10 results
Filters
Settings
Now showing1 - 10 of 10
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Damage detection in lightweight bridges with traveling masses using machine learning(Elsevier, 2025-11-01); ; ; ; Damage detection via vibration testing typically relies on damage-sensitive features, which serve as “damage indicators”, and decisions upon the existence of damage are based on comparing the damage indicators retrieved from two distinct structural states. However, the relatively low sensitivity of damage indicators to the onset of structural damage remains an open question, despite the considerable research efforts in vibration testing over the years. Low-sensitivity problems may be particularly exacerbated by the complex dynamic behavior of lightweight structures, such as lightweight bridges subjected to vehicular traffic. In particular, due to material (and, by extension, mass) reduction in lightweight bridges, vehicles essentially act as “traveling masses”, which are comparable to the structural mass and result in a coupled complex dynamic motion problem that may obscure typical damage indicators used in vibration testing. This paper presents a damage detection approach for lightweight bridges with traveling masses, leveraging the powerful feature-extraction capabilities of machine learning (ML). In particular, a convolutional neural network (CNN) is trained to classify acceleration response data, collected from vibration testing, into damage scenarios. The training data for the CNN are created via simulations of damage scenarios, using calibrated analytical models. The damage detection approach is validated in laboratory tests on a continuous beam, showcasing the capability of the CNN to classify damage scenarios of the beam. The outcome of this paper aims to serve as a starting point towards employing ML for damage detection in the context of vibration testing as well as structural health monitoring.Publicationtype: Journal Article28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dynamic instability analysis of sandwich plates with auxetic honeycomb core and three-phase hybrid composite layers stiffened by curved stiffeners using isogeometric analysis(Elsevier, 2024-06-01)18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fatigue strength of normal and high strength steel joints improved by weld profiling(2021-11-01); ; ; While some post-weld treatment techniques increase the fatigue life mainly due to induced compressive residual stress others are trying to create a smooth transition at weld toes. One of the latter is weld profiling. This study investigates the effect of weld profiling for four different steel types from S355 to S900 including one duplex stainless-steel and performs a comparison with high frequency mechanical impact (HFMI) treatment. The observed fatigue strength improvement is significantly higher than typically assumed for such techniques and comparable to increases observed for HFMI treatment. The fatigue strength further increases with parent material strength and is only slightly below the estimated fatigue strength of the parent material. Finally, fatigue design curves are proposed for weld profiling that include an increasing fatigue strength improvement for higher strength materials, but that are still conservative for low weld quality.Publicationtype: Journal Article65 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Developing a robustness index for parallel load-bearing systems(2021-10-01); The target of this study is to develop a robustness index for parallel load-bearing systems. Parallel load-bearing systems are structural systems with load-bearing elements that are similar in type and function and constitute alternative load paths. For this purpose, a conceptual model is considered. The robustness index will be calculated based on the “stress increase ratio” of the critical cable in a cable-loss scenario. For finding the stress increase ratio of the critical cable, the differential equations of the system have been used. Accordingly, the stress increase ratio of the critical cable has been calculated by deriving an approximation function. In order to maximize the accuracy of the approximation function, the least squares method (LSM) has been used. Then, a reserve-based robustness index for a parallel load-bearing system has been derived. The proposed robustness index considers different levels of the initial damage and can be expanded to account for the initial failure of several load-bearing elements. The developed robustness index has been checked by numerical models and its good accuracy has been proven.Publicationtype: Journal Article47 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment(Elsevier, 2021-04-09); ; 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 of the 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.Publicationtype: Journal ArticleScopus© Citations 24 136 522 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , New approach for shear design of reinforced concrete slabs under concentrated loads based on tests and statistical analysis(2020-09-15); ; Despite the international research activity, the shear strength of reinforced concrete slabs without shear reinforcement is not yet satisfactorily resolved. In particular, deck slabs of existing bridges often show significant deficits in design shear capacity, although no damage has been reported so far. A test series of 14 large-scale cantilever slabs subjected to concentrated loads was conducted and analysed at the Hamburg University of Technology. Varying the distance between the concentrated load and the support in a previously unexamined wide range led to new considerations regarding the shear capacity in RC slabs. The ultimate and residual loads of the test specimens, as in many other studies on this topic, clearly exceeded the values for vehicle load assumptions in the current standards. In contrast to previous studies, a large shear slenderness in the load arrangement could be realized in the tests. This was the basic requirement for one of the key findings: The critical shear crack occurs locally in the area of load application and not at the support. Thus, shifting the design section for shear close to the concentrated load is reasonable, while in many approaches a critical section close to the support is chosen. Furthermore, the often-used effective width beff, which depends on the distance of single loads to the support, does not seem justified. The shear forces should be determined by finite element analysis, a common method in practice, which can consider the spatial load transfer and the stiffness of the support in a realistic manner. The new design method presented here is therefore not primarily concerned with the shear resistance, as other investigations are, but first on the side of determining the relevant internal shear forces, which are initially higher in the design section proposed here. Only in a second step is a preliminary factor C*Rd,c for the calculated resistance determined by means of a well-founded statistical evaluation. For this purpose, a database with 45 tests on RC slabs has been established. The new design approach provides significant greater shear capacities than the current regulations.Publicationtype: Journal Article182 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Nonlinear structural dynamic analysis by a stabilized central difference method(2018-10-15); In this work, a simple stabilized central difference technique is discussed, to analyse nonlinear models. The proposed technique is unconditionally stable for linear systems and it provides enhanced stability features for nonlinear applications. The proposed method stands as a direct single step procedure, avoiding any iterative computations when solving nonlinear models; thus, it is very efficient. In addition, it is extremely accurate, providing much reduced period elongation and amplitude decay errors, compared to standard methods. The present work also introduces a criterion for updating the nonlinear system matrices, significantly reducing the computational complexity of the simulation and enhancing the efficiency of the technique. Numerical results are presented along the manuscript, illustrating the performance and accuracy of the proposed methodology.Publicationtype: Journal Article144 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Eccentric-wing flutter stabilizer for bridges – Analysis, tests, design, and costs(2018-10); ; A device is presented that aims at preventing bridge flutter. It consists of wings positioned along the sides of, and fixed to, the bridge deck. Flutter suppression effectiveness is high provided the lateral eccentricity of the wings is large. It is a passive aerodynamic device that is presumably more cost-efficient than other passive measures or devices. Moreover, it does not contain moving parts. This is an advantage over devices with moving parts, which meet resistance due to reliability and durability concerns. Wind-tunnel tests were performed in which the flutter speed of a bridge deck sectional model without wings and with wings mounted in various configurations was measured. The experimental results are presented and compared with the results of flutter analyses using finite aeroelastic beam elements. Using the analytical approach, also the effect of the distribution of the wings along the length of a bridge was studied to optimize this distribution. Preliminary design studies for the wings and their support structures as well as quantity and cost estimates are presented. For a representative example bridge and wing configuration, an increase of 22% of flutter speed is reached at a cost increase of 2.5%.Publicationtype: Journal Article161 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , An analytical study on the bending moment acting on the girder of a long-span cable-supported bridge suffering from cable failure(2018-07-15); In this study, the structural behavior of a long-span cable-supported bridge after the sudden rupture of one of its axial cables is of concern. Cable failure produces large bending moments on the girder of the bridge. Henceforth, the focus of this study is to find the “maximum bending moment” on the girder due to the cable failure. For this purpose, an analytical approach based on differential equations of the system will be used. Then, an approximation function for a simplified bridge model in a cable-loss scenario will be derived. The use of the least squares method is also applied to minimize the error of the approximation function. The proposed approximation function has been checked by numerical models, and its good accuracy has been proven. The results show that by increasing the ratio of the bending stiffness of the girder to the axial stiffness of the cables, cable failure produces a larger bending moment on the girder.Publicationtype: Journal Article140 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Bow-shaped segments in precast segmental bridgesSegmental bridges made of small precast elements have become a standard construction method for many highway and railway bridges in the world. Nevertheless some important aspects need further investigation. One is the unavoidable gap between two adjacent elements caused by the heat of hydration during segment production ('bowing effect'). This imperfection may significantly influence the bearing capacity of the structure and its serviceability. A thermo-mechanical finite element model has been developed and verified by full-scale test data to study the match-casting process. Thereafter, two real segmental bridges with perfect and imperfect segments have been modelled. The various analyses showed that compressive stresses and the load bearing capacity of the structure as well as its serviceability may be highly influenced by the bowing effect.Publicationtype: Journal Article84