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1.
  • Liu, Yungang, 1966, et al. (författare)
  • Frequency-domain dynamic analysis of cables
  • 1997
  • Ingår i: Engineering Structures. - 1873-7323 .- 0141-0296. ; 19:6, s. 499-506
  • Tidskriftsartikel (refereegranskat)abstract
    • A linear, frequency-domain, dynamic method is introduced to calculate large motions of slender structures such as towing and mooring cables, and flexible risers. The viscous, drag damping is linearized at element level by calculating linearized equivalent damping coefficients through iteration, In the introduced method the work done by the motion of the cable in the time domain is equated with that done in the frequency domain, The linearized, frequency-domain results are compared with results from nonlinear simulations for a towing cable, a mooring line and a lazy-wave riser. The influences of excitation frequency and excitation amplitude are considered.
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2.
  • Liu, Yungang, 1966, et al. (författare)
  • Influence of current and seabed friction on mooring cable response: comparison between time-domain and frequency-domain analysis
  • 1997
  • Ingår i: Engineering Structures. - 1873-7323 .- 0141-0296. ; 19:11, s. 945-953
  • Tidskriftsartikel (refereegranskat)abstract
    • For a single mooring cable, the effect of current and seabed friction on mooring-cable tension and energy dissipation are studied in both the time domain and the frequency domain. In the time domain, all nonlinearities can be taken into account. In the frequency domain, the nonlinear drag forces can be linearized either by a direct integration method or by statistical linearization techniques; for sea-floor effects, a simple lumped stiffness model and the statistical linearization method based on friction-controlled slip are combined. Two example structures, one flexible riser and one deep water mooring, are analysed. The time-domain and frequency-domain results compare well. The findings of the effects of current and friction on mooring-cable responses are discussed, they show that the linearized frequency-domain solution can produce satisfactory results.
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3.
  • Afshar, R, et al. (författare)
  • Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints
  • 2017
  • Ingår i: Engineering structures. - : ELSEVIER SCI LTD. - 0141-0296 .- 1873-7323. ; 147, s. 62-76
  • Tidskriftsartikel (refereegranskat)abstract
    • Modelling in design of new support systems necessitates the joint stiffness of the existing wooden structures. In valuable structures, e.g. in cultural heritage, or structures with inaccessible joints, these stiffness values must be estimated, e.g. by testing joints in tailored replicas of the original parts. Although a simplified structure, the replica, can call for finite element (FE) modelling to capture the stiffness parameters. The first step in such a process is to compare FE predictions with experimental tests, for validation purposes. The reasons for unavoidable differences in load-displacement behaviour between model predictions and experimental test should be identified, and then possibly remedied by an improved model. Underlying causes like the complex shape of joints, geometrical uncertainties, contact mechanisms and material nonlinearity are generally too computationally expensive to be included in a full-scale model. It is therefore convenient to collect such effects in the contact penalty stiffness in the joint contact areas where stresses are high, which influences the resulting joint stiffness. A procedure for this is here illustrated for the case of the 17th century Vasa shipwreck A replica of a section of the ship has been constructed, and its joints were tested in bending-compression, in-plane shear and rotation. The FE simulations showed stiffer behaviour than the experimental results. Therefore, a normal penalty stiffness in contact surfaces of the joint were introduced, and used as a calibration parameter to account for the simplifying assumptions or indeliberate imprecision in the model, e.g. concerning boundary conditions, material properties and geometrical detail. The difference between numerical predictions and experimental results could then be significantly reduced, with a suitable normal penalty stiffness value. Once an acceptable finite element model has been obtained, it is shown how this can be used to identify stiffness values for joints in the physical structure with compensation for degradation of material properties due to aging and conservation treatment.
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4.
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5.
  • Aggestam, Emil, 1992, et al. (författare)
  • Optimisation of slab track design considering dynamic train–track interaction and environmental impact
  • 2022
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 254
  • Tidskriftsartikel (refereegranskat)abstract
    • Modern railway tracks for high-speed traffic are often built based on a slab track design. A major disadvantage of slab track compared to conventional ballasted track is that the environmental impact of the construction is higher due to the significant amount of concrete required. In this paper, the dimensions of the rectangular cross-sections and the types of concrete used in slab tracks are optimised with the objective to minimise greenhouse gas emissions, while considering the constraint that the design must pass the static dimensioning analysis described in the European standard 16432-2. The optimised track design is also analysed using a three-dimensional (3D) model of vertical dynamic vehicle–track interaction, where the rails are modelled as Rayleigh–Timoshenko beams and the concrete parts are represented by quadratic shell elements. Wheel–rail contact forces and the time-variant stress field of the concrete parts are calculated using a complex-valued modal superposition for the finite element model of the track. For the studied traffic scenario, it is concluded that the thickness of the panel can be reduced compared to the optimised design from the standard without the risk of crack initiation due to the dynamic vehicle load. In parallel, a model of reinforced concrete is developed to predict crack widths, the bending stiffness of a cracked panel section and to assess in which situations the amount of steel reinforcement can be reduced. To reduce the environmental impact even further, there is potential for an extended geometry optimisation by excluding much of the concrete between the rails.
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6.
  • Aggestam, Emil, 1992, et al. (författare)
  • Simulation of vertical dynamic vehicle–track interaction using a three-dimensional slab track model
  • 2020
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 222
  • Tidskriftsartikel (refereegranskat)abstract
    • When improving track design, a better understanding of the track's damage modes is needed, and the railway industry is then dependent on the availability of accurate simulations of the dynamic vehicle–track interaction. In the present study, the vertical dynamic interaction between a travelling railway vehicle and a slab track is simulated in the time domain by using an extended state-space vector approach. A three-dimensional slab track model is launched where the rails are modelled using Rayleigh–Timoshenko beam elements and the concrete panel and roadbed are represented by using either shell or solid finite elements. From the parameterised track model, which is developed in Abaqus using Python scripts, the system matrices are exported to Matlab where the simulation of the dynamic vehicle–track interaction is performed. A complex-valued modal superposition technique is employed, which reduces the computational cost of the simulation. In a post-processing step, calculated wheel–rail contact forces from the dynamic analysis are used as input to the Abaqus track model where various track responses are evaluated. In particular, the time history of principal stresses is determined at critical locations in the concrete panel. Also the influence of the speed of the vehicle on the wheel–rail contact forces, and the influence of a transverse culvert below the track (modelled as a local increase of the foundation bedding modulus) on the track stiffness variation at the rail level, are investigated. A mesh convergence study for a range of track responses has been conducted including investigations of when to use linear or quadratic elements and shell or solid elements. Finally, the presented three-dimensional models have been compared to an alternative two-dimensional model to determine in what situations a two-dimensional model is sufficient.
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7.
  • Agredo Chávez, Angélica, et al. (författare)
  • Assessment of residual prestress in existing concrete bridges: The Kalix bridge
  • 2024
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 311
  • Tidskriftsartikel (refereegranskat)abstract
    • The direct socio-economic consequences of the deterioration of aging infrastructure systems have triggered a continuous process of revising and updating current design standards and guidelines for critical network components. Specifically, long-term degradation processes demand the analysis and evaluation of vital structural assets such as prestressed concrete bridges. It is crucial to develop theoretically consistent, user-friendly, and non-destructive methodologies that engineering professionals can employ to prevent and mitigate potential catastrophic outcomes during the service life of these bridges. This study provides a thorough review of the available testing methods employed over the years for prestressed concrete bridges and introduces a comprehensive framework for evaluating existing methods for residual prestress force assessment. Through a multi-criteria selection process, the three most feasible tests were designed and carried out on an existing 66-year-old balanced cantilever box girder bridge exposed to freezing temperatures that affected the instrumentation plan and test execution. Finally, predictive models compliant with standard codes were calibrated based on the experimental results and the life cycle loss of prestress forces was evaluated to assess relevant bounding intervals. Findings reveal limited on-site testing and discrepancies between calculated residual forces and predictions by standard codes. The saw cut method showed a 18% difference from the initial applied prestress according to the prestress protocol, suggesting the use of a cover meter and concrete modulus evaluation for improved accuracy. The strand cutting method resulted in a 14% difference, emphasizing the need for stress redistribution assessment. The second-order deflection method showed a 6% difference, indicating a focus on enhanced boundary conditions and thorough sensitivity analysis for future investigations.
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8.
  • Ahmed, Lamis, et al. (författare)
  • Structural dynamic and stress wave models for analysis of shotcrete on rock exposed to blasting
  • 2012
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 35:1, s. 11-17
  • Tidskriftsartikel (refereegranskat)abstract
    • During blasting in tunnels and mines, the interaction between shotcrete (sprayed concrete) and rock is influenced by propagating stress waves. Shotcrete support in hard rock tunnels is studied here through numerical analysis using three different modelling approaches. The stress response in the shotcrete closest to the rock when exposed to P-waves striking perpendicularly to the shotcrete–rock interface is simulated. The first model tested is a structural dynamic model that consists of masses and spring elements. The second is a model built up with finite element beam elements interconnected with springs. The third is a one-dimensional elastic stress wave model. The models give comparable results, although the definition of the dynamic loads is different. The analysis results can be used to estimate whether the shotcrete will fail or not for a prescribed distance to detonating explosives inside the rock.
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9.
  • Ahola, A., et al. (författare)
  • Fatigue strength capacity of load-carrying fillet welds on ultra-high-strength steel plates subjected to out-of-plane bending
  • 2019
  • Ingår i: Engineering structures. - : ELSEVIER SCI LTD. - 0141-0296 .- 1873-7323. ; 196
  • Tidskriftsartikel (refereegranskat)abstract
    • Weld root fatigue strength capacity is an important design criterion in load-carrying (LC) fillet welded joints subjected to cyclic loads. This paper elaborates on the weld root fatigue strength capacity of fillet welded LC joints made of ultra-high-strength steel (UHSS) and subjected to out-of-plane bending. Experimental fatigue tests are carried out using constant amplitude loading with an applied stress ratio of R = 0.1 with both pure axial, i.e. DOB = 0 (degree of bending, bending stress divided by total stress) and bending, i.e. DOB = 1.0, load conditions. The applicability of different approaches - nominal weld stress, effective notch stress concepts, and 2D linear elastic fracture mechanics (LEFM) - for the fatigue strength assessment of weld root capacity is evaluated. Furthermore, a parametric LEFM analysis is used to evaluate the effect of weld penetration on the root fatigue strength capacity in axial and bending loading. The results indicate that in the case of bending, nominal weld stress can be calculated using the linear stress distribution over the joint section and FAT36 as a reference curve. In the bending loading, for the joints failing from the weld toe, a mean fatigue strength of up to 185 MPa in the nominal stress system was achieved, indicating that the reference curve FAT63 is overly conservative. The ENS concept with FAT225 seemed to be slightly unconservative for assessing the root fatigue strength capacity. LEFM analyses revealed that in the case of increasing weld penetration and bending loading, weld root fatigue strength capacity seemed to correlate with the nominal weld stress calculated using effective weld throat thickness, while in axial loading, weld stress should be calculated using external throat thickness summed with penetration length.
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10.
  • Akter, Shaheda T., et al. (författare)
  • Numerical modelling of wood under combined loading of compressionperpendicular to the grain and rolling shear
  • 2021
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 244
  • Tidskriftsartikel (refereegranskat)abstract
    • Numerical modeling is an efficient tool for experimental validation and for gaining a deeper understanding of complex material phenomena, especially when causal relationships are overlaid by material variability. Wood is such a highly orthotropic and complex material, which in engineering problems however is considered as macro- homogeneous. The aim of this study is to numerically investigate stress and strain states of wood in the radial- tangential plane and the influence of the orthotropic material behavior on the structural response. Model vali-dation is based on experiments performed on clear wood of Norway spruce (Picea abies) by using a biaxial test setup. Three material models were used, namely Hill’s plasticity model, the Hoffman criterion and a novel quadratic multi-surface (QMS) criterion. After validation on the local material scale, the models were applied to the engineering problem of compression perpendicular to the grain for studying the effect of the unloaded length. As a novel part, the influence of the annual ring structure on the local material behavior and the global elasto- plastic force–displacement behavior of wood under compression perpendicular to the grain were numerically investigated. Hill’s failure criterion was found to be the least suitable at both length scales, local material behavior and global structural response. The Hoffman and the QMS criteria showed quite good agreement with the biaxial experiments in terms of force–displacement relations and strain distributions for different loading situations, especially for combinations with radial compression, while there was less agreement with experiments for  the  behavior of  combinations with tangential compression. Application of  these material models to compression perpendicular to the grain for studying the unloaded length effect yielded similar trends as observed in structural tests. A reasonable and similar force–displacement response by Hoffman and QMS criteria was observed, while Hill’s model yielded significantly overestimated force carrying capacity. Differences in force-–displacement response for different loading situations were well in line with literature findings and the infl-ence of the annual ring curvature on the overall force–displacement behavior could be quantified.
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11.
  • al-Karawi, Hassan, 1993, et al. (författare)
  • Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment
  • 2021
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 239
  • Tidskriftsartikel (refereegranskat)abstract
    • High-Frequency Mechanical Impact (HFMI) is one of the post-weld treatment methods. In this study, comparative axial fatigue tests were conducted on as-welded and HFMI-treated welded transverse attachment details. The test results demonstrated the efficiency of HFMI-treatment in fatigue life extension of cracked welded structures, providing that the existing crack size is less than 1.2 mm. Cracks were created in some specimens through fatigue testing before HFMI-treatment, while other specimens were not subjected to any fatigue loading prior to treatment. Many of the treated specimens ran out after 10 million cycles of loading when tested at a stress range of 150 MPa. Therefore, the stress range was increased to 180 MPa or 210 MPa. No remarkable difference was found between the fatigue strength of the crack-free and the cracked treated specimens. It was found that the induced compressive residual stress can exceed the material yield limit, and reach a depth larger than 1.5 mm in most cases. The induced compressive residual stress, the local material hardening, the increase in weld toe radius, the change in crack orientation and the shallowness of the crack size were the causatives of the obtained long fatigue lives of the HFMI-treated specimens. Besides, linear elastic fracture mechanics calculations were conducted to predict the fatigue lives of as-welded and HFMI-treated details. The results were in agreement with the experiment. Moreover, the calculations showed that the initial crack size, the clamping stress and the induced compressive residual stress were the main factors behind the scatter in fatigue lives.
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12.
  • Al-Ramahi, Nawres J., 1980-, et al. (författare)
  • Numerical analysis of stresses in double-lap adhesive joint under thermo-mechanical load
  • 2021
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 233
  • Tidskriftsartikel (refereegranskat)abstract
    • A numerical study for the double-lap adhesive joint made of similar adherends subjected to tensile and thermal loads is presented. A novel displacement coupling conditions which are able to correctly represent monoclinic materials (off-axis layers of composite laminates) are used to build a comprehensive numerical model. Two types of double-lap joints are considered in this study: metal–metal and composite-composite. In case of composite laminates, four lay-ups are evaluated: unidirectional ([08]T and [908]T) and quasi-isotropic laminates ([0/45/90/−45]S and [90/45/0/−45]S). The effect of different parameters (adherend stiffness, ply stacking sequence, adherend thickness, one-step or two-step manufacturing of the joint) on peel and shear stress distribution in the middle of the adhesive is studied. The comparison of the behaviour of single-lap and double-lap joint in relation to these parameters is made. The maximum peel and shear stress at the ends of the overlap with respect to the axial modulus of the adherends are presented in a form of the master curves. The analyses of results show that: the maximum peel and shear stress concentration at the overlap ends is reduced with the increase of the axial modulus of the adherend; the stress distribution in the adhesive layer can be improved (lower stress concentrations and level-out the curve) by changing the fibre orientation (which affect the stiffness) in plies connected to the adhesive layer.
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13.
  • Alabbasi, Sateh, et al. (författare)
  • A numerical and experimental investigation of a special type of floating-slab tracks
  • 2020
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 215, s. 1-16
  • Tidskriftsartikel (refereegranskat)abstract
    • Floating-Slab Tracks (FST) are predominantly used for mitigating railway-induced vibrations where the concrete slab is mounted on soft resilient bearings to provide vibration isolation. This paper presents a research study on the dynamic behavior of a special type of FST used in the recently built subway system in Doha, Qatar. The special FST has a continuous concrete slab with periodic grooves. Therefore, the track can be modeled as a periodic structure with a slab unit having two elements with different cross-sections. Extensive numerical and experimental investigations were conducted on a multi-unit full-scale mockup track representing the special FST. A fast running model based on the Dynamic Stiffness Method was developed and examined, in an initial numerical exercise, against a detailed Finite Element model for a track with a finite length. In the experimental campaign, a test was performed with an impact hammer to identify the actual vibration response of the mockup track. Results from the experimental investigations were then used for model updating of the fast running model. The model updating process was carried out according to an automated hybrid optimization approach that combines genetic algorithms with a local search method. Finally, the updated model was extended to an infinite model to investigate the influence of varying grooves thickness on the dynamic behavior of the special track with infinite length for both bending and torsion scenarios. The investigations suggested that reducing the thickness below 50% of the full thickness of the slab significantly affects the dynamic behavior of the special FST.
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14.
  • Alhasawi, Anas, et al. (författare)
  • Co-rotational planar beam element with generalized elasto-plastic hinges
  • 2017
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 151, s. 188-205
  • Tidskriftsartikel (refereegranskat)abstract
    • Slender elements in framed structures may undergo large displacement and experience highly nonlinear behavior. This paper presents a two-node co-rotational flexible beam with generalized elasto-plastic hinges at the beam ends. A Condensation procedure is used to remove the internal degrees of freedom so that the formulation is easily incorporated with the standard co-rotational approach. A family of asymmetric and convex yield surfaces of super-elliptic shape is considered for the plastic behavior of the hinges. By varying the roundness factor, an infinite number of yield surfaces are obtained making it possible to select the yield function that best fit experimental data of any type of cross-section and material. The nonlinear response of bolted connections subjected to both bending and axial forces are conveniently modeled with such a yield surface. Discrete constitutive equations for the hinge plastic deformations are derived using the implicit scheme for both smooth and non-smooth cases. Numerical examples demonstrate the accuracy of the model in predicting the large displacement inelastic response of framed structures. Effect of the roundness factor on the ultimate load strongly depends on the structure typology. It was observed that cyclic loading produces pinching effect, cyclic softening and ductile behavior. Those effects are more pronounced with anisotropic yield criteria.
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15.
  • Andersen, Michael Styrk, et al. (författare)
  • Aerodynamic stability of long span suspension bridges with low torsional natural frequencies
  • 2016
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 120, s. 82-91
  • Tidskriftsartikel (refereegranskat)abstract
    • Classical flutter of suspended bridge decks can be avoided if the torsional frequencies are lower than the vertical. Wind tunnel tests of single boxes and twin box section models with torsional natural frequencies above and below the vertical frequency has been conducted. Flutter was avoided in all tests where the torsional frequency was lower than the vertical. But too low torsional stiffness caused large static displacements of the girder at medium–high wind speeds and steady state oscillations driven by a combination of torsional divergence and stalling behavior at the critical wind seed. In order to design aerodynamically stable suspension bridges with low torsional natural frequencies it is suggested to increase the mass moment of inertia and provide adequate torsional stiffness by the main cables spacing.
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16.
  • Ansell, Anders (författare)
  • The dynamic element method for analysis of frame and cable type structures
  • 2005
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 27:13, s. 1906-1915
  • Tidskriftsartikel (refereegranskat)abstract
    • With the dynamic element method (DEM), results more accurate than with the conventional finite element method (FEM) are obtained with the same number of degrees of freedom. This is due to the introduction of shape functions of polynomial type, introducing frequency dependence into the mass matrix expressions. It is demonstrated how this affects free vibration analysis, including the solution of nonlinear eigenvalue problems. Various numerical techniques for solving these polynomial problems are discussed. The polynomial matrix formulations for stiffness and mass matrices are given for a beam, a bar and a cable element. Numerical examples demonstrate how the DEM can be implemented for modelling of frame type structures and its efficiency is compared to that of the conventional FEM
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17.
  • Arvidsson, Therese, et al. (författare)
  • Statistical screening of modelling alternatives in train-bridge interaction systems
  • 2014
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 59, s. 693-701
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of parameter variations in railway bridges subjected to train loads has been evaluated within the framework of a two-level factorial experiment. Especially, the influence of train-bridge interaction in comparison to other parameter variations is highlighted. Variations in the system parameters were introduced, corresponding to modelling alternatives considering reasonable uncertainties in a bridge design model. The dynamic effect from a passenger train set has been evaluated at, and away from, resonance in beam bridges of span lengths 6, 12, 24 and 36. m. By means of the two-level factorial design, effects from changes in a single parameter, as well as joint effects from simultaneous changes in several parameters, may be evaluated. The effect of including train-bridge interaction through a simple vehicle model as opposed to moving forces was found most distinct at resonance. The effect of the choice of load model was furthermore shown largest for the bridges of span length 24 and 36. m, where it was found more influential or comparable to the effect of other system parameter uncertainties. The high influence of the load model may well be attributed to the fact that the natural frequencies of the 24 and 36. m bridges are close to the vertical frequency of the primary suspension system of the train. The reduction of response obtained with the train-bridge interaction model are discussed in relation to bridge frequency rather than span length, and compared to the Additional Damping Method given in the European design code.
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18.
  • Atashipour, Rasoul, 1983, et al. (författare)
  • A weak shear web model for deflection analysis of deep composite box-type beams
  • 2018
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 155, s. 36-49
  • Tidskriftsartikel (refereegranskat)abstract
    • Deep box-type beams, consisting of framing members and sheathings, are sensitive to shear deformations andhence appropriate refined theories or complicated magnification factors are needed to be used to obtain accurate results. For sheathings or webs between the framing members that are weak in shear, additional shear deformations occur corresponding to the relative axial displacement between the framing members. These sandwich-type or partial interaction-type of in-plane shear behaviour between the framing members, needs to betaken into account, especially when the web shear stiffness is very low. The composite box-type beam treatedhere is composed of three framing members with sheathings on both sides. To incorporate effects of the sheathings shear deformations between the framing members on the deflection, the sheathings, here called web interlayers, are modelled as shear media with equivalent slip moduli corresponding to a partially interacting composite beam model. Governing equilibrium equations of the model are obtained using the minimum total potential energy principle and solved explicitly. The obtained results are compared with those based on different conventional beam theories and 3-D finite element (FE) simulations. It is shown that the model is capable of predicting accurately the deflection for a wide range of geometry and property parameters. It is demonstrated that the deflection of such deep box-type beams can be expressed as the summation of three different effects, namely bending deformations, conventional shear deformations in the framing members and sheathings, and additional in-plane shear deformations or shear slips of the weak web causing relative axial displacements between the framing members.
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19.
  • Bagge, Niklas, et al. (författare)
  • In-situ methods to determine residual prestress forces in concrete bridges
  • 2017
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 135, s. 41-52
  • Tidskriftsartikel (refereegranskat)abstract
    • Levels of residual prestress forces are key parameters when assessing the structural behaviour of existing prestressed concrete bridges. However, these parameters are often unknown and not easy to determine. To explore them, two existing non-destructive and destructive approaches have been further developed for practical application and demonstrated on a multi-span continuous girder bridge. The evaluation of the prestress forces was part of an extensive experimental programme aimed to calibrate and develop assessment methods. Due to the pursuit of practical applications for existing bridges, the main focus was on non-destructive methodology, combining experimental data and finite element modelling to obtain the residual prestress forces. Assuming that the initial prestress force corresponded to 85% of the characteristic 0.2% proof strength of the reinforcing steel, estimated losses in investigated sections ranged between 5 and 70%. However, determined residual prestress forces were generally higher than theoretically based estimates accounting for friction and time-dependent losses in the prestressing system. In addition to describing in detail the methods for prestress evaluation, this paper presents suggestions for improvements and further studies, based on experiences from the field tests.
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20.
  • Bagge, Niklas, et al. (författare)
  • Moment redistribution in RC beams : A study of the influence of longitudinal and transverse reinforcement ratios and concrete strength
  • 2014
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 80, s. 11-23
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the results from an experimental programme, aimed at investigating moment redistribution in statically indeterminate reinforced concrete structures, are presented and compared with theoretical analysis of the structural behaviour. Due to the nonlinear structural behaviour of reinforced concrete structures, linear elastic analysis can lead to an inaccurate assessment of the behaviour and, therefore, it can become necessary to use more advanced methodologies to achieve sufficiently accurate analysis. Furthermore, more advanced methods can enable a higher degree of performance optimisation of structures than those resulting from the simplified approaches adopted by existing design codes based on linear elastic analysis with redistribution of internal forces. In order to assess the load-carrying capacity at the ultimate limit state (ULS), a model combining plastic and nonlinear analysis is presented. The evolution of moment redistribution to structural collapse was studied experimentally for continuous two-span beams. The focus of the experiments was on the influence of the longitudinal tensile reinforcement ratio at the intermediate support, the transverse reinforcement ratio and the concrete strength. The experimental response at the ULS was further compared with the predicted distribution of internal forces according to the theoretical model. Evaluation of the experimental study indicated a highly nonlinear structural behaviour of the tested beams with the distribution of moment differing from linear elastic analysis, even for low load levels. The evolution of moment redistribution and the moment redistribution at the ULS were appreciably dependent on the arrangement of longitudinal reinforcement, whilst the transverse reinforcement ratio had a marginal impact up to yielding of the longitudinal reinforcing steel, with the concrete strength slightly reducing the degree of moment redistribution. For those beams which failed in flexure, predictions from the theoretical model presented were in good agreement with the experimental results. However, several beams collapsed in shear-related failure modes.
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21.
  • Basterrechea-Arevalo, M., et al. (författare)
  • Numerical modelling of moment-transmitting timber connections
  • 2023
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 297
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, the use of timber in construction substantially increased due to the material's renewable nature, lower climate impact and increased economic competitiveness. Another driving factor is great improvements in modelling techniques for the design of timber structures. Suitable prediction of the connection behaviour, as a fundamental part of the structural behaviour of timber structures, is crucial for a more economic and reliable design. However, the more realistic and complete connection models, the more complex and difficult to handle they are, which might hinder their practical application. A good trade-off between complexity and computational efficiency can be achieved with the so-called Beam-On-Foundation (BOF) method, which is applied herein in a 2-step hierarchical model to analyse and predict the rotational stiffness, ductile capacity and load distribution among fasteners of four different configurations of moment transmitting beam-to-column timber-to-timber connections. The connection model is validated with experiments on the global response of the connection as well as with a 3-D solid FEM model. The herein proposed connection model well predicted the overall connection response and provided insight into the local fastener behaviour. As compared to the 3-D solid model, which additionally gives access to more realistic local stresses in the timber, the 2-step model is however much more efficient with a great reduction of computation time. This makes the approach suitable for parametric studies and the analysis and engineering design of timber structures.
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22.
  • Battini, Jean-Marc, et al. (författare)
  • A simple finite element to consider the non-linear influence of the ballast on vibrations of railway bridges
  • 2011
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 33:9, s. 2597-2602
  • Tidskriftsartikel (refereegranskat)abstract
    • This article proposes a new and simple finite element which can be used to analyze vertical vibrations in railway bridges. The main feature of the element is that the effect of the ballast is introduced through a non-linear longitudinal stiffness associated to the slip at the interface between the bridge and the ballast. Two numerical applications show that this element can be used to model the variation of the natural frequencies of the bridge as a function of the amplitude of vibration.
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23.
  • Bayane, Imane, et al. (författare)
  • An unsupervised machine learning approach for real-time damage detection in bridges
  • 2024
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 308
  • Tidskriftsartikel (refereegranskat)abstract
    • The bridge network is progressively aging, with an alarming proportion of bridges over 100 years. This situation engenders substantial risks to the overall reliability of transportation networks, requiring innovative methods for efficient management. Monitoring can provide a direct source of information about structural behavior generating alerts when changes occur. Real-time alerts enable effective infrastructure management and decision-making during damage or anomalous situations. However, monitoring can result in a large amount of data that is often difficult to convert into valuable information in real time. This paper presents an approach for real-time detection of abrupt damage occurrence in bridges using unsupervised anomaly detection algorithms and strain/acceleration measurements. The approach incorporates the separation of measurements into events having the same loading nature and the construction of three feature matrices based on statistical features, time-frequency features, and wavelet spectrum features. It includes the evaluation of five anomaly detection algorithms including Isolation Forest, One-Class Support Vector Machine, Robust Random Cut Forest, Local Outlier Factor, and Mahalanobis Distance. The approach is illustrated with a case study of a steel-bascule-railway bridge, that has experienced a brittle cracking event during monitoring. Results highlight the robustness of One-Class Support Vector Machine, Isolation Forest, and Local Outlier Factor algorithms in promptly detecting abrupt changes across different features. The separation of strain and acceleration data into loading-based events, coupled with the comparison of previous and new event features, provides robust feature matrices for effective damage detection. Enhanced detection and higher scores are particularly attributed to time-frequency domain features during damage occurrence. The presented approach can be used as a base on how to perform real-time anomaly detection within the context of bridge monitoring.
  •  
24.
  • Bayoglu Flener, Esra, et al. (författare)
  • Dynamic testing of a soil-steel composite railway bridge
  • 2009
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 31:12, s. 2803-2811
  • Tidskriftsartikel (refereegranskat)abstract
    • Actual dynamic response of a long-span corrugated steel culvert railway bridge is studied. The bridge, which is a type of soil-steel composite structures, has a span of 11 m. Tests were carried out by measuring strains and displacements during passages of a locomotive at different speeds. Vertical ballast accelerations as well as the effects of braking forces were also measured. The tests showed that the speed has a large influence on the displacements, thrusts and moments. The measured dynamic displacements and thrusts are as much as 20% larger than the corresponding static response. This is greater than the values specified in bridge design codes. Dynamic amplification factors as high as 1.45 were obtained for the moments at the quarter point which is found to be much larger than the values for the crown point. This type of bridge structure is believed to be less sensitive to resonance from passing trains than other common bridge types, due to the high damping values obtained from the forced vibration tests.
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25.
  • Bergenudd, Jens, et al. (författare)
  • Dynamic testing and numerical modelling of a pedestrian timber bridge at different construction stages
  • 2023
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 279
  • Tidskriftsartikel (refereegranskat)abstract
    • This article studies the dynamic properties of a single span pedestrian timber bridge by in-situ testing and numerical modelling. The in-situ dynamic tests are performed at four different construction stages: (1) on only the timber structure, (2) on the timber structure with the railings, (3) on the timber structure with railings and an asphalt layer during warm conditions and (4) same as stage 3 but during cold conditions. Finite element models for the four construction stages are thereafter implemented and calibrated against the experimental results. The purpose of the study is to better understand how the different parts of the bridge contribute to the overall dynamic properties. The finite element analysis at stage 1 shows that longitudinal springs must be introduced at the supports of the bridge to get accurate results. The experimental results at stage 2 show that the railings contributes to 10% of both the stiffness and mass of the bridge. A shell model of the railings is implemented and calibrated in order to fit with the experimental results. The resonance frequencies decrease with 10–20% at stage 3 compared to stage 2. At stage 3 it is sufficient to introduce the asphalt as an additional mass in the finite element model. For that, a shell layer with surface elements is the best approach. The resonance frequencies increase with 15–30% between warm (stage 3) and cold conditions (stage 4). The stiffness of the asphalt therefore needs to be considered at stage 4. The continuity of the asphalt layer could also increase the overall stiffness of the bridge. The damping ratios increase at all construction stages. They are around 2% at warm conditions and around 2.5% at cold conditions for the finished bridge.
  •  
26.
  • Berrocal, Carlos Gil, 1986, et al. (författare)
  • The effect of fibres on steel bar corrosion and flexural behaviour of corroded RC beams
  • 2018
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 163, s. 409-425
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper reports the results of an experimental programme aimed at investigating the influence of fibre reinforcement on the corrosion process of conventional steel rebar embedded in cracked concrete and on the flexural behaviour of reinforced concrete beams. Un- and pre-cracked reinforced concrete beams were subjected to natural corrosion through cyclic exposure to a 10% chloride solution for a period of three years. Subsequently, flexural tests were carried out under three-point bending configuration. Gravimetric measurements showed higher corrosion levels for bars in plain concrete compared to fibre reinforced concrete, and visual inspection of the bars revealed that fibres promoted a more distributed corrosion pattern. From detailed examination of the bars through 3D laser scanning technique, the main parameter controlling the local corrosion level of individual pits appears to be the local interfacial conditions; grater loads during pre-cracking and repeated load cycles yielded greater cross-sectional losses. Moreover, there was a tendency for more localized corrosion in beams with open cracks, indicating a possible impact of crack width on the extension of corrosion. The results from the flexural tests showed a consistent increase of load capacity for fibre reinforced beams compared to their plain concrete counterparts but only a marginal influence of the fibres on the rotation capacity. Furthermore, the rotation capacity of the beams was found to decrease several times faster than the load capacity with increasing loss of rebar cross-sectional area.
  •  
27.
  • Blomfors, Mattias, 1990, et al. (författare)
  • Engineering bond model for corroded reinforcement
  • 2018
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 156, s. 394-410
  • Tidskriftsartikel (refereegranskat)abstract
    • Corrosion of the reinforcement in concrete structures affects their structural capacity. This problem affects many existing concrete bridges and climate change is expected to worsen the situation in future. At the same time, assessment engineers lack simple and reliable calculation methods for assessing the structural capacity of structures damaged by corrosion. This paper further develops an existing model for assessing the anchorage capacity of corroded reinforcement. The new version is based on the local bond stress-slip relationships from fib Model Code 2010 and has been modified to account for corrosion. The model is verified against a database containing the results from nearly 500 bond tests and by comparison with an empirical model from the literature. The results show that the inherent scatter among bond tests is large, even within groups of similar confinement and corrosion level. Nevertheless, the assessment model that has been developed can represent the degradation of anchorage capacity due to corrosion reasonably well. This new development of the model is shown to represent the experimental data better than the previous version; it yields similar results to an empirical model in the literature. In contrast to many empirical models, the model developed here represents physical behaviour and shows the full local bond stress-slip relationship. Using this assessment model will increase the ability of professional engineers to estimate the anchorage capacity of corroded concrete structures.
  •  
28.
  • Blomfors, Mattias, 1990, et al. (författare)
  • Incorporation of pre-existing cracks in finite element analyses of reinforced concrete beams without transverse reinforcement
  • 2021
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 229
  • Tidskriftsartikel (refereegranskat)abstract
    • Cracking in reinforced concrete (RC) bridges and other structures is common and not necessarily detrimental. However, some cracks may grow past specified limits and, aside from aesthetic and durability aspects, may influence the ductility and structural capacity of an RC member. This is not generally reflected in current assessment methods and, therefore, improved methods are needed. The aim of the current work was to develop a modelling methodology to incorporate pre-existing cracks into finite (FE) analysis for improved structural assessments. Two different approaches were investigated: (1) weakening the continuum elements at the position of a crack and (2) introducing discrete crack elements with weakened properties. In both approaches, a total-strain based model was used in the continuum elements. These modelling approaches were applied to analyses of experiments, in which concrete beams had been pre-cracked and tested in four-point bending. The pre-existing cracks led to differing failures limiting the deformation capacity, plus varying ultimate capacity and ductility. In the current study the weakened-elements approach captured the failure characteristics, ultimate capacity and ductility more accurately than a standard FE analysis without cracks included; the discrete-crack approach, on the other hand, did not. Furthermore, the bending stiffness differed between the experimental tests and the FE analyses. Damaged bond properties and closure of cracks in the compressive zone were identified as probable causes. Moreover, the choice of shear retention used for the weakened elements was shown to noticeably affect the predicted capacity and ductility. In conclusion, the weakened-elements approach was the most straightforward to implement. It was less time-consuming and led to better agreement with experimental results, compared to the discrete-crack approach. Based on this study, the weakened-elements approach is regarded as a promising approach for the structural assessments of tomorrow.
  •  
29.
  • Blomfors, Mattias, 1990, et al. (författare)
  • Partial safety factors for the anchorage capacity of corroded reinforcement bars in concrete
  • 2019
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 181, s. 579-588
  • Tidskriftsartikel (refereegranskat)abstract
    • Many reinforced concrete bridges in Europe and around the world are damaged by reinforcement corrosion and the annual maintenance costs are enormous. It is therefore important to develop reliable methods to assess the structural capacity of corroded reinforced concrete structures and avoid unnecessary maintenance costs. Although there are advanced models for determining the load carrying capacity of structures, it is not obvious how they should be used to verify the performance of existing structures. To confidently assess the bond of corroded reinforcement in concrete, for example, the calculation model must give a sufficient safety margin. When designing new structures, semi-probabilistic approaches (such as the partial safety factor method) are adopted to achieve the target reliabilities specified in structural design codes. This paper uses probabilistic methods to develop partial factors for application in an existing bond model, to assess the safety of corroded reinforced concrete structures. The response of the bond model was studied using Monte Carlo (MC) simulations for several design cases, with probability distributions fitted to the results. Partial factors were then derived, based on these distributions. Furthermore, an MC-based simulation technique called “importance sampling” was used to study the reliability of several deterministic bond assessments conducted using these partial factors. The results show that deterministic assessments which use the proposed partial factors lead to a safety level at least equal to the target value. The results presented in this paper will support the assessment of reinforced concrete structures with anchorage problems and give a reasonable approximation of the anchorage capacity with sufficient safety margin. When generalised to cover other failure modes and structural configurations, this will enable better utilisation of damaged structures and lead to major environmental and economical savings for society.
  •  
30.
  • Bolmsvik, Åsa, 1975-, et al. (författare)
  • Damping Assessment of Light Wooden Assembly With and Without Damping Material
  • 2013
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 49, s. 434-447
  • Tidskriftsartikel (refereegranskat)abstract
    • Damping elastomers are often used in lightweight wooden constructions and are believed to have good sound insulating effects. In the present study the influence on the structural behaviour by using elastomer damping material (Sylomer®) in the joints, with particular respect to footsteps and floor vibrations, has been investigated. A full scale wooden mock-up was assembled with two different joint configurations and studied under free-free boundary conditions. In the first configuration, the joints between the floor and underlying walls were screwed together. In the second configuration the floor was resting free on top of ribs of elastomer damping material, equivalent to normal building practice when this material is used. Both configurations were analysed and evaluated using experimental modal analysis, in the frequency interval 10-115 Hz. The relative (viscous) damping ratios of the modes were found to be on average 1.2% for the screwed configuration and 2.1% for the configuration with elastomer damping material in the joints. The damping was found to vary significantly between modes in the elastomer case. It was found that at low frequencies damping was high for modes with large motion on the edge where the elastomer material was. At higher frequencies (above approx. 40 Hz), however, the damping for this configuration decreased. This is believed to be caused by a vibration isolation effect of the elastomer, decoupling the floor from the walls at higher frequencies. To assess the differences in vibration levels between the two configurations, mean acceleration levels of well spread points on the different building parts where computed and evaluated. It was found that above approximately 70 Hz, the mean vibration level in the elastomer configuration was significantly lower than for the screwed configuration. Below 70 Hz, however, for many frequencies the mean vibration level for the elastomer configuration was significantly higher than for the screwed configuration (as should be expected in vibration isolation). Problems with springiness and footsteps are due to loads in the frequency range of 10 to 50 Hz, this could indicate that elastomers, used as in the present study, could worsen these types of problems, although improving higher frequency acoustic performance.
  •  
31.
  • Bolmsvik, Åsa, 1975-, et al. (författare)
  • FE Modelling of Light Weight Wooden Assemblies : parameter study and comparison between analyses and experiments
  • 2014
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 73, s. 125-142
  • Tidskriftsartikel (refereegranskat)abstract
    • A finite element (FE) analysis of a model representing a mock-up structure previously investigated experimentally is investigated in this study. The aim is to make a correlation and calibration between test and analysis of the full scale wooden structure; both eigenmodes and acceleration levels are compared. Large scatter is found in material properties used for light weight wooden structures in literature. In this study, a parameter evaluation is therefore made to show how different properties influence the dynamic behaviour of the structure. It is shown that the wood beam material properties influence the behaviour of the light weight wooden structure FE model most.Two types of junctions are modelled and evaluated; a tied connection is used to simulate screwed junctions and spring/dashpot elements are used to represent elastomer junctions between the floor and the walls. The springs and dashpots used to model the elastomer in the junction work well in the bearing direction but need to be improved to obtain correct rotational stiffness, shear motion and friction. There are still many unknown parameters in a complex wooden structure that remain to be investigated. However, the results presented in this paper add data to be used for FE modelling of a complex wooden structure.
  •  
32.
  • Cantero, Daniel, et al. (författare)
  • Numerical evaluation of the mid-span assumption in the calculation of total load effects in railway bridges
  • 2016
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 107, s. 1-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Maximum load effects in simply supported railway bridges traversed by trains are generally investigated at the mid-span section. However, this assumption is not necessarily correct. The true maximum load effect might occur at some other bridge section and its magnitude could be significantly greater. This paper quantifies the underestimation of the load effects as a result of exclusively considering the middle section, with special emphasis on resonant situations. A 2D numerical model of a vehicle-track-bridge system was used to evaluate different vehicle velocities, bridge properties and track irregularity conditions. The error due to the mid-span assumption depends on the particular case considered but can be related to the relative energy content of the higher modes of vibration. The results show that the error is greatest for accelerations, smaller for bending moments and is almost negligible for displacements.
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33.
  • Cantero, Daniel, et al. (författare)
  • The Virtual Axle concept for detection of localised damage using Bridge Weigh-in-Motion data
  • 2015
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 89, s. 26-36
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper proposes a new level I damage identification method for short span statically indeterminate bridges using the information provided by a Bridge Weigh-in-Motion system. Bridge Weigh-in-Motion systems measure the bridge deformation due to the crossing of traffic to estimate traffic attributes, namely axle weights and distances between axles for each vehicle. It is theoretically shown that it is convenient to introduce a fictitious weightless axle, which has been termed 'Virtual Axle', in the Bridge Weigh-in-Motion calculations to derive a damage indicator. The latter can be used both as a new robust output-only model-free level I Structural Health Monitoring technique and as a new self-calibration method for Bridge Weigh-in-Motion systems. The response of a fixed-fixed beam traversed by a 2-axle vehicle travelling over an irregular profile is used to validate the proposed method. By means of Monte Carlo simulation the influence of the key parameters such as the degree and location of damage, noise levels, span lengths and profile irregularities on the accuracy of the method are investigated. The results show that the 'Virtual Axle' method is able to detect small local damages in statically indeterminate structures.
  •  
34.
  • Challamel, Noel, et al. (författare)
  • Lateral-torsional buckling of vertically layered composite beams with interlayer slip under uniform moment
  • 2012
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 34, s. 505-513
  • Tidskriftsartikel (refereegranskat)abstract
    • The lateral-torsional stability of vertically layered composite beams with interlayer slip is investigated in this paper, based on a variational approach. Vertically layered elements are typically used in timber engineering but also in case of laminated glass elements. Both across-longitudinal or vertical slip due to rotation and longitudinal or horizontal slip due to lateral deflection are discussed. The theoretical framework of the lateral-torsional buckling problem is given, and some engineering closed-form solutions are presented for partially composite beams under uniform bending moment. Simplified kinematical relationships neglecting the axial and vertical displacements of the sub-elements give unrealistic values for the lateral-torsional buckling moment. Refined kinematical assumptions remove this peculiarity and render sound buckling moment results. Inclusion of the horizontal and vertical slips significantly affect the lateral-torsional buckling moment of these vertically laminated elements. A single lateral-torsional buckling formulae is derived, depending on both the horizontal and the vertical connection parameters. (C) 2011 Elsevier Ltd. All rights reserved.
  •  
35.
  • Challamel, Noel, et al. (författare)
  • Variationally-based theories for buckling of partial composite beam-columns including shear and axial effects
  • 2011
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 33:8, s. 2297-2319
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper is focused on elastic stability problems of partial composite columns: the conditions for the axial load not to introduce any pre-bending effects in composite columns; the equivalence, similarities and differences between different sandwich and partial composite beam theories with and without the effect of shear, with and without the effect of axial extensibility, and also the effect of eccentric axial load application. The basic modelling of the composite beam-column uses the Euler-Bernoulli beam theory and a linear constitutive law for the slip. In the analysis of this reference model, a variational formulation is used in order to derive relevant boundary conditions. The specific loading associated with no pre-bending effects before buckling is geometrically characterized, leading to analytical buckling loads of the partial composite column. The equivalence between the Hoff theory for sandwich beam-columns, the composite action theory for beam-columns with interlayer slip and the corresponding Bickford-Reddy theory, is shown from the stability point of view. Special loading configurations including eccentric axial load applications and axial loading only on one of the sub-elements of the composite beam-column are investigated and the similarity of the behaviour to that of imperfect ordinary beam-columns is demonstrated. The effect of axial extensibility on kinematical relationships (according to the Reissner theory), is analytically quantified and compared to the classical solution of the problem. Finally, the effect of incorporating shear in the analysis of composite members using the Timoshenko theory is evaluated. By using a variational formulation, the buckling behaviour of partial composite columns is analysed with respect to both the Engesser and the Haringx theory. A simplified uniform shear theory (assuming equal shear deformations in each sub-element) for the partial composite beam-column is first presented, and then a refined differential shear theory (assuming individual shear deformations in each sub-element) is evaluated. The paper concludes with a discussion on this shear effect, the differences between the shear theories presented and when the shear effect can be neglected. 
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36.
  • Chen, Teresa E, 1988, et al. (författare)
  • Assessment of the mechanical behaviour of reinforcement bars with localised pitting corrosion by Digital Image Correlation
  • 2020
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 219
  • Tidskriftsartikel (refereegranskat)abstract
    • Corrosion of reinforcement in concrete impairs the mechanical behaviour of rebars by decreasing their strength and deformation capacity. In this study, uniaxial tensile tests were carried out on 61 rebars taken from 22 pre- and un- cracked reinforced concrete beams subjected to drying and wetting cycles in chloride solution for over three years. A 3D-scanning technique was used to characterise the maximum local corrosion level, μmax, and different pit shape parameters. Digital Image Correlation (DIC) was used to capture the displacement field of the test bars; the engineering strain was measured through the virtual extensometers created in the DIC post-processing software. The proof and ultimate forces showed linear decreasing trends of μmax, while the proof and ultimate strengths (based on the minimum residual cross-sectional area) were not obviously affected by corrosion. The ultimate strain of corroded bars depended on the gauge length due to strain localisation in the pit. Thus, it was emphasised that the ultimate strain may be overestimated if measured based on a short gauge across the pit. It was also observed that when μmax exceeded a critical local corrosion level (μcrit depending on the ratio between the yield and ultimate strengths of the steel), the region outside the pit did not develop yielding. A lower bound of ultimate strain was further derived as a function of the mechanical parameters of uncorroded steel and maximum local corrosion level. This provided a good comparison with the experimental results. Ultimately, a hypothesis for time-dependent assessment of strain capacity is proposed, considering the evolution of corrosion morphology over time.
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37.
  • Dackman, David, 1990, et al. (författare)
  • A framework for evaluating steel loss from the evolution of corrosion-induced deflections in reinforced concrete beams with non-uniform reinforcement corrosion
  • 2024
  • Ingår i: Engineering Structures. - 1873-7323 .- 0141-0296. ; 317
  • Tidskriftsartikel (refereegranskat)abstract
    • Describing corrosion propagation throughout the corrosion process, prior to the extraction and assessment of reinforcement bars, is challenging. In this paper, a framework is proposed for describing corrosion propagation from corrosion-induced variations in deflection for reinforced concrete beams, based on the experimental results of beams simultaneously subjected to either an imposed relative displacement or cyclic loading along with accelerated corrosion through impressed current. Strain measurements from distributed optical fiber sensors were used to calculate the deflection and crack distribution over time. Given the characterization of the initial current density, the framework allowed for the calculation of corrosion development based only on the measured corrosion-induced deflections. The framework was verified, as revealed by the strong agreement between the pit volume loss obtained from 3D scanning of the reinforcement bars and the losses calculated using Faraday's law. Moreover, a second mechanism contributing to corrosion-induced variations in deflection, in addition to the reduced stiffness due to pitting corrosion, was observed for the case with cyclic loading and attributed to bond degradation. Furthermore, for load cycles with similar load level, it was shown that the increase in deflection occurred only when there were intermediate load cycles with a higher load level, suggesting that the assumed bond degradation occurs only when the load surpasses a previous threshold.
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38.
  • Derkowski, Wit, 1972-, et al. (författare)
  • Prestressed hollow core slabs for topped slim floors : Theory and research of the shear capacity
  • 2021
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 241
  • Tidskriftsartikel (refereegranskat)abstract
    • This research paper discusses the influence of the flexibility of girders in Slim Floor structures on the reduced load capacity of prestressed HC slabs. The current state of knowledge in the field of the transverse behaviour of hollow core slabs is presented. Contradictory information provided in the literature as well as the computational comparative analysis of the existing theoretical models has demonstrated the need for better recognition of the issue of the effect of reinforced concrete topping layer on the load capacity of HC slabs. The paper includes the presentation of experimental tests, the purpose of which was to reproduce the actual work conditions of hollow core slabs depending on their location on the floor and the numerical analyses supplemented these studies. As a result of the conducted tests and analyses, it was found that the increased flexibility of the support beam resulted in an adverse change in the stress state of the hollow core slab, which may lead to the exceedance of the limit state of shear capacity, while laying an additional layer of structural topping on precast hollow core slabs significantly increased the shear capacity of the floor, and thus the safety of the structure. The research also indicates that in all the tested topped elements full composite action up to the failure was shown.
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39.
  • Dorn, Michael, et al. (författare)
  • Experiments on dowel-type timber connections
  • 2013
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 47, s. 67-80
  • Tidskriftsartikel (refereegranskat)abstract
    • Dowel-type connections are commonly used in timber engineering for a large range of structural applications. The current generation of design rules is largely based on empiricism and testing and lacks in many parts a stringent mechanical foundation. This often blocks an optimized use of the connections, which is essential for the design of economically efficient structures. Moreover, it severely limits the applicability of the design rule, such as restrictions regarding splitting behavior or maximum ductility (e.g. maximum allowable deformations) are missing. Therefore, the demands due to a large and quickly evolving variety of structural designs in timber engineering are not reflected. The aim of this work is to study the load-carrying behavior of the connection in detail, including all loading stages, from the initial contact between dowel and wood up to the Ultimate load and failure. Distinct features during first loading as well as during unloading and reloading cycles are identified and discussed. The knowledge of the detailed load-carrying behavior is essential to understanding the effects of individual parameters varied in relation to the material and the connections design. The suitability of the current design rules laid down in Eurocode 5 (EC5) is assessed and deficiencies revealed. Tests on 64 steel-to-timber dowel-type connections loaded parallel to the fiber direction were performed. The connections were single-dowel connections with dowels of twelve millimeter diameter. The test specimens varied in wood density and geometric properties. Additionally, the effects of dowel roughness and lateral reinforcement were assessed. The experiments confirmed that connections of higher density show significantly higher ultimate loads and clearly evidenced that they are more prone to brittle failure than connections using light wood. The latter usually exhibit a ductile behavior with an extensive yield plateau until final failure occurs. With increased dowel roughness, both, ultimate load and ductility are increased. The test results are compared with corresponding design values given by EC5 for the strength and the stiffness of the respective single-dowel connections. For connections of intermediate slenderness, EC5 provided conservative design values for strength. Nevertheless, in some of the experiments the design values overestimated the actual strengths considerably in connections of low as well as high slenderness. As for the stiffness, a differentiation according to the connection width is missing, which gives useful results only for intermediate widths. Furthermore, the test results constitute valuable reference data for validating numerical simulation tools, which are currently a broad field of intensive interest.
  •  
40.
  •  
41.
  • Dvinskikh, Sergey V., et al. (författare)
  • NMR imaging study and multi-Fickian numerical simulation of moisture transfer in Norway spruce samples
  • 2011
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 33:11, s. 3079-3086
  • Tidskriftsartikel (refereegranskat)abstract
    • Wood has potential as a renewable material for a large variety of applications that often call for improved properties such as dimensional stability, moisture insensitivity, and durability. Moisture migration in wood is a particularly important factor in determining the cost-effective service life of wooden construction. Within the present research, proton NMR imaging was applied for recording the moisture spatial distribution of various samples of Norway Spruce. Moisture distribution along the radial, tangential and longitudinal directions in wood was monitored at different times upon three consecutive changes of relative humidity: (1) from 65% to 94%; (2) from 94% to 33%; (3) from 33% to 65%. Uncoated samples and specimens treated with different types of surface coatings were studied. The experiments were numerically simulated by using the multi-Fickian model. The model describes the moisture transport process in wood which is characterized by three phenomena: (a) bound water diffusion, (b) water vapor diffusion and (c) coupling between the two phases through sorption. The model is implemented into the Abaqus FEM code. The numerical results are found to be in agreement with the experimental data.
  •  
42.
  • Edskär, Ida, et al. (författare)
  • Dynamic Properties of Cross-Laminated Timber and Timber Truss Building Systems
  • 2019
  • Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 186, s. 525-535
  • Tidskriftsartikel (refereegranskat)abstract
    • Incorrect prediction of dynamic properties of tall buildings can lead to discomfort for humans. It is therefore important to understand the dynamic characteristics such as natural frequency, mode shape and damping and the influence they have on acceleration levels. The aim of this study is to compare two timber building system, one with cross laminated panels and one with post-and-beam elements with diagonals for stabilisation. Empirical formulae for predicting the natural frequency and mode shape are compared to measured and numerical results. Tall building assumptions such as ‘line-like’ behaviour and lumped mass at certain points were evaluated for both systems. The post-and-beam system showed a stiffer behaviour than the cross laminated system where more shear deformation occurred. Empirical formulae should be used with care until more data is collected.  For the post-and-beam systems an assumption of linearity may be appropriate, but for cross laminated systems the approximation can give results on the unsafe side. Finally, the relationship between stiffness and mass for cross laminated timber systems and its effect on dynamic properties needs to be further investigated.
  •  
43.
  • Ekholm, Kristoffer K J, 1982, et al. (författare)
  • Effect of vertical interlaminar shear slip and butt joints in narrow stress-laminated-timber bridge decks
  • 2014
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 72, s. 161-170
  • Tidskriftsartikel (refereegranskat)abstract
    • Interlaminar slip occurs in stress-laminated-timber (SLT) decks subjected to concentrated loads, such as vehicles. Butt joints in SLT decks can be regarded as local discontinuities with increased load transfer resulting in increased frictional forces. Multiple tests were performed with different combinations of pre-stress level, number of loads, span-to-depth ratio, beam width and butt-joint configurations. The results of the tests have been analysed and compared with non-linear finite element analyses using solid elements and contact properties. The experimental results and the analysis showed that, in the case of a high span-to-depth ratio in the deck and without butt joints, there is little or no interlaminar slip. Test elements without butt joints showed little slip at pre-stress levels of 300 kPa or higher. A significant reduction in post-slip stiffness was observed for the test elements with butt joints. (C) 2014 Elsevier Ltd. All rights reserved.
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44.
  • Ekström, Jonas, 1985, et al. (författare)
  • Spalling in concrete subjected to shock wave blast
  • 2016
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 122, s. 72-82
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper studies the response in a concrete wall subjected to shock wave blast, leading to spalling failure. This situation is important since spalled-off fragments in protective structures may cause severe injury to the persons or equipment it is supposed to protect. Many theoretical expressions indicates that spalling occurs when and where the tensile strength of a strain-softening material like concrete is reached regardless of the time duration of the applied load. By using a simple uni-axial numerical model, this study shows that spalling instead might occurs when the cyclic response from a blast wave gradually increase the inelastic strains in the concrete. This means that spalling takes place after several loading cycles and not necessarily at the depth where tensile strength is firstly reached. Furthermore, the study shows that the cyclic response in the material model used for numerical simulation has a decisive influence on the position and extent of the resulting spalling crack.
  •  
45.
  • Fall, David, 1983, et al. (författare)
  • Reinforcing tailor-made concrete structures: Alternatives and challenges
  • 2012
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 44, s. 372-378
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent advances in automated concrete production make it possible to produce geometrically complex concrete structures. The purpose of this paper is to review reinforcement alternatives suitable for such structures and to analyse the problems associated with the geometrical complexity, not only in the reinforcement itself, but also in design. A review of the literature on reinforcement alternatives and governing standards shows that conventional steel reinforcement load bearing structures cannot easily be set aside. Any deviation from the standard structural elements, e.g. beams, walls and slabs, introduces design problems for most structural engineers. Approaches to problems of this complex nature are discussed here. Further developments needed are indicated: being able to choose the reinforcement direction, and optimisation with regard to parameters other than the reinforcement amount, e.g. feasibility of production. Furthermore, the need for a rational design process is discussed and some key issues, such as software incompatibilities are raised.
  •  
46.
  • Fall, David, 1983, et al. (författare)
  • Two-way slabs: Experimental investigation of load redistributions in steel fibre reinforced concrete
  • 2014
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 80, s. 61-74
  • Tidskriftsartikel (refereegranskat)abstract
    • In the design of two-way reinforced concrete slabs, e.g. using the strip or yield line design method, the possibility of redistributing the load between different loading directions is used. The main aim of the present study was to investigate how fibres affect the structural behaviour such as the possibility for redistribution, crack patterns and load-carrying capacity. The investigation was conducted by means of experiments on two-way octagonal slabs, simply supported on four edges, centrically loaded with a point load. The slabs spanned 2.2 m in both directions and the reinforcement amount was twice as large in one direction as in the other, in order to provoke uneven load distribution. Three slabs of each reinforcementconfiguration were produced and tested: conventionally reinforced slabs, steel fibre reinforced slabs and a combination of both reinforcement types. The reaction force on each supported edge was measured on five rollers per edge. A moderate fibre content (35 kg/m3) of double hook-end steel fibres was used. The steel fibres affected the structural behaviour significantly by providing post-cracking ductility and by increasing the ultimate load-carrying capacity by approximately 20%. Most significant, the steel fibres influenced the load redistribution in such a way that more load could be transferred to supports in theweaker direction after cracking. Further, more evenly distributed support reactions were obtained in the slabs containing both reinforcement types compared to the case when only conventional reinforcement was used. The slabs reinforced by steel fibres alone did not experience any bending hardening; however, a considerable post-cracking ductility was observed. Furthermore, the work presented in this paper will provide results suitable for use in benchmarking numerical and analytical modelling methodsfor steel fibre reinforced concrete, as the experimental programme also included extensive testing ofmaterial properties.
  •  
47.
  • Fernandez, Ignasi, 1984, et al. (författare)
  • Mechanical model to evaluate steel reinforcement corrosion effects on σ-ε and fatigue curves. Experimental calibration and validation
  • 2016
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 118, s. 320-333
  • Tidskriftsartikel (refereegranskat)abstract
    • An experimental study to characterise the annular distribution of the mechanical properties throughout the cross-section of TEMPCORE® steel bars is presented. Thereafter a sectional fibre model, which allows obtaining σ-ε and fatigue curves of corroded steel, is described. The model is calibrated using an extensive experimental study of artificially corroded steel bars tested under cyclic and monotonic loads. Local pitting effects such as stress concentration, local bending or non-uniform material properties distribution are considered. Validation of the model is done using different experimental work in the literature, which encompassed naturally and artificially corroded bars, for both fatigue and tensile tests. © 2016 Elsevier Ltd.
  •  
48.
  • Fernandez, Ignasi, 1984, et al. (författare)
  • Two-dimensional strain field analysis of reinforced concrete D-regions based on distributed optical fibre sensors
  • 2023
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 278
  • Tidskriftsartikel (refereegranskat)abstract
    • The introduction of Distributed Optical Fibre Sensing in experimental testing of reinforced concrete structures has enabled the acquisition of measurements with an unparalleled level of detail, providing an accurate and ubiquitous description of cracking and deflections throughout an element. However, most of the available research using this technology has focused on the study of beam specimens and high quality data for the calibration and development of models that can describe accurately the behaviour of D-regions in service is still lacking. For that reason, the application of distributed optical fibre sensing in D-regions remains a subject of interest. In this work a method for the deployment of fibre sensors in a multilayer configuration is presented for a wall element. An interpolation approach is then proposed, which combined with the distributed nature of the sensors enabled the description of detailed heat maps for the global and principal strain fields. The results indicated that shear strains can reveal the position of shear cracks well before they are formed whereas the maximum and minimum principal strains clearly show the crack pattern and crack development as well as the load transfer mechanisms including, for the first time, the experimental identification of a secondary strut-and-tie mechanisms.
  •  
49.
  • Ferreira, Gonçalo, et al. (författare)
  • Critical analysis of the current Eurocode deck acceleration limit for evaluating running safety in ballastless railway bridges
  • 2024
  • Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 312
  • Tidskriftsartikel (refereegranskat)abstract
    • The assessment of running safety of railway bridges is conditioned by the Eurocode EN 1990 A2 by limiting vertical deck acceleration. On ballastless track bridges, this value is 5 m/s2. The background for this value is not clear, and it is believed that it originates in the application of an arbitrary safety factor of 2 on accelerations around 1 g to avoid loss of wheel–rail contact. However, studies show that the level of acceleration may not be directly related to the occurrence of derailment. In this work, this idea is expanded by assessing both vertical and lateral dynamics, comparing acceleration values with the Unloading and Nadal derailment criteria. The parametric study is comprised of a set of five representative single-track slab bridges with spans between 10 m and 30 m with two levels of track irregularities, corresponding to a well-maintained track and an Alert limit situation. A three-dimensional articulated FE model based on the load properties of the EN 1991-2 High-Speed Load Model A is presented, crossing the bridges at running speeds from 150 km/h to 400 km/h. Despite the complexity of the models, a large amount (1461) of full 3D train–track–bridge interaction dynamic analyses are performed, to produce a data set representative of the phenomenon. Results show a weak correlation between the criteria and deck acceleration (maximum r2 of 0.47 for Unloading and 0.15 for Nadal). Additionally, track quality is shown to be a more conditioning factor for derailment when compared to resonance. This work contributes to discussing the thesis of using deck acceleration as an indicator of running safety, considering lateral dynamics.
  •  
50.
  • Flodén, Ola, et al. (författare)
  • The effect of modelling acoustic media in cavities of lightweight buildings on the transmission of structural vibrations
  • 2015
  • Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 83, s. 7-16
  • Tidskriftsartikel (refereegranskat)abstract
    • Determining the dynamic behaviour of lightweight buildings by means of finite element analyses requires models representing the geometry involved in great detail, resulting in systems having many millions of degrees of freedom. It is, therefore, important to avoid unnecessarily detailed models by carefully considering what is essential to include in the models and the level of details required for describing the phenomena of interest accurately. In the study presented here, it was investigated whether or not air and insulation in cavities of multi-storey wood buildings affect the transmission of low-frequency structural vibrations. It was concluded, by means of numerical studies, that including air and insulation in cavities, modelled as acoustic media, affects the transmission from a floor to the underlying ceiling and surrounding walls. (C) 2014 Elsevier Ltd. All rights reserved.
  •  
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