Bartłomiej Błachowski, Ph.D., Eng.

Department of Intelligent Technologies (ZTI)
Division of Safety Engineering (PIB)
position: specialist
telephone: (+48) 22 826 12 81 ext.: 192
room: 419
e-mail: bblach
personal site: http://bluebox.ippt.pan.pl/~bblach

Doctoral thesis
2005Optymalne sterowanie drganiami masztów z odciągami 
supervisor -- Prof. Witold Gutkowski, Ph.D., Dr. Habil., Eng., IPPT PAN
585
 
Recent publications
1.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, 2017
Abstract:

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.

Keywords:

structural health monitoring, truss structures, damage detection

Affiliations:
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)
2.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, 2017
Abstract:

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.

Keywords:

damage localization, rank-revealing QR decomposition, damage sensitivity, truss structure, structural health monitoring

Affiliations:
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)
3.Błachowski B.D., 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, pp.1-6, 2017
Abstract:

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.

Keywords:

structural dynamics, optimal design, elasto-plastic structures, short-time dynamic loading

Affiliations:
Błachowski B.D.-IPPT PAN
Tauzowski P.-IPPT PAN
Lógó J.-University of Technology and Economics, Budapest (HU)
4.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, 2016
Abstract:

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.

Keywords:

Bolted flange connection, Contact forces, Friction forces, Non-linear FEM analysis, Substructuring, Telecommunication tower, Structural connection damage, Structural health monitoring

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-other affiliation
5.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, 2016
Abstract:

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.

Keywords:

degree of dispersion, transient response-based damage detection, robust damage localization, shear buildings, beam structures

Affiliations:
An Y.-Dalian University of Technology (CN)
Błachowski B.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
6.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, 2016
Abstract:

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.

Keywords:

complex bolted lap connection, frame structure, wavelet analysis, damage detection

Affiliations:
Pnevmatikos N.G.-Technological Educational Institute Athens (GR)
Błachowski B.-IPPT PAN
Hatzigeorgiou G.D.-Hellenic Open University (GR)
Świercz A.-IPPT PAN
7.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, 2016
Abstract:

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.

Keywords:

Detectable damages, Bolted connections, Experimental modal analysis, Ultrasonic measurements, Steel frames, Analytical dynamics

Affiliations:
Błachowski B.-IPPT PAN
Świercz A.-IPPT PAN
Gutkiewicz P.-IPPT PAN
Szelążek J.-IPPT PAN
Gutkowski W.-other affiliation
8.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, 2014
Abstract:

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.

Keywords:

discrete structural optimization, combinatorial optimization, structural dynamics, stochastic loading, problem oriented optimization, graphs

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-other affiliation
9.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, 2014
Abstract:

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.

Keywords:

structural optimization, discrete optimization, structural vibrations, omposite floor structure

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-other affiliation
10.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, 2010
Abstract:

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.

Keywords:

Structural optimization, Problem oriented optimization, Discrete optimization, Combinatorial optimization, Graphs

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-other affiliation
11.Błachowski B.D., Gutkowski W., Discrete structural optimization by removing redundant material, ENGINEERING OPTIMIZATION, ISSN: 0305-215X, Vol.40, No.7, pp.685-694, 2008
Abstract:

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.

Keywords:

structural optimization, combinatorial optimization, structural dynamics

Affiliations:
Błachowski B.D.-IPPT PAN
Gutkowski W.-other affiliation
12.Błachowski B., Gutkowski W., Dyskretna optymalizacja konstrukcji sterowana zmiennymi stanu, MODELOWANIE INŻYNIERSKIE, ISSN: 1896-771X, Vol.36, pp.27-34, 2008
Abstract:

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.

Keywords:

discrete optimization, truss structures

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-other affiliation
13.Błachowski B.D., Model based predictive control of guyed mast vibration, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.45, No.2, pp.405-423, 2007
Abstract:

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.

Keywords:

structural vibrations, vibration control, guyed masts, wind fluctuations

Affiliations:
Błachowski B.D.-IPPT PAN
14.Błachowski B., Identyfikacja obciążeń dynamicznych przy ograniczonej liczbie czujników, MODELOWANIE INŻYNIERSKIE, ISSN: 1896-771X, Vol.33, pp.19-26, 2007
Abstract:

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.

Keywords:

load identification, limited number of sensors

Affiliations:
Błachowski B.-IPPT PAN

List of chapters in recent monographs
1.
197
Jankowski Ł., Sekuła K., Błachowski B.D., Wikło M., Holnicki-Szulc J., Smart technologies for safety engineering, rozdział: Dynamic load monitoring, Wiley, Holnicki-Szulc J. (Ed.), pp.105-151, 2008

Conference papers
1.Ortiz A.R., Błachowski B., Hołobut P., Franco J.M., Marulanda J., Thomson P., Modeling and Measurement of a Pedestrian’s Center-of-Mass Trajectory, 35th IMAC, XXXV International Modal Analysis Conference, A Conference and Exposition on Structural Dynamics 2017, 2017-01-30/02-02, Garden Grove, CA. (US), DOI: 10.1007/978-3-319-54777-0_20, pp.159-167, 2017
Abstract:

This paper presents the measurement and model updating of a pedestrian’s center of mass trajectory. A mathematical model proposed by the authors is updated using the actual trajectory of a pedestrian. The mathematical model is based on the principle that a human’s control capability tries to maintain balance with respect to the pedestrian’s center of mass (CoM), independently of the surface type. In this research, the human is considered as a mass point concentrated at CoM. The parameters of the models are updated using experimental identification of the human walking trajectory on a rigid surface. The proposed measurement technique uses a depth sensor, which enable skeletal tracking of the pedestrian walking on rigid or flexible structures. Experiments were performed using a mobile platform with the time-of-flight commercial camera Microsoft Kinect for Windows 2.0. The velocity of the mobile platform is set to maintain a 1 m separation from the pedestrian in order to provide high resolution. The results of the measurement technique allowed the identification of the human’s CoM trajectory. The results of the model updating process present the probability density function of the parameters which could be used for modeling the CoM’s trajectory of the pedestrian.

Keywords:

Human-structure interaction, Pedestrian’s trajectory, Human-induced vibrations, MS Kinect sensor

Affiliations:
Ortiz A.R.-Universidad del Norte (CO)
Błachowski B.-other affiliation
Hołobut P.-IPPT PAN
Franco J.M.-Universidad del Valle (CO)
Marulanda J.-Universidad del Valle (CO)
Thomson P.-Universidad del Valle (CO)
2.Błachowski B., Hołobut P., Ortiz A., Caicedo J.M., Simple human-structure interaction model of walking on a flexible surface, ISMA 2016 / USD 2016, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2016-09-19/09-21, Leuven (BE), pp.559-570, 2016
Abstract:

We present a new human-structure interaction (HSI) model of walking on a flexible surface. A human is considered as a mass point, located at the body’s center of mass (COM). The mass moves along a predefined trajectory, which deforms together with the surface on which the human walks. The forces of motion, equal to the sum of inertial and gravitational forces acting on the mass, are transfered to the surface at prescribed foot positions. The motion of the surface is described using a few selected mode shapes, corresponding damping ratios, and natural frequencies. The equations of motion of the system are time-dependent and discontinuous. They can be written in the form of the second order differential equations of structural dynamics, but with the right-hand forcing dependent on the deformation of the surface. We present a numerical example of a human walking on a long beam structure. The motion of the beam is described by three mode shapes, representing its vertical, lateral, and torsional deflections.

Keywords:

Human induced vibrations, Dynamics of bridges, Human walking model

Affiliations:
Błachowski B.-IPPT PAN
Hołobut P.-IPPT PAN
Ortiz A.-Universidad del Norte (CO)
Caicedo J.M.-University of South Carolina (US)
3.Błachowski B., An Y., Spencer Jr. B.F., Substructure-level based method for damage quantification in determinant trusses, ISMA 2016 / USD 2016, International Conference on Noise and Vibration Engineering / International Conference on Uncertainty in Structural Dynamics, 2016-09-19/09-21, Leuven (BE), pp.3283-3294, 2016
Abstract:

The purpose of this study is to introduce a new method of damage quantification for truss structures. Its advantage is that it can be directly applied to engineering structures without identifying modal parameters or solving a global optimization problem. The damage is localized and quantified based only on measured acceleration signals, distributed across the structure. Moreover, the method is implemented in a decentralized way rather than a centralized one; that is, for quantification of damage in a given substructure, only a small subset of sensors is considered. The method possesses higher sensitivity to damage than other frequently used methods such as Damage Locating Vectors. Validation of the method has been conducted on a numerical example and a laboratory-scale model of a truss bridge, showing its efficiency and robustness.

Keywords:

structural health monitoring, damage detection, truss structures

Affiliations:
Błachowski B.-IPPT PAN
An Y.-Dalian University of Technology (CN)
Spencer Jr. B.F.-University of Illinois at Urbana-Champaign (US)
4.Błachowski B., Świercz A., Pnevmatikos N., Experimental verification of damage location techniques for frame structures assembled using bolted connections, COMPDYN 2015, 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, 2015-05-25/05-27, Crete Island (GR), pp.C1511-1-12, 2015
Abstract:

This work is focused on experimental verification of existing techniques for localization of a loosened bolted connection. To this end, a laboratory-scale 2-meter-long steel frame is used. 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: a healthy and a damaged one. The damage is introduced by means of loosening two out of three bolts at one of the frame connections. Experimental modal analysis reveals that the loosened bolts in the connection cause a shift only in some of the frame’s natural frequencies, while the others remain insensitive to the damage.

Keywords:

bolted lap connection, frame structure, experimental modal analysis, damage location

Affiliations:
Błachowski B.-IPPT PAN
Świercz A.-IPPT PAN
Pnevmatikos N.-Technological Educational Institute Athens (GR)
5.Błachowski B.D., Gutkowski W., Wiśniewski P., Reduced order model of circular flange-bolted connection and its application to dynamic substructuring of telecommunication towers, COMPDYN 2015, 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, 2015-05-25/05-27, Crete Island (GR), pp.C1504-1-12, 2015
Abstract:

The paper deals with a nonlinear analysis of a tall tower, with Circular Flange Bolted Connections (CFBC), in which friction and contact effects are taken into account. Due to these nonlinearities, a detailed dynamic model of the whole structure would lead to very complex computational problem, unable for practical solutions. To overcome these difficulties a reduced order model of CFBC is proposed. Such a model enables the simulation of the whole tower including nonlinearities in connections. The paper is illustrated with an example of model reduction and dynamic calculations for a contemporary telecommunication tower. The tower is assembled of 4 truss segments, of triangular cross section, interconnected with CFBCs. Finally, the influence of the number of modes, included in the reduced order model, on the accuracy and computational effect, is discussed.

Keywords:

Reduced order modeling, Circular flange-bolted connections, Dynamic substructuring, Nonlinear contact and friction effects, Telecommunication towers

Affiliations:
Błachowski B.D.-IPPT PAN
Gutkowski W.-other affiliation
Wiśniewski P.-IPPT PAN
6.An Y., Błachowski B., Ou J., Numerical study on LDLT decomposition-based damage locating vector method for truss structures, PLSE 2015, Second International Conference on Performance-based and Life-cycle Structural Engineering, 2015-12-09/12-11, Brisbane (AU), pp.256-260, 2015
Abstract:

Real-time structural health monitoring is very important for truss structures especially those having large-spans. In recent years, many methods have been proposed for damage monitoring of truss structures. However, damage sensitivity of these methods is still required to be improved. In this work an efficient damage localization technique for truss structures is proposed, which is based on the LDLT decomposition of the flexibility difference matrix and the Damage Locating Vectors (DLV) method. Compared with the present Stochastic DLV (SDLV) method, the proposed method is modified in two ways. First of all, the way of calculating the damage locating vectors is modified by using LDLT decomposition instead of Singular Value Decomposition. Secondly, in order to compute the flexibility, the mass matrix which is obtained from the finite element model is used to mass-normalize mode shapes identified from ambient excitations. As a result, the proposed LDLT-DLV method has a higher sensitivity to damage for different types of truss members. The effectiveness of the proposed LDLTDLV method is validated with the numerical example of a laboratory-scale Bailey truss bridge.

Keywords:

Damage localization, damage localization, LDLT-DLV method, truss structure, structural health monitoring

Affiliations:
An Y.-Dalian University of Technology (CN)
Błachowski B.-IPPT PAN
Ou J.-Dalian University of Technology (CN)
7.Ruiz Sandoval Hernández M.E., Błachowski B., Spencer Jr. B.F., Uso de sensores inalámbricos en la obtención de parámetros modales, XVIII Congreso Nacional de Ingeniería Estructural, 2012-10-31/11-03, Acapulco (MX), pp.1-10, 2012
Abstract:

This article presents the implementation of wireless sensors in obtaining modal parameters. The Imote2 platform is used. This is an open platform developed by Intel. The application example is a simply supported wooden plate. It explains how to use the Imote2 sensor and how to extract modal information from the raw data.

Keywords:

wireless sensors, modal analysis

Affiliations:
Ruiz Sandoval Hernández M.E.-other affiliation
Błachowski B.-IPPT PAN
Spencer Jr. B.F.-University of Illinois at Urbana-Champaign (US)
8.Gutkowski W., Błachowski B., Revised assumptions for monitoring and control of 3D lattice structures, 11th Pan-American Congress of Applied Mechanics, 2010-01-04/01-08, Paraná (BR), pp.PAC0366-59, 2010
Abstract:

A successful structural monitoring and control systems should be able to discern critical events, scan frequencies and dynamic ranges. This, in turn, requires that models, applied in these systems, are as close as possible to real structural behavior. Many structures, among them, electricity transmission towers, windmills, radio and TV masts, bridges and parabolic dishes, concentrating solar energy, are build as trusses. All of them are subjected dynamic loadings coming, mostly from wind gusts, water waves and thermal activity of sun. The paper is revising assumptions, commonly made for trusses. The main assumption made is that systems of rods are pin joint. Such structures don’t exist, in real engineering design. All, above, mentioned structures are made with rigid or flexible joints. The “pin joint” assumption was made for static analyses. It stated that if joint displacements caused by rod bending can be neglected, comparing with displacements caused by rod elongations, the structural system can be considered as pin joint. As it is commonly known, such cases occur when some necessary conditions joining number of joints and hinges are fulfilled. The “pin joint”, static assumptions has been, without any formal justification, taken for granted in dynamics. Simple examples presented in the paper show that “pin joint” assumption can lead to considerable errors. The paper is illustrated with two numerical examples (simple 2 bar structure and 25 bar transmission tower). Presented examples allowing to compare results of different assumptions applied for structural elements connections.

Keywords:

lattice structures, monitoring, control, structural dynamics

Affiliations:
Gutkowski W.-other affiliation
Błachowski B.-IPPT PAN
9.Błachowski B., Gutkowski W., Optimal vibration control of guyed masts, ICTAM XXI, 21st International Congress of Theoretical and Applied Mechanics, 2004-08-15/08-21, Warszawa (PL), pp.SM3-10457, 2004
Abstract:

Topics considered in this paper include: dynamic properties of the mast and nonlinearities present in the problem, linearized equations governing guyed mast motion, conditions of stability, contollability and observability. Control forces are exerted by an anchored mechanism in such a way, that they change tension in guy cables. A control algorithm ensuring robust optimal control is also proposed. Finally, the paper is verified by a numerical simulation of a vibration control process.

Keywords:

guyed mast, vibration control

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-IPPT PAN

Conference abstracts
1.Błachowski B., Gutkowski W., Lagrangian dynamics based approach for 3D modelling of human gait, CMM-2017, 22nd International Conference on Computer Methods in Mechanics, 2017-09-13/09-16, Lublin (PL), pp.MS09-33-MS09-34, 2017
Abstract:

The purpose of this study is the mechanism of the spatial movement of a human during walking. The human is considered to be a rigid body with six degrees of freedom, and its mobility is reduced by two constraints. One of the constraints is related to an assumption of constant length of the leg, foot of which is moving along given straight line. The second constraint corresponds to an assumption that human’s centre of mass can move only in vertical plane. The dynamic model of the mechanism is built under above assumptions connected to the human gait kinematics. Then, kinetic energy function is derived. In the next step of the study the muscle force in the stance leg, together with its potential, is discussed. It is assumed that this force is piecewise-linear, which can be reasonably approximated by a cubic polynomial. For that purpose a smoothing procedure is proposed and finally with the aid of the Lagrange function dynamic equations for the 3D human gait are formulated. The last part of the paper is devoted to the numerical solution of obtained nonlinear equations, arising from the Lagrange procedure.

Keywords:

human walking, gait analysis, lagrangian dynamics

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-IPPT PAN
2.Błachowski B., Gutkowski W., Wiśniewski P., Dynamic substructuring approach for human induced vibration of a suspension footbridge, PCM-CMM 2015, 3rd Polish Congress of Mechanics and 21st Computer Methods in Mechanics, 2015-09-08/09-11, Gdańsk (PL), pp.307-308, 2015
Abstract:

A substructuring method for the prediction of the dynamic response of footbridges subjected to loadings induced by a pedestrian is presented. The dynamic system is composed of two independent subsystems. The first one is the model of the suspension footbridge, and the second one is the model of a pedestrian. The former is obtained using the standard finite element method, while the latter is created by applying a two-step identification approach. The first step is an inverse kinematics based on an experimental human motion analysis. The second one relies on Proper Orthogonal Decomposition extracting a number of most important modes, describing the motion of the pedestrian. The presented methodology will be demonstrated by a numerical example of the pedestrian-footbridge interaction.

Keywords:

dynamic substructuring, human-structure interaction, suspension footbridges

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-other affiliation
Wiśniewski P.-IPPT PAN
3.Błachowski B., Gutkowski W., Discrete optimization of structures subjected to dynamic loads using graph representation, CMM 2011, 19th International Conference on Computer Methods in Mechanics, 2011-05-09/05-12, Warszawa (PL), pp.054-1-2, 2011
Abstract:

A relatively simple method of finding discrete minimum structural weight is proposed. It is based on a tree graph, representing discrete values of the structural volume. In the proposed method, the number of analyses is limited to the order of two. The paper is illustrated with an example containing up to 42 to the power 38 combinations.

Keywords:

structural optimization, problem oriented optimization, discrete optimization, combinatorial optimization, graphs, structural static and dynamic analyses, time domain, frequency domain

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-other affiliation
4.Błachowski B., Gutkowski W., Verification of assumptions in dynamics of lattice structures, SolMech 2010, 37th Solid Mechanics Conference, 2010-09-06/09-10, Warszawa (PL), pp.284-285, 2010
Abstract:

The paper is illustrated with numerical examples of two bar and 25 bar tower structures. Results of different assumptions, applied to the structural elements connections are discussed.

Keywords:

Transmission towers, monitoring of structures

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-IPPT PAN
5.Błachowski B., Gutkowski W., A Hybrid Continuous-Discrete Approach to Large Discrete Structural Optimization Problems, SolMech 2008, 36th Solid Mechanics Conference, 2008-09-09/09-12, Gdańsk (PL), pp.368-369, 2008
Abstract:

In this study, the idea of removing redundant material is enhanced by combining the continuous and discrete solutions. At the end of the paper, several numerical examples, with numbers of combinations up to 308 are presented and their effectiveness is validated.

Keywords:

discrete optimization, removing redundant material

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-IPPT PAN
6.Błachowski B., Gutkowski W., Vibration control of masts with tendons, SolMech 2002, 34th Solid Mechanics Conference, 2002-09-02/09-07, Zakopane (PL), 2002
Abstract:

The objective of this paper is a numerical simulation of vibration control of a mast supported by tendons. This problem requires knowledge from many different disciplines such as multibody dynamics, control theory and numerical methods.

Keywords:

vibration control, wind disturbances

Affiliations:
Błachowski B.-IPPT PAN
Gutkowski W.-IPPT PAN

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pdf
201610141896
2016-03-10
105651537A
2016-06-08
An Y., Błachowski B., Ou J.
High-damage-sensitivity truss structure damage real-time monitoring system
CN, DALIAN UNIVERSITY OF TECHNOLOGY
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