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Computational modeling strategy of steel connections

Bjälkensäter, Carl-Michael LU and Holmgren, Carl LU (2019) In TVSM-5000 VSMM01 20191
Department of Construction Sciences
Structural Mechanics
Abstract
When designing large complex steel structures numerical calculation methods are always used to some extent. The simulation technology of today is advanced and can with proper modeling technique provide detailed analyses which captures the structural response accurately. For most projects it is not reasonable to analyze a complete structure in exact detail and therefore simplified methods are used based on linear elastic theory since they provide conservative results. There is however a need for more detailed analyses for special parts of a structure that differs from the elementary cases described in Eurocode. A technique of how to establish a finite element model of the critical parts would save significant computational time and still... (More)
When designing large complex steel structures numerical calculation methods are always used to some extent. The simulation technology of today is advanced and can with proper modeling technique provide detailed analyses which captures the structural response accurately. For most projects it is not reasonable to analyze a complete structure in exact detail and therefore simplified methods are used based on linear elastic theory since they provide conservative results. There is however a need for more detailed analyses for special parts of a structure that differs from the elementary cases described in Eurocode. A technique of how to establish a finite element model of the critical parts would save significant computational time and still present accurate results for many cases and will, therefore, contribute to a more efficient and careful design of structures. The goal for this study is to optimize the modeling process by creating a link between traditional beam models and more detailed modeling of steel connections. The modeling strategy includes whether force controlled or displacement controlled loading should be used, how boundary conditions should be set and how the extracted forces or displacements from the traditional beam model should be applied. The main focus for the model is to predict an accurate behavior with a conservative approach. In order to evaluate a modeling strategy two case studies were performed where several detailed models of the connection were created and benchmarked to a reference model, which consists of the whole structure combined with a detailed part of the connection.
In order to evaluate the different models of the connection, output acquired from the reference model was extracted as well and inserted into the separate detailed models of the connection. If the model is reliable for the specific case, the simulations with the output from the reference model should provide an almost precise behavior. The use of output from the traditional beam model will decide if it will serve its purpose and whether it is possible to combine these two simulation methods or not.
During the study it was found that the output extracted from the traditional beam model and the reference model differed significantly. The cause for this was deemed to be due to a difference in the stiffness of the joint between the beam model and the reference model. The section forces, displacements and rotations extracted from the beam model therefore do not provide identical behavior when inserted into a detailed analysis of a single joint. The use of force controlled loading generally generated more stable and conservative results compared to the models with displacement controlled loading. Even if the models with displacement control were found to provide almost perfect results with the correct input, they proved to be sensitive to differences in the input. The output extracted from the traditional beam model led to inaccurate bending compared to the reference model, if not boundary conditions that eliminated shear forces were present. The best models proved to be the ones where the forces were applied at a distance from the area of interest. Preferably with an external beam length applied to the model. (Less)
Popular Abstract (Swedish)
När byggnader och broar ska dimensioneras är det viktigt att knutpunkterna för
konstruktionen är noggrant beräknade. För att utföra beräkningar som tar hänsyn till knäckning och andra fenomen används ofta datorberäkningar i viss utsträckning. Det tar ofta oerhört lång tid, både för användaren att skapa en modell för konstruktionen i den grad av detalj som behövs, samt för datorprogrammet att beräkna modellen. Om man istället skulle skapa en detaljerad modell av endast den knutpunkt man är intresserad av, och åstadkomma liknande resultat, skulle beräkningsprocessen kortas ner väsentligt.
Please use this url to cite or link to this publication:
author
Bjälkensäter, Carl-Michael LU and Holmgren, Carl LU
supervisor
organization
course
VSMM01 20191
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
FEM, steel, connection, joint
publication/series
TVSM-5000
report number
TVSM-5235
ISSN
0281-6679
language
English
id
8992523
alternative location
http://www.byggmek.lth.se/english/publications/tvsm-5000-present-2014/
date added to LUP
2019-08-22 10:09:51
date last changed
2019-08-22 10:09:51
@misc{8992523,
  abstract     = {When designing large complex steel structures numerical calculation methods are always used to some extent. The simulation technology of today is advanced and can with proper modeling technique provide detailed analyses which captures the structural response accurately. For most projects it is not reasonable to analyze a complete structure in exact detail and therefore simplified methods are used based on linear elastic theory since they provide conservative results. There is however a need for more detailed analyses for special parts of a structure that differs from the elementary cases described in Eurocode. A technique of how to establish a finite element model of the critical parts would save significant computational time and still present accurate results for many cases and will, therefore, contribute to a more efficient and careful design of structures. The goal for this study is to optimize the modeling process by creating a link between traditional beam models and more detailed modeling of steel connections. The modeling strategy includes whether force controlled or displacement controlled loading should be used, how boundary conditions should be set and how the extracted forces or displacements from the traditional beam model should be applied. The main focus for the model is to predict an accurate behavior with a conservative approach. In order to evaluate a modeling strategy two case studies were performed where several detailed models of the connection were created and benchmarked to a reference model, which consists of the whole structure combined with a detailed part of the connection.
In order to evaluate the different models of the connection, output acquired from the reference model was extracted as well and inserted into the separate detailed models of the connection. If the model is reliable for the specific case, the simulations with the output from the reference model should provide an almost precise behavior. The use of output from the traditional beam model will decide if it will serve its purpose and whether it is possible to combine these two simulation methods or not.
During the study it was found that the output extracted from the traditional beam model and the reference model differed significantly. The cause for this was deemed to be due to a difference in the stiffness of the joint between the beam model and the reference model. The section forces, displacements and rotations extracted from the beam model therefore do not provide identical behavior when inserted into a detailed analysis of a single joint. The use of force controlled loading generally generated more stable and conservative results compared to the models with displacement controlled loading. Even if the models with displacement control were found to provide almost perfect results with the correct input, they proved to be sensitive to differences in the input. The output extracted from the traditional beam model led to inaccurate bending compared to the reference model, if not boundary conditions that eliminated shear forces were present. The best models proved to be the ones where the forces were applied at a distance from the area of interest. Preferably with an external beam length applied to the model.},
  author       = {Bjälkensäter, Carl-Michael and Holmgren, Carl},
  issn         = {0281-6679},
  keyword      = {FEM,steel,connection,joint},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVSM-5000},
  title        = {Computational modeling strategy of steel connections},
  year         = {2019},
}