blades are decreased. Although more detailed testing is necessary, this preliminary results show the advantages of nonlinear model predictive control for floating wind turbines.Item Open Access Design of adhesively bonded timber-concrete composites : bondline properties(2023) Grönquist, Philippe; Müller, Katharina; Mönch, Simon; Frangi, AndreaItem Open Access Nonlinear model predictive control of floating wind turbines with individual pitch control(2014) Raach, Steffen; Schlipf, David; Sandner, Frank; Matha, Denis; Cheng, Po WenIn this work a nonlinear model predictive controller with individual pitch control for a floating offshore wind turbine is presented. An aerodynamic model of the collective pitch control approach is extended by describing pitching and yawing moments based on rotor disk theory. This extension is implemented in a reduced nonlinear model of the floating wind turbine including disturbance preview of wind speed, linear vertical and horizontal wind shear, and wave height to compute optimal input trajectories for the individual pitch control inputs and the generator torque. An extended cost functional for individual pitch control is proposed based on the collective pitch control approach. The controller is evaluated in aero-servo-hydro-elastic simulations of a 5MW reference wind turbine disturbed by a three-dimensional stochastic turbulent wind field. Results show a significant blade fatigue load reduction compared to a baseline controller through minimizing yawing and pitching moments on the rotor hub while maintaining the advantages of the model predictive control approach with collective pitch control.