1,720,958 research outputs found
General formulation of equivalent moment factor for elastic lateral torsional buckling of slender rectangular sections and I-sections
No full textIn the past decades, great progress has been made in analyzing lateral torsional buckling of slender beams. The phenomena has been accurately described by differential equations, closed form solutions are available for specific cases and the solution for any load and any boundary condition can be obtained by finite element analysis. Timber and steel design standards provide a procedure based on equivalent moment factors. With this procedure, beams can be designed straightforwardly. However, modern designers continue to push the envelope and more irregular load patterns are found, on which the design standards do not provide solutions. Consequently, designers are forced to determine the equivalent moment factors based on case-specific literature and/or conservative assumptions. Unfortunately, this makes many challenging modern designs uneconomical. Furthermore, significant inconsistencies between the different design procedures are found. For that purpose, this paper proposes a solution in the form of a general formulation to determine equivalent moment factors for any loading on a single-span beam for both free and restrained lateral bending and/or warping at the supports, for both I-sections and rectangular slender sections loaded in the shear center. It is shown that the obtained moment factors are accurate and in good agreement with design standards and literature, and a wide range of irregular load patterns is considered
Finite Element Modeling of Hardwood Fracture Energy
No full textThe fracture energy for hardwood was modeled using finite element modeling (FEM) software DIANA. The results of the model was compared to the fracture energy experimental research performed by Boerenveen (2019). The fracture energy results obtained by the model are similar to the results obtained from the experimental research. An model fracture energy over tested fracture energy ratio of 1.02 was found.Civil Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Comparison study of computational modeling approaches for calcium silicate elements masonry structures
No full textThe increased seismicity due to the exploitation of natural gas in the Groningen region has put many residential buildings in the region at risk of sustaining seismic induced damages. This has prompted many studies on the seismic behavior of the residential buildings, particularly the ones built from unreinforced masonry (URM). One experimental study has been conducted at TU Delft on a two-story CS element structure simulating a terraced house unit. Several numerical studies have also been carried out in the interest of assessing the viability of numerical models for engineering purposes. This research project will examine the viability of several modeling approaches for practical use in analyzing CS element structures. The assessment will be conducted by performing numerical analyses on several models and comparing the results from each analysis with the experimental results. The performance of each model is assessed in terms of hysteretic behavior, interstory drift, cracking patterns and failure mechanisms. Two modeling approaches will be considered in this research project, the continuum element-based macro-modeling approach and the block-based micro-modeling approach with each modeling approach having several variations with different constitutive models. Shell finite elements will be used for all numerical models. In addition to the numerical analyses on the numerical models, several additional analyses will also be conducted on the macro-models. A sensitivity study on the macro-models will be carried out to examine how changes in the considered material parameters affect the results of the numerical analyses on the macro-models. The effects of the inclusion of interface elements in the wall-pier connections of the macro-models will also be investigated in this report. All numerical analyses are carried out using the structural analysis software package DIANA 10.3. The constitutive elements considered for the numerical models will be limited to those already available in the software package
Determination of the displacement demand for the out-of-plane seismic response of unreinforced masonry walls for the Groningen Case
No full textThis research describes the demand of a Displacement-based approach for the assessment of out-of plane behaviour of one-way vertically-spanning unreinforced masonry (URM) walls of terraced and detached houses in the Groningen Province. One of the most vulnerable components of a typical Dutch unreinforced masonry building subjected to earthquake excitation is the face-loaded walls. As the Dutch masonry walls are quite slender, this matter is of significant importance. Up to now, codes and standards evaluate the structural integrity of unreinforced masonry face-loaded walls with either force-based or displacement-based approaches. The latter present beneficial advantages, since the rocking mechanism of an out-of-plane wall is considered to be an instability problem. Particularly, for the definition of the demand (in terms of mid-height displacement for an out-of-plane unreinforced masonry wall) for the Groningen Case, it will be based on the design response outlined in New Zealand Society for Earthquake Engineering Standard (NZSEE) for the Seismic Assessment of Unreinforced Masonry Buildings. Nonetheless, a new rendition of the Shape Factor Coefficient Ci(Tp) and Height Coefficient CHi is necessary, in order to relate the design response with the genuine characteristics of Groningen seismicity. The Shape Factor or Part Coefficient indicates the interaction between the seismic responses of the structural parts and the building, while the Height Coefficient indicates the amplification of the peak ground accelaration through the height of building. The procedure towards the description of the out-of-plane seismic demand is analysed by three parts. In the first part, a series of Nonlinear Time History (NLTH) analyses are performed in single degree of freedom (SDOF) systems. In total, seven SDOF systems are modelled in Opensees. Each of them represents the equivalent SDOF system, according to Eurocode 8, of the considered structures for this research. The SDOF system characteristics as well as the ground motion records for five areas in the Groningen Province are provided from in-house studies of BAM Advies en Engineering. The ground motion records are related to the Draft NPR 9998:2017. Furthermore, two hysteresis rules for the structures are included in the Opensees Models. Hysteretic Rule 1 accounts for low-to-moderate energy dissipation, while Hysteretic Rule 2 for moderate energy dissipation. The hysteretic rules are in accordance with hysteretic behaviour of URM piers under in-plane loading. The geometry, loading conditions and mechanical properties of the piers are chosen to represent the piers in typical Dutch terraced and detached houses. These piers were tested at the Stevin Laboratory of the Delft University of Technology, which provided the data of the tests. Two specific in-plane wall specimens (COMP-2 and COMP-3) are used in this work. The Opensees parameters describing the aforementioned hysteretic rules, are calibrated according to the cyclic tests of these specimens. Next, the NLTH analyses are performed. The deliverables are the Floor Response Spectra (FRS) of each equivalent structure, per hysteretic rule, area and direction. Generally, a response spectrum is a plot that indicates the maximum response of linear oscillators with varying natural frequency or period. The oscillators are excited under the same vibration. Analogously, a FRS indicates the maximum seismic accelaration that the structural parts attract, if they are placed on the respective floor. Since a significant amount of FRS is provided from the NLTH analyses of the 1D Models, the production of Design Floor Accelaration Spectra per area is aimed. Design Floor Accelaration Spectra are “smooth” spectra that can be described by equations and act as an upper bound envelope for all the FRS produced per area. For their derivation, the Newmark-Hall method is applied to the mean Floor Response Spectra of all the structures per area. Consequently, a Design Spectrum per area is produced along with the equations that describe the Shape Factor Coefficient Ci(Tp). The Design Floor Accelaration Spectra efficiently describe the demand expressed in the response spectra of the 1D Models. Nevertheless, in some of the FRS, narrow high amplified spectra are observed with spectral values greater than the design plateau value. These cases are related to stiff structures that did not show proper plastic behaviour in direction X (“weak” direction of the structures governed by openings and rocking piers) and to all the structures in direction Y (“strong” direction of the structures governed by large shear walls), where they remain elastic, with the FRS to be bell shaped curves, highly amplified in a narrow period range around the fundamental period. This raises the necessity of examining if out-of-plane walls can potentially be subjected to these greater accelarations indicated by the narrow high amplified spectra. Therefore, the incorporation of a set of out-of-plane walls in the Opensees Models is decided, in order to compare their actual NLTH out-of-plane responses with their design responses ph. For the definition of the design response, the produced Shape Factor Coefficient Ci(Tp) for the Groningen Case is used. Hence, the second part of this research deals with the extended 1D Models, which are described as two degree of freedom mass-spring systems (2DOF systems). In the extended 1D Models, the nonlinear springs are in series and portray the hysteresis of the buildings and the out-of-plane walls. The hysteretic behaviour of the out-of-plane walls in the Opensees Models are calibrated to the experimental test of one-way spanning, double-clamped out-of-plane wall specimen COMP-7, performed at the Stevin Laboratory of the Delft University of Technology. Twelve wall configurations are considered, as a result of the 4 boundary conditions in the edges of one-way spanning walls presented in NZSEE Norm and 3 considered overburden loads (5 kN, 15 kN and 30 kN). The sensitivity studies in Opensees indicate that the design responses are larger than the NLTH responses for the non-failing walls and predict the failure when it is indicated in the NLTH responses. As a result, the Shape Factor Coefficient Ci(Tp) satisfies also the cases in which the FRS present higher values than the design plateau value. In the third part of the research, NLTH analyses are carried out in a 3D Model that resembles four two storey terraced houses with rigid diaphragms. The finite element method (FEM) software that is used for the NLTH analyses is ANSR-II and the Macro-element based modelling approach is adopted. ANSR-II allows the definition of nonlinear membrane elements to model the structural components. For shear walls and spandrels, specific in-plane backbone curves and hysteresis profiles are provided, being in agreement with the provisions of NZSEE Norm and Draft NPR 9998:2017. Regarding the in-plane rocking piers, no hysteresis is involved. However, the rocking capacity is in accordance with the Norms mentioned above. Triaxial excitations of the 3D Model with 11 sets of ground motions per area are performed in ANSR-II, following the requirements of Annex F of Draft NPR 9998:2017. From the NLTH analyses, the Floor Response Spectra are produced for each of the two floors of the 3D Model. These FRS are compared with the Design Floor Accelaration Spectra derived from the simplified 1D Models. A good predictabilty of the Response Spectra from the Design Spectra is found. Moreover, the Height Coefficient CHi is obtained as the ratio of the Peak Floor Accelaration (PFA) over the Peak Ground Accelaration (PGA). Linear regression analysis related to PFA/PGA ratios in the two floor levels of the structure is implemented per direction and area. The output is the linear equation describing the height effect as a function of height h. This equation has the same format with the one describing the Height Coefficient in NZSEE Norm, hence they are directly comparable. Similar to the 1D Models and for analogous purposes, sensitivity studies of one-way vertically-spanning out-of-plane walls in ANSR-II are conducted. The variation of the walls is retained the same. The out of plane walls in the 3D Model are modelled as beam elements that can rock out of their plane. The behaviour of these beam elements under dynamic excitation in ANSR-II is described by elastic loading and unloading, so no hysteresis is introduced. That is a major difference compared with the Opensees Models. In spite of that, the behaviour of the out-of-plane beam elements in ANSR-II is based on the rigid bodies assumption and rocking mechanism of an out-of-plane wall according to Nonlinear Kinematic Analysis (NLKA). In fact, a good agreement is observed between the capacity curves of the considered out-of-plane walls in ANSR-II and the capacity curves derived from the NLKA method. The results of the sensitivity studies in ANSR-II lead to same conclusions as the ones derived from the sensitivity studies in Opensees Models. That enhances the ability of the Shape Factor Coefficient Ci(Tp) and the Height Coefficient CHi to provide the appropriate design response. As an overall conclusion, it is stated that the Shape Factor Coefficient Ci(Tp) and the Height Coefficient CHi produced in this thesis, can be used for the definition of the displacement demand of one-way spanning out of-plane walls for the Groningen Case, using the displacement-based methodology described in NZSEE Norm. The deliverables serve all the possible factors and parameters that distinguish the characteristics of the Dutch scenario. As the number of the Opensees Models is already satisfying, it is recommended to carry out NLTH analyses in more 3D Models. It is believed that this would further raise the consistency of the deliverables
Sub-increment Based Iterative Constitutive Model for Cyclic Cracking-Crushing-Shearing in Masonry Interface Elements
No full textMasonry is one of the most commonly used construction materials for residential buildings and historic buildings around the world. Some of these buildings are located at seismic zones, while unreinforced masonry structures are vulnerable to seismic loads. To assess the existing masonry buildings and to design new masonry structures, nonlinear seismic simulations are conducted with macro modelling or micro modelling approach. The macro modelling approach, which smears out the details of the bricks and joints as a homogenous material, can efficiently and robustly model complete masonry structures. A commonly used orthotropic constitutive model is the Engineering Masonry Model of the DIANA FEA, which is based on the Total Strain Method that eliminates the mapping-back process in conventional elastoplastic constitutive models. The micro modelling approach, which explicitly models the bricks and joints, can better represent the mechanical behaviours of masonry. However, most of the constitutive models used in micro modelling are based on elastoplasticity that usually causes numerical difficulties due to its mapping-back process. The lack of a robust constitutive model has severely hindered the application of this accurate analysis approach.So, this thesis proposes a sub-increment based iterative constitutive model for interface elements, based on Multi-surface Plasticity Criterion. This model aims to enhance the robustness and accuracy of the constitutive model used for micro modelling. It eliminates the conventional mapping-back process in elastoplastic constitutive models by introducing the ideas of sequential uni-axial loading algorithm and an extra damage iterative calculation algorithm. These algorithms are robust even when the stress state is at the corners of the yield surface. The model also introduces the concept of sub-increments to consider the path dependency in plastic process. All the formulations of this constitutive model are derived based on a simple mechanical model. Formulas and examples are provided for obtaining the input parameters from material tests. The proposed constitutive model is tested on a single integration point level and found to be stable and reliable. It is further applied on the component level, by modelling three masonry walls of different dimensions and boundary conditions, under cyclic loading. For the verification of these wall models, the numerical results are compared with the experimental results in terms of force-displacement curve and crack pattern. Finally, the thesis presents a brief study on parameter sensitivity to provide guidelines for the level of accuracy needed for each input parameter, in order to get satisfactory numerical results.The constitutive model is found to be robust for all the wall analyses conducted, without encountering divergence. The comparison between numerical results and experimental results shows that this constitutive model can cover the majority of shear and flexural failure mechanisms and mimic the crack patterns well. It is capable of modelling shear failure with high accuracy. It can also model flexural failure well with a few parameters calibrated. The fact that the model is little sensitive to parameters that are hard to be measured from experiments, such as tensile strength and tensile fracture energy, ensures its feasibility in engineering practices.<br/
Design of a multi-use, demountable, timber arena: A research in re-usable timber structures
No full textThe goal of this thesis is to research multi-purpose, re-usable timber structures as a step towards sustainable construction. To reach it, the work was divided into four parts. The project starts with an introduction explaining the motivations behind this work. It continues by grounding the problem in the context of major sports events. Indeed, the temporary quality of such manifestations, as well as their promotion of innovative solutions made it ideal for this study. Moreover, reviewing Olympic legacies showed the need for a structure capable to be re-used in different contexts. The second part of the research englobes a literature review on two subjects. Exploring sustainable construction highlighted the main principles in environmentally friendly structural design. Life cycles assessments are identified as the main tool for evaluating the ecological performances and their process is therefore described. Moreover, reviewing existing LCA on timber constructions showed hotspots in the manufacturing of timber such as the importance of local sourcing. Additionally, the second part examines existing work on designing for re-use. Multiple factors should be incorporated to ensure the re-usability of a construction. The most essential one, demountability was explored in length and a table showing the related design criterion, such as minimizing the number of different connectors, was devised. A review of existing constructions designed for re-use concludes this second part. The third part applies the findings of the second to the selection of timber solutions. To narrow the possible products, the roof structure of an indoor arena is preselected for the case study. Locally sourced glue-laminated timber is chosen for its dimensional stability, whereas assemblies using glued-in rods and steel connectors show great versatility and are therefore preferred. Considering the structural system adapted for multi-purpose re-use, a truss was selected for the origin structure because of its inherent standardization. The third part is concluded by the development of a structural solution for the case study.The fourth part concerns the design of the roof and façade structures of a badminton arena. To maximize re-use options, the structural elements are designed to be applicable to different contexts such as the main structure of a high school. The designed solution was finally assessed using the developed guidelines and an LCA-based study. The study shows that multi-purpose re-use is a structurally feasible alternative. Indeed, through careful planning, and by using the developed guidelines, it is possible to re-use the structural elements from a 60-meter span roof in a 6.3-meter span high school with relatively high efficiency. Moreover, the environmental study, although superficial, showed a reduction in global warming potential of 60-90% depending on the re-use scenario compared with a one-off design
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