1. |
Tauzowski P., Błachowski B., Lógó J.^{♦}, Topology optimization of elasto-plastic structures under reliability constraints: a first order approach,
COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2020.106406, Vol.243, pp.106406-1-15, 2021Streszczenie: The objective of this study is to propose a relatively simple and efficient method for reliability based topology optimization for structures made of elasto-plastic material. The process of determining the optimal topology of elasto-perfectly plastic structures is associated with the removal of material from the structure. Such a process leads to weakening of structural strength and stiffness causing at the same time increase the likelihood of structural failure. An important aspect of engineering design is to track this probability during the optimization process and not allow the structure safety to exceed a certain level specified by the designer. The purpose of this work is to combine the previously developed yield-limited topology optimization method with reliability analysis using first order approach. Effectiveness of the proposed methodology is demonstrated on benchmark problems proposed by Rozvany and Maute, and the elasto-plastic topology design of L-shape structure which is frequently used in different approaches for stress constrained topology optimization. Słowa kluczowe: topology optimization, reliability analysis, elasto-plastic analysis Afiliacje autorów:
Tauzowski P. | - | IPPT PAN | Błachowski B. | - | IPPT PAN | Lógó J. | - | University of Technology and Economics (HU) |
| | 140p. |
2. |
Ostrowski M., Błachowski B., Popławski B., Pisarski D., Mikułowski G., Jankowski Ł., Semi‐active modal control of structures with lockable joints: general methodology and applications,
STRUCTURAL CONTROL AND HEALTH MONITORING, ISSN: 1545-2255, DOI: 10.1002/stc.2710, pp.e2710-1-24, 2021Streszczenie: In this study, a novel modal control strategy by means of semi-actively lockable joints is proposed. The control strategy allows for a directed flow of energy between vibrational modes, which makes it suitable not only for vibration attenuation purposes but also for energy scavenging driven by electromechanical energy harvesters. The proposed control strategy is an extension of the prestress-accumulation release (PAR) technique; however, it introduces also new concepts that increase the efficiency of the overall control system. Contrary to the PAR, the proposed method requires measurement of both strains in the vicinity of the semi-active joints and translational velocities that provide global information about system behavior. The latter aspect requires the control system to be organized within a hierarchical feedback architecture. The benefit from this higher complexity of the control system is its better performance compared to the PAR. The proposed semi-active modal control not only attenuates structural vibration faster, but it also achieves this goal with a smaller number of switches implemented in the joints. The effectiveness of the proposed methodology has been demonstrated on structures equipped with two lockable joints. Two practical examples have been investigated: one employs the concept of vibration-based energy harvesting for a two-story frame structure, while the second one reduces vibration of an eight-story frame structure subjected to kinematic excitation. Słowa kluczowe: energy harvesting, lockable joint, modal coupling, semi-active control, vibration attenuation Afiliacje autorów:
Ostrowski M. | - | IPPT PAN | Błachowski B. | - | IPPT PAN | Popławski B. | - | IPPT PAN | Pisarski D. | - | IPPT PAN | Mikułowski G. | - | IPPT PAN | Jankowski Ł. | - | IPPT PAN |
| | 140p. |
3. |
Błachowski B., Świercz A., Ostrowski M., Tauzowski P., Olaszek P.^{♦}, Jankowski Ł., Convex relaxation for efficient sensor layout optimization in large‐scale structures subjected to moving loads,
Computer-Aided Civil and Infrastructure Engineering, ISSN: 1093-9687, DOI: 10.1111/mice.12553, Vol.35, No.10, pp.1085-1100, 2020Streszczenie: This paper proposes a computationally effective framework for load‐dependent optimal sensor placement in large‐scale civil engineering structures subjected to moving loads. Two common problems are addressed: selection of modes to be monitored and computational effectiveness. Typical sensor placement methods assume that the set of modes to be monitored is known. In practice, determination of such modes of interest is not straightforward. A practical approach is proposed that facilitates the selection of modes in a quasi‐automatic way based on the structural response at the candidate sensor locations to typical operational loads. The criterion used to assess sensor placement is based on Kammer's Effective Independence (EFI). However, in contrast to typical implementations of EFI, which treat the problem as a computationally demanding discrete problem and use greedy optimization, an approach based on convex relaxation is proposed. A notion of sensor density is applied, which converts the original combinatorial problem into a computationally tractable continuous optimization problem. The proposed framework is tested in application to a real tied‐arch railway bridge located in central Poland. Słowa kluczowe: optimal sensor placement, effective independence method, Fisher information matrix Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Świercz A. | - | IPPT PAN | Ostrowski M. | - | IPPT PAN | Tauzowski P. | - | IPPT PAN | Olaszek P. | - | Instytut Badawczy Dróg i Mostów (PL) | Jankowski Ł. | - | IPPT PAN |
| | 140p. |
4. |
Pnevmatikos N.^{♦}, Konstandakopoulou F.^{♦}, Błachowski B., Papavasileiou G.^{♦}, Broukos P.^{♦}, Multifractal analysis and wavelet leaders for structural damage detection of structures subjected to earthquake excitation,
Soil Dynamics and Earthquake Engineering, ISSN: 0267-7261, DOI: 10.1016/j.soildyn.2020.106328, Vol.139, pp.106328-1-4, 2020Streszczenie: This work is an effort to join, for the first-time, multifractal analysis and damage detection in civil structures subjected to strong ground seismic motions. Specifically, based on the singularity spectrum quantitative and qualitative criteria are proposed. The qualitative criteria are based on the concave of singularity spectrum of damage and undamaged structure. The proposed quantitative criterion is based on calculation of damage index taken the parameters of singularity spectrum. In order to achieve the above goal, a robust signal processing method, which is known as multifractal wavelet leader (MFWL) is used. The multifractal analysis is a tool to calculate fractal properties as well as scaling behavior of the structural response excited by an earthquake. The singularity spectrum is obtained from the Legendre-transformation to Holder exponents. In this paper, a parameter which is based on the shape of singularity spectrum and can identify the damage in the structure is proposed. The proposed method is an output-only approach for damage detection. Considering that the dynamic behavior of an inelastic system subjected to strong ground motion appears to be a non-stationary process, the above procedure of multifractal wavelet leader is suitable to retrieve the simulation response data. The findings from the analysis show that the MFWL is an appropriate scheme for structural damage detection. Słowa kluczowe: multifractal wavelet leader, damage detection, singularity spectrum, earthquake engineering, structural safety Afiliacje autorów:
Pnevmatikos N. | - | Technological Educational Institute Athens (GR) | Konstandakopoulou F. | - | inna afiliacja | Błachowski B. | - | IPPT PAN | Papavasileiou G. | - | University of the Highlands and Islands (GB) | Broukos P. | - | inna afiliacja |
| | 100p. |
5. |
Błachowski B., Tauzowski P., Lógó J.^{♦}, Yield limited optimal topology design of elastoplastic structures,
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-019-02447-9, pp.1-24, 2020Streszczenie: This study is devoted to a novel method for topology optimization of elastoplastic structures subjected to stress constraints. It should be noted that in spite of the classical solutions of the different type of elastoplastic topology problems are more than 70 years old, the integration of the Prandtl-Reuss constitutive equations into the topology optimization process is not very often investigated in the last three decades. In the presented methodology where the classical variational principles of plasticity and the functor-oriented programming technique are applied in topology design, the aim is to find a minimum weight structure which is able to carry a given load, fulfills the allowable stress limit, and is made of a linearly elastic, perfectly plastic material. The optimal structure is found in an iterative way using only a stress intensity distribution and a return mapping algorithm. The method determines representative stresses at every Gaussian point, averages them inside every finite element using the von Mises yield criterion, and removes material proportionally to the stress intensities in individual finite elements. The procedure is repeated until the limit load capacity is exceeded under a given loading. The effectiveness of the methodology is illustrated with three numerical examples. Additionally, different topologies are presented for a purely elastic and an elastoplastic material, respectively. It is also demonstrated that the proposed method is able to find the optimal elastoplastic topology for a problem with a computational mesh of the order of tens of thousands of finite elements. Słowa kluczowe: topology optimization, elastoplastic structures, minimum-weight design, stress constraints Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Tauzowski P. | - | IPPT PAN | Lógó J. | - | University of Technology and Economics (HU) |
| | 100p. |
6. |
Ostrowski M., Błachowski B., Bocheński M.^{♦}, Piernikarski D.^{♦}, Filipek P.^{♦}, Janicki W.^{♦}, Design of nonlinear electromagnetic energy harvester equipped with mechanical amplifier and spring bumpers,
BULLETIN OF THE POLISH ACADEMY OF SCIENCES: TECHNICAL SCIENCES, ISSN: 0239-7528, DOI: 10.24425/bpasts.2020.135384, Vol.68, No.6, pp.1-11, 2020Streszczenie: The main drawback of vibration-based energy harvesting is its poor efficiency due to small amplitudes of vibration and low sensitivity at frequencies far from resonant frequency. The performance of electromagnetic energy harvester can be improved by using mechanical enhancements such as mechanical amplifiers or spring bumpers. The mechanical amplifiers increase range of movement and velocity, improving also significantly harvester efficiency for the same level of excitation. As a result of this amplitude of motion is much larger comparing to the size of the electromagnetic coil. This in turn imposes the need for modelling of electromagnetic circuit parameters as the function of the moving magnet displacement. Moreover, high velocities achieved by the moving magnet reveal nonlinear dynamics in the electromagnetic circuit of the energy harvester. Another source of nonlinearity is the collision effect between magnet and spring bumpers. It has been shown that this effect should be carefully considered during design process of the energy harvesting device. The present paper investigates the influence of the above-mentioned nonlinearities on power level generated by the energy harvester. A rigorous model of the electromagnetic circuit, derived with aid of the Hamilton's principle of the least action, has been proposed. It includes inductance of the electromagnetic coil as the function of the moving magnet position. Additionally, nonlinear behaviour of the overall electromagnetic device has been tested numerically for the case of energy harvester attached to the quarter car model moving on random road profiles. Such a source of excitation provides wide band of excitation frequencies, which occur in variety of real-life applications. Słowa kluczowe: energy harvesting, velocity amplification, nonlinear electromagnetic circuit, spring bumper, quarter car model Afiliacje autorów:
Ostrowski M. | - | IPPT PAN | Błachowski B. | - | IPPT PAN | Bocheński M. | - | Lublin University of Technology (PL) | Piernikarski D. | - | inna afiliacja | Filipek P. | - | Lublin University of Technology (PL) | Janicki W. | - | inna afiliacja |
| | 100p. |
7. |
Ostrowski M., Błachowski B., Jankowski Ł., Pisarski D., Modal energy transfer by controlled structural connections,
DIAGNOSTYKA, ISSN: 1641-6414, DOI: 10.29354/diag/116692, Vol.21, No.1, pp.61-70, 2020Streszczenie: This paper describes a semi-active control strategy that allows to transfer the vibration energy from an arbitrarily induced to a selected structural mode. The intended aim of the proposed control strategy is energy harvesting from structural vibrations. Another potential application is related to structural safety. In the paper, a mathematical model is first introduced to describe the phenomenon of vibrational energy transfer, and then, based on this model, an efficient semi-active control strategy is proposed. Finally, some problems related to measurement techniques are discussed. The effectiveness of the proposed methodology is demonstrated in an example of energy transfer between vibrational modes of a three-bar planar frame structure. Słowa kluczowe: vibration energy, modal control, lockable joint, modal coupling Afiliacje autorów:
Ostrowski M. | - | IPPT PAN | Błachowski B. | - | IPPT PAN | Jankowski Ł. | - | IPPT PAN | Pisarski D. | - | IPPT PAN |
| | 20p. |
8. |
Błachowski B., Ostrowski M., Tauzowski P., Świercz A., Jankowski Ł., Sensor placement for structural damage identification by means of topology optimization,
AIP Conference Proceedings, ISSN: 0094-243X, DOI: 10.1063/5.0007817, Vol.2239, No.1, pp.020002-1-11, 2020Streszczenie: The success of virtually all structural health monitoring (SHM) methods depends on the information content of the measurements, and thus on the placement of the available sensors. This paper presents an efficient method for finding optimal sensor distribution over structural system with many degrees of freedom (DOFs). The objective function is based on the classical Fisher information matrix. Originally, this yields a computationally hard discrete optimization problem. However, the proposed numerical solution method is based on a concept taken from structural topology optimization, where a discrete optimization problem is replaced with a continuous one. Two numerical examples demonstrate the effectiveness of the proposed methodology. These are a 5-bay truss with 24 DOFs and a two-story frame structure whose finite element model has been condensed to 14 DOFs. Słowa kluczowe: optimal sensor placement, structural damage identification, topology optimization Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Ostrowski M. | - | IPPT PAN | Tauzowski P. | - | IPPT PAN | Świercz A. | - | IPPT PAN | Jankowski Ł. | - | IPPT PAN |
| |
9. |
Tauzowski P., Błachowski B., Lógó J.^{♦}, Functor-oriented topology optimization of elasto-plastic structures,
Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2019.102690, Vol.135, pp.102690-1-11, 2019Streszczenie: The paper deals with a novel approach to development of optimality criteria based finite element code for topology optimization of elasto-plastic structures. The novelty of this work is related to the concept of function object called functor and its application to efficient FE code development. First, the general problem of topology optimization under stress constraints is briefly formulated. Then, the programming aspects of topology optimization using traditional object-oriented and functor based programming are discussed. The advantages of the functor based approach are related to simplicity of designing the FE code architecture and reusability of this code. In particular the metric known as 'Lack of cohesion of methods' is useful in comparing these two different paradigms. Finally, the paper is also illustrated with numerical examples of topology optimization using the proposed methodology. Słowa kluczowe: topology optimization, function object, functor programming, optimal design, elasto-plastic structures, finite element programming Afiliacje autorów:
Tauzowski P. | - | IPPT PAN | Błachowski B. | - | IPPT PAN | Lógó J. | - | University of Technology and Economics (HU) |
| | 140p. |
10. |
An Y.^{♦}, Chatzi E.^{♦}, Sim S.^{♦}, Laflamme S.^{♦}, Błachowski B., Ou J.^{♦}, Recent progress and future trends on damage identification methods for bridge structures,
STRUCTURAL CONTROL AND HEALTH MONITORING, ISSN: 1545-2255, DOI: 10.1002/stc.2416, Vol.26, No.10, pp.e2416-1-30, 2019Streszczenie: Damage identification forms a key objective in structural health monitoring. Several state-of-the-art review papers regarding progress in this field up to 2011 have been published. This paper summarizes the recent progress between 2011 and 2017 in the area of damage identification methods for bridge structures. This paper is organized based on the classification of bridge infrastructure in terms of fundamental structural systems, namely, beam bridges, truss bridges, arch bridges, cable-stayed bridges, and suspension bridges. The overview includes theoretical developments, enhanced simulation attempts, laboratory-scale implementations, full-scale validation, and the summary for each type of bridges. Based on the offered review, some challenges, suggestions, and future trends in damage identification are proposed. The work can be served as a basis for both academics and practitioners, who seek to implement damage identification methods in next-generation structural health monitoring systems. Słowa kluczowe: arch bridge, beam bridge, cable‐stayed bridge, damage identification, suspension bridge, truss bridge Afiliacje autorów:
An Y. | - | Dalian University of Technology (CN) | Chatzi E. | - | Eidgenössische Technische Hochschule Zürich (CH) | Sim S. | - | Ulsan National Institute of Science and Technology (KR) | Laflamme S. | - | Iowa State University (US) | Błachowski B. | - | IPPT PAN | Ou J. | - | Dalian University of Technology (CN) |
| | 140p. |
11. |
Błachowski B., Modal sensitivity based sensor placement for damage identification under sparsity constraint,
Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.13888, Vol.63, No.2, pp.432-445, 2019Streszczenie: The present study deals with a comprehensive approach for damage identification of spatial truss structures. The novelty of the proposed approach consists of a three-level analysis. First, sensitivity of assumed modal characteristics is calculated. Second, natural frequency sensitivity is used to determine hardly identifiable structural parameters and mode shape sensitivity is applied to select damage-sensitive locations of sensors. Third, two sparsity constrained optimization algorithms are tested towards efficient identification of applied damage scenarios. These two algorithms are based on ℓ1-norm minimization and non-negative least square (NNLS) solution. Performances of both proposed algorithms have been compared in two realistic case studies: the first one concerned a three-dimensional truss girder with 61 structural parameters and the second one was devoted to an upper-deck arch bridge composed of 416 steel members. Słowa kluczowe: sensor placement, damage identification, ℓ1-norm minimization, sparsity constrained optimization Afiliacje autorów:
| | 40p. |
12. |
Błachowski B., Pnevmatikos N.^{♦}, Neural network based vibration control of seismically excited civil structures,
Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11601, Vol.62, No.3, pp.620-628, 2018Streszczenie: This study proposes a neural network based vibration control system designed to attenuate structural vibrations induced by an earthquake. Classical feedback control algorithms are susceptible to parameter changes. For structures with uncertain parameters they can even cause instability problems. The proposed neural network based control system can identify the structural properties of the system and avoids the above mentioned problems. In the present study it is assumed that a full state of the structure is known, which means the at each floor horizontal displacements and rotations about the vertical axis are measured. Additionally, it is assumed the acceleration signal coming from the earthquake is also available. The proposed neural control strategy is compared with the classical linear quadratic regulator (LQR) not only in terms of displacement responses, but also required control forces. Moreover, the influence of different weighting matrices on performance of the proposed control strategy has been presented.
The effectiveness of the neuro-controller has been demonstrated on two numerical examples: a simple single degree of freedom (DOF) structure and a multi-DOF structure representing a twelve story building. Both structures under consideration have been excited with El Centro acceleration signal. The results of numerical simulations on the SDOF system indicate that using neuro-controller it would be possible to obtain smaller amplitudes as compared with the LQ regulator, but it would require higher control effort. Słowa kluczowe: vibration control, artificial neural networks, seismic excitation Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Pnevmatikos N. | - | Technological Educational Institute Athens (GR) |
| | 15p. |
13. |
Błachowski B., An Y.^{♦}, Spencer Jr. B.F.^{♦}, Ou J.^{♦}, Axial strain accelerations approach for damage localization in statically determinate truss structures,
Computer-Aided Civil and Infrastructure Engineering, ISSN: 1093-9687, DOI: 10.1111/mice.12258, Vol.32, No.4, pp.304-318, 2017Streszczenie: This work proposes an efficient and reliable method for damage localization in truss structures. The damage is localized on the basis of measured acceleration signals of the structure followed by simple statistical signal processing. It has three main advantages over many existing methods. Firstly, it can be directly applied to real engineering structures without the need of identifying modal parameters or solving any global optimization problem. Secondly, the proposed method has higher sensitivity to damage than some other frequently used methods and allows to localize damage as small as a few percents. Thirdly, it is a model-free method, which does not require precise finite element model development or updating. Validation of the method has been conducted on numerical examples and laboratory-scale trusses. Two types of frequently used trusses have been selected for this study, namely Howe and Bailey trusses. The presented experimental validation of the method shows its efficiency and robustness for damage localization in truss structures. Słowa kluczowe: structural health monitoring, truss structures, damage detection Afiliacje autorów:
Błachowski B. | - | IPPT PAN | An Y. | - | Dalian University of Technology (CN) | Spencer Jr. B.F. | - | University of Illinois at Urbana-Champaign (US) | Ou J. | - | Dalian University of Technology (CN) |
| | 45p. |
14. |
An Y.^{♦}, Błachowski B., Zhong Y.^{♦}, Hołobut P., Ou J.^{♦}, Rank-revealing QR decomposition applied to damage localization in truss structures,
STRUCTURAL CONTROL AND HEALTH MONITORING, ISSN: 1545-2255, DOI: 10.1002/stc.1849, Vol.24, No.2, pp.e1849-1-15, 2017Streszczenie: The purpose of this work is the development of an efficient and high-sensitive damage localization technique for truss structures, based on the rank-revealing QR decomposition (RRQR) of the difference-of-flexibility matrix. The method is an enhancement of the existing techniques of damage detection, which rely on the set of so-called damage locating vector (DLV). The advantages of the RRQR decomposition-based DLV (RRQR-DLV) method are its less computational effort and high sensitivity to damage. Compared with the frequently used stochastic DLV (SDLV) method, RRQR-DLV offers higher sensitivity to damage, which has been validated based on the presented numerical simulation. The effectiveness of the proposed RRQR-DLV method is also illustrated with the experimental validation based on a laboratory-scale Bailey truss bridge model. The proposed method works under ambient excitation such as traffic excitation and wind excitation; therefore, it is promising for real-time damage monitoring of truss structures. Słowa kluczowe: damage localization, rank-revealing QR decomposition, damage sensitivity, truss structure, structural health monitoring Afiliacje autorów:
An Y. | - | Dalian University of Technology (CN) | Błachowski B. | - | IPPT PAN | Zhong Y. | - | Dalian University of Technology (CN) | Hołobut P. | - | IPPT PAN | Ou J. | - | Dalian University of Technology (CN) |
| | 35p. |
15. |
Błachowski B., Tauzowski P., Lógó J.^{♦}, Modal Approximation Based Optimal Design of Dynamically Loaded Plastic Structures,
Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11016, Vol.61, No.4, pp.987-992, 2017Streszczenie: The purpose of this study is to present an optimal design procedure for elasto-plastic structures subjected to impact loading. The proposed method is based on mode approximation of the displacement field and assumption of constant acceleration of impacted structure during whole time of deformation process until the plastic displacement limit is reached. Derivation of the method begins with the application of the principle of conservation of linear momentum, followed by determination of inertial forces. The final stage of the method utilizes an optimization technique in order to find a minimum weight structure. Eventually, effectiveness and usefulness of the proposed method is demonstrated on the example of a planar truss structure subjected to dynamic loading caused by a mass impacting the structure with a given initial velocity. Słowa kluczowe: structural dynamics, optimal design, elasto-plastic structures, short-time dynamic loading Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Tauzowski P. | - | IPPT PAN | Lógó J. | - | University of Technology and Economics (HU) |
| | 15p. |
16. |
Błachowski B., Gutkowski W.^{♦}, Effect of damaged circular flange-bolted connections on behaviour of tall towers, modelled by multilevel substructuring,
ENGINEERING STRUCTURES, ISSN: 0141-0296, DOI: 10.1016/j.engstruct.2015.12.018, Vol.111, pp.93-103, 2016Streszczenie: The paper deals with non-linear analysis of a telecommunication tower with circular flange-bolted connections (CFBCs). They are composed of two flanges, welded to the structural tubes, and then connected together with pre-tensioned bolts. A rigorous FEM analysis is performed for finding the connection stiffness in two cases. One deals with all bolts undamaged and the second one with one or more bolts broken.
The analysis, which includes contact and friction forces, shows that when joints are under tension, the bolts are not only subjected to axial forces, but also to bending moments due the prying effect. The value of stresses caused by bending depends strongly on the bolt pre-tension and flange thickness. Removing one of the six connection bolts significantly increases stresses in the remaining bolts. Knowing the behaviour of the connection, it is possible to study the behaviour of the whole structure. This is achieved by applying the multilevel substructuring approach. The first levels is related to the flanges and bolts, whereby the connection model is simplified, and compared with the rigorous one, the second level is related to the assembly of the whole tower.
The paper is illustrated with several examples of connections of different thicknesses, and different bolt pre-tensions. The considered tower comes from a real design. Słowa kluczowe: Bolted flange connection, Contact forces, Friction forces, Non-linear FEM analysis, Substructuring, Telecommunication tower, Structural connection damage, Structural health monitoring Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Gutkowski W. | - | inna afiliacja |
| | 35p. |
17. |
An Y.^{♦}, Błachowski B., Ou J.^{♦}, A degree of dispersion-based damage localization method,
STRUCTURAL CONTROL AND HEALTH MONITORING, ISSN: 1545-2255, DOI: 10.1002/stc.1760, Vol.23, pp.176-192, 2016Streszczenie: We present an efficient and robust damage localization method. Its applications therefore include defect location in shear buildings and beam structures. The proposed method is based on the knowledge of the difference of curvatures, computed for a structure before and after damage occurs. However, instead of using modal shapes for this purpose, as is frequently performed, the present method computes the curvature directly from acceleration signals, without identifying modal shapes of the structure. Additionally, the accelerations are subjected to averaging, which reduces measurement noise, and logarithm extraction, which renders the method independent of the amplitude of the loading impulse used for damage location. Another important feature of the method is that it does not require any calibration of numerical models, because it is solely based on measurement data. The presented method of damage location is illustrated with two examples, which involve experimental tests on laboratory-scale structures. The first example concerns defect location in a shear-building structure, and the second one in a spatially excited simply supported steel beam. Both cases confirm the effectiveness of the method, and its robustness to measurement noise. Słowa kluczowe: degree of dispersion, transient response-based damage detection, robust damage localization, shear buildings, beam structures Afiliacje autorów:
An Y. | - | Dalian University of Technology (CN) | Błachowski B. | - | IPPT PAN | Ou J. | - | Dalian University of Technology (CN) |
| | 35p. |
18. |
Pnevmatikos N.G.^{♦}, Błachowski B., Hatzigeorgiou G.D.^{♦}, Świercz A., Wavelet analysis based damage localization in steel frames with bolted connections,
SMART STRUCTURES AND SYSTEMS, ISSN: 1738-1584, DOI: 10.12989/sss.2016.18.6.1189, Vol.18, No.6, pp.1189-1202, 2016Streszczenie: This paper describes an application of wavelet analysis for damage detection of a steel frame structure with bolted connections. The wavelet coefficients of the acceleration response for the healthy and loosened connection structure were calculated at each measurement point. The difference of the wavelet coefficients of the response of the healthy and loosened connection structure is selected as an indicator of the damage. At each node of structure the norm of the difference of the wavelet coefficients matrix is then calculated. The point for which the norm has the higher value is a candidate for location of the damage. The above procedure was experimentally verified on a laboratory-scale 2-meter-long steel frame. The structure consists of 11 steel beams forming a four-bay frame, which is subjected to impact loads using a modal hammer. The accelerations are measured at 20 different locations on the frame, including joints and beam elements. Two states of the structure are considered: healthy and damaged one. The damage is introduced by means of loosening two out of three bolts at one of the frame connections. Calculating the norm of the difference of the wavelet coefficients matrix at each node the higher value was found to be at the same location where the bolts were loosened. The presented experiment showed the effectiveness of the wavelet approach to damage detection of frame structures assembled using bolted connections. Słowa kluczowe: complex bolted lap connection, frame structure, wavelet analysis, damage detection Afiliacje autorów:
Pnevmatikos N.G. | - | Technological Educational Institute Athens (GR) | Błachowski B. | - | IPPT PAN | Hatzigeorgiou G.D. | - | Hellenic Open University (GR) | Świercz A. | - | IPPT PAN |
| | 30p. |
19. |
Błachowski B., Świercz A., Gutkiewicz P., Szelążek J., Gutkowski W.^{♦}, Structural damage detectability using modal and ultrasonic approaches,
MEASUREMENT, ISSN: 0263-2241, DOI: 10.1016/j.measurement.2016.02.033, Vol.85, pp.210-221, 2016Streszczenie: An experimental and analytical study of the relation between local defect, in a steel structure, and its higher frequencies and higher modes is discussed. The structure is a plane steel frame, assembled of beams, joined together with bolted connections. Removing some bolts from a given connection simulates the damage. In the experiment, an impulse force induced structural vibrations. Effects of vibrations were shown by data from gages, measuring accelerations with a high accuracy. From the data, it could be observed, that mode shapes, for the healthy and damaged structures didn’t show any differences for low frequencies. Only modes around thirteen showed significant gap between picks of Frequency Response Functions, for healthy and damaged frame. Moreover, looking at mode shapes, it could be observed that structural configuration may have some influence on defects to be observable. This aspect is discussed in a separate section. The experiment performed on the whole structure allows finding the place where the defect is localized. However, it can’t give detailed information on the defect itself, here defect of a bolt. For finding it, an ultrasonic measurement of pre-tensioning forces in bolts was applied. It allowed not only to determine stresses in the bolt, but also to verify, if in the process of assembling the structure was not pre-stressed. Słowa kluczowe: Detectable damages, Bolted connections, Experimental modal analysis, Ultrasonic measurements, Steel frames, Analytical dynamics Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Świercz A. | - | IPPT PAN | Gutkiewicz P. | - | IPPT PAN | Szelążek J. | - | IPPT PAN | Gutkowski W. | - | inna afiliacja |
| | 30p. |
20. |
Błachowski B., Gutkowski W.^{♦}, Graph based discrete optimization in structural dynamics,
BULLETIN OF THE POLISH ACADEMY OF SCIENCES: TECHNICAL SCIENCES, ISSN: 0239-7528, DOI: 10.2478/bpasts-2014-0011, Vol.62, No.1, pp.91-102, 2014Streszczenie: In this study, a relatively simple method of discrete structural optimization with dynamic loads is presented. It is based on a tree graph, representing discrete values of the structural weight. In practical design, the number of such values may be very large. This is because they are equal to the combination numbers, arising from numbers of structural members and prefabricated elements. The starting point of the method is the weight obtained from continuous optimization, which is assumed to be the lower bound of all possible discrete weights. Applying the graph, it is possible to find a set of weights close to the continuous solution. The smallest of these values, fulfilling constraints, is assumed to be the discrete minimum weight solution. Constraints can be imposed on stresses, displacements and accelerations. The short outline of the method is presented in Sec. 2. The idea of discrete structural optimization by means of graphs. The knowledge needed to apply the method is limited to the FEM and graph representation. Słowa kluczowe: discrete structural optimization, combinatorial optimization, structural dynamics, stochastic loading, problem oriented optimization, graphs Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Gutkowski W. | - | inna afiliacja |
| | 25p. |
21. |
Błachowski B., Gutkowski W.^{♦}, Minimum weight design of composite floors under human induced vibrations,
Journal of Civil Engineering, Environment and Architecture, ISSN: 2300-5130, DOI: 10.7862/rb.2014.25, Vol.XXXI, No.61, pp.5-14, 2014Streszczenie: The paper is concerned with a minimum weight design of composite floors subjected to dynamic loading, deriving from the rhythmic activity of a group of people. The floor structure consists of concrete slab cast, on thick trapezoidal deck, which is supported by a grid of steel beams. The structure is vibration-prone and exhibits a number of natural frequencies, which are within a range of loading function. Minimum weight design consists in assigning, from catalogues of prefabricated plates and beams appropriate elements assuring fulfillment of imposed constraints on displacements and accelerations. Applied, practical discrete optimization method is based on graph theory and finite element analysis. Efficiency of the proposed design is demonstrated in an example of real-world engineering structure. Słowa kluczowe: structural optimization, discrete optimization, structural vibrations, omposite floor structure Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Gutkowski W. | - | inna afiliacja |
| | 5p. |
22. |
Błachowski B., Gutkowski W.^{♦}, A hybrid continuous-discrete approach to large discrete structural problem,
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, Vol.41, No.6, pp.965-977, 2010Streszczenie: Many optimum structural designs are based on searching for the best of all combinations, arising from the number of structural members, and parameters of listed rolled proﬁles. Even, in a relatively simple design, the number of such combinations is of an order higher than ten. All known methods of ﬁnding discrete minimum of structural weight require very large number of analyses often of an order of four. In this study, are relatively simple method of solving such problems is presented. It is based on a tree graph, representing discrete values of the structural volume. The structure can be subjected to multi static loadings with constraints imposed on displacements and stresses. The number of analyses, in the proposed algorithm, is limited to the order of two. The knowledge needed to apply the method is limited to FEM and graph representation. The paper is illustrated with two examples with numbers of combinations up to 42 to the power 38. Słowa kluczowe: Structural optimization, Problem oriented optimization, Discrete optimization, Combinatorial optimization, Graphs Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Gutkowski W. | - | inna afiliacja |
| | 32p. |
23. |
Błachowski B., Gutkowski W.^{♦}, Discrete structural optimization by removing redundant material,
ENGINEERING OPTIMIZATION, ISSN: 0305-215X, Vol.40, No.7, pp.685-694, 2008Streszczenie: A very simple method for ﬁnding the minimum weight of a structure designed from a list of available parameters is presented. The structure can be subjected to multiple loading conditions with constraints imposed on displacements, stresses and eigenfrequency. The method consists of a recursive removal of redundant material, starting from the heaviest structure. The number of analyses required is a factor of 10 to the power 2 less than for most stochastic methods. The knowledge needed for application of the method is limited to the ﬁnite-element method.
Słowa kluczowe: structural optimization, combinatorial optimization, structural dynamics Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Gutkowski W. | - | inna afiliacja |
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24. |
Błachowski B., Gutkowski W.^{♦}, Dyskretna optymalizacja konstrukcji sterowana zmiennymi stanu,
MODELOWANIE INŻYNIERSKIE, ISSN: 1896-771X, Vol.36, pp.27-34, 2008Streszczenie: A very simple discrete optimization algorithm for minimum structural weight is presented. The main idea consists in assigning initial cross-sections to a given structure, and then searching for its least stressed elements. In the second stage of the algorithm, the cross-section of the element with minimum stress is reduced to the next catalogue entry. Such reduction of cross-sections is continued until imposed bounds are met. The presented algorithm was positively tested on example configurations with complexity of 10 to the power 10 and 30 to the power 8 combinations. Słowa kluczowe: discrete optimization, truss structures Afiliacje autorów:
Błachowski B. | - | IPPT PAN | Gutkowski W. | - | inna afiliacja |
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25. |
Błachowski B., Model based predictive control of guyed mast vibration,
JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.45, No.2, pp.405-423, 2007Streszczenie: The purpose of this work is to present an algorithm for optimal vibration control of guyed masts and an example of its application to a numerical simulation. The objective of the proposed control system is to minimize amplitudes of transverse vibrations of the top of a mast induced by wind pressure acting on the structure. Control forces are assumed to be physically realized through changes of tension in guy cables, supporting the mast. The only required measurements are velocities of guy cables at the anchor-points. On the basis of those, a complete state of deformation of the structure is obtained by using the Kalman ﬁlter. The Davenport spectral density function is adopted as a model of the stochastic action of the wind.
Słowa kluczowe: structural vibrations, vibration control, guyed masts, wind ﬂuctuations Afiliacje autorów:
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26. |
Błachowski B., Identyfikacja obciążeń dynamicznych przy ograniczonej liczbie czujników,
MODELOWANIE INŻYNIERSKIE, ISSN: 1896-771X, Vol.33, pp.19-26, 2007Streszczenie: In the paper two methods of real-time load identification are proposed. The first one is based on information about frequency characteristics of loading, while the second one uses only information about deformation of structure. Theoretical considerations are illustrated by numerical calculations on a example of simply supported beam. Słowa kluczowe: load identification, limited number of sensors Afiliacje autorów:
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