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- Larsson, Gustaf
(författare)
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High capacity timber joints : Proposal of the shear plate dowel joint
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An increased use of wood can reduce the environmental footprint of the building sector by being a renewable and ecological material. In order to improve the competitiveness of heavy timber structures, this thesis presents a novel type of timber connection with a high degree of prefabrication, which utilizes a resilient bond line.It has previously been shown that a large conventional stiff adhesive bond line acting in shear can be made stronger by using a less stiff bond line, by e.g. introducing an intermediate rubber foil. The scientific contribution of this thesis starts by comparing such resilient bond lines to conventional non-resilient bond lines. It is numerically shown that the strength of the bond line is increased from 40% to 80% of the local shear strength by introducing a resilient bond line in large lap joints. Unlike other types of connections, a resilient bond line enables design of the stiffness depending on the application by varying the hardness and thickness of the intermediate bond layer.Using the concept of the resilient bond line in a heavy timber connection design aiming for a high degree of prefabrication, the novel Shear Plate Dowel Joint (SPDJ) is proposed. Initially designed for truss nodes, the connection shows promising results in full scale tensile tests with an average shear stress at failure of 3.3 MPa. A bond line model to be used in FE analysis of the SPDJ is proposed and used in parameter studies of the connection. It is found that a softer bond line will increase the slip, but also the strength which asymptotically aligns with theory of perfect plasticity.The strengths of the SPDJ design are high load carrying capacity and simplicity in design, but duration of load effects and fire resistance are, among other things, in need of further research prior to structural application.
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- Andersson, Linus
(författare)
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Reduced order modeling in structural dynamics : Consideration of local nonlinearities
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A structural design process may include various load cases for which a sufficient load-bearing capacity must be demonstrated. In addition to static load cases, a verification of dynamic loads, e.g. accidental loads such as blast and impact loading, may be required. To this end, the response may be estimated using a computational model representing an idealized structure. Particularly in the conceptual design phase, a time-efficient and straightforward modelingapproach can be of great utility, allowing for an interactive design process where alternative designs may be tested. Furthermore, a dynamic response analysis often requires some form of time (or frequency) discretization and can therefore become computationally expensive compared to the corresponding static analysis. The balance between performance and accuracy as well as the purpose, i.e. the output quantities of interest, are thus important aspects in a dynamic response analysis.A structural dynamics analysis typically requires a model being accurate as well as computationally efficient. The model accuracy is particularly important in a verification of structurescharacterized by brittle failure modes, i.e. that do not deform plastically before failure. Furthermore,to avoid a too conservative design and to ensure sufficient accuracy, it can be necessary to consider the nonlinear response of a structure, e.g. due to contact interactions or nonlinear material behavior. However, a nonlinear structural dynamic problem often requires computationallyexpensive solution methods. Consequently, there is a need for modeling strategies that enable time-efficient, accurate analyses and a straightforward modeling approach, appropriate in a structural design process. To achieve this, a reduced order model can be established providing an accurate prediction of important output quantities.Dynamic substructuring turns out to be an important aspect in the process of developing reduced order models. By subdivision of the structure into substructures, dynamic substructuring can be employed to effectively adjust the level of accuracy for different parts of the structure. For example, substructures that remain linear elastic can typically be modeled using mode-superposition methods whereas substructures which exhibit a nonlinear behavior can berepresented by a refined submodel.In the dissertation, strategies for reduced order modeling are investigated on the basis of structural engineering applications within two different areas, namely concrete structures subjected to blast loading and glass structures subjected to soft-body impact. Interestingly, however, some of the challenges with regard to the structural dynamics problems are similar. In particular, the response of higher order modes may be of importance and, moreover, an accuraterepresentation of the structural behavior may necessitate a model considering local nonlinearities.By means of dynamic substructuring, computationally efficient analysis techniques are developed for evaluating concrete structures subjected to blast loading, appropriate for use in a structural design process. In particular, a comparison to commonly used modeling strategies, using equivalent single-degree-of-freedom systems, suggests that the developed models providean increased accuracy of the shear force. Brittle failure modes such as shear failure are typically critical for concrete structures subjected to blast loading.Furthermore, reduced order models are established for verification of glass panels subjected to soft-body impact. In particular, a non-linear viscous single-degree-of-freedom system is proposed for reduced modeling of the standardized EN 12600 impactor. Further, the response of higher order modes is considered using a set of load-dependent mode shapes. The developed models are validated by experimental tests of impact on glass panels.Finally, a review of various reduced order modeling techniques is presented which, in a broader perspective, provide a basis for developing reduced order models in various structural engineering applications.
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- Austrell, Per Erik, et al.
(författare)
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Survey of Design Methods and Material Characteristics in Rubber Engineering
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The unique properties of elastomeric materials are taken advantage of in many engineering applications. Elastomeric units are used as couplings or mountings between stiff structures. Examples of these are shock absorbers, vibration insulators, flexible joints, seals and suspensions.The development of computers and of analysis programs in this area has given engineers a new tool for the design of elastomeric components. Computer simulation by finite element analysis has become increasingly important, allowing the mechanical behavior of products with for complex geometries, as well as loading cases of different kinds to be evaluated. Computer simulations enable both static and dynamic aspects to be analyzed. These matters have been recognized by the manufacturers of rubber products and by their customers. The benefits are shorter time for product development and also quality improvements.However, the possibilities available for finding less complicated technical solutions at lower cost with the use of elastomers, has not been fully utilized. Rubber components could be employed more frequently in design if engineers were more familiar with materials of this sort.Part of the problem lies in education and in the dissemination of information. Engineers working in the design area tend to not be very familiar with elastomeric materials and their properties. The offerings of courses on the mechanics of polymers at schools and universities are very limited. Skillful engineers in this field have usually acquired their knowledge through many years of experience and not formal education.Moreover, the complicated nature of the material behavior involved makes it difficult to devise general design rules and design tools. Only recently have computers and analysis programs become powerful enough for the analysis of nonlinear elastic problems involving large strains.It is essential, if one is to become competitive in high-tech applications, to possess a thorough knowledge of computer methods, material models and test methods available.There has likewise been a lack of relevant data for the computer analysis of elastomeric materials. The design tools employed rely on the material models available and on the test data required for the calibration of these models. In many cases, the only information available for analysis is a value for the hardness of the rubber in question. The wide variety of rubber compounds is also a problem. The characterization of different materials is costly and time-consuming. There is thus a need for simple and reliable methods to characterize the different vulcanizates.
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| 34. |
- Danielsson, Henrik
(författare)
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Design and perpendicular to grain tensile stress in double-tapered glulam beams
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Design and stress analysis of regular double-tapered beams and double-tapered beams with a flattened apex region is considered, focusing on perpendicular to grain tensile stress in apex region. Double-tapered beams with flattened apex region are analyzed since the geometry is such that the perpendicular to grain tensile stress may be reduced compared to a regular double-tapered beam of corresponding geometry. The Eurocode 5 design criteria for regular double-tapered beams regarding bending stress, shear stress and perpendicular to grain tensile stress are reviewed. Design with respect to perpendicular to grain tensile stress is based on an approximate solution for maximum stress and Weibull type considerations for influence of size of stressed volume and heterogeneity in stress distribution on the strength. The maximum stress, the size of the stressed volume and heterogeneity in stress distribution are analyzed by linear elastic finite element analysis for regular double-tapered beams and for double-tapered beams with a flattened apex region. For both geometry types, loading by a uniformly distributed load and point loads in the two quarter points of the beam is considered. Based on the FE-analysis, proposals for design criterion with respect to perpen\-dicular to grain tensile stress are also presented. The proposals consist of modifications of the Eurocode 5 design approach for regular double-tapered beams.
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| 36. |
- Danielsson, Henrik, et al.
(författare)
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Strength and stiffness of cross laminated timber at in-plane beam loading
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report concerns element strength and stiffness of cross laminated timber (CLT) at in-plane beam loading and includes presentation of experimental investigations and a review of some analytical models for structural analysis. A total of 20 individual tests were carried out, divided into five different test series which each comprise four nominally equal tests. The test series include prismatic beams (two test series), beams with a hole (two test series) and beams with an end-notch (one test series). All CLT elements were composed of 5 layers of laminations, with three layers of longitudinal laminations of width 40 mm and two layers of transversal laminations of width 20 mm.Test results relating to beam strength are presented in terms of maximum applied load and also in terms of stress components as calculated by analytical models. The review of models for stress analysis reveals significant influence of the element layup and laminations width on the predicted stresses. Test results relating to beam stiffness are present as element shear stiffness and element local and global modulus of elasticity, evaluated based on the European test standard EN 408.
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| 37. |
- Danielsson, Henrik
(författare)
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Strength tests of glulam beams with quadratic holes - Test report
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report deals with strength tests of glulam beams with quadratic holes with rounded corners. A total of 36 individual tests were carried out, divided into nine test series with four nominally equal tests in each test series. There were four para\-meters varied within these test series: beam size, bending moment to shear force ratio, material strength class and also hole placement with respect to the height of the beam. The latter parameter seems to never have been investigated before since all previously performed tests found in the literature have been carried out on beams with holes placed centrically in the beam height direction. The test results indicate a strong size effect. The influence of eccentric placement of the hole on the crack load was found to be small.
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| 38. |
- Danielsson, Henrik
(författare)
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The strength of glulam beams with holes - A survey of tests and calculation methods
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A compilation of available test results relating to the strength of glulam beams with holes is presented. A total of 182 individual tests from 8 different sources are described concerning material, test setup and recorded crack loads and failure loads. A brief description of some available methods for strength analysis of timber is given and specific calculation approaches for the strength of glulam beams with holes are compiled. Design rules according to some European codes are reviewed and compared to experimental test results. Fundamentally different design approaches are found among the reviewed codes and the comparison reveals significant discrepancies between the predicted strengths according to the different codes.
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| 40. |
- Davidsson, Peter
(författare)
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Finite Element Analysis of Structure-acoustic Systems : Methods and Applications
- 2001. - 1
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Paper 1The problem in which a flexible structure interacts with an acoustic fluid is analysed by use of the finite element method. With increasing complexity of the geometry and when increasing the frequency limit is of interest, the number of degrees of freedom needed to describe the system becomes very large. To reduce the coupled system, modal analysis is performed in the structural and in the fluid domain separately. The uncoupled eigenvectors are then used to reduce the coupled problem. A method for choosing which uncoupled eigenvectors to include in this operation is derived, further reducing the system. A numerical example is provided, demonstrating the efficiency of the method.Paper 2The unsymmetrical eigenvalue problem involved in analysing structure-acoustic problems by use of the finite element method with a pressure formulation in the fluid domain can be reduced through transforming it into a symmetric standard eigenvalue problem. The paper shows that when hysteretic damping is introduced in both the structural and the fluid domain, the problem can still be treated as a symmetric standard eigenvalue problem, which becomes complexvalued due to the damping.Paper 3This paper, which is based on the results reported in Paper 1 and 2, describes the implementation of structure-acoustic finite element analysis in an integrated modelling environment, one which has interfaces to programs for meshing and for finite element analysis. The aim is to determine the vehicle interior noise on the basis of the force applied to the structure. An interface to a code developed for performing structure-acoustic analysis involving coupled modal analysis andfrequency response analysis, is created. The possibilities this modelling environment provides are demonstrated. Use of this approach simplies cooperation between researchers and their interaction with industrial groups.Paper4Double leaf walls consisting of sheet-metal wall studs covered with plaster boards are studied. Acoustic behavior in the low frequency range is evaluated, aimed at determining the influence of the wall properties on sound reduction.The wall parameters studied are wall thickness, the number of plaster boards used, the stiffness of the wall stud web, and the boundary conditions.The influence of the dimensions of the connecting rooms is also studied.It is concluded that in the low frequency range the sound reduction a wall achieves can only be predicted by studying the actual room-wall-room conguration in question.
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| 41. |
- Davidsson, Peter
(författare)
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Structure-acoustic analysis; finite element modelling and reduction methods
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates structure-acoustic systems by use of finite element analysis. The systems studied here are limited to those that consist of an enclosed acoustic fluid cavity, which is coupled to a flexible structure and/or a porous sound absorbing material domain. This type of analysis is applicable to a wide range of engineering problems, for example, studying the interior noise in a vehicle or the sound transmission loss in a wall between two dwellings. The geometrical properties of the studied system and the frequency limit of interest for the analysis determine the size of the system of equations to be solved. This size often becomes very large and the solution time becomes long. To decrease the size of the system, and thereby speeding up the analysis, methods are investigated and developed, using substructuring and modal reduction, for the analysis of structure-acoustic problems. The geometric problem domain is divided into a number of subdomains and a reduced set of basis vectors is derived for each of these subdomains. The set of basis vectors for each domain is derived to include information about both the internal behaviour of the subdomain and the coupling to the other subdomains. The reduced description enables efficient solution of the total system. An important feature is to include the description of porous sound absorbing materials in the reduction process of the structure-acoustic problems. The derived procedures are employed in engineering applications; particularly in the study of the sound transmission loss of lightweight double-leaf walls in the low-frequency range. The objective is to include a detailed geometric description of the problem enabling a structured evaluation of the influence of various geometrical and material properties of the studied wall on the predicted sound transmission loss.
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| 44. |
- Forsman, Karin
(författare)
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Fracture behaviour of acetylated wood : Material characterisation and dowel-type connections
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to increase the competitiveness of timber as a building material in outdoor applications, durability and dimensional stability must be ensured. Acetylation enables an environmentally friendly way to increase both durability and dimensional stability of wood, without introducing harmful substances to the environment. The focus of the present research is to examine the possibility of adding a structural value by acetylation of wood species native to the Nordic region, rarely used for loadbearing structures outdoors due to poor durability and dimensional stability. Yet, before a large scale use is possible, the mechanical properties of acetylated wood must be examined. The research presented in this dissertation focuses on the brittleness of acetylated wood, both at a clear wood level as well as in structural applications.Fracture characteristics are hereby defined by properties that influence the brittleness, considered by the stiffness, tensile strength and fracture energy. For Scots pine conditioned at a relative humidity of 60% and a temperature of 20◦C, no significant impact of the acetylation process was found for the stiffness along the grain, nor for the tensile strength perpendicular to the grain. However, for Scots pine and birch examined at various relative humidity levels, the fracture energy was found to be significantly reduced for acetylated wood at relative humidity levels up to 97%. The largest difference between unmodified and acetylated wood of the same species and at equal climate conditions was approximately 50%. The studies demonstrated a clear moisturedependencyof the fracture energy for both unmodified and acetylated wood, but it was suggested that the fracture energy is lower for acetylated wood compared to unmodified wood at similar moisture contents. The lower fracture energy of acetylated wood when compared to unmodified wood at equal relative humidity levels can thus partly, but not solely, be explained by the reduced hygroscopicity of acetylated wood.To evaluate the implications of the increased brittleness in terms of structural applications, single doweltype connections made from acetylated and unmodified Scots pine were studied. Results were compared to Eurocode 5 estimations to evaluate the validity of current design provisions for acetylated wood. It was found that, for all the tested enddistances for loading parallel to the grain, joints made from acetylated wood failed in a brittle manner. Nevertheless, connections made from acetylated wood demonstrated a significantly higher embedment strength and loadbearing capacity parallel to the grain, and Eurocode 5 provided conservative estimations. For loading perpendicular to the grain, a reduced splitting capacity was found for acetylated wood compared to unmodified wood, and here the loadbearing capacity wasoverestimated by Eurocode 5.The most important conclusion from the research presented herein is the increased brittleness of acetylated wood compared to unmodified wood. Special attention is, hence, required in structural design using acetylated Scots pine and birch. In case of doweltype connections, or other loading situations where stress concentrations occur, measures should be taken to avoid premature brittle failure modes. This risk may for instance be limited by increasingm spacings between fasteners as well as endand edgedistances, and/or reinforcement of joints. Further studies are needed to increase the knowledge of how the acetylation process will impact loadbearing structures. Although the research presented herein reveals one disadvantage with acetylated wood, it can still outperform unmodified wood in moist conditions thanks to e.g. increased dimensional stability and durability.
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| 46. |
- Fröling, Maria
(författare)
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Strength Design Methods for Glass Structures
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, user friendly and efficient methods for the design of glass structures are developed. The glass structures comprise various boundary conditions. Several types of glass are considered: single layered glass as well as laminated and insulated glass units. Typical load cases for strength design of glass are applied. A recently developed finite element is suggested to be suitable for the modeling of laminated glass structures. It is shown that the new finite element is superior to standard solid elements for modeling of laminated glass. The results show that the element provides excellent capabilities for modeling of complex laminated glass structures with several bolted or adhesive joints. The new element is utilized in the development of a method to compute stress concentration factors for laminated glass balustrades with two horizontal rows with two bolt fixings. The stress concentration factors are represented graphically in design charts. The use of the design charts allow the maximum principal stresses of the balustrade to be determined without using finite element analysis or advanced mathematics. The shear-capacity of adhesive glass-joints is tested in a short-term load-case. Commonly used stiff and soft adhesives are considered. Finite element models of the test are developed to determine the material models of the adhesives. The material models are verified through large-scale tests. For the stiff adhesives and the main part of the soft adhesives, the material models are experimentally validated for both small-scale and large-scale tests. For a group of the soft adhesives, further research is necessary to validate the material models for a large-scale joint. A reduced model for determining the maximum principal stresses of a glass subjected to dynamic impact load is developed and validated. The developed model is general in the sense that it is applicable to arbitrary location of the impact as well as to structures of arbitrary boundary condition. The validation is made for a four-sided supported glass pane and centric applied impact as well as excentric applied impact. It is shown that the model is applicable to small and medium sized structures. Finally it is proven that the model performs very well for a laminated glass balustrade of standard dimensions and with clamped fixings. Finally, insulated glass subjected to soft body impact is analyzed be means of structureacoustic analysis. A parametric study is made with respect to in-plane dimensions, glass thickness and thickness of the gas layer. For quadratic panes, a larger glass has a larger center displacement but lower stresses than a smaller glass. A single layered glass is proven to have only marginally greater stresses than the corresponding double glass. The air layer thickness has almost no influence on the stresses of the insulated glass but the thickness of the glass has a large influence. Finally, there is almost nothing to be gained to add a third glass pane to the insulated unit.
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