Mohammed M. Ettouney

Structural Health Monitoring as a Bridge Management Tool

Bridge management main tenets are ensuring safety while minimizing costs. Some of the procedures that are used to achieve these tenets are inspection, maintenance, and repair. There are numerous qualitative and quantitative tools that aid management of bridges. Structural health monitoring can aid in several aspects of bridge management, such as reducing inspection costs while improving quality, prioritizing repair/maintenance schedules, and increasing accuracy of both deterioration estimations and the decisionmaking process. This paper briefly describes the possible role structural health monitoring can play in bridge maintenance and management aspects.

SOME PRACTICAL APPLICATIONS OF THE USE OF SCALE INDEPENDENT ELEMENTS FOR DYNAMIC ANALYSIS OF VIBRATING SYSTEMS

Abstract Discrete deterministic methods such as finite elements offer great flexibility in analyzing the dynamic response of vibrating systems. However, these methods can easily grow beyond available computer resources as frequencies of interest grow higher. In this paper we present a new approach for the frequency domain dynamic analysis of structures. A theory is developed for the analysis of systems which are uniform along a single coordinate axis, but otherwise arbitrary in geometry and material composition. This approach, termed the scale independent element, is shown to be an accurate, efficient and general method for the analysis of vibrating systems. This technique extends the applicability of discrete deterministic finite element based modeling to higher frequencies and is capable of bridging the gap to frequency regimes where statistical energy methods become applicable.

Development of An Analytical Database to Support a Fast Running Progressive Collapse Assessment Tool

Rapid assessment of structures for vulnerability to progressive collapse has become a major concern in today’s world environment. Homeland Security and Overseas U. S. government agencies need the ability to quickly, and realistically, evaluate buildings to determine the risk of progressive collapse and understand how proposed retrofits would improve the building risk. To support the development of a fast running assessment tool, a series of simplified finite element simulations were conducted to generate a response data base. Models of simplified concrete and steel frames were run under gravity collapse conditions to determine displacements, forces and moments transmitted to adjacent structural members. The simulations were performed using Weidlinger Associates’ FLEX finite element code. This paper will discuss the salient issues involved in the nonlinear, dynamic modeling of progressive collapse. The FLEX modeling used to develop the data base and confirm expected response is also described in detail. Finally, the simplified analytical tool that was developed from the simulation data base development effort will be described.

Theory of multihazards for bridge structures

Multihazard consideration for infrastructure applications is gaining popularity due to the anticipated overall cost reduction it offers while maintaining the needed safety levels. This approach considers increasing the complexity of the structural systems to meet the demands of the current environment and takes advantage of the recent developments and innovations in computing, analytical, and sensing technologies. However, at present, no quantitative methods have been developed to fulfill such a promise. This paper discusses the need for multihazards considerations in infrastructure applications and provides a quantitative approach to multihazards considerations. A general theory of multihazards in infrastructure is introduced and applied to structural analysis, design, life cycle costing, risk assessment, and structural health monitoring. In all, groundwork is laid for quantification of multihazards considerations. Utilization/furthering of such quantitative treatment of multihazards theory in these fiel...

Blast Load Effects on Highway Bridges. I: Modeling and Blast Load Effects

AbstractNumerous terrorist events during the last decade, including the 2001 attack on the World Trade Center, have heightened concern about the safety of bridges during intentional/unintentional blast load effects. Analysis of highway bridges under blast loads requires accurate generation and application of blast loads and good understanding of the behavior of components of a bridge during high strain rate loading encountered during blast loads. In this paper, a new approach for the application of blast loads on bridge components has been presented. This approach can apply realistic loads and can simulate both reflection and diffraction of blast loads. Using this approach, verification of simulation of blast loads in LS-DYNA has been carried out by using available blast tests on two types of beams. A high fidelity model of a typical three-span highway bridge has been developed for investigation of blast load effects on a three-span reinforced concrete bridge. It is observed that the range of demands impo...

Health monitoring of complex structures

A basic step in the monitoring of health of any structure is detection of damage levels and location of the damage in the system. Several damage detection schemes have been proposed in recent years. Published applications of these methods are typically for simplified models of realistic structures. This leaves open the question of the accuracy and efficiency of the available damage detection methods when applied to large and complex structural models. This paper will investigate the accuracy of different damage detection techniques to complex structural models. A typical multi- jointed steel bridge, which is damaged by cracks of different sizes, is considered. The damage will be simulated analytically in the structural model, and the damage detection algorithms will be applied to both the damaged and the undamaged structures. Three damage detection algorithms are investigated, namely the change of stiffness, the change of flexibility and the damage index methods. Some modifications and extensions of the change of stiffness and change of flexibility methods were incorporated in this study. These extensions helped inaccurate comparisons between different methods. It was found that all three algorithms produced adequate damage detection results. More analytical studies are recommended. Also, experimental testing for complex structures is recommended.

Blast Load Effects on Highway Bridges. II: Failure Modes and Multihazard Correlations

AbstractBridges with different seismic design levels and concrete compressive strengths have been analyzed for three levels of underdeck blast loads. It is observed that there are several other damage modes besides failure of bridge columns that may contribute to a complete collapse of the bridge. In general, it is demonstrated that an increased seismic resistance leads to improved performance during blast loads. Both concrete strength and seismic capacity are equally effective for bridges designed with higher seismic resistance. Extensive simulations have been performed to establish a correlation between the ratio of ductility and strength reduction factor, μ/R, and pier top displacement for concrete with different compressive strengths. It has been observed that the pier top displacement decreases drastically for μ/R>6. Moreover, it is observed from results of 27 simulations that bridge piers with μ/R>6 survive high levels of blast loads (without failure of piers).

Long-term Issues Related to Structural Health of FRP Bridge Decks

Use of FRP bridge decks has been steadily increasing over the past few years, because of the several long-term benefits they offer over conventional materials such as steel and concrete. These benefits include low weight, anticipated long-term durability with low life-cycle costs, and increased corrosion resistance. There have been several experimental and analytical studies to investigate the behaviour of FRP bridge decks, but an integrated study covering their structural health issues is not available. This paper identifies issues related to FRP decks requiring further attention, and then utilizes Structural Health in Civil Engineering (SHCE) concepts to identify steps for future research. Materials, design, manufacturing, erection, transportation, inspection, and maintenance aspects as well as capacity vs. demand and component vs. system considerations are discussed in an integrated fashion. This study also shows the interaction and inter-dependability between various parameters and the FRP deck respon...

Automated analysis of long-term bridge behavior and health using a cyber-enabled wireless monitoring system

A worthy goal for the structural health monitoring field is the creation of a scalable monitoring system architecture that abstracts many of the system details (e.g., sensors, data) from the structure owner with the aim of providing “actionable” information that aids in their decision making process. While a broad array of sensor technologies have emerged, the ability for sensing systems to generate large amounts of data have far outpaced advances in data management and processing. To reverse this trend, this study explores the creation of a cyber-enabled wireless SHM system for highway bridges. The system is designed from the top down by considering the damage mechanisms of concern to bridge owners and then tailoring the sensing and decision support system around those concerns. The enabling element of the proposed system is a powerful data repository system termed SenStore. SenStore is designed to combine sensor data with bridge meta-data (e.g., geometric configuration, material properties, maintenance history, sensor locations, sensor types, inspection history). A wireless sensor network deployed to a bridge autonomously streams its measurement data to SenStore via a 3G cellular connection for storage. SenStore securely exposes the bridge meta- and sensor data to software clients that can process the data to extract information relevant to the decision making process of the bridge owner. To validate the proposed cyber-enable SHM system, the system is implemented on the Telegraph Road Bridge (Monroe, MI). The Telegraph Road Bridge is a traditional steel girder-concrete deck composite bridge located along a heavily travelled corridor in the Detroit metropolitan area. A permanent wireless sensor network has been installed to measure bridge accelerations, strains and temperatures. System identification and damage detection algorithms are created to automatically mine bridge response data stored in SenStore over an 18-month period. Tools like Gaussian Process (GP) regression are used to predict changes in the bridge behavior as a function of environmental parameters. Based on these analyses, pertinent behavioral information relevant to bridge management is autonomously extracted.

Global Instability Induced Failure of Tall Steel Moment Frame Buildings

AbstractThis paper examines the behavior of steel moment frames under the scenario of a column removal at their ground floor. Through a material and geometric nonlinear analysis, this work evaluates a global loss-of-stability progressive collapse mode for steel frames. This collapse mode appears while the components of the structure remain in the elastic zone and involves the loss of stability of the structure. The results of the analysis show that after the removal of the column, the appearance of limited fiber yielding of the components of the structure can progressively lead to the loss of stability and the collapse of the entire structure. The main contribution is the identification of the global loss-of-stability progressive collapse mode through the production of pushdown curves. The work focuses on the need to analyze a structural system as a whole, rather than as individual components, during a progressive collapse analysis.