Structural Control and Health Monitoring

Gattulli, Vincenzo; Potenza, Francesco; Spencer, Billie F.

doi: 10.1002/stc.2167pmid: N/A

Design criteria for a visco‐elastic connection of two simple oscillators under seismic excitation are proposed. The dissipative connection is described by Kelvin–Voigt rheological model. The features of the selected criteria are explored for the system parameter set based on the analytical solutions of the associated eigenvalue problem and to the closed‐form solutions of the stochastic system response. Design maps are drawn in the nondimensional space of the relevant system parameters in which a direct comparison of the obtained design values is possible. Furthermore, performance indices are used to assess the response of the two simple coupled oscillators subject to natural excitation to demonstrate the robustness with respect to nonstationary excitation.

Wang, Da; Liu, Yongming; Liu, Yang

doi: 10.1002/stc.2179pmid: N/A

Spatial and temporal temperature variations are critical for the accurate stress analysis of a suspension bridge with a steel–concrete composite deck system. This issue has been widely investigated in recent years in the open literature. In current codes, only the vertical temperature gradient (VTG) is considered in the thermal stress calculation. A complete 3D temperature profile has rarely been investigated. In the proposed study, the Aizhai Suspension Bridge with a steel–concrete composite deck system in China was investigated to determine the realistic 3D temperature‐gradient distributions and their effects on the structural performance using a finite element method. First, the distributions of the spatial‐temperature gradient including the VTG, the transversal temperature gradient (TTG), and the longitudinal temperature gradient (LTG) were investigated based on a structural health monitoring system. The results showed that the values of these gradients were far greater than those suggested by the Chinese code. Next, a 3D finite element model was proposed to investigate the thermal stress variation in the steel–concrete composite bridge deck system. The thermal‐induced stresses due to the VTG, TTG, and LTG were obtained using the monitored temperature data and the proposed 3D finite element model. The coupling effects of the 2D (coupling of the VTG and TTG) and 3D (coupling of the VTG, TTG, and LTG) temperature gradients were obtained and compared with those of the 1D approximation and Chinese code. Possible reasons for the 3D temperature‐gradient effect were also discussed. Following this, conclusions and recommendations for future bridge analysis and design were provided based on the proposed study.

Gaebler, Karl O.; Hedegaard, Brock D.; Shield, Carol K.; Linderman, Lauren E.

doi: 10.1002/stc.2182pmid: N/A

Large‐scale, long‐term structural health monitoring systems have become more feasible in recent years as the required data acquisition and analysis systems are more affordable to deploy. These long‐term systems must process and store vast amounts of data without wasting computational power and storage capacity with redundant or poor quality data. While not a primary system for damage detection, large‐scale, long‐term vibration monitoring systems aim to leverage changes in the dynamic signature of a structure to assess global structural changes. Although the ability to continually collect vibration data at high rates exists, it is not always feasible to store all these data long term. As more long‐term monitoring systems are deployed, efficient methods need to be developed to quickly and efficiently analyze large quantities of vibration data so that only the most pertinent information is archived. Previous researchers have used scheduled approaches, eg, taking data every hour, or triggered sensing systems. A monitoring system on the I‐35W St. Anthony Falls Bridge, which crosses the Mississippi River in Minneapolis, Minnesota, has been collecting vibration and temperature data since the structure's opening in 2008. This provides a uniquely large data set to establish the characteristics of a good signal for output‐only system identification to consistently and efficiently capture natural frequencies and mode shapes. To this end, a system identification routine using a novel signal selection approach and modal sorting routine that leverages NExT‐ERA/DC is proposed to analyze this large data set. The resulting information allows long‐term and temperature‐based trends to be identified.

Gebai, Sarah; Hammoud, Mohammad; Khachfe, Hassan

doi: 10.1002/stc.2177pmid: N/A

Passive absorbers are designed to be attached to upper limb systems to reduce tremor of patients suffering from Parkinson's disease. Several works were done previously to show the effectiveness of the low cost passive controllers, which can reduce the undesired vibrations without power requirements. An improved type of such controllers is suggested in this paper. The mechanical absorber is a two‐degree‐of‐freedom (DOF) system, which is formed by an elastic absorber connected in series to a viscous damper one, naming the system the Series Elastic Viscous Damper (SEVD). It was able to cause a high reduction in the amplitude of the tremor and operate over a wide frequency range. The lumped parameters of each absorber within the SEVD absorber are chosen to satisfy the tuning conditions. The device is tested numerically on the forearm of a biodynamic upper limb structure to check its capability in reducing the tremor at the limb's proximal joints. The limb was modeled as rigid segments with a three DOF flexion‐extension angular motion in the horizontal plane. This study seeks to analyze the effect of the SEVD damping coefficient, total mass, and mass distribution on the reduction of the displacement amplitude at the joints, with stiffness chosen to satisfy the tuning condition for the undesired frequency of tremor. It was found that very low damping coefficients are not suitable to provide reduction at all joints simultaneously; high absorber's total mass can slightly increase the performance and equally, distributed dual masses can be a good selection.

Singh, M.P.; Elbadawy, M.Z.; Bisht, S.S.

doi: 10.1002/stc.2181pmid: N/A

It has been a common practice to utilize measured linear acceleration responses for structural health monitoring primarily because it is perhaps easiest to collect data on these. This paper, on the other hand, is focused on the utilization of measured strain responses as they provided more complete and useful information for health monitoring, especially for structural frames. The measured strain responses are used to extract strain mode shapes and frequencies of the system using the well‐known Stochastic System Identification or NExT‐ERA algorithms. The extracted strain mode shapes and frequencies are then utilized to identify the element stiffness characteristics using a two‐step pseudoinversion approach. The first pseudoinversion step involves the calculation of the least squares estimates of the system mode shapes from the strain mode shapes followed by the second step of calculating the element stiffness values again by second pseudoinversion using single or multiple system modes. Numerical results are presented to examine the effects of the two inversion steps, the utilization of single and multiple modes, and the measurement error on the accuracy of the calculated stiffness values and on the identification of the damaged elements. It is observed that in framed structures with asymmetric configuration of structural elements, it may be necessary to use multiple modes with optimally selected mode contributions factors to accurately identify the damage levels and locations. The proposed approach is seen to work very well in identifying the locations and levels of damage in multiple structural elements in a frame.

Keshtegar, Behrooz; Etedali, Sadegh

doi: 10.1002/stc.2163pmid: N/A

A novel adaptive dynamic harmony search (ADHS) algorithm is proposed based on the dynamical parameters that are adjusted using the previous results of the harmony memory with a simple formulation. The accuracy and efficiency of ADHS algorithm are compared with the several improved versions of harmony search through mathematical benchmark examples. The optimum design database of tuned mass damper (TMD) parameters for a damped main system under white‐noise base excitation is extracted by the ADHS algorithm for applicable engineering problem. Four mathematical models are calibrated using the nonlinear training approach‐based ADHS for approximating the optimum tuning TMD parameters. By considering the root mean square error and confidence index, a best nonlinear model is selected among the proposed models using ADHS training scheme and several existing empirical models. A 10‐story benchmark structural example under earthquake excitation is considered for validation of the proposed nonlinear model. The simulation results demonstrate that the ADHS provides more accurate and efficient results than the improved harmony search algorithms for mathematical benchmark examples. The proposed nonlinear model also performs with the efficient computational burdens compared with the optimization algorithms for optimum tuning of TMD parameters of a 10‐story structure, more accurately.

Amarante dos Santos, Filipe; Leitão, Cláudio

doi: 10.1002/stc.2186pmid: N/A

The present paper provides an innovative insight into the design of column–base connections, for steel moment resisting frames, with superelastic shape‐memory alloy cables. The proposed strategy is to prevent damage in these connections due to the rotation demands associated with seismic events, by using lateral restraining cables working in phase opposition. A simplified experimental prototype of the proposed connection is tested, under several loading scenarios, proving to be a versatile solution in terms of rotational stiffness, with significant energy dissipating features and re‐centering capabilities. A series of numerical simulations are also performed, providing a clear evidence of the good seismic performance of the proposed superelastic connection in real‐scale civil engineering structures.

doi: 10.1002/stc.2097pmid: N/A

No abstract is available for this article.

Kijanka, Piotr; Staszewski, Wieslaw J.; Packo, Pawel

doi: 10.1002/stc.2172pmid: N/A

The paper presents an efficient and exact method for the calculation of excitability curves and for the analysis of numerical models for guided waves. The proposed procedure makes use of the wave equation and through‐thickness‐only discretisation of anisotropic, layered plates to obtain the Lamb wave amplitude characteristics. Thereby, the method can be used for any arbitrarily selected anisotropic (layered structures, such as composites) material in a straightforward manner. A general framework for the proposed analysis is given, along with application examples. For this purpose, orthogonality conditions based on the reciprocity theorem are derived for the numerical model. Although the developed mathematical framework is verified and application examples are given based on the local interaction simulation approach for elastic waves propagation, the proposed methodology can easily be adopted for other numerical methods (eg, finite elements and cellular automata for elastodynamics). The method can also be used to study the influence of discretisation parameters on excitability curves estimates.

Chen, Yulu Luke; Abdelbarr, Mohamed; Jahanshahi, Mohammad R.; Masri, Sami F.

doi: 10.1002/stc.2198pmid: N/A