1,003 research outputs found
Flow dependent processes in settlement of intertidal bivalve larvae
No full textIn estuariumgebieden ontwikkelen schelpdierlarven zich door middel van een planktonisch stadium, waarin zij vrij zwemmen in de waterkolom. Tijdens deze fase worden de larven verspreid door waterstromingen. Op een gegeven moment vestigen zij zich op de bodem. Dit belangrijke vestigingsproces is een korte fase, waarover weinig bekend is. Zowel voor, na als tijdens dit proces kan veel sterfte optreden en een beter inzicht hierin kan er onder meer aan bijdragen dat de aanwezigheid van toekomstige jaarklassen van commercieel beviste soorten (zoals kokkels) beter voorspeld kan worden. Promovendus Iris Hendriks onderzocht in hoeverre het vestigingsproces van de schelpdierlarven door waterstroming wordt bepaald. Zij voerde hiertoe experimenten uit in het veld en in het laboratorium, met stroomgoot en het kweken van larven. Haar onderzoek toont onder andere aan dat turbulentie, veroorzaakt door bodemstructuren, een belangrijke rol kan spelen in het vestigingsproces. Het wegvissen van deze bodemstructuren zou in dat geval de mate van vestiging van larven kunnen beïnvloeden
Typescript Bill H.R. 20819 for the Construction of Roads and other Permanent Improvements
No full textTypescript draft of Bill H.R. 20819 to provide for the construction of roads and other permanent improvements at or near the Grand Canyon. The sum of $110,000 dollars is to be appropriated for the project under the direction of the Secretary of Agriculture
Modelling the seismic response of an unreinforced masonry structure
No full textOne of the tests in the ESECMaSE project is the large scale earthquake test on a building. The finite element model that is discussed in this thesis is based on this pseudo-dynamic test. The material model follows from a macro modelling approach and has smeared-cracks. The mode shape and eigenfrequencies are obtained through an eigenvalue analysis. The seismic load is applied in a fixed force ratio with the aid of an auxiliary frame in order to perform a displacement controlled analysis. A sensitivity study to several modelling aspects and modelling parameters was carried out to verify modelling assumptions. It is concluded that a cyclic pushover analysis approximates the results from the test the best. The crack patterns in both models are similar and the shear capacity in the weakest direction is approached up to 29%.Structural MechanicsStructural EngineeringCivil Engineering and Geoscience
Integration of manufacturing and structural design of 3D concrete printed bridges
No full text3D concrete printing (3DCP) is a new, innovative construction method in which concrete structures are produced layer-by-layer using a 3D printer. A printed concrete structure, can be self-supporting, which means no formwork is required anymore, increasing the freedom of form, while decreasing construction cost and material use. However, the engineer designing 3DCP structures is challenged, because the construction process is completely different than from designing conventional concrete structures. The fresh concrete structure must be stiff and stable enough to resist the increasing self-weight of the subsequent layers and the material properties can become anisotropic due to a limited bond-strength between two layers. The objective of this research is to integrate the manufacturing process into the structural design of a simply supported 3DCP cyclist bridge, to provide guidelines for designers and for future research. Using a parametric research model, the performance and feasibility of the design can be assessed as a function of 22 parameters describing the bridge geometry, material properties (fresh and hardened) and printing process parameters. The model is built in Grasshopper and Python by using analytical formulations only. The use of FE software is omitted to make the model as fast as possible. Like this, a global sensitivity analysis based on thousands of parameter combinations could be conducted, revealing the most important parameters for determining the design's performance and feasibility, as well as the absolute effect of specific parameters. These results were used in an optimisation run, seeking the most cost-efficient and sustainable design. The research shows that integrating the manufacturing process into the structural design of 3DCP objects yields more optimal designs and the analytical model that has been developed has proven to be a useful tool for research and design.Civil Engineering | Structural Engineerin
Innovative Ways of Dealing with Existing Problems: How to reliably Assess the Cause of Damage of Masonry Structures in an Area with Man-induced Earthquakes?
No full textGroningen, a province in the northern part of the Netherlands, suffers from earthquakes because of gas drilling. The residential building stock in Groningen was not designed for these loads. Over the years a lot of smaller and larger damage has developed, possibly - but not necessarily - caused by the effects of gas drilling. Delft University of Technology was asked by the Dutch government to come up with a method to reliably assess the cause of damage of masonry structures in Groningen. This paper discusses the developed approach for reliably assessing the causes of failure of masonry structures in earthquake-prone areas and the way innovative monitoring techniques were applied.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Mechanic
Efficient material use through smart flexible formwork method
No full textConcrete is an excellent material for application in free-form architecture as a result of its initial fluid state. Double-curved building shapes have been realized in various fibre-reinforced mixtures, using advanced CNC-milled formwork systems. However, a substantial reduction of material use is still possible on two ends: by using a flexible formwork very thin and structurally efficient elements can be manufactured, reinforced with fibres or textiles. Moreover, the reusability of the flexible formwork considerably limits the waste material that was always remaining after the use of milled formwork systems. This paper discusses experiments with both formwork and mixtures in a PhD-study of the first author, demonstrating the ecological potential of this innovative production method.Structural EngineeringCivil Engineering and Geoscience
Shrinkage behaviour of 3D printing concrete mixture: An experimental and numerical study
No full textConcrete is one of the most widely used construction materials across the world. Although, the traditional construction techniques are being improved for efficiency, cost and material optimization, there are disadvantages as well, such as the use of formwork, highly labourintensive and limited architectural freedom for design and material savings. 3D printing of concrete structures is one of the emerging technologies promising the automation in construction industry. However, 3D printed concrete structures pose higher risks of shrinkage as compared to the conventional concrete structures due to their different construction techniques and material composition. Shrinkage can raise issues such as reduction in strength of the structures, poor durability and aesthetically unpleasant structures. The research aims to study the shrinkage behaviour of the 3D printing concrete mixture in different restrained and curing conditions. Based on the experimental data, a finite element model has been developed to predict the shrinkage behaviour over time. The free shrinkage test was performed on cast samples and 3D printed samples of dimensions 160x40x40 mm3. The specimens were kept in two curing conditions: covered with plastic sheet and (2) uncovered or exposed to environment from the time of casting. The shrinkage behaviour was studied for up to 60 days at relative humidity of 65% and temperature 20°C. A higher shrinkage values as compared to normal and highperformance concrete is observed in both 3D printed and cast samples. The 3D printed samples showed a higher shrinkage of 1518% as compared to cast samples due to the 3D printing processes. Restrained ring test were performed for three curing conditions: (1) exposed to environment, (2) covered with plastic sheet and (3) sealed with waterproof tape. The sample exposed to drying cracked within 3 days followed by covered with plastic sheets in 4 days and the specimen in third condition cracked within 8 days. The experiment indicated that the autogenous shrinkage is so high in the concrete mixture to induce shrinkage cracking. A finite element model has been developed to simulate the shrinkage behaviour of the concrete mixture based on the experiment results of the free shrinkage test of cast specimens. The capillary tension approach has been used as the theoretical framework. It uses the KelvinLaplace equation to calculate the capillary stresses and the Bentz deformation model to calculate the corresponding shrinkage strain. It is applicable for ambient relative humidity of more than 40%. The required input for the model are: degree of hydration over time, elastic modulus and distribution of relative humidity over time. The degree of hydration has been calculated using HYMOSTRUC software. The experimental results of the free shrinkage test for cast samples have been simulated in ANSYS. An inverse analysis has been used to obtain the material parameters required to model the moisture diffusion process. Transient heat equation has been used to model the diffusion process. Since the concrete mixture has a low watercement ratio, the effect of autogenous shrinkage has been taken into account as well. The calibrated finite element model gave an error of 810% as compared to the experimental results. The moisture profile obtained from the model has been compared to an analytical model to validate the model. It shows good agreement, especially for upto 28 days. Finally the developed finite element model has been applied on three case studies to assess the accuracy of the model. First, the restrained ring test has been simulated to validate the model based on the prediction of the cracking time. It showed that to accurately predict the shrinkage induced stresses, the creep and the relaxation phenomenon plays a crucial role as well. Second, the model has been used to simulate the shrinkage in a 3D printed flower pot restrained at varying time. Third, a parametric study has been designed using the developed model. Overall the study concludes that the shrinkage in 3D printing concrete mixture is quite high as compared to the normal concrete even if conventionally cast. The 3D printing processes can increase the shrinkage further. The developed finite element model can be used as a tool to estimate the shrinkage strain
3D Concrete Printing: Exploration into stability of 3D printed thin-walled concrete elements during manufacturing
No full textAn exploration into the stability of 3D printed thin-walled concrete elements during manufacturing is presented. The failure mechanisms, material parameters and analysis methods are presented. Self-buckling is the dominant failure mechanism, where the Young's modulus plays an important role. Material experiments to assess the Young's modulus are performed and presented. Predictive analysis methods to evaluate the printability of objects are discussed, where finite element modelling and the mechanistic model of Suiker are compared.Civil Engineering | Structural Engineerin
Predicting the printability of concrete structures: The influence of temperature on the mechanical properties of fresh concrete and numerical modelling of the 3D printing process
No full textIn this thesis a parametric finite element model has been developed to predict the printability of concrete structures of arbitrary geometries. The model can be used to effectively explore design and process parameters to optimize printed objects. In addition, the model can be used to improve the reliability of the printing process, reduce the number of failures during production and enhance the production capabilities of complex geometries. A comprehensive experimental programme was designed in which uniaxial compression tests have been performed to determine the development of the mechanical properties of the concrete during the printing process. A novel method was created by which test samples could be extracted directly from printed concrete in order to incorporate the influence of the full printing process on the properties of the concrete. Moreover, from both literature and the valuable experience in printing of Bruil it was known that the temperature of the concrete mix can have a major influence on the mechanical properties of concrete. Therefore, the performance of the concrete under elevated temperatures was included in the research too. On top of that, printing experiments were conducted in which two geometries were printed multiple times to characterize the reliability of the printing process, and to verify the finite element models with.Civil Engineering | Structural Engineerin
Cosmetic Testing on Animals
No full textPushing the Humane Cosmetics Act (H.R.4148) both to Remove Harmful Ingredients from Cosmetics and Promote the Health and Welfare of AnimalsFall 2014Accompanied by video fil
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