The monitoring of dams represents an important task in the management of hydroelectric systems. Their economic, social and environmental value imposes to know well the real behavior of the structure and its foundations. This paper shows in two practical cases the possibility to improve the quality of deformation measurements by an appropriate fiber optics sensor network. The first case is a study showing the technical and economical feasibility to install an extended, spatial fiber optics deformation sensor network to detect the relative deflection of an entire shell dam. At this purpose of theoretical study has been evaluated on the base of typical load situations with their effective deflections on the Schiffenen dam, a shell-shaped concrete structure near Fribourg. The second case concerns the development and realization of two long fiber optics deformation sensors anchored in the rock to monitor the displacement of the dam relatively to its underground. These sensors have been installed in the Emosson shell dam.

Recent advances in smart materials and structures sensor technology offer many unique opportunities to assess the structural integrity of large civil structures. However, the remote operational environment of large civil structures such as highways, buildings, and bridges, makes condition- based health monitoring for damage assessment difficult in the event of a natural disaster. During such disasters, electrical power is lost and cellular phone lines are under heavy usage. This limits the retrieval of very important sensor data. However, recent rulings by the Federal Communication Commission coupled with advances in wireless communication products has now made it possible to circumvent existing wired and cellular infrastructure to retrieve data from smart sensors remotely and more economically. This paper discusses a novel approach using smart sensors and wireless communication technology to monitor the health of large civil structures remotely. Specifically, a remote health monitoring system for large civil structures is developed using spread spectrum wireless modems, data communication software and conventional strain sensors. This system is used to monitor the loads on a laboratory test specimen with a bolted lap joint from as far away as one mile. Commands are issued from a notebook personal computer to instruct the health monitoring system to either excite the structure or acquire data from sensors mounted externally to the structure. Data from measurements made on the structure are then transmitted wirelessly back to a notebook computer for processing and analysis. The state of damage in the structure is assessed using modal system identification and damage detection algorithms.

The bridge Weigh-In-Motion (WIM) system uses bridge structures as weigh scales to measure axle and gross vehicle weights and vehicle configurations without stopping or detouring the vehicles. Because the system is mobile and is almost invisible to the truck drivers, it can be used to collect unbiased traffic data for transportation and loadometer study. The WIM + RESPONSE system, which is an expansion of the original WIM system, was developed to collect additional bridge response data and perform bridge structural evaluation. These additional bridge response data provide bridge engineers with information necessary for improving bridge design and evaluation procedures. Bridge health monitoring and damage detection may also be conducted with long term installation of the WIM + RESPONSE system. This paper discusses what has been achieved by the WIM + RESPONSE system and how the system can be further improved to enhance its functions in a smart bridge.

The intent of bridge management systems is to help engineers and managers determine when and where to spend bridge funds such that commerce and the motoring public needs are satisfied. A major shortcoming which states are experiencing is the NBIS data available is insufficient to perform certain functions required by new bridge management systems, such as modeling bridge deterioration and predicting costs. This paper will investigate how modal based nondestructive damage evaluation techniques can be integrated into bridge management using quality management principles. First, quality from the manufacturing perspective will be summarized. Next, the implementation of quality management in design and construction will be reinterpreted for bridge management. Based on this, a theory of approach will be formulated to improve the productivity of a highway transportation system.

Self-healing concretes have embedded adhesives which are released from hollow fibers inside the concrete when and where cracking of the matrix and the fibers occurs. It was found that the adhesive improves the strength of the cracked portions of the concrete and increases its ability to deflect under load. Structural materials subjected to dynamic events such as earthquakes and impacts can have improved response by the noise of adhesive type which can impart improved damping, lateral stiffness, or deflection. Testing also assessed the improvement of the bond strength in structures. In laboratory tests the internal adhesive repair system improved the bond between the reinforcing steel and the concrete to prevent pullout failure or debonding at the interface.

In 1996, our laboratory fitted a highway bridge near Geneva with more than 100 low-coherence fiber optic deformation sensors. The Versoix Bridge is a classical concrete bridge consisting in two parallel pre-stressed concrete beams supporting a 30 cm concrete deck and two overhangs. To enlarge the bridge, the beams were widened and the overhang extended. In order to increase the knowledge on the behavior between the old and the new concrete, we choose low- coherence fiber optic sensors to measure the displacements of the fresh concrete during the setting phase and to monitor its long term deformations. The aim is to retrieve the spatial displacements of the bridge in an earth-bound coordinate system by monitoring its internal deformations. The curvature of the bridge is measured locally at multiple locations along the bridge span by installing sensors at different distances from the neutral axis. By taking the double integral of the curvature and respecting the boundary conditions, it is then possible to retrieve the deformation of the bridge. The choice of the optimal emplacement of the sensor and the sensor network are also presented.

The Moesa railway bridge is a composite steel concrete bridge on three spans of 30 m each. The 50 cm thick concrete deck is supported on the lower flanges of two continuous, 2.7 m high I-beams. The bridge has been constructed alongside an old metallic bridge. After demolishing this one, the new bridge has been slid for 5 m by 4 hydraulic jacks and positioned on the refurbished piles of the old bridge. About 30 fiber optic, low-coherence sensors were imbedded in the concrete deck to monitor its deformations during concrete setting and shrinkage, as well as during the bridge sliding phase. In the days following concrete pour it was possible to follow its thermal expansion due to the exothermic setting reaction and the following thermal and during shrinkage. The deformations induced by the additional load produced by the successive concreting phases were also observed. During the bridge push, which extended over six hours, the embedded and surface mounted sensors allowed the monitoring of the curvature variations in the horizontal plane due to the slightly uneven progression of the jacks. Excessive curvature and the resulting cracking of concrete could be ruled out by these measurements. It was also possible to observe the bridge elongation under the heating action of the sun.

In reinforced concrete structures, steel reinforcing bars (rebars) corrode with time and thus reduce their life span. Composite rebars can be used in lieu of steel rebars to overcome this problem. The conventional composite rebars designed to take tensile force are composed of unidirectional fibers in a resin matrix, and are linearly elastic till failure; thus providing a brittle behavior. The problems of corrosion and brittle behavior can be solved by using a composite rebar which fails gradually under tension. The rebar consists of a hybrid composite system in conjunction with helical fibers. The hybrid system gives the rebar its initial stiffness and enables pseudo-yielding at lower strains. As the strain increase, the load is gradually transferred from the hybrid core to the helical fibers, which enables the rebar to undergo large elongations before failure. Embedded fiber optic sensors in the rebar can be used for health monitoring over a long period of time. The proof of concept and preliminary test results are described in the paper.

Intrinsic Fabry-Perot optical fiber sensors were attached to a steel girder of the Sungsan Bridge which is one of the longest span bridges in Han River in Seoul, Korea. The tests were performed as parts of safety diagnosis of the bridge. We performed the visual inspection first, then we chose three spans for System Identification of the bridge. We applied numbers of strain gauges, acceleration sensors and a deflection gauge as well as optical fiber sensors. Static and dynamic loads were applied to the bridge with 30 ton weigh trucks. The optical fiber sensor system showed good responses to the static and dynamic loading with a resolution of approximately 0.12 (mu) strain. In conclusion,the optical fiber sensors can be used as elements of bridge monitoring system.

We report on applications of surveillance and test systems for civil engineering structures. The system key elements are optical-fiber Bragg grating sensors and conventional resistance strain gauges. A recently built stay cable bridge with a world novelty of two carbon-fiber-reinforced-polymer cables was equipped with both types of sensors. The sensor system on the bridge is now operational for ten months and the bridge is open for traffic for 4 months. Results of the bridge surveillance are presented. To monitor a large concrete structure, the electrical power dam of Luzzone in the Swiss Alps, a prototype sensor rod was designed. First measurements with a sensor rod embedded in a concrete test prism are discussed. Several redundant measurements are made to compensate for temperature drift and to monitor the reliability of the measurement chain.

We describe the monitoring of the dynamic strain response of an in-service I-10 interstate bridge due to traffic loading. FBG sensors were attached to the center support girder of one span of the structure. Using a fiber Bragg grating interrogation system based on a wavelength division multiplexer, the sensors were monitored for various vehicle loading conditions.

In recent years tapered beams become increasingly popular in continuous frame construction due to their efficient utilization of structural material. Although analysis and design methods have been presented by many authors and three experimental programs have been carried out in recent years, further studies and design recommendations are needed. One of the ways to optimize structural components subjected to lateral loads is to generate variable cross sections.Ideally, if all sections must process the minimum amount of required properties then individual sections will be unique for particular loading conditions thus, consequently extremely expensive to construct. In this study, the mathematical formulation and the computer implementation of the elastic stability analysis of doubly symmetric tapered beams are presented. Solutions in the form of tables, charts and approximate formulas for the lateral buckling load are presented for a variety of beam geometry, end restraints and loading conditions. THe critical loads corresponding to various buckling modes are plotted versus non-dimensionalized parameters in an effort to establish the parameter ranges at which local buckling or lateral- torsional buckling controls. Since it is practically impossible to non-dimensionalize the many parameters in tapered sections, solutions were obtained for a range of tapered members used in present-day practice. The loading consists of uniform contribution bending loads. The end restraints are applied at the end of the columns with fixed pinned, roller and pinned connections.

Cable-stayed bridges have been known since 18th century with aesthetics design. The structural system and the structural behavior are significantly different from those of continuous bridges. Compared to continuous bridge, cable- stayed bridges have more flexure bridge deck than those of continuous bridges.On the other hand, cable-stayed bridges have less stiffness to resist wind loading especially for lateral loads. The first considering of bridge engineering is safety. In 1940's, Tacoma Narrows Suspension Bridge destroyed by wind loading is a good example even though it is not a cable-stayed bridge. After the bridge was destroyed, a lot of research articles have been published regarding cable supported bridge subjected to wind loading. In recent days, high strength materials have been served. The bridge engineers use the advantages to expand the span length of cable-stayed bridges. Due to the span length increased and the use of high strength materials, cable- stayed bridges have more significant nonlinear behavior subjected to wind loading. In this paper, a slice bridge deck of cable-stayed bridge connected to internal support cables is considered. The deck has been considered to be subjected to lateral static wind loading. Since cables can not take compressive force, the deck has strongly nonlinear behavior even though the materials are linear elastic. Several primary load combinations have ben considered in this paper such as the bridge deck supposed to be moved horizontally without rotation or the bridge deck supposed to be moved horizontally with rotational deformation. The mathematical formulas and the numerical solutions are found and represented in graphical forms. The results can be provided to bridge designers and researchers for further study of this type of structure subjected to wind loading.

It is common practice in applied mechanics to develop finite element models for mechanical system behavior. Most structural integrity monitoring techniques, proposed to date, rely on an accurate model of the structure at hand. In many situations the structure being monitored is already built; in those cases, it is good engineering practice to ensure that the finite element model matches the behavior of the physical structure. However, no general-purpose technique exists or formally, statistically judging the quality of the finite element model. This paper applies a formal statistical procedure for the validation of finite element models of structural systems, when data taken during operation of the system are available. The statistical validation procedure is based on the bootstrap, and it seeks to build a tool for assessing whether or not a finite element model is an acceptable representation of the structure. The approach uses experimental data to construct confidence bounds that permit the assessment of the model. The case of a finite element model of an aluminum plate is presented.

A global damage detection method for civil engineering structures is proposed. This method provides the capability of determining the reduction in both stiffness and damping parameters of the structural elements. The proposed method uses the state-space representation of the structural dynamics to make the diagnosis of structural integrity. Given that the state-space representation of any system is not unique, the damage detection procedure is developed for the physical coordinates of the state-space representation. A transformation matrix to get any arbitrary state-space representation into the physical coordinates is also utilized. The feasibility of the proposed method is verified on a numerical example as well as on a simulated three-bar truss structure with 3 degrees of freedom.

This paper presents the work we have done on a health monitoring technique called active non-destructive evaluation (ANDE) for detecting delaminations in full-scale C-channel structural elements of glass-fiber reinforced polymer (GFRP) composites using active ferromagnetic tagging. Conventional non-destructive evaluation methods are not very effective in monitoring the material conditions of GFRP composite and adhesive joints. A technology that has been proposed to enhance inspection of such non-conductive and non-magnetic GFRP composites is the particle tagging technique. This technique, previously demonstrated on small scale laboratory samples is being developed for full-scale C-channel composite elements. This technique relies on comparing changes in local-area mechanical properties of the structure to identify delaminations. Unlike conventional passive tagging NDE inspection, our technique uses an electromagnetic exciter to interrogate tagged composites over a broad frequency range. As the vibration excitation approaches the resonant frequency of the area of the disbondment, the response amplitude obtained for a given force input increases. Therefore, at frequencies around the transverse resonance of the layer above a defect, the response for a given force will be greater than the response in flawless regions of the structure. Thus, the ANDE test may be based on response measurements alone. The technique is most sensitive if excitation is applied at the plate resonant frequency. Since this frequency is dependent on defect size and depth, a broad band of frequencies must be covered. A laser Doppler vibrometer is a high-sensitivity, high-speed and non-contacting instrument used for detecting surface vibrations. The frequency response curves are obtained using a fast Fourier transform signal processor. An algorithm based on training a neural network to detect significant differences between healthy and damaged structures is then applied to recognize delaminations in full scale structural elements. This method provides the fundamental technology needed for developing a commercial system to monitor the integrity of composite structures, both during manufacturing and during their lifetime as structural elements.

This paper addresses the issue of localizing and quantifying damage using changes in the vibrational characteristics of structures. The method considers the mode shapes of the structure pre- and post-damage measured via modal analysis. Values of the modal shapes are used to compute the strain energy distribution in the structural elements. Using the assumption that the element modal strain energy is the same pre- and post-damage, and characterizing the damage as a scalar quantity of the undamaged stiffness matrix, an expression is obtained for element damage factors that quantify the magnitude of the damage for each mode shape. Due to numerical instabilities in the computation of this expression, filters are applied that overcome some of the instabilities but reduce the true amplitude of damage. The modified-filtered expression was very effective in localizing the actual damage. After localization, the magnitudes of damage are computed using the original unfiltered expression. The method is tested using experimental data from a 3D scale model of a space structure, subjected to 18 different damage scenarios. The damage forms consist of a 180 degree cut (Type I), a 50 percent reduction of the area over one-third the element length (Type II), and a complete cut through the element section (Type III). These types of damages correspond to magnitudes of (alpha) equal to -0.17, -0.5, and -1.0 respectively. The method is ale to detect Type I damage for only one of four cases, Type II for all the three cases and Type III damage for all single and double-location cases, excluding the cases that involves a damage insensitive element.

The objective of this paper is to develop appropriate nondestructive damage detection algorithms for 2D plates. Two methods, one using the coal compliance and the other using local modal strain energy, are presented and compared in this paper. The compliance method is derived simply from the governing differential equations of motion presented in the classical plate theory. The second method is developed from expressions for the elastic strain energy of a plate. A damage index, used to indicate local damage, is defined and expressed in terms of modal displacements that are obtained numerically from mode shapes of the undamaged and the damaged structures. The possible damage locations in the structure are determined by the application of damage indicators according to previously developed decision rules. The damage indices, which are obtained for each mode, are transformed to probability space and superposed as weighted general means (WGM). In the WGM, the fraction of modal energy for the element is used as the weight of each mode. Each of the two methods is demonstrated by using a numerical example of a simply supported plate with simulated damage. Finally, the relative performances of the two methods are compared.

The objective of this paper is to apply and evaluate the relative performance of classification algorithms for nondestructive damage detection (NDD). The classification algorithm are obtained form various forms of Baye's Rule. An established theory of damage localization, which yields information on the location of the damage directly form changes in mode shapes, is selected. Next, the application of classification is performed to the existing theory of damage localization. Expressions for the classification algorithms using the damage indicator functions from the damage localization theory are generated. Criteria for the evaluation of the proposed classification algorithms are then generated. Using the classification algorithms, damage localization is attempted in a numerical model of a 3D truss structure which contains simulated damage at various locations. Finally, the accuracy and reliability of the classification algorithms is evaluated using the established criteria.

A methodology to identify a baseline modal model of a complicated 3D structure using limited structural and modal information is experimentally examined. In the first pat, a system's identification theory for the methodology to identify baseline modal responses of the structure is outlined. Next, an algorithm is designed to build a generic finite element model of the baseline structure and to calibrate the model by using only a set of post-damage modal parameters. In the second part, the feasibility of the methodology is examined experimentally using a field-tested truss bridge for which only post-damaged modal response were measured or a few vibration modes. For the complex 3D bridge with many members, we analyzed to identify unknown stiffness parameters of the structure by using modal parameters of the initial two modes of vibration.

For the seismic design of steel framed structures the randomness in yield strength due to different origins is an important aspect in view of the structural regularity, because the energy dissipation capacity should be shared by possible plastic hinges distributed as uniformly as possible over the structure. In this study the influence of the randomness in yield strengths on the energy dissipation capacity of steel framed structures represented as behavior factors is investigated with 7 steel framed models. Also 4 artificial accelerograms simulated with a given spectrum are applied to check the randomness in seismic inputs. To execute numerous time-step calculations for the investigation a time-step analysis method is developed and applied to determine the action effects after the reliability estimation.

Nondestructive damage testing (NDT) techniques yields the damage location and its size, from the modal characteristics of a pre-damaged and post-damaged structures. To predict the system reliability of the aging structure, results from NDT are integrated into the element/component failure probabilities. The element/component failure probabilities can be calculated from failure functions for each element/component with the aid of techniques from structural reliability analysis. In this paper, a method to estimate the system reliability of a structure, based on the reliabilities of elements/components in a given structure, is presented. A simple rigid frame subjected to random vertical and horizontal loads is investigated to demonstrate the proposed method.

Base isolation provides a very effective passive method of protecting the structure from the hazards of earthquakes. The proposed smart isolation system combines the laminated rubber bearing with the device made of shape memory alloy (SMA). The constitutive law for superelastic materials is extended to describe a hardening of the stress-strain relation of SMA at large strain levels. The smart base isolation utilizes the different response of the SMA at different levels of strain to control the displacements of the rubber bearing at various excitation levels. At the same time the hysteresis of the alloy is used to increase the energy dissipation capacity. The performance of the smart base isolation is compared with the response of laminated rubber bearing with and without lead core to quantified the benefits of applying SMA for isolation of three story building.

Generally, geometric nonlinearities of cable-stayed bridges depend on the behaviors of cables, pylons, the bridge deck and their interactions. These are geometry change, cable sag, and the interactions of axial forces, the bending moment and their deformations in the pylons and bridge deck. Therefore, a large cable-stayed bridges system having a large number of cables can be analyzed under different load conditions. In investigating nonlinear behaviors of cable- stayed bridges, the nonlinear behavior of cables needs to be considered because it may cause the nonlinear behavior of whole bridge system. The nonlinear behavior of a cable gained from its sag. With an increasing axial load, the elongation of the cable is increased but the total cable sag is decreased. Cable-stayed bridge uses cables instead of the internal piers to support the bridge deck. Usually, cable- stayed bridge decks are straight with a little camber compared to the total length of the bridge. Keeping the bridge deck in the position where is the designer desired is not only for bridge aesthetics but also for people on the bridge in terms of psychological effect of improving confidence in structure and engineering considerations. To achieve the serviceability and engineering requirements, preloading of the cable is necessary. In this paper, one such a bridge with geometry similarly to an existing cable- stayed bridge. Quincy Bayview Bridge, located in Illinois, USA, has been considered. Quincy Bayview Bridge has 58 cables in the two planes. Four methods have been considered in this paper to make the optimum selection of cable preloading. The objective is to select appropriate method to determine cable prestrains in order to minimize the deformations and stresses due to dead load of the bridge. Thus, it is not a trivial problem since a change in the prestress of a cable influence the deformation every where in the structure. The best method would be determined by comparing the calculated bending and vertical displacements of the bridge deck.

The feasibility of estimating structural damage using a formulation of the element flexibilities is examined. A system of sensitivity equations is generated from the physical parameters of the structural elements of an initial structure and from measured modal parameters of the damaged structure. As opposed to previous methods, the formulation does not rely on element stiffnesses but rather on element flexibilities. A special algorithm is used to reason from the contribution of the flexibility of the structural members to the sensitivities of the modal parameters to changes on the flexibilities of the members. A numerical experiment on a mechanical system with elastic truss members as well as elastic joints is performed to validate the approach. Modal parameters of the damaged structure are computed vial solving the general eigenvalue problem. Knowing only the modal response and the physical parameters of the initial structure, the theory is used to recapture the damage in the structure. The results demonstrate excellent agreement between the prediction and the simulation.