| 1. |
- Almutairi, Mohammad, et al.
(författare)
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A methodological approach towards evaluating structural damage severity using 1D CNNs
- 2021
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Ingår i: Structures. - : Elsevier. - 2352-0124. ; 34, s. 4435-4446
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Tidskriftsartikel (refereegranskat)abstract
- Evaluating the severity of structural damage is a critical component of Structural Health Monitoring (SHM). Convolutional Neural Networks (CNNs) have been used before to detect structural damage and evaluate its severity by utilising only raw vibration data. However, these vibration-based CNN applications were limited to discrete user-defined levels of damage. To provide a more accurate representation of structural damage, this paper aims to design and validate a framework for evaluating structural damage severity within a continuous range of damage levels, using 1D CNNs and distributed raw acceleration data. To this purpose, a simple Finite Element (FE) cantilever model with non-rigid rotational spring support was adopted. Damage was simulated at the support as reduction of the rotational spring stiffness. The performance of the proposed framework was assessed under different excitation scenarios and data pre-processing techniques. The results demonstrate the ability of 1D CNNs to evaluate damage severity with high accuracy. By estimating the reduced value of the rotational spring stiffness, the proposed framework can also be used towards FE model updating in parallel with damage severity evaluation.
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| 2. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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Influence of grain inclination angle on shear buckling of laminated timber sheathing products
- 2018
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 13, s. 36-46
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in timber production industries have enabled production of new innovative laminated timberproducts having layers with grain inclination angle. This paper is aimed to study influence of grain inclinationangle in the laminated veneer lumber (LVL) and plywood sheathings on their shear buckling loads. Two extremeedge conditions of simply supported and clamped edges are considered. First, an accurate differential quadrature(DQ) computational code is developed using MAPLE programming software to obtain eigen buckling values andtheir corresponding eigen mode shapes. Next, for convenience of engineering calculations, approximate algebraic formulae are presented to predict critical shear buckling loads and mode shapes of LVL and plywood panels having layers with grain inclination angle, with adequate accuracy. Furthermore, finite element (FE) modelling is conducted for several cases using ANSYS software to show validity and accuracy of the predicted results for theproblem. It is shown that the highest shear buckling loads of LVL sheathings is achievable when the inclination angle of about 30° with respect to the shorter edges is considered for production of LVL panels, whereas the same angle with respect to the long edges of the LVL sheathings results in a relatively lower buckling load. Considering similar inclination angle with respect to any edges of a plywood sheathings will also results in its highest prebuckling capacity. It is also demonstrated that, under optimal design and certain loading circumstances, LVL shows a higher shear buckling capacity compared to a similar plywood sheathing.
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| 3. |
- Avci, Onur, et al.
(författare)
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Operational modal analysis and finite element model updating of a 230 m tall tower
- 2022
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Ingår i: Structure. - : Elsevier. - 2352-0124. ; 37, s. 154-167
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic response levels are critical for tall and slender civil structures. Studying the dynamic behavior of large civil structures with finite element modeling techniques requires detailed and accurate modeling of structural geometry, material properties, member fixities, connection types, and accompanying assumptions. Still, the finite element model results are approximations that could be away from representing the actual structural behavior. Structures are dynamically tested at their operational conditions to validate the finite element model results. This paper presents Operational Modal Analysis (OMA) and finite element model updating of a tall structure located in the West Bay area of Doha (Qatar). The structure is a reinforced concrete building with shear wall cores situated towards the center of the building plan, which was constructed between 2012 and 2016. With 53 stories above the ground and two stories below ground, the 230 m (755 ft) tall building is being used for residential and hotel purposes. For the finite element model updating and calibration tasks presented in this paper, the authors intentionally introduced drastic model changes for the first two model updates so that the results from the first two attempts guide how to proceed with a more reasonable update for the third calibration of the finite element model. While this is a non-standard technique that represents a specific condition where the initial attempts on the finite element model are very crude approximations, it is a systematized demonstration of how to operate when the structural parameters are sparse or uncertain for modeling purposes. While in theory, the finite element model updates can always be fine-tuned in a way to further decrease the error between the measured and predicted OMA results, in this paper, the authors predominantly focused on the presentation of three finite element model updates to demonstrate the way they have improved the modal assurance criteria plots and lowered the average absolute errors by visiting two drastic and then one moderate finite element model updates. The material presented here in this paper is arguably the first published work on large-scale dynamic testing of a civil structure in the State of Qatar. © 2021 Institution of Structural Engineers
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| 4. |
- Battini, Jean-Marc, 1968-
(författare)
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Analysis of Dampers for Stay Cables Using Non Linear Beam Elements
- 2018
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Ingår i: Structures. - : Elsevier Ltd. - 2352-0124. ; 16, s. 45-49
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a numerical approach to evaluate the damping properties of a stay cable with an external viscous damper. The idea is to model the cable by using non-linear corotational beam elements and to study small vibrations around the static deformed equilibrium configuration. This gives a complex eigenvalue problem from which the modal damping ratios can be calculated. The performance of the proposed method is assessed through two numerical applications. Compared with the analytical methods based on differential equations widely used in the literature, the proposed non-linear finite element approach has the advantages that the effect of the sag is considered in an accurate way and that there is no limitation regarding the number and the value of the structural parameters that can be introduced in the model.
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| 5. |
- Bergenudd, Jens, et al.
(författare)
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Dynamic analysis of a pedestrian timber truss bridge at three construction stages
- 2024
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 59
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates the dynamic behaviour of a single span pedestrian timber truss bridge by in situ testing and numerical modelling. The in situ dynamic tests were performed at three different construction stages: (1) on only the truss structure, (2) on the finished bridge without the asphalt layer and (3) on the finished bridge with the asphalt layer. The objective is to better understand how the different parts of the bridge contribute to the overall dynamic properties. The experimental results show that the damping ratios increased significantly for the first lateral mode (from 1.0 to 3.8%) and the first torsional mode (from 1.2 to 3.5%) between stage 2 and stage 3 due to the asphalt layer. The damping ratio is around 1.6% for the first bending mode for the finished bridge. The experimental and numerical results indicate that the stiffness of the asphalt layer is important to consider at stage 3 (10 degrees C) for the first lateral and torsional mode, but not for the first bending mode. Finally, it was concluded that longitudinal springs must be applied at the pot bearings in order to get agreement with the experimental results at all the three stages.
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| 6. |
- Colmenares, Daniel, et al.
(författare)
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An analytical solution of the maximum response of the coupled multiple parallel modulated pedestrian-bridge system
- 2023
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 57, s. 105160-
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies analytically the steady state response of the generalised coupled modulated pedestrian-beam system. Pedestrians are considered as modulated spring–mass–damper systems with and without a partially attached mass to the structural system. The governing non-dimensional parameters that defined the system's behaviour are found in an analytical framework. An application of the expression is developed, and a parametric analysis is presented considering a reference pedestrian. The frequency shift effect and the dynamic amplification factor, DAFHSI, of the coupled pedestrian-beam system are characterised. The main contribution of this paper is to provide a closed-form solution of the generalised coupled modulated pedestrian-beam system. This solution can consider any distribution of pedestrians and any definition of the pedestrian SDOF properties. A simple and representative example is presented to demonstrate the utility of the found expression in the context of footbridge dynamics.
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| 7. |
- Colmenares, Daniel, et al.
(författare)
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Quantification of the human–structure interaction effect through full-scale dynamic testing: The Folke Bernadotte Bridge
- 2023
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Ingår i: Structures. - : Elsevier Ltd. - 2352-0124. ; 55, s. 2249-2265
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Tidskriftsartikel (refereegranskat)abstract
- An analytical expression for the frequency response function of a coupled pedestrian-bridge system is presented and evaluated using an experimental measurement campaign performed on the Folke Bernadotte Bridge in Stockholm, Sweden. A finite element model and the modal models that consider the human–structure interaction effect are calibrated with respect to the measurements. The properties of the spring–mass–damper model representing the pedestrians were identified, considering the different structural modes of the system. Good agreement was obtained between the experimental and theoretical frequency response functions. A sensitivity analysis of the obtained solution was performed, validating the determined analytical expression for the frequency response function of the coupled pedestrian-bridge system that takes into account the human–structure interaction effect.
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| 8. |
- Crocetti, R., et al.
(författare)
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Nailed Steel Plate Connections : Strength and Ductile Failure Modes
- 2016
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 8, s. 44-52
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with theoretical and experimental investigations of nailed steel plate connections. For the experimental part, a total of 99 laboratory tests have been carried out in order to study failure mechanism and shear capacity of nailed steel plate connections. The testing programme comprised two nail lengths, two steel plate thicknesses and five nailing patterns. All tests related to loading of the plate in the direction of the grain of the wood. The nail patterns were designed to give ductile joint failure by yielding of the nails and/or bearing failure of the wood. The failure load was recorded and the mode and course of failure noted. For some of the specimens, deformation of the nails during loading was studied by means of an X-ray equipment. Deviations between the test results and contemporary consensus as manifested in the SS-EN 1995-1-1:2004 and the Johansen theory for ductile failure were found in several respects: development of the plastic hinges in the nails, influence of nail length, steel plate thickness and nail-to-nail and edge distances. The paper also presents an empirical equation based on multiple regression analysis of the test results was proposed as an attempt to predict the load-carrying capacity of nailed connections in shear.
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| 9. |
- Dogar, Attiq Ur Rahman, et al.
(författare)
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Experimental investigations on inelastic behaviour and modified Gerber joint for double-span steel trapezoidal sheeting
- 2020
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Ingår i: Structures. - : Elsevier. - 2352-0124. ; 24, s. 514-525
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Tidskriftsartikel (refereegranskat)abstract
- Cold-formed steel trapezoidal profiles provide efficient solutions for roofing and often use the Gerber joint to effectively utilize capacities. The previous design of Gerber joint was sensitive to uneven distribution of loads and accidental loads, which imposed bending moments in the joint and lead to its failure. In this experimental program, the design of Gerber joint has been modified to work as a hinge under service loads and carry moments in accidental conditions. Also, the design of CFS is based on elastic methods that underestimate their capacity, especially for multi-span systems. Full-scale tests were conducted on highly stiffened double-span trapezoidal sheeting profiles with modified Gerber joint to investigate elastic capacity, inelastic behaviour, moment redistribution in the post-elastic phase, ultimate load capacity and feasibility of modified Gerber joint. Comparison of elastic load capacity with EWM and DSM predictions revealed that EWM design predictions were conservative by 30% while DSM predictions were accurate. For multi-span application, residual moment capacity ratios of 0.76 and 0.81 in the post-elastic phase allowed for moment redistribution and increased ultimate load capacity by 7.14% and 8.80% for 0.85 mm and 1 mm thick profiles respectively. Performance of modified Gerber joint to behave as a hinge under service loads and as continuous in the post-elastic phase was also found to be satisfactory. The study concluded that the economy in design and capacity utilization of multi-span CFS profiles can be improved by allowing for moment redistribution and using the modified Gerber joint.
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| 10. |
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| 11. |
- Gottsäter, Erik, et al.
(författare)
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Validation of Temperature Simulations in a Portal Frame Bridge
- 2018
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 15, s. 341-348
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Tidskriftsartikel (refereegranskat)abstract
- In the design of bridges, thermal loads are important to take into account since they can cause cracking if the structure or structural part is restrained from changing its size. Accurate thermal load values must therefore be used in bridge design, based on knowledge of the actual temperature distribution in the bridge. This paper presents the validation of a model for temperature simulation, to be used in future work in the determination of temperature differences between deck and abutments in portal frame bridges. The validation is performed by comparing simulated temperatures with temperatures measured at 13 locations in a portal frame bridge during a period of 12 months. The simulation model uses measured air temperature, wind speed and long- and short wave radiation as input to calculate the temperature for every hour in the time period, and includes the soil beside the bridge. The results show that the model was capable of predicting the temperature distribution adequately, and that conservative values of the temperature difference between the structural parts can be obtained by adding no more than a ΔT of 1.5 °C to the simulated temperature difference, depending on the application.
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| 12. |
- Heng, Piseth, et al.
(författare)
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Residual stiffness and strength of shear connectors in steel-concrete composite beams after being subjected to a pull-out pre-damaging : An experimental investigation
- 2017
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Ingår i: Structures. - : Elsevier. - 2352-0124. ; 11, s. 189-205
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Tidskriftsartikel (refereegranskat)abstract
- Horizontal stability of the medium rise steel frame structures is usually ensured by vertical bracings and diaphragm action of composite floors. Load transfer within the composite floor system is made through shear connectors, e.g. headed studs. In an event of explosion, such connectors must reserve sufficient residual stiffness and strength in order to avoid a sudden or delayed collapse of the building. These remaining capacities have not been experimentally studied yet in the literature. This paper presents large scale horizontal push out tests to determine the residual stiffness of the shear connectors after being initially damaged by explosion. The initial damaging is reproduced by a pull-out test using a quasi-static loading. Two types of numerical simulation have also been developed using ABAQUS/CAE software to provide a better understanding of the experimental results.
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| 13. |
- Klasson, Anders, et al.
(författare)
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Design for lateral stability of slender timber beams considering slip in the lateral bracing system
- 2018
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 16, s. 157-163
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the significance of potential slip in the bracings of simply supported slender timber members. Three bracing configurations are considered. The first case is that of a timber beam braced at one point at mid-span, the second one braced at two points and the third one braced at three points. Possible slip in the bracing members can for example be due to joint deformation, initial crookedness of purlins and slack (or relaxation) of cables in the stabilizing bay (catenary action). In this study, it is shown that slip in the bracing system can result in a reduced load-bearing capacity (due to larger beam stresses) of the beams. Also, the greater the slip, the greater lateral deflections and consequent bracing forces of the braced member. A simplified approach, using a larger initial geometrical imperfection, to account for potential slip in bracings is also evaluated. This approach is found to work reasonably well in terms of stresses and bracing forces, but underestimates the lateral displacements.
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| 14. |
- Klasson, Anders, et al.
(författare)
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Slender Roof Structures - Failure Reviews and a Qualitative Survey of Experienced Structural Engineers
- 2018
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 15, s. 174-183
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Tidskriftsartikel (refereegranskat)abstract
- Many slender roof structures have collapsed due to snow loading and instability. Although accurate stability calculations can be performed using theoretical models, these calculations may not always reflect the behaviour of real structures as a result of the uncertainties relating to e.g. loading, material behaviour, geometry, initial imperfections and the actual boundary conditions of the structure. As a result, the approach to stability design requires subjective decisions by the structural engineer concerning loading and modelling assumptions. This paper investigates the significance of these types of decisions made by structural engineers in designing slender roof structures. This investigation is based on a review of previous failure studies together with a survey of 17 experienced structural engineers. The results of this investigation indicate that most structural failures are a result of human errors; thus, a suitable strategy for avoiding errors is through quality control and design checking. Moreover, a significant discrepancy was observed concerning design assumptions made by the engineers in the study. Some of these assumptions, e.g. a non-conservative choice of the buckling length of a beam, have a significant negative impact to structural safety. It is therefore recommended that the structural engineers involved in the design of a structure have adequate experience and a holistic mindset. Another recommendation is that both drawings and design calculations are thoroughly reviewed before construction. Also, temporary bracing to be used during construction should be included in design. Finally, it is important that the communication between different partners in the design of a structure is satisfying.
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| 15. |
- Klasson, Anders, et al.
(författare)
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Slender steel columns : How they are affected by imperfections and bracing stiffness
- 2016
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 8, s. 35-43
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Tidskriftsartikel (refereegranskat)abstract
- Finite-element programs can be used for designing columns and their bracing systems. It is well known, however, that the output obtained from such programs is highly dependent upon the input (such as imperfections and stiffness properties). In the present study, the effects of imperfections on the predicted strength and stiffness requirements of steel columns and of their bracing systems are investigated. Two different systems are analyzed: 1) a braced non-sway column and 2) a braced sway column. It was found that a poor choice of the shape of the initial imperfections can provide unrealistic results in terms of both the buckling load on the columns and the predicted reactions of the bracings. It was also found that superimposing different imperfection shapes can contribute to obtaining realistic and trustworthy results. Furthermore, it was shown that the shapes of the initial imperfections that lead to the lowest buckling load and those that result in the strongest bracing forces, are generally not the same.
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| 16. |
- Klasson, Anders, et al.
(författare)
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The effects on the bracing stiffness of timber structures of the stiffness of its members
- 2019
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 19, s. 41-47
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The design of slender structures is often associated with a number of assumptions made by engineers in checking on the stability of the structure. Not seldom, these assumptions are rather uncertain. In the present paper the effects of the stiffness of different members on the bracing stiffness of timber structures is studied. Both full-scale laboratory testing and FE-modelling are employed here in the investigation. In particular, two different bracing approaches are analysed, those of (1) cross bracing (wind trusses) and (2) diaphragm action (through use of steel sheeting) in the plane of the roof. In addition, the effects of the connections and the number of fasteners used in the structure are evaluated. The stiffness of the connections is obtained by means of an FE-updating approach, i.e. that the relevant parts included in the FE-model are calibrated to ensure that the FE-results match the laboratory results. The findings obtained indicated, (1) that the connections can have a significant effect on the stiffness of the bracing systems, (2) that the cross bracings close to the mid-span of the structure are less effective than those close to the supports, (3) that the lateral stiffness obtained using a diaphragm approach is closely related to the number of fasteners between the steel sheet and the timber parts in the roof that are employed, and (4) that the two different bracing approaches used provide about the same lateral stiffness of the roof. Finally, it should be emphasized that FE-models can markedly overestimate the stiffness of timber structures. If the connections are not modelled accurately, the engineers involved are advised to seek safe sided assumptions regarding them.
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| 17. |
- Li, Jiejie, et al.
(författare)
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Exact closed-form solution for vibration characteristics of multi-span beams on an elastic foundation subjected to axial force
- 2024
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 60
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the vibration characteristics of multi-span beams resting on an elastic foundation and subjected to axial forces. A comprehensive analytical expression of the dynamic response of multi-span beams on an elastic foundation that is developed to address various boundary conditions. The vibration equation is derived by employing Newton's second law. By Laplace transformations and the Green's function method, the solution of this governing equation can be obtained. Subsequently, a unified description is implemented for distinct types of boundary conditions using matrix representations. The correctness is verified through reference results and finite element methods (FEM). The effects of different parameters such as support stiffness, foundation elastic and shear layer stiffness, and axial force on the vibration characteristics are analyzed. This study demonstrates two findings: First, there are two thresholds for support stiffness, and the stiffness value is divided into three intervals. In the same interval, multi-span beams show the same properties. Second, for a rigidly supported multi-span beam, the critical axial force with a natural frequency of zero is just the corresponding Euler's buckling load; for elastically supported multi-span beams, the critical axial force falls between the Euler's buckling load corresponding to single-span and multi-span beams.
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| 18. |
- Lim, Hyeong Uk, et al.
(författare)
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Uncertainty quantification of wood floor system modal frequencies resulting from variable densities in members
- 2023
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Ingår i: Structures. - 2352-0124. ; 53, s. 1425-1434
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Tidskriftsartikel (refereegranskat)abstract
- Low-frequency vibration in a multi-story wood building is of concern because failure in mitigation of such vibration may lead to occupant discomfort. Ultimately, it may cause damage to their health. Variability in material properties of the members of a wooden floor system significantly influences vibration response characteristics such as eigenfrequencies and mode shapes. In this study, we investigate the uncertainty in low-frequency characteristics of a selected wood floor system, resulting from uncertainty in the members’ material properties. We use a surrogate model developed using polynomial chaos expansion, based on a few training samples computed using a finite element model of an experimental-scale structure comprised of seven load-bearing joists of spruce. We estimate the hyperparameters needed for accurate surrogate model development and, with these, we predict probability distributions for each of the floor-system modal frequencies. Also, we perform local and global sensitivity analyses to assess how material property variation affects the modal frequencies. Results confirm the accuracy and efficiency of the developed surrogate models in prediction of the modal frequencies, resulting from uncertainty in wood material properties. The accuracy of the results is comparable to those based on more expensive Monte Carlo simulation.
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| 19. |
- Liu, Fangzhou, et al.
(författare)
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Experimental and Numerical Dynamic Analyses of Hollow Core Concrete Floors
- 2017
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Ingår i: Structures. - : Elsevier. - 2352-0124. ; 12, s. 286-297
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Tidskriftsartikel (refereegranskat)abstract
- Due to their low self-weight and high strength, precast and prestressed hollow core concrete slabs are widely used in construction. However, the combination of low self-weight and long span implies that the slabs are sensitive to vibrations induced by human activities. In this work, experimental tests and numerical analyses are performed in order to understand the dynamic behaviour of hollow core concrete floors. For the experiments, a test floor of dimension 10 m × 7.2 m and consisting of 6 hollow core elements was built. Very good agreements between experimental and numerical results have been obtained. Comprehensive numerical parametric analyses have been performed in order to determine the optimal value of the material parameters.
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| 20. |
- Malmborg, J., et al.
(författare)
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Numerical study on train-induced vibrations : A comparison of timber and concrete buildings
- 2024
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Ingår i: Structures. - 2352-0124. ; 62
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the prediction of train-induced building vibrations by using a numerical framework. The framework is based on a sub-structure approach, where a sequence of different models are used. The free-field ground vibrations and the track receptance are calculated using 2.5D technique where the railway track is represented by finite elements that couple to a dynamic stiffness of the underlying soil, which in turn is obtained from the Green's function of a horizontally layered half-space using a layer transfer matrix approach. A planar multi-body model of the train, coupled to the track receptance, is used for calculating the train–track interaction forces as the train runs over an uneven rail. Finally, the building response to the incident wavefield is calculated using a 3D finite element model, accounting for the soil dynamic stiffness. The framework is used to evaluate the vibrations in two buildings with identical layout, one lightweight wooden building and one heavyweight concrete building, due to a passenger train passing by at two different speeds. It was found that the difference in response between the two buildings were small. Compared to the incident wavefield, an amplification of the response inside the building was found in frequency bands around the fundamental natural frequencies of the slabs; however for higher frequencies and in terms of the 1 s running RMS velocity the building response was reduced. Further, it was found that accounting for soil-structure-interaction, as opposed to simply enforcing the free-field displacements at the building foundations, significantly reduced the building response in terms of 1 s RMS velocity.
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| 21. |
- Mehri, Hassan, et al.
(författare)
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Unequally spaced lateral bracings on compression flanges of steel girders
- 2015
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 3, s. 236-243
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Tidskriftsartikel (refereegranskat)abstract
- In the bridge sector, lateral bracings can be provided e.g. in the form of metal decks or horizontal truss bracings. Those bracings are more efficient at the regions of maximum lateral shear deformations generated from destabilizing forces of compression flanges e.g. near to the twisting supports. A model is presented in this paper, which relates the lateral buckling length of compression flange of steel girders to their lateral torsional buckling moment and can be used to investigate stiffness requirement of lateral bracings applied on the compression flanges between the twisting restraints. Analytical solutions were derived for the effects of bracing locations and bracing stiffness values on buckling length of compression flanges. Moreover, an exact and a simplified solution for the effect of rotational restraint of shorter-spans on critical load value of the compression members with unequally spanned lateral bracings were derived. The model can be suitable for design engineers to preliminary size the cross-section of beams and lateral bracings.
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| 22. |
- Paik, Jeom Kee, et al.
(författare)
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Full-scale collapse testing of a steel stiffened plate structure under cyclic axial-compressive loading
- 2020
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Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 26, s. 996-1009
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Tidskriftsartikel (refereegranskat)abstract
- Plate panels of ships and floating offshore structures are likely subjected to cyclic loads arising from waves at sea. Depending on sea states, e.g., whipping in harsh sea states, the maximum amplitude of the cyclic loads may reach over 70% of ultimate loads. Of concerns is how the cyclic loads will affect the ultimate strength compared to a case of monotonically increasing loads. The aim of this paper is to experimentally investigate the ultimate strength characteristics of a steel stiffened plate structure under cyclic axial-compressive loading. A full-scale collapse testing in association with bottom structures of an as-built 1,900 TEU containership was conducted. It is concluded that the effects of cyclic loading on the ultimate compressive strength of steel stiffened plate structures are small as far as fatigue damages are not suffered due to the small number of load cycles and/or local structural members do not reach the ultimate strength during cyclic axial-compressive loading. Details of the test database are documented, which will be useful to validate computational models for the ultimate strength analysis.
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| 23. |
- Sitnikov, Vasily
(författare)
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Ice Formwork for High-Performance Concrete : A Model of Lean Production for Prefabricated Concrete Industry
- 2019
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Ingår i: STRUCTURES. - : ELSEVIER SCIENCE INC. - 2352-0124. ; 18, s. 109-116
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Tidskriftsartikel (refereegranskat)abstract
- This article describes an alternative material system for the fabrication of concrete precast elements using ice-based CNC-milled formwork. The use of ice as formwork resolves several systematic problems related to sustainability which are associated with the production of free-form prefabricated concrete elements, including the issue of material waste produced with existing models of fabrication. On the one hand, automation of formwork production by means of CNC machinery allows for the production of complex and precise geometries; on the other hand, as ice naturally melts away once the concrete has structurally set, the manual labor involved in the whole cycle of production is reduced dramatically. The Ice Formwork system is based on the utilization of a frost-resistant design of high-performance concrete (HPCfr). Numerous tests have proven that the Ice Formwork method of casting provides a high quality geometric transfer from ice to concrete, ensuring that no deformation of formwork occurs during the casting process. A key question is whether the trade-off in energy spent on refrigeration to maintain subfreezing temperature throughout the process of fabrication will negate Ice Formworks validity as an alternative to traditional concrete formwork. A preliminary assessment of that question shows that the energy required to produce Ice Formwork won't outweigh the benefits of the proposed fabrication process, enabling a cost efficient and environmentally sustainable solution to casting concrete for a variety of uses.
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