Current design of rectangular steel silos: limitations and improvement, Abdelbarr, Mohamed H., Ramadan Osman M. O., Hilal Alhussein, Sanad A. M., and Abdalla Hany A. , 2024, Volume 71, Issue 1, p.77, (2024) AbstractWebsite

This study proposes a modification for the current design approach for square and rectangular silos that accounts for silos’ wall flexibility. First, the authors investigated the effect of wall stiffness symbolized by the wall width-to-thickness ratio (a/t) and silo’s dimensions, on the wall-filling pressure using a recently validated 3D finite element model (FEM). The model was then employed to predict the pressures acting on silos’ walls accounting for the stress state in stored granular materials. Most design formulas and guidelines assume silos’ walls to be rigid. This assumption is acceptable for the case of rigid wall concrete silos; however, it is questionable for semi-rigid, flexible wall metal silos. Consequentially, it is crucial to determine the minimum wall stiffness necessary to secure the applicability of the current design rigid wall assumptions and to propose a way to deal with semi-rigid and flexible walls. To this end, several wall pressure distributions that correspond to filling steel silos with varied wall thicknesses were studied. A new adjustment to the Janssen technique was proposed for a better estimate of the wall-filling pressures for square and rectangular silos. In the case of prismatic silos, the Eurocode uses the Janssen equation together with an equivalent radius of a corresponding circular silo (with the same hydraulic radius) to determine the wall pressure. This method predicts pressure values that are practically accurate for rigid-wall silos, but its accuracy decreases for semi-rigid and flexible-wall silos. As an enhancement, the Janssen equation was modified in this research to generate more accurate pressure estimates based on the equivalent volume concept. The finite element results of several developed models with the same granular material were compared to the estimations of the newly established approach to verify the broad range of its applicability.

An Experimental Investigation for Detection, Localization, and Quantification of Compound Changes in Complex Uncertain Systems, Abdelbarr, Mohamed H., Hernandez-Garcia Miguel R., Caffrey John P., and Masri Sami F. , Journal of Engineering Mechanics, Volume 150, Number 1, p.04023109, (2024) AbstractWebsite

The field of (practical) data-driven approaches that utilize the vibration signature of target systems for developing mathematical models (for computational purposes, control, or anomaly detection for structural health monitoring) is still an active research area, despite the fact that several powerful system identification techniques have been developed in the system dynamics field to analyze such measurements. However, there is still a paucity of comprehensive experimental studies that investigate the range of validity of such identification techniques, particularly those applicable to realistic situations encountered in the structural engineering field, with the focus on detecting, quantifying, locating, and classifying observed changes, especially when there are significant inherent nonlinearities in the reference (undamaged) complex target structure, and where there are unavoidable sources of errors and uncertainties in the measurements and the attendant data analysis procedures. The research team constructed a well-instrumented, reconfigurable test apparatus (resembling a tall building) that allows the introduction of quantifiable levels of composite changes at various locations, orientations, and types of linear and/or nonlinear changes, with the aim of investigating a subset of the aforementioned challenges facing researchers who are interested in assessing the utility of some practical system identification approaches. The primary focus of the identification approach is on a decomposition procedure that is ideally suited for certain types of structures that possess some topological features that can be exploited to enhance the detectability of small changes. A companion paper provides a detailed description of the testbed features and its instrumentation. The present paper focuses on the analysis of some of the very extensive data sets that were created to study the usefulness of some practical dimensionless probabilistic measures that not only provide normalized change indices but also simultaneously attach a confidence level to each of these indices.

Structural Identification and Monitoring of the Light Poles on the Skyway Span of San Francisco-Oakland Bay Bridge, Abdelbarr, Mohamed H., Wahbeh Mazen A., and Masri Sami F. , 8WCSCM, (2022)
Structural Identification of a 52-Story High-Rise in Downtown Los Angeles Based on Short-Term Wind Vibration Measurements, H., Abdelbarr Mohamed, D. Kohler Monica, and F. Masri Sami , Journal of Structural EngineeringJournal of Structural Engineering, 2023, Volume 149, Issue 1, p.05022002, (2023) AbstractWebsite
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Three-Dimensional Finite Element Analysis for Pressure on Flexible Wall Silos, Hilal, Alhussein, Sanad Abdel M., Abdelbarr Mohamed H., Ramadan Osman M. O., and Abdalla Hany A. , Applied Sciences, 2022, Volume 12, Issue 18, (2022) Abstract

A 3D finite element model (FEM) for predicting the distribution of lateral pressure in a square flexible walled steel silo during the filling phase was analyzed in this study. The numerical approach, developed using Abaqus software, predicts the stress state in bulk solids, as well as the pressures exerted on the silo walls. An elasto-plastic model using the Drucker–Prager criterion was employed to simulate the behavior of the granular materials. The FEM simulates the behavior of the bulk solid and its interaction with the silo’s wall and base using a surface-to-surface discretization model. The model’s predictions were validated by previous experimental measurements. The results revealed good agreement between the FEM predictions and the experimental measurements. The research confirms that the lateral pressure distribution is not uniform at any silo level. This highlights the fact that many available theories and current design codes are not accurate for flexible steel walls. As a result of the wall’s deformability, pressure regimes on the silo wall change significantly in the horizontal direction at any level. The results showed that the horizontal variations of lateral pressure change drastically with regard to wall stiffness. The FEM has been used to investigate the effect of critical parameters on wall pressure distribution, such as properties of bulk solids, wall thickness, and silo type, whether deep or flat.

A Re-configurable Testbed Structure for System Identification Studies of Uncertain Nonlinear Systems, Abdelbarr, Mohamed H., Hernandez-Garcia Miguel R., Caffrey John P., and Masri Sami F. , 2022, Volume 20, Issue 8, p.941 - 956, (2022) AbstractWebsite

A comprehensive analytical and experimental study was conducted to investigate and study some challenging problems related to the development of mathematical models and simulations capable of describing accurately the dynamic behavior of distributed, nonlinear systems with uncertain characteristics. A sophisticated, re-configurable test apparatus was designed and built for the investigation of generic types of mechanical components and subsystems including linear, and complex nonlinear phenomena widely encountered in the applied mechanics field. The apparatus was utilized as a major element of a global computer-controlled loop to automatically conduct different physical experiments to collect a statistically significant ensemble of measurements from the system, while its properties were modified. The physical structural properties were automatically adjusted (for each test loop) through a smart adaptive nonlinear component. The performed tests were subsequently used to build different reduced-order and classes of models to gage their utility to provide a better understanding of the physics of the underlying linear and nonlinear changes, and the associated uncertainties involving the model parameters. Thus two different approaches: the nonparametric chain-like system identification approach (ChainID) and a global identification approach (NExT/ERA) were implemented. The results of this study demonstrate that the structural health monitoring approach discussed is capable of accurately detecting, locating, and quantifying structural changes in the monitored systems.

Decomposition Approach for Damage Detection, Localization, and Quantification for a 52-Story Building in Downtown Los Angeles, Abdelbarr, Mohamed H., Massari Anthony, Kohler Monica D., and Masri Sami F. , Journal of Engineering Mechanics, Volume 146, Number 9, p.04020089, (2020) Abstract

Among the most challenging problems in the field of damage detection and condition assessment in large structures is the ability to reliably detect, locate, and quantify relatively small changes in their dynamic response, based on vibration signal analysis. In this study, a substructuring approach, which uses a nonparametric identification method, was applied to simulated damage data from a high-fidelity and validated three-dimensional (3D) finite element model of a 52-story high-rise office building, located in downtown Los Angeles. Results of this study indicate that the approach not only yields identification results that match well-known global (linear) system identification methods, such as NExT/ERA, but it also provides additional benefits that global identification approaches suffer from. These benefits include: (1) enhanced sensitivity to small structural parameter changes, (2) ability to provide location information about the region in the large structure in which damage has occurred, and (3) not assuming that the underlying structure is linear. Thus, the approach is capable of detecting, quantifying, and classifying changes, when they do occur, if the actual building is subjected to strong earthquake ground motion.

Fusing State-Space and Data-Driven Strategies for Computational Shock Response Prediction, Brewick, Patrick T., Abdelbarr Mohamed, Derkevorkian Armen, Kolaini Ali R., Masri Sami F., and Pei Jin-Song , AIAA Journal, Volume 56, Number 6, p.2308-2321, (2018) AbstractWebsite

This paper proposes a state-space-based approach for computational simulation and prediction of shock response for both time histories and shock response spectra. The method operates by developing a nominal model for the system through state-space identification and then modeling the resulting residual through an artificial neural network. The model for the residual is then folded back into the nominal system via Kalman filtering, allowing for forward computational simulation without any measurement information. The proposed identification method is applied to a three-degree-of-freedom system and a high-fidelity finite element model built in Abaqus. The proposed method provides reasonable predictions for time histories of excitations not seen during training or identification and produces useful predictions of the associated shock response spectra.

Color and Depth Data Fusion Using an RGB-D Sensor for Inexpensive and Contactless Dynamic Displacement-Field Measurement, Chen, Yulu Luke, Abdelbarr Mohamed, Jahanshahi Mohammad R., and Masri Sami F. , Structural Control and Health Monitoring, Volume 24, Number 11, p.e2000, (2017) AbstractWebsite

Summary There are numerous applications in the field of structural dynamics that require the accurate measurement of evolving deformation fields. Although there are several sensors for direct displacement measurements at a specific point in a uniaxial direction or multicomponent deformations, there are only very limited, and relatively quite expensive, methodologies for obtaining the 3-dimensional components of a displacement of a dynamically evolving (i.e., not pseudostatically) deformation field. This paper reports the results of a comprehensive experimental study to assess the accuracy and performance of a class of inexpensive vision-based sensors (i.e., RGB-D sensors) to acquire dynamic measurements of the displacement field of a test structure. The sensor was subjected to a broad variety of different dynamic motions of varying amplitude and spectral characteristics and with varying configurations of the position and orientation of the sensor with respect to the target structure. Particular attention was devoted to quantifying the influence of various test conditions, such as amplitude, frequency, sampling rate, spatial distortion, and relationships between the RGB pixel-based measurements and the depth measurements. It is shown that the class of sensors under discussion, when operated under the performance envelope discussed in this paper, can provide, with acceptable accuracy, a very convenient and simple means of quantifying 3-dimensional displacement fields that are dynamically changing at relatively low-frequency rates typically encountered in the structural dynamics field.

Reconfigurable Swarm Robots for Structural Health Monitoring: A Brief Review, Jahanshahi, Mohammad R., Shen Wei-Men, Mondal Tarutal Ghosh, Abdelbarr Mohamed, Masri Sami F., and Qidwai Uvais A. , International Journal of Intelligent Robotics and Applications, Sep, Volume 1, Number 3, p.287–305, (2017) AbstractWebsite

Autonomous monitoring of infrastructure systems offers a promising alternative to manual inspection techniques which are mostly tedious, expensive and prone to error. Robot-based autonomous monitoring systems not only provide higher precision, but they also allow frequent inspection of infrastructure systems at a much lower cost. Recent advancements in robotic systems have led to the development of reconfigurable swarm robots (RSR) that can change their shape and functionality dynamically, without any external intervention. RSR have the advantages of being modular, on-site reconfigurable, multifunctional, incrementally assemble-able, reusable, fault-tolerant, and even repairable on the orbit. Newly-developed reconfigurable robots are expected to bring a radical change in the prevailing structural health monitoring techniques, thus augmenting the efficiency, accuracy and affordability of inspection operations. This paper presents a holistic review of the previous studies and state-of-the-art technologies in the field of RSR, and argues that RSR offer great potential advantages from the perspective of monitoring and assessment of civil and mechanical systems. A roadmap for future research has also been outlined based on the limitations of the current methods and anticipated needs of future inspection systems.

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