We report the first direct measurements of clamping strains within individual wires of a 19 paral... more We report the first direct measurements of clamping strains within individual wires of a 19 parallel wire strand constrained by a clamshell clamp. In these measurements neutron diffraction was used to determine the elastic strains along three orthogonal axes for all of the individual wires across the strand cross section underneath the clamp for various clamping loads. We observed that, while, for all clamping loads, the clamping strains within individual wires were heterogeneously distributed, increasing the clamping force significantly decreased the strain heterogeneity. In contrast, no strain heterogeneity was observed in a rigorous companion finite-element model of the strand unless dimensional variations in the wire diameters were introduced. Our results are in agreement with the hypothesis by Gjelsvik, which states that, within a parallel wire bridge cable, local variations in wire diameter due to manufacturing tolerances can lead to large variations in clamping constraint.
Conference Proceedings of the Society for Experimental Mechanics Series, 2014
Statistical pattern recognition based structural damage detection is often developed exploiting t... more Statistical pattern recognition based structural damage detection is often developed exploiting the methods of outlier analysis. In this context, damage occurrence is assessed by analyzing whether a set of features extracted from the response of the system under unknown conditions departs from the population of features extracted from the response of the healthy system. The metric dominantly used for this purpose is the Mahalanobis Squared Distance (MSD). Evaluation of MSD of a point from a population requires the use of the inverse of the population's covariance matrix. It is known that when the feature dimensions are comparable or larger than the number of observations, the covariance matrix is ill-conditioned and numerically problematic to invert in the former case, while singular and not even invertible in the latter. To overcome this difficulty, three alternatives to the canonical damage detection procedure are investigated: data compression through Discrete Cosine Transform, use of pseudo-inverse of the covariance matrix, and use of shrinkage estimate of the covariance matrix. The performance of the three methods is compared using the experimental data recorded on a four story steel frame excited at the base by means of the shaking table available at the Carleton Laboratory at Columbia University.
The elastic strains induced in the constituent
wires of parallel wire strands under tensile loadi... more The elastic strains induced in the constituent wires of parallel wire strands under tensile loading were measured using neutron diffraction. The elastic strains carried by the individual wires depended very strongly on the boundary conditions at the grips and on radial clamping forces. The friction forces between the wires were quite significant and should not be neglected in analytical or numerical formulations of strain partitioning in parallel wire cables.
The identification of modal parameters has been performed for the New Carquinez suspension bridge... more The identification of modal parameters has been performed for the New Carquinez suspension bridge in California. By using multiple ambient vibration data sets recorded through a wind-motion monitoring system in the bridge, the baseline modal parameters were obtained in order to investigate dynamic behavior of the bridge in operating conditions. For the modal parameters identification, the data-driven stochastic subspace identification technique was implemented. For each data set, the modal parameters for structural modes were estimated by examining the estimation error between measured data and reconstructed one from the identified modes. Based on the results, variability of the identified modal parameters was also investigated.
Journal of Civil Engineering and Architecture, 6(3), 280-299, Mar 2012
This paper aims at investigating the efficacy of different state-of-art damage detection methods ... more This paper aims at investigating the efficacy of different state-of-art damage detection methods when applied to real world structures subjected to ground motion excitations, for which the literature contributions are, at present, still not fully comprehensive. To this purpose the paper analyses two test structures: (1) a four-story scaled steel frame tested on a shake table in a controlled laboratory conditions, and (2) a seven-story reinforced concrete building monitored during the seismic excitations of the 1999 Chi-Chi (Taiwan) Earthquake main shock and numerous fore and aftershocks. Some model based damage approaches and statistics based damage indexes are reviewed. The different methodologies and indexes are, then, applied to the two test structures with the final aim of analysing their performance and validity within the case of a laboratory scaled model and a real world structure subjected to input ground motion.
Page 1. Evaluating the Strength of Suspension Bridge Cables Yuwei Shi Ph.D. Candidate Department ... more Page 1. Evaluating the Strength of Suspension Bridge Cables Yuwei Shi Ph.D. Candidate Department of Civil Engineering Columbia University, New York ys2052@columbia.edu Raimondo Betti Professor Department of Civil Engineering Columbia University, New York ...
This paper presents output-only observer/Kalman filter identification (O3KID), an effective metho... more This paper presents output-only observer/Kalman filter identification (O3KID), an effective method for the identification of the dynamic model of a structure and its underlying modal parameters using only output time histories measured on the field. The method is suitable for structural health monitoring based on modal parameters, in particular, for those civil infrastructures whose excitation is random in nature and in the way that it is applied to the structure (e.g., wind and traffic) and therefore is difficult to measure. O3KID is based on a linear-time-invariant state-space model and is derived from an established and successful approach for input–output system identification, known as observer/Kalman filter identification. The paper rigorously proves the applicability of the approach to the output-only case, presents the resulting new algorithms, and demonstrates them via examples on both numerical and experimental data.
ABSTRACT In this work we focus on experimental studies of polymer-nanocomposites intended for pas... more ABSTRACT In this work we focus on experimental studies of polymer-nanocomposites intended for passive protection of civil structures. The material consists of a polyurea-matrix enhanced by different quantities of multiwalled carbon nanotubes. Several tensile and cyclic tests are performed to evaluate and characterize the mechanical behaviour of this new material. Furthermore, we subject the material to accelerated thermal aging and study its performance deterioration which is fairly unknown. The results on the unaged specimens are intuitive and indicate that an arbitrary amount of CNTs may result in suboptimal performance. More specifically, 1% in weight of CNTs yields the best mechanical performance. However, after a long aging term, our findings are interesting and counterintuitive as these nanocomposites become more brittle and break quickly while the virgin polyurea gives the best performance.
A new methodology to determine the safety of suspension bridge main cables is proposed in this pa... more A new methodology to determine the safety of suspension bridge main cables is proposed in this paper and illustrated on a corrosion-deteriorated cable composed of 9,061 wires. The approach is the first one to use a finite element (FE) model to predict the cable's failure load, to account for load recovery due to friction in broken wires and to simulate the reduced strength of the cable as a three dimensional random field. In order to obtain the cable's failure load, the load is increased gradually, having individual wires break according to their spatially variable random residual strength. Because of the load transfer to surrounding wires, the breakage of an individual wire affects the stress state of its surrounding wires. Consequently, as the load is increased, this local damage spreads to its immediate vicinity and eventually the entire cable fails. Because of the complexity of the problem, the breaking load of the cable is determined through a Monte Carlo simulation approach that accounts for the uncertainty in the spatial variability of the residual strength of the cable's wires. The probability distribution of the load that will drive a suspension bridge cable to failure is provided.
We report the first direct measurements of clamping strains within individual wires of a 19 paral... more We report the first direct measurements of clamping strains within individual wires of a 19 parallel wire strand constrained by a clamshell clamp. In these measurements neutron diffraction was used to determine the elastic strains along three orthogonal axes for all of the individual wires across the strand cross section underneath the clamp for various clamping loads. We observed that, while, for all clamping loads, the clamping strains within individual wires were heterogeneously distributed, increasing the clamping force significantly decreased the strain heterogeneity. In contrast, no strain heterogeneity was observed in a rigorous companion finite-element model of the strand unless dimensional variations in the wire diameters were introduced. Our results are in agreement with the hypothesis by Gjelsvik, which states that, within a parallel wire bridge cable, local variations in wire diameter due to manufacturing tolerances can lead to large variations in clamping constraint.
Conference Proceedings of the Society for Experimental Mechanics Series, 2014
Statistical pattern recognition based structural damage detection is often developed exploiting t... more Statistical pattern recognition based structural damage detection is often developed exploiting the methods of outlier analysis. In this context, damage occurrence is assessed by analyzing whether a set of features extracted from the response of the system under unknown conditions departs from the population of features extracted from the response of the healthy system. The metric dominantly used for this purpose is the Mahalanobis Squared Distance (MSD). Evaluation of MSD of a point from a population requires the use of the inverse of the population's covariance matrix. It is known that when the feature dimensions are comparable or larger than the number of observations, the covariance matrix is ill-conditioned and numerically problematic to invert in the former case, while singular and not even invertible in the latter. To overcome this difficulty, three alternatives to the canonical damage detection procedure are investigated: data compression through Discrete Cosine Transform, use of pseudo-inverse of the covariance matrix, and use of shrinkage estimate of the covariance matrix. The performance of the three methods is compared using the experimental data recorded on a four story steel frame excited at the base by means of the shaking table available at the Carleton Laboratory at Columbia University.
The elastic strains induced in the constituent
wires of parallel wire strands under tensile loadi... more The elastic strains induced in the constituent wires of parallel wire strands under tensile loading were measured using neutron diffraction. The elastic strains carried by the individual wires depended very strongly on the boundary conditions at the grips and on radial clamping forces. The friction forces between the wires were quite significant and should not be neglected in analytical or numerical formulations of strain partitioning in parallel wire cables.
The identification of modal parameters has been performed for the New Carquinez suspension bridge... more The identification of modal parameters has been performed for the New Carquinez suspension bridge in California. By using multiple ambient vibration data sets recorded through a wind-motion monitoring system in the bridge, the baseline modal parameters were obtained in order to investigate dynamic behavior of the bridge in operating conditions. For the modal parameters identification, the data-driven stochastic subspace identification technique was implemented. For each data set, the modal parameters for structural modes were estimated by examining the estimation error between measured data and reconstructed one from the identified modes. Based on the results, variability of the identified modal parameters was also investigated.
Journal of Civil Engineering and Architecture, 6(3), 280-299, Mar 2012
This paper aims at investigating the efficacy of different state-of-art damage detection methods ... more This paper aims at investigating the efficacy of different state-of-art damage detection methods when applied to real world structures subjected to ground motion excitations, for which the literature contributions are, at present, still not fully comprehensive. To this purpose the paper analyses two test structures: (1) a four-story scaled steel frame tested on a shake table in a controlled laboratory conditions, and (2) a seven-story reinforced concrete building monitored during the seismic excitations of the 1999 Chi-Chi (Taiwan) Earthquake main shock and numerous fore and aftershocks. Some model based damage approaches and statistics based damage indexes are reviewed. The different methodologies and indexes are, then, applied to the two test structures with the final aim of analysing their performance and validity within the case of a laboratory scaled model and a real world structure subjected to input ground motion.
Page 1. Evaluating the Strength of Suspension Bridge Cables Yuwei Shi Ph.D. Candidate Department ... more Page 1. Evaluating the Strength of Suspension Bridge Cables Yuwei Shi Ph.D. Candidate Department of Civil Engineering Columbia University, New York ys2052@columbia.edu Raimondo Betti Professor Department of Civil Engineering Columbia University, New York ...
This paper presents output-only observer/Kalman filter identification (O3KID), an effective metho... more This paper presents output-only observer/Kalman filter identification (O3KID), an effective method for the identification of the dynamic model of a structure and its underlying modal parameters using only output time histories measured on the field. The method is suitable for structural health monitoring based on modal parameters, in particular, for those civil infrastructures whose excitation is random in nature and in the way that it is applied to the structure (e.g., wind and traffic) and therefore is difficult to measure. O3KID is based on a linear-time-invariant state-space model and is derived from an established and successful approach for input–output system identification, known as observer/Kalman filter identification. The paper rigorously proves the applicability of the approach to the output-only case, presents the resulting new algorithms, and demonstrates them via examples on both numerical and experimental data.
ABSTRACT In this work we focus on experimental studies of polymer-nanocomposites intended for pas... more ABSTRACT In this work we focus on experimental studies of polymer-nanocomposites intended for passive protection of civil structures. The material consists of a polyurea-matrix enhanced by different quantities of multiwalled carbon nanotubes. Several tensile and cyclic tests are performed to evaluate and characterize the mechanical behaviour of this new material. Furthermore, we subject the material to accelerated thermal aging and study its performance deterioration which is fairly unknown. The results on the unaged specimens are intuitive and indicate that an arbitrary amount of CNTs may result in suboptimal performance. More specifically, 1% in weight of CNTs yields the best mechanical performance. However, after a long aging term, our findings are interesting and counterintuitive as these nanocomposites become more brittle and break quickly while the virgin polyurea gives the best performance.
A new methodology to determine the safety of suspension bridge main cables is proposed in this pa... more A new methodology to determine the safety of suspension bridge main cables is proposed in this paper and illustrated on a corrosion-deteriorated cable composed of 9,061 wires. The approach is the first one to use a finite element (FE) model to predict the cable's failure load, to account for load recovery due to friction in broken wires and to simulate the reduced strength of the cable as a three dimensional random field. In order to obtain the cable's failure load, the load is increased gradually, having individual wires break according to their spatially variable random residual strength. Because of the load transfer to surrounding wires, the breakage of an individual wire affects the stress state of its surrounding wires. Consequently, as the load is increased, this local damage spreads to its immediate vicinity and eventually the entire cable fails. Because of the complexity of the problem, the breaking load of the cable is determined through a Monte Carlo simulation approach that accounts for the uncertainty in the spatial variability of the residual strength of the cable's wires. The probability distribution of the load that will drive a suspension bridge cable to failure is provided.
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Papers by Raimondo Betti
wires of parallel wire strands under tensile loading were
measured using neutron diffraction. The elastic strains
carried by the individual wires depended very strongly on
the boundary conditions at the grips and on radial clamping
forces. The friction forces between the wires were quite
significant and should not be neglected in analytical or
numerical formulations of strain partitioning in parallel wire
cables.
wires of parallel wire strands under tensile loading were
measured using neutron diffraction. The elastic strains
carried by the individual wires depended very strongly on
the boundary conditions at the grips and on radial clamping
forces. The friction forces between the wires were quite
significant and should not be neglected in analytical or
numerical formulations of strain partitioning in parallel wire
cables.