Lennart Elfgren - Profile on Academia.edu (original) (raw)
Papers by Lennart Elfgren
Numerical Analysis of High-Speed Train Induced Aerodynamic Load on Noise Barrier Considering Wind Effect
Lecture notes in civil engineering, 2023
Data Validation of Strain-Based Monitoring Systems in Low Temperature Conditions, Case Study: The Kalix Bridge
Lecture notes in civil engineering, 2023
Over the last decades, economic growth and sustained development have enforced the need to ensure... more Over the last decades, economic growth and sustained development have enforced the need to ensure reliable and long-lasting infrastructure network to guarantee serviceability and safety. Nevertheless, detrimental effects can lead over time to insufficient structural performance under increasing service loadings and extreme events. Hence, Structural Health Monitoring (SHM) arises as a solution to cope with the need of having timely and continuous data to assess the state of crucial structural assets, such as prestressed concrete bridges. On this matter, the validation of the retrieved data becomes essential for the risk-based decision making in the assessment of bridges, where selecting the most suitable monitoring system could allow to addressed main causes to the right phenomena of deterioration during the service life of the bridge. Consistently with these efforts, this paper deals with a comparative study between the data acquired by different strain-based sensors such as Fiber optic systems (FOS) and strain gauges that were installed to monitor a proof loading test developed on a 65-year-old balanced cantilever prestressed concrete bridge located in Northern Sweden. The monitored data led to establish main differences between emerging types of monitoring systems such as FOS to the well-based strain gauges when exposed to low temperature conditions. Conclusions regarding the influencing parameters between both retrieved data are drawn when evaluating the structural response under serviceability loading conditions is performed, supporting decision makers when different levels of structural assessment are required.
Effects of Temperature and NaCl Concentration on the Adsorption of C-S-H Gel in Cement Paste: A Multi-fidelity Molecular Dynamics Simulation
Lecture notes in civil engineering, 2023
Project: Anchorage in Concrete Structure
Tests of the load-bearing capacity of anchor bolts
IABSE Congress Report, 2016
When assessing the structural behaviour of prestressed concrete bridges, understanding the level ... more When assessing the structural behaviour of prestressed concrete bridges, understanding the level of prestressing is crucial. However, for existing structures, this is usually an unknown parameter and the literature only describes a few methods of experimentally determining the residual prestress forces. For this paper, a non-destructive testing approach has been evaluated based on testing of a multi-span continuous girder bridge. The method, consisting of in-situ measurements in combination with finite element (FE) simulations, revealed prestress levels in the range 25 % to 82 % of the reinforcement steel yield strength, depending on the section tested. A comparison with theoretically calculated residual prestress forces, taking into account friction and timedependent losses, indicated values of the same order but with some inconsistencies.
IABSE Congress Report, 2016
In this study, a three-dimensional model was developed to investigate the temperature fields duri... more In this study, a three-dimensional model was developed to investigate the temperature fields during a doublesided laser welding process of T-joints, and the correlations between the thermal characteristics and the mechanical properties were researched in details. To verify the modelling results, welding experiments were conducted with two different welding parameters and the geometrical dimensions of the weld pool were measured. It was found that there was a good agreement between the calculated and the measured results. The calculated results showed that the temperature profile was bilateral symmetry along the stringer centre, and the temperature gradient became greater as running far from the stringer centre, especially on the skin side. All of the tensile specimens were fractured along the fusion line on the skin panels for the head and the hoop tensile tests. The loss of the alloying elements near the fusion line on the skin side resulted in the lowest micro-hardness value appeared here, and made it to be the weakest region of the welded T-joints. The calculated thermal cycles indicated that the materials closest to the fusion line on the skin side had been staying at higher temperature for a longer time, and which is the essential reason for the fracture behaviour, micro-hardness distribution and alloying elements distribution of the double-sided laser welded T-joint.
Bärförmåga hos skadade betongsliprar
Modelling of temperature and shrinkage induced cracking risks in young concrete
Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure ... more Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure desired service life and function of concrete constructions. Making reliable stress estimations, and ...
Innovative Intelligent Management of Railway Bridges - A European Horizon 2020 Project
IABSE Congress Report, 2016
Innovative Intelligent Railways, In2Rail, is a European Horizon 2020 Project with the objective t... more Innovative Intelligent Railways, In2Rail, is a European Horizon 2020 Project with the objective to enhance capacity, increase reliability and reduce Life Cycle Costs of European Railways. Bridges and Tunnels is the main focus in Work Package 4. The aim is to study, benchmark and further develop new Inspection Technologies in order to create more proactive maintenance procedures. In this paper some preliminary results are presented.
Energetically Modified Cement (EMC) and Ordinary Portland cement (OPC) a comparison
Validation of an Experimental Methodology for Measuring Concrete Fracture Energy in Existing Structures
Lecture notes in civil engineering, 2023
Railway Bridge Research : A Survey 2005 Sustainable Bridges SB-D1.4
An overview is reported of current research regarding railway bridges. Research themes and active... more An overview is reported of current research regarding railway bridges. Research themes and active institutes and organisations are listed. The work has been carried out during 2004/2005 in the proj ...
A schematic view of the North Spur Ridge illustrating one of the stability problems. When the wat... more A schematic view of the North Spur Ridge illustrating one of the stability problems. When the water level is raised 22 m, from WL= +17 m to WL= +39 m, an immense hydraulic force Nw starts to act on the cut-off wall. The question, among others, is if the shear resistance related to the stress increase along a possible slip surface (red dotted line) is big enough to balance the force Nw in the triggering phase of a progressive failure. Here o denotes the in-situ stress before the rise of the water level. The lower left figure illustrates the material properties of the soil with a shear stress/strain (deformation) () diagram showing a peak shear stress s and a residual shear stress sR due to strain-softening. The red dotted line indicates the classic plastic Limit Equilibrium Method (LEM) assumption with no deformation-related reduction of the shear strength. When the force Nw starts to act on the cut-off wall, the soil behind the wall starts to deform ( and the shear stresses ( ) will rise in accordance with the stress-strain diagram. When the shear stresses approach and pass beyond the maximum value s, the soil softens and finally the resistance will be reduced to the residual value sR close to the wall. The maximum force increase that the soils behind the wall may resist applying progressive failure analysis isNcrit = ∫ )dx, as illustrated in the lower right figure. For the slope to remain stable, Ncrit must at least balance the force Nw i.e. the Safety Factor (Fs) being equal to 1,0. Yet, in Soil Mechanics normally a minimum value of Fs > 1.5 is prescribed. Hence, the main objective of a stability analysis is defining the value of Ncrit for relevant strain-softening material properties and proper assumptions regarding the initiating failure plane. If unrealistic ideal plastic properties are assumed (green dotted line), there will obviously in many cases, falsely, be no apparent stability problem 2 nd revised version, November 2017 1 st version, July 2017, titled "Riverbank stability in loosely layered clays"
Infästningar i betongkonstruktioner analyserade med brottmekanik
Bygg & Teknik, 1990
Full-scale failure test of a reinforced concrete bridge in order to calibrate assessment models for load and resistance
Nordic concrete research, 2008
Full-scale failure test of a reinforced concrete bridge in order to calibrate assessment models f... more Full-scale failure test of a reinforced concrete bridge in order to calibrate assessment models for load and resistance
Utmattningshållfasthet för betongkonstruktioner : Rapport från tre pågående forskningsprojekt vid Tekniska högskolan i Luleå
Utmattningshallfasthet for betongkonstruktioner : Rapport fran tre pagaende forskningsprojekt vid... more Utmattningshallfasthet for betongkonstruktioner : Rapport fran tre pagaende forskningsprojekt vid Tekniska hogskolan i Lulea
Utmattning av betong i kallt klimat : vinterbygge
Ingjutningsbruk : Tidsberoende egenskaper : Hållfasthet, krympning och krypning hos ingjutningsbruk avsedda för förankringar i betongfundament
Egenskaperna hos fem olika ingjutningsbruk har provats under ett ar. Krympningen under denna tid ... more Egenskaperna hos fem olika ingjutningsbruk har provats under ett ar. Krympningen under denna tid varier mellan 0,5 och 3,4 promille for de olika bruken.
Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure ... more Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure desired service life and function of concrete infrastructures. Making reliable stress estimations, and thereby conclusions about cracking risks caused by temperature movements and shrinkage involves advanced modelling of material properties and structural restraint. The paper presents the main outline of a model for description of material properties needed. Special focus is given to a creep model denoted LLM (Linear Logarithmic Model), which is shown to be robust, easy to use, and capable to extrapolate short-term test into long-term effects. Applications of the presented model using the computer program ConTeSt Pro demonstrates that it can be used to decide what measures to be taken to minimize the risk of cracking during the hardening phase for concrete structures.
Numerical Analysis of High-Speed Train Induced Aerodynamic Load on Noise Barrier Considering Wind Effect
Lecture notes in civil engineering, 2023
Data Validation of Strain-Based Monitoring Systems in Low Temperature Conditions, Case Study: The Kalix Bridge
Lecture notes in civil engineering, 2023
Over the last decades, economic growth and sustained development have enforced the need to ensure... more Over the last decades, economic growth and sustained development have enforced the need to ensure reliable and long-lasting infrastructure network to guarantee serviceability and safety. Nevertheless, detrimental effects can lead over time to insufficient structural performance under increasing service loadings and extreme events. Hence, Structural Health Monitoring (SHM) arises as a solution to cope with the need of having timely and continuous data to assess the state of crucial structural assets, such as prestressed concrete bridges. On this matter, the validation of the retrieved data becomes essential for the risk-based decision making in the assessment of bridges, where selecting the most suitable monitoring system could allow to addressed main causes to the right phenomena of deterioration during the service life of the bridge. Consistently with these efforts, this paper deals with a comparative study between the data acquired by different strain-based sensors such as Fiber optic systems (FOS) and strain gauges that were installed to monitor a proof loading test developed on a 65-year-old balanced cantilever prestressed concrete bridge located in Northern Sweden. The monitored data led to establish main differences between emerging types of monitoring systems such as FOS to the well-based strain gauges when exposed to low temperature conditions. Conclusions regarding the influencing parameters between both retrieved data are drawn when evaluating the structural response under serviceability loading conditions is performed, supporting decision makers when different levels of structural assessment are required.
Effects of Temperature and NaCl Concentration on the Adsorption of C-S-H Gel in Cement Paste: A Multi-fidelity Molecular Dynamics Simulation
Lecture notes in civil engineering, 2023
Project: Anchorage in Concrete Structure
Tests of the load-bearing capacity of anchor bolts
IABSE Congress Report, 2016
When assessing the structural behaviour of prestressed concrete bridges, understanding the level ... more When assessing the structural behaviour of prestressed concrete bridges, understanding the level of prestressing is crucial. However, for existing structures, this is usually an unknown parameter and the literature only describes a few methods of experimentally determining the residual prestress forces. For this paper, a non-destructive testing approach has been evaluated based on testing of a multi-span continuous girder bridge. The method, consisting of in-situ measurements in combination with finite element (FE) simulations, revealed prestress levels in the range 25 % to 82 % of the reinforcement steel yield strength, depending on the section tested. A comparison with theoretically calculated residual prestress forces, taking into account friction and timedependent losses, indicated values of the same order but with some inconsistencies.
IABSE Congress Report, 2016
In this study, a three-dimensional model was developed to investigate the temperature fields duri... more In this study, a three-dimensional model was developed to investigate the temperature fields during a doublesided laser welding process of T-joints, and the correlations between the thermal characteristics and the mechanical properties were researched in details. To verify the modelling results, welding experiments were conducted with two different welding parameters and the geometrical dimensions of the weld pool were measured. It was found that there was a good agreement between the calculated and the measured results. The calculated results showed that the temperature profile was bilateral symmetry along the stringer centre, and the temperature gradient became greater as running far from the stringer centre, especially on the skin side. All of the tensile specimens were fractured along the fusion line on the skin panels for the head and the hoop tensile tests. The loss of the alloying elements near the fusion line on the skin side resulted in the lowest micro-hardness value appeared here, and made it to be the weakest region of the welded T-joints. The calculated thermal cycles indicated that the materials closest to the fusion line on the skin side had been staying at higher temperature for a longer time, and which is the essential reason for the fracture behaviour, micro-hardness distribution and alloying elements distribution of the double-sided laser welded T-joint.
Bärförmåga hos skadade betongsliprar
Modelling of temperature and shrinkage induced cracking risks in young concrete
Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure ... more Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure desired service life and function of concrete constructions. Making reliable stress estimations, and ...
Innovative Intelligent Management of Railway Bridges - A European Horizon 2020 Project
IABSE Congress Report, 2016
Innovative Intelligent Railways, In2Rail, is a European Horizon 2020 Project with the objective t... more Innovative Intelligent Railways, In2Rail, is a European Horizon 2020 Project with the objective to enhance capacity, increase reliability and reduce Life Cycle Costs of European Railways. Bridges and Tunnels is the main focus in Work Package 4. The aim is to study, benchmark and further develop new Inspection Technologies in order to create more proactive maintenance procedures. In this paper some preliminary results are presented.
Energetically Modified Cement (EMC) and Ordinary Portland cement (OPC) a comparison
Validation of an Experimental Methodology for Measuring Concrete Fracture Energy in Existing Structures
Lecture notes in civil engineering, 2023
Railway Bridge Research : A Survey 2005 Sustainable Bridges SB-D1.4
An overview is reported of current research regarding railway bridges. Research themes and active... more An overview is reported of current research regarding railway bridges. Research themes and active institutes and organisations are listed. The work has been carried out during 2004/2005 in the proj ...
A schematic view of the North Spur Ridge illustrating one of the stability problems. When the wat... more A schematic view of the North Spur Ridge illustrating one of the stability problems. When the water level is raised 22 m, from WL= +17 m to WL= +39 m, an immense hydraulic force Nw starts to act on the cut-off wall. The question, among others, is if the shear resistance related to the stress increase along a possible slip surface (red dotted line) is big enough to balance the force Nw in the triggering phase of a progressive failure. Here o denotes the in-situ stress before the rise of the water level. The lower left figure illustrates the material properties of the soil with a shear stress/strain (deformation) () diagram showing a peak shear stress s and a residual shear stress sR due to strain-softening. The red dotted line indicates the classic plastic Limit Equilibrium Method (LEM) assumption with no deformation-related reduction of the shear strength. When the force Nw starts to act on the cut-off wall, the soil behind the wall starts to deform ( and the shear stresses ( ) will rise in accordance with the stress-strain diagram. When the shear stresses approach and pass beyond the maximum value s, the soil softens and finally the resistance will be reduced to the residual value sR close to the wall. The maximum force increase that the soils behind the wall may resist applying progressive failure analysis isNcrit = ∫ )dx, as illustrated in the lower right figure. For the slope to remain stable, Ncrit must at least balance the force Nw i.e. the Safety Factor (Fs) being equal to 1,0. Yet, in Soil Mechanics normally a minimum value of Fs > 1.5 is prescribed. Hence, the main objective of a stability analysis is defining the value of Ncrit for relevant strain-softening material properties and proper assumptions regarding the initiating failure plane. If unrealistic ideal plastic properties are assumed (green dotted line), there will obviously in many cases, falsely, be no apparent stability problem 2 nd revised version, November 2017 1 st version, July 2017, titled "Riverbank stability in loosely layered clays"
Infästningar i betongkonstruktioner analyserade med brottmekanik
Bygg & Teknik, 1990
Full-scale failure test of a reinforced concrete bridge in order to calibrate assessment models for load and resistance
Nordic concrete research, 2008
Full-scale failure test of a reinforced concrete bridge in order to calibrate assessment models f... more Full-scale failure test of a reinforced concrete bridge in order to calibrate assessment models for load and resistance
Utmattningshållfasthet för betongkonstruktioner : Rapport från tre pågående forskningsprojekt vid Tekniska högskolan i Luleå
Utmattningshallfasthet for betongkonstruktioner : Rapport fran tre pagaende forskningsprojekt vid... more Utmattningshallfasthet for betongkonstruktioner : Rapport fran tre pagaende forskningsprojekt vid Tekniska hogskolan i Lulea
Utmattning av betong i kallt klimat : vinterbygge
Ingjutningsbruk : Tidsberoende egenskaper : Hållfasthet, krympning och krypning hos ingjutningsbruk avsedda för förankringar i betongfundament
Egenskaperna hos fem olika ingjutningsbruk har provats under ett ar. Krympningen under denna tid ... more Egenskaperna hos fem olika ingjutningsbruk har provats under ett ar. Krympningen under denna tid varier mellan 0,5 och 3,4 promille for de olika bruken.
Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure ... more Control of thermal and shrinkage cracking in hardening concrete is of great importance to ensure desired service life and function of concrete infrastructures. Making reliable stress estimations, and thereby conclusions about cracking risks caused by temperature movements and shrinkage involves advanced modelling of material properties and structural restraint. The paper presents the main outline of a model for description of material properties needed. Special focus is given to a creep model denoted LLM (Linear Logarithmic Model), which is shown to be robust, easy to use, and capable to extrapolate short-term test into long-term effects. Applications of the presented model using the computer program ConTeSt Pro demonstrates that it can be used to decide what measures to be taken to minimize the risk of cracking during the hardening phase for concrete structures.
The aim of the report is to present a simple rational method for the determination of the load-ca... more The aim of the report is to present a simple rational method for the determination of the load-carrying capacity of reinforced concrete beams loaded in combined torsion, bending and shear